Stumble Sensation in Ovedrive

[kens96]

Changed the original gas filter out with 146K on it about 4 months ago just because.. was not giving me any trouble. Air filter looks clean.

[BodybyFisher]

Thanks Mike,

That's why I was asking about ther hesitation from a stop. Kind of bogs down through the first few MPH under load and then picks up. If it were an older car I would say it feels like the points gap was off or a float was stuck in the low position. Remember those days... repairs were easier to diagnose.

Wait, I missed this hesitation from a stop under load. It is sounding like fuel like britt hinted. It is sounding like you are starving for fuel, or you have an vacuum leak, but you are not getting a lean code, so I am thinking a fuel problem, but again if you are starving for fuel, wouldn't an O2 sensor pick up the lean condition?

[BodybyFisher]

Do you have a fuel pressure gage with a long enough hose to tape to your window? That is what I would do.

[kens96]

Don't have a pressure gauge. I need to add it to the list. The good news is it is not the tranny or motor mounts, It is something to do with engine runability. Will replace the fuel regulator tonight if it is not too big a job and see where we go from there.

The other news is he says the car needs front wheel bearings. I hear a slight droan from the front that you can hear with with the radio and AC off but have always attributed that to tire noise from the all weather Michelin Destiny Tires.

No change in sounds turning left or right and no side sounds louder than the other. Do I really need bearings? How do I test for this?

[BodybyFisher]

Don't have a pressure gauge. I need to add it to the list. The good news is it is not the tranny or motor mounts, It is something to do with engine runability. Will replace the fuel regulator tonight if it is not too big a job and see where we go from there.

The other news is he says the car needs front wheel bearings. I hear a slight droan from the front that you can hear with with the radio and AC off but have always attributed that to tire noise from the all weather Michelin Destiny Tires.

No change in sounds turning left or right and no side sounds louder than the other. Do I really need bearings? How do I test for this?

Do you know at the beginning of a car race you see the drivers warming up there tires doing S's, you want to do S's and see if you can induce any change in the noise you hear. Try it at the speed you hear the noise normally, and be careful doing the S's, don't do them as violently as the race car drivers, if you hear a groaning noise that changes with loading and unloading the bearings, a bearing is worn

[kens96]

Here is the summary:

New Fuel Filter October 07 141K (Replaced the original one the car left the plant with)

At 151K with no codes

New Wires

New Plugs

Cleaned Throttle Body (on the car)

Added Prestone Fuel Conditioner to a full tank of Shell (that's all I've bought)

Had tranny checked (it is good)

Replaced the FPR

Misted the engine with water without the beauty cover (No light show)

Cleaned the PCV

Sprayed the injectors , coils and wires with silicone

We no longer have hesitation.

Still have a slight chuggle/ fish bite while maintaining steady speed.

What's next guys? There can't be much left other than something fails comlpletely so we can replace it.

BTW - Tranny guy was right. Wheel bearings change sound when steering left to right Like BBF suggested. Will save that job for another weekend.

[BodybyFisher]

Ken do you have a laptop?

What do you guys think about a crank sensor or a cam sensor acting up? Does this happen when the car is HOT and COLD? What about a bad connector on a Crank Sensor or CAM sensor?

This sounds SO MUCH like what MIKE D is experiencing, doesn't it? Mike D has done some diagnostics and found that he is low in compression in his #1 cylinder.

Ken, what about doing a compression test?

Consider buying a new coil and swapping it into each position and see if the problem continues

Check the tightness of the ICM and all associated grounds

Check the plugs at the ICM

What causes a cylinder to misfire? Basically, it's one of three things: loss of spark; the air/fuel mixture is too far out of balance to ignite; or loss of compression. Loss of spark includes anything that prevents coil voltage from jumping the electrode gap at the end of the spark plug. Causes include worn, fouled or damaged spark plugs (NEW), bad spark plug wires (NEW) or even a cracked distributor cap (NA). A weak coil or excessive rotor gas inside a distributor would affect all cylinders, not just a single cylinder, (Except the NS that has 4 coils).

"Lean misfire" can occur when the air/fuel mixture is too lean (not enough gasoline in the mixture) to burn. This can be caused by a dirty, clogged or inoperative fuel injector; air leaks; or low fuel pressure because of a weak pump, restricted filter or leaky pressure regulator. Low fuel pressure would affect all cylinders rather than an individual cylinder, as would most air leaks. A leaky EGR valve can also have the same effect as an air leak.

Loss of compression means the cylinder loses most of its air/fuel mixture before it can be ignited. The most likely causes here are a leaky (burned) exhaust valve or a blown head gasket. If two adjacent cylinders are misfiring, it's likely the head gasket between them has failed. Also, if an engine is overheating or losing coolant, it's likely the head gasket is the culprit.

Intermittent misfires are the worst kind to diagnose (you can say that again!) because the misfire comes and goes depending on engine load or operating conditions. They seem to occur for no apparent reason. The engine may only misfire and run rough when cold but then smooth out as it warms up. Or, it may start and idle fine but then misfire or hesitate when it comes under load (or in OD when a load is on the engine). Also, it may run fine most of the time but suddenly misfire or cut out for no apparent reason. Intermittent misfires can be a real challenge to diagnose.

