Fuel Injectors

[BodybyFisher]

You know, with the kinds of problems we have been seeing, rough idle, rough till warms up, back fires and unsolvable issues, I thought we would delve into the topic of Fuel Injectors. It seems to me that we have not explored injectors too deeply and that they might be responsible for a multitude of symptoms. And we are talking about something we can't actually see operate.

I would like to understand what they do and when they are suppose to do it, while I have a general understanding I want to understand them in depth.

For instance what happens when I turn my key off?, do they hold pressure?, or is pressure released from them due to the regulator diverting it back to the tank?

We have lifted our fuel rails with the key on, to look for a leaky injector. How often does an injector leak to cause problems?

How important is injector cleaning, matching, resistance drift, and mechanical wear on injector performance?

Does it make sense to at say, at 100,000 miles, have them professionally cleaned, rebuilt, matched and spec'd?

I mean, these little work horses are largely over looked in my opinion

Can the filter in them become clogged or rusted?

How common is it to have an uneven spray pattern that causes sluggish performance

Can poor injector performance lurk below the O2 sensor operating range.

Can an inbalance between the eight injectors cause roughness?, not setting off a misfire?

Can the pour in the tank injector cleaner, tier 1 gas, gas with Techron affectively clean the injectors over 10 years and thousands of miles?, or is cleaning and rebuilding needed at some point due to sediment, buildup, gum, etc

Electronics drift over time, if the resistance drifts how will an injector react?

Post your experience and whatever you know about injector performance, balance, resistence drift, leaking, spray patterns. whateve. Lets post as much as we can on this subject, and lets KEEP TO THE SUBJECT and try not to drift off topic. Post ONLY what you know or find about FUEL INJECTORS, its electronics, EMF impacts, FUEL in relation to injectors, and the impact on performance. If a post gets off topic I will ask Bruce to prune it, so don't get upset. We need to know more about this topic as a group. True life stories and experiences and advice (ie, replace the o-rings) are considered on topic also

[Bruce Nunnally]

I have come to believe now that despite the graphics from fuel-injector cleaning commercials, injectors are fairly digital and either work or don't work.

I replaced all 8 injectors in my 1992 STS 4.9L at ~120K miles with the hope that this would yield some performance improvement. It made NO difference

in the performance or drive-ability of the car. If an injector is working and is not leaking it is likely to be just operating fully within performance spec.

[BodybyFisher]

Bruce your post highlights the belief that injectors either work or don't work, and I have heard the same premise. What i am saying is that we need to delve into that thought a little deeper. I have heard the same thing, they work or don't work. Is that true?, or can there be performance loss (bad idle, hesitation, surging) from any reason? Remember we are talking about subtle problems that members are getting a little roughness here, a little roughness there..

Check this site, can this be snake oil?, it seems to make sense to me:

<a href="http://www.witchhunter.com/injectorfaq1.php4" target="_blank">http://www.witchhunter.com/injectorfaq1.php4</a>

[JimD]

....

For instance what happens when I turn my key off?, do they hold pressure?, or is pressure released from them due to the regulator diverting it back to the tank?

The pressure will slowly bleed off through the check valve in the fuel pump. I monitored the fuel pressure and timed the decay; after five minutes, the pressure had fallen only 4 PSI (from 38 to 34).

How important is injector cleaning, matching, resistance drift, and mechanical wear on injector performance?

Not sure what you mean by resistance drift. There will be a resistance value range specified for a given injector type. As long as the coil resistance falls within that range at a specific temperature, the injector coil will operate as designed. You could easily have one coil at the high end of the range and another at the low end of the range; but you would not see any performance problems caused by the difference in resistance.

The resistance will change as the temperature changes, but all 8 coils will exhibit the same change.

Does it make sense to at say, 100,000 miles have them professionally cleaned, rebuilt, matched and spec'd?

Not in my limited experience. They either work properly or they fail in some obvious manner. I don't believe there is any way to adjust the fuel flow to match them. It would be possible to measure the flow on a batch of injectors and pick the set of 8 that are flowing nearest the same volume, but the payback would be difficult to measure.

Can pour in the tank, tier 1 gas, gas with Techron affectively clean the injectors over 10 years and thousands of miles....

Again my limited experience indicates yes, the fuel is washing the injectors constantly. My '98 was born 9 years and 11 months ago and at 168,7xx miles I have not had any fuel delivery problems.

[BodybyFisher]

By resistence drift I mean, that the resistence drifts on its own due to years of fuel washing over its windings. One would assume that all 8 would drift in unison, but what if that is not the case and for one reason on another, its resistence has impacted its intended reaction.

[Logan]

Fuel System Overview

The fuel tank stores the fuel supply. The electric fuel pump supplies fuel through an in-line fuel filter to the fuel injection system. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pressure regulator maintains the correct fuel pressure to the fuel injection system. A separate pipe returns unused fuel to the fuel tank.

Fuel Tank

The fuel tank (5) stores the fuel supply. The fuel tank is located in the rear of the vehicle. The fuel tank is held in place by 2 metal straps that attach to the frame. The fuel tank is molded from high density polyethylene.

Fuel Fill Pipe

The fuel fill pipe has a built-in restrictor and deflector in order to prevent refueling with leaded fuel.

Fuel Filler Cap

Notice: If a fuel tank filler cap requires replacement, use only a fuel tank filler cap with the same features. Failure to use the correct fuel tank filler cap can result in a serious malfunction of the fuel and EVAP system.

The fuel fill pipe has a tethered fuel filler cap (1). A torque-limiting device prevents the cap from being over tightened. To install the cap, turn the cap clockwise until you hear audible clicks. This indicates that the cap is correctly torqued and fully seated. A built-in device indicates that the fuel filler cap is fully seated. A fuel filler cap that is not fully seated may cause a malfunction in the emission system.

Fuel Sender Assembly

The fuel sender assembly consists of the following major components:

The fuel level sensor (5)

The fuel tank pressure sensor (1)

The fuel tank fuel pump module (3)

The fuel strainer (4)

Fuel Level Sensor

The fuel level sensor consists of a float, a wire float arm, and a ceramic resistor card. The position of the float arm indicates the fuel level. The fuel level sensor contains a variable resistor which changes resistance in correspondence with the amount of fuel in the fuel tank. The PCM sends the fuel level information via the Class II circuit to the instrument panel (IP) cluster. This information is used for the IP fuel gauge and the low fuel warning indicator, if applicable. The PCM also monitors the fuel level input for various diagnostics.

Fuel Pump

The fuel pump is mounted in the fuel sender assembly reservoir (3). The fuel pump is an electric high pressure pump. Fuel is pumped to the fuel rail at a specified flow and pressure. Excess fuel from the fuel rail assembly returns to the fuel tank through the fuel return pipe. The fuel pump delivers a constant flow of fuel to the engine even during low fuel conditions and aggressive vehicle maneuvers. The powertrain control module (PCM) controls the electric fuel pump operation through a fuel pump relay. The fuel pump flex pipe acts to dampen the fuel pulses and noise generated by the fuel pump.

Fuel Strainer

The fuel strainer (1) attaches to the lower end of the fuel sender. The fuel strainer is made of woven plastic. The functions of the fuel strainer are to filter contaminants and to wick fuel. The fuel strainer is self-cleaning and normally requires no maintenance. Fuel stoppage at this point indicates that the fuel tank contains an abnormal amount of sediment or water.

Fuel Filter

The fuel filter is located on the fuel feed pipe, between the fuel pump and the fuel injectors. The paper filter element (2) traps particles in the fuel that may damage the fuel injection system. The filter housing (1) is made to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. There is no service interval for fuel filter replacement. Replace a restricted fuel filter.

Fuel Feed and Return Pipes

The fuel feed pipe carries fuel from the fuel tank to the fuel rail assembly. The fuel return pipe carries fuel from the fuel rail assembly back to the fuel tank. The fuel pipes consist of 2 sections:

The rear fuel pipe assemblies are located from the top of the fuel tank to the chassis fuel pipes. The rear fuel pipes are constructed of nylon.

The chassis fuel pipes are located under the vehicle and connect the rear fuel pipes to the fuel rail pipes. These pipes are constructed of steel.

Nylon Fuel Pipes

Caution: In order to reduce the risk of fire and personal injury observe the following items:

• Replace all nylon fuel pipes that are nicked, scratched or damaged during installation, do not attempt to repair the sections of the nylon fuel pipes

• Do not hammer directly on the fuel harness body clips when installing new fuel pipes. Damage to the nylon pipes may result in a fuel leak.

• Always cover nylon vapor pipes with a wet towel before using a torch near them. Also, never expose the vehicle to temperatures higher than 115°C (239°F) for more than one hour, or more than 90°C (194°F) for any extended period.

• Apply a few drops of clean engine oil to the male pipe ends before connecting fuel pipe fittings. This will ensure proper reconnection and prevent a possible fuel leak. (During normal operation, the O-rings located in the female connector will swell and may prevent proper reconnection if not lubricated.)

Nylon pipes are constructed to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. There are 3 sizes of nylon pipes used: 3/8 inch ID for the fuel feed, 5/16 inch ID for the fuel return, and 1/2 inch ID for the vent. Heat resistant rubber hose or corrugated plastic conduit protect the sections of the pipes that are exposed to chafing, high temperature, or vibration.

Nylon fuel pipes are somewhat flexible and can be formed around gradual turns under the vehicle. However, if nylon fuel pipes are forced into sharp bends, the pipes kink and restrict the fuel flow. Also, once exposed to fuel, nylon pipes may become stiffer and are more likely to kink if bent too far. Take special care when working on a vehicle with nylon fuel pipes.

Quick-Connect Fittings

Quick-connect fittings provide a simplified means of installing and connecting fuel system components. The fittings consist of a unique female connector and a compatible male pipe end. O-rings, located inside the female connector, provide the fuel seal. Integral locking tabs inside the female connector hold the fittings together.

Fuel Pipe O-Rings

O-rings seal the threaded connections in the fuel system. Fuel system O-ring seals are made of special material. Service the O-ring seals with the correct service part.

Fuel Rail Assembly

The fuel rail assembly (1) attaches to the engine intake manifold. The fuel rail assembly performs the following functions:

Positions the injectors (5) in the intake manifold

Distributes fuel evenly to the injectors

Integrates the fuel pressure regulator (10) with the fuel metering system

Fuel Injectors

The top-feed fuel injector assembly is a solenoid operated device, controlled by the PCM, that meters pressurized fuel to a single engine cylinder. The PCM energizes the injector solenoid, which opens a ball valve, allowing fuel to flow past the ball valve, and through a recessed flow director plate. The director plate has multiple machined holes that control the fuel flow, generating a conical spray pattern of finely atomized fuel at the injector tip. Fuel is directed at the intake valve, causing the fuel to become further atomized and vaporized before entering the combustion chamber. An injector stuck partly open can cause a loss of pressure after engine shutdown. Consequently, long cranking times would be noticed on some engines.

Fuel Pressure Regulator Assembly

The fuel pressure regulator is a vacuum operated diaphragm relief valve with fuel pump pressure on one side and regulator spring pressure and intake manifold vacuum on the other side. The fuel pressure regulator maintains a constant pressure differential across the injectors at all times. The pressure regulator compensates for engine load by increasing fuel pressure as the engine vacuum drops.

Fuel Metering Modes of Operation

The powertrain control module (PCM) monitors voltages from several sensors in order to determine how much fuel to give the engine. The fuel is delivered under one of several conditions called modes. The PCM controls all modes.

Starting Mode

With the ignition switch in the ON position, before engaging the starter, the PCM energizes the fuel pump relay for 2 seconds allowing the fuel pump to build up pressure. The PCM first tests speed density, then switches to the mass air flow (MAF) sensor. The PCM also uses the engine coolant temperature (ECT), the throttle position (TP), and the manifold absolute pressure (MAP) sensors to determine the proper air/fuel ratio for starting. The PCM controls the amount of fuel delivered in the starting mode by changing the pulse width of the injectors. This is done by pulsing the injectors for very short times.

Clear Flood Mode

If the engine floods, clear the engine by pressing the accelerator pedal down to the floor and then crank the engine. When the throttle position (TP) sensor is at wide open throttle, the PCM reduces the injector pulse width in order to increase the air to fuel ratio. The PCM holds this injector rate as long as the throttle stays wide open and the engine speed is below a predetermined RPM. If the throttle is not held wide open, the PCM returns to the starting mode.

Run Mode

The run mode has 2 conditions called Open Loop and Closed Loop. When the engine is first started and the engine speed is above a predetermined RPM, the system begins Open Loop operation. The PCM ignores the signal from the heated oxygen sensor (HO2S) and calculates the air/fuel ratio based on inputs from the ECT, MAF, MAP, and TP sensors. The system stays in Open Loop until meeting the following conditions:

Both HO2S have varying voltage output, showing that they are hot enough to operate properly. This depends upon the engine temperature.

The ECT sensor is above a specified temperature.

A specific amount of time has elapsed after starting the engine.

Specific values for the above conditions exist for each different engine, and are stored in the electrically erasable programmable read-only memory (EEPROM). The system begins Closed Loop operation after reaching these values. In Closed Loop, the PCM calculates the air/fuel ratio (injector on-time) based upon the signal from various sensors, but mainly from the HO2S. This allows the air/fuel ratio to stay very close to 14.7:1.

Acceleration Mode

When the driver pushes on the accelerator pedal, air flow into the cylinders increases rapidly, while fuel flow tends to lag behind. To prevent possible hesitation, the PCM increases the pulse width to the injectors to provide extra fuel during acceleration. The PCM determines the amount of fuel required based upon the throttle position, the coolant temperature, the manifold air pressure, the mass air flow, and the engine speed.

Deceleration Mode

When the driver releases the accelerator pedal, air flow into the engine is reduced. The PCM reads the corresponding changes in throttle position, manifold air pressure, and mass air flow. The PCM shuts OFF fuel completely if the deceleration is very rapid, or for long periods, such as long, closed-throttle coast-down. The fuel shuts OFF in order to protect the catalytic converters.

Battery Voltage Correction Mode

When the battery voltage is low, the PCM compensates for the weak spark delivered by the ignition system in the following ways:

Increasing the amount of fuel delivered

Increasing the idle RPM

Increasing the ignition dwell time

Fuel Cutoff Mode

The PCM cuts off fuel from the fuel injectors when the following conditions are met in order to protect the powertrain from damage and improve driveability:

The ignition is OFF. This prevents engine run-on.

The ignition is ON but there is no ignition reference signal. This prevents flooding or backfiring.

The engine speed is too high, above red line.

The vehicle speed is too high, above rated tire speed.

During an extended, high speed, closed throttle coast down. This reduces emissions and increases engine braking.

During extended deceleration, in order to protect the catalytic converters.

Short Term Fuel Trim

The short term fuel trim values change rapidly in response to the HO2S signal voltages. These changes "fine tune" the engine fueling. The ideal fuel trim values are around 0 percent. A positive fuel trim value indicates that the PCM is adding fuel in order to compensate for a lean condition. A negative fuel trim value indicates that the PCM is reducing the amount of fuel in order to compensate for a rich condition.

When the PCM determines that the short term fuel trim is out of the operating range, the following DTCs will set:

DTC P0171 Bank 1 Too Lean

DTC P0172 Bank 1 Too Rich

DTC P0174 Bank 2 Too Lean

DTC P0175 Bank 2 Too Rich

Long Term Fuel Trim

The long term fuel trim is a matrix of cells arranged by RPM and manifold absolute pressure (MAP). Each cell of the long term fuel trim is a register like the short term fuel trim. As the engine operating conditions change, the PCM will switch from cell to cell to determine what long term fuel trim factor to use in the base pulse width equation.

While in any given cell, the PCM also monitors the short term fuel trim. If the short term fuel trim is far enough from 0 percent, the PCM will change the long term fuel trim value. Once the long term fuel trim value is changed, it should force the short term fuel trim back toward 0 percent. If the mixture is still not correct, the short term fuel trim will continue to have a large deviation from the ideal 0 percent. In this case, the long term fuel trim value will continue to change until the short term fuel trim becomes balanced. Both the short term fuel trim and long term fuel trim have limits which vary by calibration. If the mixture is off enough so that long term fuel trim reaches the limit of its control and still cannot correct the condition, the short term fuel trim would also go to its limit of control in the same direction. If the mixture is still not corrected by both short term fuel trim and long term fuel trim at their extreme values, a fuel trim diagnostic trouble code (DTC) will likely result. When the PCM determines that the long term fuel trim is out of the operating range, the following DTCs will set:

DTC P0171 Bank 1 Too Lean

DTC P0172 Bank 1 Too Rich

DTC P0174 Bank 2 Too Lean

DTC P0175 Bank 2 Too Rich

Under the conditions of power enrichment, the PCM sets the short term fuel trim to 0 percent until power enrichment is no longer in effect. This is done so the Closed Loop factor and the long term fuel trim will not try to correct for the power enrichment condition.

[JimD]

By resistence drift I mean, that the resistence drifts on its own due to years of fuel washing over its windings. One would assume that all 8 would drift in unison, but what if that is not the case and for one reason on another, its resistence has impacted its intended reaction.

It would require a serious and measureable deviation from the specified resistance range to impact the electrical operation of the injector. The electrical portion of the injector is about as simple as a circuit can be. The coil will produce sufficient magnetic flux to open the valve as long as the observed DC resistance of the coil is within the specified range. In fact, there will be more than enough flux density produced by a coil that measures well outside the specified DC resistance range. The actual resistance is not a critical factor.

As far as the PCM is concerned, the injector valve is either pulsed open by the coil, or slammed closed by the spring; there is no in-between (disregard the microseconds required for the valve to change position).

You are far more likely to have a some kind of failure in the hydraulic half of the injector.

[JasonA]

Most ads from injector cleaner companies shows a mechanical failure of the spray pattern of the injector. This goes beyond the electrical operation of the injector and affects the actual output of the injector. The common (and possibly misinformed) opinion is that a "deposit" of some sort has formed over the injector's opening and has affected the spray. This is often a problem in seasonal engines (such as your lawn mower), but I'd surmise that any automobile, driven even halfway regularly, isn't really prone to this same condition. I suppose it's still possible to get some trash in there somehow...but it'd probably be of a nature that a solvent couldn't fix.

[BodybyFisher]

Logan, do you care to add a little more to your post, other than, imply that I don't know diddily about fuel systems (which is probably true) by posting here are the basics? The reason I started this was to understand more about injectors.

I would like to hear what you think, do injectors have a mid point to where they are not operating at 100% in either way, rich or lean? Can buildup mess up the spray pattern. Lets face the facts these are high compression engines that develop carbon in some cases can this carbon get to the fuel injector at all or can bad valve seals cause oil to be burned on to the injector tip?

[BodybyFisher]

By resistence drift I mean, that the resistence drifts on its own due to years of fuel washing over its windings. One would assume that all 8 would drift in unison, but what if that is not the case and for one reason on another, its resistence has impacted its intended reaction.

It would require a serious and measureable deviation from the specified resistance range to impact the electrical operation of the injector. The electrical portion of the injector is about as simple as a circuit can be. The coil will produce sufficient magnetic flux to open the valve as long as the observed DC resistance of the coil is within the specified range. In fact, there will be more than enough flux density produced by a coil that measures well outside the specified DC resistance range. The actual resistance is not a critical factor.

As far as the PCM is concerned, the injector valve is either pulsed open by the coil, or slammed closed by the spring; there is no in-between (disregard the microseconds required for the valve to change position).

You are far more likely to have a some kind of failure in the hydraulic half of the injector.

The spring can't weaken and allow more fuel to pass, those suckas get pretty hot. How long can a leaky injector (s) go on before its detected do you think? How common is it for them to leak?

[JimD]

The spring can't weaken and allow more fuel to pass, those suckas get pretty hot. How long can a leaky injector (s) go on before its detected do you think?

Someone who pays attention to fuel consumption patterns (with a spreadsheet for instance) would pick up on the possibility of a leaky injector within one or two tanks of fuel.

How common is it for them to leak?

In my experience, injector leaks do not occur.

[BodybyFisher]

I found this at www.Autotap.com

QUICK DIAGNOSIS WITH A CODE

On OBD II cars, the OBD II system will not only identify misfires but also coil and injector problems. Consequently, if the MIL lamp is on and you find a code for a misfiring cylinder and a second code indicating an injector fault for the same cylinder, bingo, the engine probably has a bad fuel injector. Likewise, if you find a misfire code for a cylinder and also a code indicating a coil fault for a multi-coil distributorless ignition system or coil-on-plug ignition, you can probably bet on a bad ignition coil.

In cases where there's a cylinder misfire code but no other codes, the ignition or fuel delivery system may be borderline and not yet bad enough to set a code of its own. A shorted or open fuel injector solenoid, or a shorted or open coil will usually set a code, but a dirty or weak fuel injector or a weak coil probably won't set a code.

I want to point out that you guys don't think the highlighted statement can occur to a fuel injector. I actually do. And I am going to set out to find someone to visually demonstrate bad injectors to me/us.

<a href="http://www.autotap.com/Articles/Analyzing_...n_Misfires.html" target="_blank">http://www.autotap.com/Articles/Analyzing_...n_Misfires.html</a>

[BodybyFisher]

I realize we are talking about very clean filtered fuel here, but as with any restrictive orfice full or partial blockages can occur or even restrictions. I have seen it in oil burner guns, burning torches, needle valves on carburators, etc. I want to find some outfit that will do a demonstration for us, i want to understand this better

[winterset]

I once worked on a 1987 oldsmobile. I removed all 6 injectors, and found that a few had rust deposits in some sort of filter that was part of the injector. I'm not sure if NS injectors have this filter. it's my belief that these rust pellets floating around / packed in the filter would have affected the flow of fuel enough to change the spray pattern.

[Logan]

Fisher #1- I was not trying to dis you. I just thought that was a good GM overview of the fuel system. Information about the 'modes' was what I was really posting.

Fisher #2- Talk to this guy: http://www.lindertech.com/dirty_dzn.htm . The injector guru.

As for diagnostics, I have personally seen very few injector issues. 3 interesting cases I can think of:

One car had 2 Autozone 'rebuilt' injectors. Was able to figure out pretty quick that the 2 'rebuilt' ones had a different flow rate then the original 4 other GM injectors. About 30% different if I remember correctly. 2 new GM injectors fixed that one.

Another, TBI injection on a mid '80s Seville (the one with the goofy trunk). 2 injector TBI, the 'bad' injector had been replaced before I entered the picture. The new injector was also, not working. The fix on that was a reman ECM, it had a bad driver. The original 'bad' injector was reinstalled.

Another, long crank Corvette. That car would sit for months at a time. This one did have 2 leaking injectors, a rotted gas filter, and more..

Also have worked on many GM CPI units..most of those were either the pressure regulator or the fuel pump pressure.

[BodybyFisher]

Fisher #1- I was not trying to dis you. I just thought that was a good GM overview of the fuel system. Information about the 'modes' was what I was really posting.

Fisher #2- Talk to this guy: <a href="http://www.lindertech.com/dirty_dzn.htm" target="_blank">http://www.lindertech.com/dirty_dzn.htm</a> . The injector guru.

As for diagnostics, I have personally seen very few injector issues. 3 interesting cases I can think of:

One car had 2 Autozone 'rebuilt' injectors. Was able to figure out pretty quick that the 2 'rebuilt' ones had a different flow rate then the original 4 other GM injectors. About 30% different if I remember correctly. 2 new GM injectors fixed that one.

Another, TBI injection on a mid '80s Seville (the one with the goofy trunk). 2 injector TBI, the 'bad' injector had been replaced before I entered the picture. The new injector was also, not working. The fix on that was a reman ECM, it had a bad driver. The original 'bad' injector was reinstalled.

Another, long crank Corvette. That car would sit for months at a time. This one did have 2 leaking injectors, a rotted gas filter, and more..

Also have worked on many GM CPI units..most of those were either the pressure regulator or the fuel pump pressure.

Thanks Logan, I was kidding about the dissing..., I was interested in what you had to say. I will look at the 'modes' that you were referring to also. I have seen Lindertech before also, will visit their web site. Thanks

[BodybyFisher]

This paragraph came from www.lindertech.com

How do injectors become clogged?

Injectors become clogged one of two ways. First there is clogging from fuel system contamination. This means that the injector is restricted at the fuel inlet. It can happen from many different situations. You may be buying dirt at your local gas station and not realizing it. (Do you ever fill your tank while a transport truck is unloading fuel at the station?) Sometimes fuel, do to a lack of additives, may react with your fuel system components and cause deterioration. Lack of fuel in your tank promotes condensation, which can cause rust. Someone may sabotage your fuel system. Secondly, an injector can become clogged or restricted at the discharge end. This may happen do to lack of additives in the fuel that reduce carbon build. It could be from driving habits. Another reason is injector design or engine design. The end result is carbon or coking at the discharge end of the injector that restricts fuel flow or distorts the spray pattern. If injectors clog at the discharge end, it is recommended that an intake cleaning be done before installing a different set of injectors.

How do I know if I need to have my injectors serviced?

The most correct answer to this question is that you have had them diagnosed by a professional technician and they were deemed faulty. There are other reasons to have them serviced or at least checked out.

You are rebuilding the engine.

It’s a high mileage vehicle and you've noticed increased fuel consumption.

Your “check engine” light is on and there is a fuel system related code.

You have failed an emission inspection.

You noticed a driveability problem: Poor idle, loss of performance, hesitation, hard starting, detonation, surging or misfiring.

Note: If an injector is leaking external from the body or the connector area it needs to be discarded. This is usually from an internal o-ring and is non-repairable.

Does gas tank additive injector cleaner work?

The primary purpose of tank additive cleaner is maintenance. Even though some have been known to clean up injectors with minor restrictions. In most cases you get what you pay for, the more it costs the better it works. Depending on type of fuel used and driving characteristics, adding tank additive a couple times a year is good preventative maintenance.

What are “pattern failure” injectors?

Through the years, Linder Technical has identified many injectors the fail. It may be from the coil winding shorting out, an internal o-ring that causes them to leak externally or they are prone to dripping from the discharge, even if you clean them. Once we identify a “pattern failure” injector, LTS finds a suitable replacement that can be installed without any modifications. This way our customers can install a fresh set of injectors worry free.

[BodybyFisher]

Double Post

[WarrenJ]

"Baby," you might recall, suffered a Viking Funeral at just about 130K miles. She spun like a finely balanced top and purred/growled like a cat that might upset your dawg (only louder). Never a plug/wire/injector problem.

You'll understand then, why at 72K current miles, I'm not deeply concerned about such things.

Just the same, while researching, I came across the following in a '99 FSM. I was unaware the system compensated for system voltage; nor did I think it was necessary:

"The Northstar fueling system has several automatic adjustments to compensate for differences in fuel system hardware, driving conditions, fuel used, and vehicle aging. The basis for fuel control is the pulse width calculation described above. Included in this calculation are an adjustment for battery voltage, short term fuel trim, and long term fuel trim. The battery voltage adjustment is necessary since changes in voltage across the injector affect injector flow rate. Short term and long term fuel trims are fine and gross adjustments to pulse width designed to maximize driveability and emissions control. These fuel trims are based on feedback from oxygen sensors in the exhaust stream and are only used when the fuel control system is in closed loop."

I thought that interesting; herewith the entire document (wherein paragraph #7 is the one I referred to):

Fuel System Description

System Operation

The function of the fuel and air control system is to manage fuel and air delivery to each cylinder to optimize the performance and driveability of the engine under all driving conditions. The fuel supply is stored in a High Density Polyethylene (HDPE) fuel tank located in front of the rear wheels. The fuel sender allows retrieval of fuel from the tank and also provides information on fuel level. A fuel pump contained in the modular fuel sender pumps fuel through nylon pipes and an in-line fuel filter to the fuel rail. The pump is designed to provide fuel at a pressure above the regulated pressure needed by the injectors. Fuel is then distributed through the fuel rail to eight injectors inside the intake manifold. Fuel pressure is controlled by a pressure regulator mounted on the fuel rail. The fuel system in this vehicle is recirculating; this means that excess fuel that is not injected into the cylinders is sent back to the fuel tank by a separate nylon pipe. This removes air and vapors from the fuel as well as keeping the fuel cool during hot weather operation. Each fuel injector is located directly above each cylinder's two intake valves. An accelerator pedal in the passenger compartment is linked to a throttle valve in the throttle body by a cable. The throttle body regulates air flow from the air cleaner into the intake manifold, which then distributes this air to each cylinder's two intake valves. This allows the driver to control the air flow into the engine, which then controls the power output of the engine.

Engine Fueling

Unleaded fuel must be used with all gasoline engines for proper emission control system operation. Using unleaded fuel will also minimize spark plug fouling and extend engine oil life. Leaded fuel can damage the emission control system, and its use can result in loss of emission warranty coverage.

All vehicles with gasoline engines are equipped with an Evaporative Emission Control (EVAP) System that minimizes the escape of fuel vapors to the atmosphere. Information on this system is found in Driveability and Emissions (Powertrain and Emissions System).

The Northstar engine is fueled by eight individual injectors, one for each cylinder, that are controlled by the PCM. The PCM controls each injector by energizing the injector coil for a brief period generally once every other engine revolution. The length of this brief period, or pulse, is carefully calculated by the PCM to deliver the correct amount of fuel for proper driveability and emissions control. The length of time the injector is energized is called the pulse width and is measured in milliseconds (thousandths of a second).

While the engine is running, the PCM is constantly monitoring its inputs and recalculating the appropriate pulse width for each injector. The pulse width calculation is based on the injector flow rate (mass of fuel the energized injector will pass per unit of time), the desired air/fuel ratio, and actual air mass in each cylinder and it is adjusted for battery voltage, short term and long term fuel trim. The calculated pulse is timed to occur as each cylinders intake valves are closing to attain largest duration and most vaporization.

Fueling during crank is slightly different than during engine run. As the engine begins to turn, a prime pulse may be injected to speed starting. As soon as the PCM can determine where in the firing order the engine is, it begins pulsing injectors. The pulse width during crank is based on coolant temperature and barometric pressure.

The Northstar fueling system has several automatic adjustments to compensate for differences in fuel system hardware, driving conditions, fuel used, and vehicle aging. The basis for fuel control is the pulse width calculation described above. Included in this calculation are an adjustment for battery voltage, short term fuel trim, and long term fuel trim. The battery voltage adjustment is necessary since changes in voltage across the injector affect injector flow rate. Short term and long term fuel trims are fine and gross adjustments to pulse width designed to maximize driveability and emissions control. These fuel trims are based on feedback from oxygen sensors in the exhaust stream and are only used when the fuel control system is in closed loop.

Under certain stringent conditions, the fueling system will not energize injectors, individually or in groups, for a period of time. This is referred to as Fuel shut-off. Fuel shut-off is used to improve traction, save fuel, improve starting, and protect the vehicle under certain extreme or abusive conditions.

In case of a major internal problem, the PCM is equipped with a back-up fueling system that will run the engine until service can be performed.

Notice

Do not operate the engine in the back-up fuel for extended periods. Back-up fueling will negatively impact driveability and fuel economy, and may cause damage to the emissions system.

As part of the fueling system, the PCM records and sends data about fueling to the IPC from which the IPC calculates fuel economy, range, and fuel used displays. The PCM calculates the amount of fuel delivered to the engine through the injectors based on injector pulse width and flow rate. This data is accumulated and sent to the IPC periodically via the data link.

The PCM controls the fuel injectors based on information it receives from several information sensors. Each injector is fired individually in engine firing order, which is called Sequential Multiport Fuel Injection. This allows precise fuel metering to each cylinder and improves driveability under all driving conditions.

Fuel Quality

Due to increasing awareness towards vehicle emissions (Evaporative and Exhaust) and their impact on the environment, federal regulations are limiting certain characteristics of fuel. These limitations are causing driveability problems that are extremely difficult to diagnose. In order to make a diagnosis, a basic understanding of fuel and its effects on the vehicles fuel system must be gained.

Octane

Octane is a measure of a fuel's ability to resist spark knock. Spark knock occurs in the combustion chamber just after the spark plug fires, when the air/fuel mixture in the cylinder does not completely burn. The remaining mixture spontaneously combusts due to temperature and pressure. This secondary explosion causes a vibration that is heard as a knock (ping). Fuel with a high octane number has a greater resistance to spark knock. This vehicle requires 91 octane ([R+M]/2 method) in order to ensure proper performance of the fuel control system. Using fuel with an octane rating lower than 91 can create spark knock, which would cause the PCM to retard ignition timing to eliminate the knock. In a case such as this, poor engine performance and reduced fuel economy could result. Also, in severe knock cases, engine damage may occur.

Volatility

Volatility is a fuel's ability to change from a liquid state to a vapor state. Since liquid gasoline will not burn, it must vaporize before entering the combustion chamber. The rate at which gasoline vaporizes determines the amount of evaporative emissions released from the fuel system, and therefore has made volatility an environmental concern. The federal government has lowered the maximum allowable volatility, but certain driveability conditions have resulted.

Volatility can be determined through three different tests: the Vapor-Liquid Ratio, the Distillation Curve, and the Reid Vapor Pressure Test (RVP). The Vapor-Liquid Ratio test determines what temperatures must exist to create a vapor-liquid ratio of 20. The distillation curve is a graph showing the relationship between temperature and the percentage of fuel evaporated. The fuel components that boil at relatively low temperatures (below about 90°F) are known as light ends and those that boil at about 300°F are known as heavy ends. The light ends are important for cold starting and cold weather driveability. Heavy ends provide engine power and are important for hot weather driveability. It is the proper mixture of these components that provide proper operation across a wide range of temperatures. However, the distillation curve of a gasoline usually requires laboratory testing. The Reid Vapor Pressure (RVP) test measures the pressure (psi) vaporized fuel exerts within a sealed container when heated to 100°F. Volatility increases proportional to RVP. While RVP can easily be measured in the field, it may be misleading because it is possible for two fuels with the same RVP to have different distillation curves, and therefore, different driveability characteristics.

As stated, improper volatility can create several driveability problems. Low volatility can cause poor cold starts, slow warm ups, and poor overall cold weather performance. It may also cause deposits in the crankcase, combustion chambers and spark plugs. Volatility that is too high could cause high evaporative emissions and purge canister overload, vapor lock, and hot weather driveability conditions. Since volatility is dependent on temperature, different fuels are used during certain seasons of the year, thus creating problems during sudden temperature changes.

Fuel System Deposits

Fuel system deposits can cause various driveability problems. Deposits usually occur during hot soaks after key Off. Poor fuel quality or driving patterns such as short trips followed by long cool down periods can cause injector deposits. This occurs when the fuel remaining in the injector tip evaporates and leaves deposits. Leaking injectors can increase injector deposits. Deposits on fuel injectors affect their spray pattern, which in turn could cause reduced power, unstable idle, hard starts and poor fuel economy.

Intake valve deposits can also be related to fuel quality. While most fuels contain deposit inhibitors, some do not and the effectiveness of deposit inhibitors varies by manufacturer. If intake valve deposits occur, fuel may be suspected. These deposits can cause symptoms such as excessive exhaust emissions, power loss and poor fuel economy.

Sulfur Content

The sulfur content in fuel is also regulated to a certain standard. Premium grades of fuel generally have a lower sulfur content than the less expensive blends. A high sulfur content can promote the formation of acidic compounds that could deteriorate engine oil and increase engine wear. It could also produce excessive exhaust emissions or a rotten egg smell from the exhaust system.

Oxygenated Fuels and Alcohol Content

Notice

Do not use fuels containing methanol in order to prevent damage and corrosion to the fuel system.

Methanol can corrode metal parts in the fuel system, and can also damage plastic and rubber parts.

Oxygenated fuels contain oxygen in their chemical structure. The advantages that oxygenated fuels offer are improved octane quality, better combustion, and reduced carbon monoxide emissions. To provide cleaner air, all gasolines in the United States are now required to contain additives that will help prevent deposits from forming in the engine and fuel system. Therefore, nothing should be added to the fuel. The most commonly used oxygenated fuels are ethanol (grain alcohol) and MTBE (Methyl Tertiary Butyl Ether).

[bobbnsueb@sbcglobal.net]

The spring can't weaken and allow more fuel to pass, those suckas get pretty hot. How long can a leaky injector (s) go on before its detected do you think?

Someone who pays attention to fuel consumption patterns (with a spreadsheet for instance) would pick up on the possibility of a leaky injector within one or two tanks of fuel.

How common is it for them to leak?

In my experience, injector leaks do not occur.

-----------------------------------------------------------------

HI,

My 91 STS 4.9 had a leaky injector at approximately 90,000 miles.

It showed up in the cylinder balance test when after testing that cylinder, it wouldn't seal and the pressure wouldn't build up for the next test.

Later, after adding techron injector cleaner to 1/2 tank of gas, I had rough running, A measurement of the resistances found three to have only 2-3 ohms. (digital fluke meter) replaced the injectors and it fixed it.

Smoothed the idle and improved the actual mileage making it match the computer readout.

Don't know if the additive shorted the windings or if it was old age. But it was only a half tank of gas, os maybe the stuff was too strong.

Bob B

[bobbnsueb@sbcglobal.net]

The spring can't weaken and allow more fuel to pass, those suckas get pretty hot. How long can a leaky injector (s) go on before its detected do you think?

Someone who pays attention to fuel consumption patterns (with a spreadsheet for instance) would pick up on the possibility of a leaky injector within one or two tanks of fuel.

How common is it for them to leak?

In my experience, injector leaks do not occur.

-----------------------------------------------------------------

HI,

My 91 STS 4.9 had a leaky injector at approximately 90,000 miles.

It showed up in the cylinder balance test when after testing that cylinder, it wouldn't seal and the pressure wouldn't build up for the next test.

Later, after adding techron injector cleaner to 1/2 tank of gas, I had rough running, A measurement of the resistances found three to have only 2-3 ohms. (digital fluke meter) replaced the injectors and it fixed it.

Smoothed the idle and improved the actual mileage making it match the computer readout.

Don't know if the additive shorted the windings or if it was old age. But it was only a half tank of gas, os maybe the stuff was too strong.

Bob B

[Ranger]

Later, after adding techron injector cleaner to 1/2 tank of gas

A measurement of the resistances found three to have only 2-3 ohms.

Don't know if the additive shorted the windings or if it was old age. But it was only a half tank of gas, or maybe the stuff was too strong.

That is exactly what our old Guru (GM engineer) always warned us about.

[BodybyFisher]

This is interesting that GM would put this bulletin out for injectors that don't become dirty or clogged I found this on a Corvette site:

Document ID# 2043811

Subject: Various Driveability Symptoms Due to Clogged Fuel Injectors, MIL/SES DTCs P0171, P0172, P0174, P0300, P1174, P1175 (Clean Fuel Injectors and/or Perform Injector Test With AFIT - CH-47976) #03-06-04-030F - (12/10/2007)

This bulletin is being revised to update the model year to 2008. Please discard Corporate Bulletin Number 03-06-04-030E (Section 06 -- Engine/Propulsion System).

Condition

Some customers may comment on any of the following various driveability symptoms:

• Extended Crank Time

• Hard to Start

• MIL/SES Illuminated with DTCs

• Hesitation

• Lack of Power

• Surge or Chuggle

• Rough Idle

• Light or Intermittent Misfire

Cause

Due to various factors, the fuel injectors may become restricted. Extensive testing has demonstrated that fuel related issues are the cause of clogged injectors. At this point, no specific fuel, fuel constituent, or engine condition has been identified as causing the restriction.

The restriction causes the engine to operate at a lean air fuel ratio. This may either trigger the MIL to illuminate or the engine to develop various driveability symptoms.

Correction

Fuel injector restrictions, deposits can be cleaned on the vehicle using the following procedure. Under NO circumstances should this procedure be modified, changed or shortened. As a long term solution, and to prevent reoccurrence, customers should be encouraged to use Top Tier Detergent Gasoline .

For further information on Top Tier detergent gasoline and fuel retailers, please refer to the following Corporate Bulletin Numbers:

• 04-06-04-047G (U.S. Only)

• 05-06-04-022D (Canada ONLY)

Notice: GM UPPER ENGINE AND FUEL INJECTOR CLEANER is the only injector cleaning agent approved for use with General Motors fuel system components. Other injector cleaners may cause damage to plastics, plated metals or bearings.

General Motors has completed extensive laboratory testing of GM Upper Engine and Fuel Injector Cleaner, and can assure its compatibility with General Motors fuel system components, as long as the cleaning procedure is followed correctly.

Injector Cleaning Procedure

The following tools, or their equivalent, are required:

• CH-47976 Active Fuel Injector Tester (AFIT)

• J 35800-A Fuel Injector Cleaner

• J 37287 Fuel Line Shut-off Adapter

• J 42964 Fuel Line Shut-off Adapter

• J 42873 Fuel Line Shut-off Adapter

• * One bottle of GM Upper Engine and Fuel Injector Cleaner, P/N 88861802 (in Canada, P/N 88861804)

• * One bottle of GM Fuel System Treatment Plus, P/N 88861011 (in Canada, P/N 88861012)

Active Fuel Injector Tester (AFIT- CH-47976)

Some dealers may not have an Active Fuel Injector Tester (AFIT- CH-47976). Dealers can contact 1-800-GM-TOOLS (1-800-468-6657) to order an AFIT- CH-47976.

Dealers still can test the fuel injectors without an AFIT. Refer to Fuel Injector Diagnosis (w/ J 39021 or Tech 2®) in SI.

Important: As mentioned in the AFIT User Guide, vehicles that are not listed in the AFIT menu can still be tested with the AFIT. Depending on the model, it may be possible to enter the previous model year and proceed with testing using the DLC connection.

If this is not possible on the model that you are working on, it will be necessary to use the direct connection method outlined in the AFIT User Guide (See Pages 17-31).

General Motors recommends that the Active Fuel Injector Tester (AFIT) be used in testing fuel injectors. If the SI diagnostics do not isolate a cause for this concern, use the Active Fuel Injector Tester (AFIT - CH-47976) to perform an "Injector Test" as outlined in the AFIT User Guide.

The AFIT "Injector Test" measures the flow characteristics of all fuel injectors, which is more precise when compared with the standard Tech 2® fuel injector balance test. As a result, the AFIT is more likely to isolate the cause of a P1174 DTC (for example: if it is being caused by a fuel injector concern).

The CH-47976 (Active Fuel Injector Tester - AFIT) can also be used to measure fuel pressure and fuel system leak down. Also, as mentioned in the P1174 SI diagnosis, if the misfire current counters or misfire graph indicate any misfires, it may be an indicator of the cylinder that is causing the concern. Refer to Fuel Injector Diagnosis (w/CH-47976) in SI for additional instructions.

Training (U.S.)

To access the training video on AFIT, take the following path at the GM Training Website:

After logging into the gmtraining.com website, choose the link on the left side of the page titled "web video library."

Then choose "technical."

Next, within the search box, type in September course number "10206.09D.

This will bring up a link with this course. Scroll through to choose "feature topic."

At this point, the seminar can be chosen to view or the video related to the AFIT.

Additional training is available from the gmtraining.com website. Please see TECHassist 16044.18T2 Active Fuel Injector Tester and also see 16044.14D1 GM Powertrain Performance for more information on GM Upper Engine and Fuel Injector Cleaner.

Also, dealers can now download software updates for the AFIT at GM Dealer Equipment (GMDE) on the web at http://www.gmde.net/AFIT.cfm.

Training (Canada)

To access the training video on AFIT, take the following path at the GMPro LMS Training Website:

After logging into the <www.gmprocanada.com> website, choose the link on the left side of the page titled "Catalog."

Then choose "Catalog Search."

Next, within the search box, Select Course Number - Contains - "T" then select search.

This will bring up a list of TECHassist courses. Scroll through to choose "Active Fuel Injector Tester" and select "View."

At this point, a new window will open and the program can be Launched.

Also, dealers can now download software updates for the AFIT at GM Dealer Equipment (GMDE) on the web at http://www.gmde.net/softwareupdates/.

Techlink

Additional information can be found on AFIT (June 2006 Edition) and GM Upper Engine and Fuel Injector Cleaner (November 2006 Edition) in Techlink. To access the articles, take the following path:

Go to GM DealerWorld (U.S.) or the GM infoNET (Canada).

Click on the Service Tab in DealerWorld (GM infoNET for Canada).

Click on the GM Techlink Hyperlink.

Click on the Archives Hyperlink at GM Techlink.

• Click on 06-2006 in the Archives Section and Click on the Active Fuel Injector Tester Link in the June 2006 Techlink Article.

• Click on 11-2006 in the Archives Section and Click on the GM Top Engine Cleaner Replaced Link in the November 2006 Techlink Article.

Injector Cleaning Procedure

Notice: GM UPPER ENGINE AND FUEL INJECTOR CLEANER is the only injector cleaning agent recommended. DO NOT USE OTHER CLEANING AGENTS AS THEY MAY CONTAIN METHANOL, WHICH CAN DAMAGE FUEL SYSTEM COMPONENTS. Under NO circumstances should the GM Upper Engine and Fuel Injector Cleaner be added to the vehicle fuel tank.

Do not exceed the recommended cleaning solution concentration. Testing has demonstrated that exceeding the recommended cleaning solution concentration does not improve the effectiveness of this procedure.

Important: Vehicles with less than 160 km (100 mi) on the odometer should not have the injectors cleaned. These vehicles should have any out of specification injectors replaced.

For 4, 5 and 6 cylinder engines, empty two of the 30 ml (1 oz) reservoirs of the GM Upper Engine and Fuel Injector Cleaner container into the J 35800-A - Injector Cleaning Tank then add 420 ml (14 oz) of regular unleaded gasoline.

If you are using any other brand of cleaning tank, you will need a total of 60 ml (2 oz) mixed with 420 ml (14 oz) of regular unleaded gasoline.

For 8 cylinder engines, empty two of the 30 ml (1 oz) reservoirs of the GM Upper Engine and Fuel Injector Cleaner container into the J 35800-A - Injector Cleaning Tank then add 420 ml (14 oz) of regular unleaded gasoline.

If you are using any other brand of cleaning tank, you will need a total of 60 ml (2 oz) of Upper Engine and Fuel Injector Cleaner mixed with 420 ml (14 oz) of regular unleaded gasoline. This procedure will need to be repeated for a second time for an 8 cylinder engine (8 cylinder engines receive 960 ml total fluid - 120 ml (4 oz) of Upper Engine and Fuel Injector Cleaner and 840 ml (28 oz) of gasoline.

Be sure to follow all additional instructions provided with the tool.

Electrically disable the vehicle fuel pump by either removing the fuel pump fuse or the fuel pump relay and disconnecting the oil pressure switch connector, if equipped.

Turn the ignition to the OFF position.

Relieve fuel pressure and disconnect the fuel feed and return lines at the fuel rail. Plug the fuel feed and return lines coming off the fuel rail with J 37287, J 42873 or J 42964 as appropriate for the fuel system.

Connect the J 35800-A to the vehicle fuel rail.

Pressurize the J 35800-A to 510 kPa (75 psi).

Start and idle the engine until it stalls, due to lack of fuel. This should take approximately 15-20 minutes.

Turn the ignition to the OFF position.

Disconnect the J 35800-A from the fuel rail.

Reconnect the vehicle fuel pump relay and oil pressure switch connector, if equipped.

Remove the J 37287, J 42873 or J 42964 and reconnect the vehicle fuel feed and return lines.

Start and idle the vehicle for an additional two minutes to ensure residual injector cleaner is flushed from the fuel rail and fuel lines.

Pour the entire contents of GM Fuel System Treatment Plus (P/N 88861011 [in Canada, P/N 88861012]) into the tank and advise the customer to fill the tank.

Review the benefits of using Top Tier Detergent gasoline with the customer and recommend that they add a bottle of GM Fuel System Treatment Plus to the fuel tank at every oil change. Regular use of GM Fuel System Treatment Plus should keep the customer from having to repeat the injector cleaning procedure.

Road test the vehicle to verify that the customer concern has been corrected

[BodybyFisher]

Then I found this, yes they get dirty, but don't YOU use anything as a PM

Document ID# 1548749

2005 Chevrolet Corvette

--------------------------------------------------------------------------------

Info -Maintenance Cleaning of Fuel Injectors #04-06-04-051A - (Sep 3, 2004)

Maintenance Cleaning of Fuel Injectors

2005 and Prior All General Motors Passenger Cars and Trucks

2003-2005 HUMMER H2

This bulletin is being revised to add text for clarification. Please discard Corporate Bulletin Number 04-06-04-051 (Section 06 -- Engine/Propulsion System).

General Motors is aware that some companies are marketing tools, equipment and programs to support fuel injector cleaning as a preventative maintenance procedure. General Motors does not endorse, support or acknowledge the need for fuel injector cleaning as a preventative maintenance procedure. Fuel injector cleaning is approved only when performed as directed by a published GM driveability or DTC diagnostic service procedure.

Due to variation in fuel quality in different areas of the country, the only preventative maintenance currently endorsed by GM regarding its gasoline engine fuel systems is the addition of GM Fuel System Treatment, P/N 12345104 (in Canada, 89020804), added to a tank of fuel at each oil change. Refer to Corporate Bulletin Number 03-06-04-030A for proper cleaning instructions.

Important

The addition of GM Fuel System Treatment should not be necessary for those customers who exclusively use Top Tier Detergent Gasolines only. Refer to Corporate Bulletin Number 04-06-04-047A.