[BodybyFisher]

Here is the summary:

New Fuel Filter October 07 141K (Replaced the original one the car left the plant with)

At 151K with no codes

New Wires

New Plugs

Cleaned Throttle Body (on the car)

Added Prestone Fuel Conditioner to a full tank of Shell (that's all I've bought)

Had tranny checked (it is good)

Replaced the FPR

Misted the engine with water without the beauty cover (No light show)

Cleaned the PCV

Sprayed the injectors , coils and wires with silicone

We no longer have hesitation.

Still have a slight chuggle/ fish bite while maintaining steady speed.

What's next guys? There can't be much left other than something fails comlpletely so we can replace it.

BTW - Tranny guy was right. Wheel bearings change sound when steering left to right Like BBF suggested. Will save that job for another weekend.

Add to that your engine mounts are good.

What caused your hesitation to go away, the fuel pressure regulator?

You say you cleaned your PCV? No codes bothers me, if this is a lean misfire, but it is intermittant. Have you cleaned your EGR valve?, now that is a stretch because I think if it was sticking you would set a pindle position code

This seems to be happening when the engine is loaded.

*********************************************************

Check this out from Autotap

Engine hesitates, stumbles or lacks normal power

The computer uses this information to determine how much fuel is needed to maintain the correct air/fuel mixture, and when extra fuel is needed if the throttle suddenly opens wide.

Symptoms:

Engine Hesitation

Lacks Power

Throttle Position Sensor (TPS) full range test

Mass Airflow (MAF) Graph and Fuel Trim Readings

Probable Causes:

Lean Fuel (P0171, P0174)

Throttle Position (P0120 or P0124) or (P0222 or P0229)

An engine that hesitates, stumbles or misfires when accelerating or when it is under load, is an engine that is either sucking too much air, not getting enough fuel, or misfiring. If the Check Engine Light comes on, you may find any of the following codes:

P0171, P0174 Lean fuel condition codes

P0120 to P0124 Throttle position sensor codes

P0222 to P0229 Throttle position sensor codes

P0400 to P0409 EGR related codes

If there are no misfire codes, a common cause of acceleration stumble is a bad throttle position sensor (TPS). The TPS tells the computer how far the throttle is open. The computer uses this information to determine how much fuel is needed to maintain the correct air/fuel mixture and when extra fuel is needed if the throttle suddenly opens wide. Figure 6 shows a properly functioning TPS. Another common cause are dirty fuel injectors. If varnish deposits have built up in the tips of the injectors, they won’t spray as much fuel as they normally do, or will “dribble” fuel instead of spraying a fine mist. This creates a lean fuel mixture and conditions that are ripe for stumble and hesitation (also misfire). Look at short term fuel trim (STFT) and long term fuel trim (LTFT) with your scantool. If the numbers are high, it tells you the engine is running lean and the injectors need cleaning. Treat mild cases with a high quality fuel-injector cleaner additive. Severe cases require professional cleaning equipment. Other problems that cause acceleration stumble include vacuum leaks, low fuel pressure, a weak spark caused by low coil voltage or bad coil(s), retarded ignition timing, and contaminated gas. Look at the following with your scantool (as shown in Figure 7): throttle position, mass airflow (MAF), short term fuel trim (STFT), long term fuel trim (LTFT), ignition timing, and fuel pressure (if a PID is available). Throttle Position Sensors (TPS) typically wear in the idle and just above idle positions, but they may also have dead spots at any point in their range of travel. With the key on, engine off, graph the sensors output while slowly opening the throttle all the way. The graph should look like a relatively smooth ramp, with no suddenly drops or flat spots

See this link

http://www.autotap.com/DIY_booklet.html#prob4

[kens96]

Thnsk Mike,

Read all the posts about hesitation, chuggle and fish bite and I was also thinking about what Mike D. had with the crank positon sensor episode. Did some searching on the Web and found an article about and Oldsmobile that had similar symptons and it ended up being the crank positon sensor. The only thing that keeps me from going with it all the way is that they would get a stall and or a difficult to start symptom. I have not had those, but who knows.

Think I'll stay on the top of the engine for now and buy a coil pack and swap it around. To change the TPS I know I need a volt meter. I have the tap connector for and 86 Corvette that I used to tap into the TPS and set it to .45 volts. I need to see if it will fit the Northstar as well as the procedure for setting the TPS position. Will buy gas from a different gas station(BP or GATE) and change the filter just to see if it has an affect. I have a laptop and 4 GM cars. I think the Autotap or Protech with the bluetooth look like the way to go !

Will keep knocking things off the list until we get to the root cause.

[BodybyFisher]

Do you want to borrow my Autotap?

[BodybyFisher]

Thnsk Mike,

Read all the posts about hesitation, chuggle and fish bite and I was also thinking about what Mike D. had with the crank positon sensor episode. Did some searching on the Web and found an article about and Oldsmobile that had similar symptons and it ended up being the crank positon sensor. The only thing that keeps me from going with it all the way is that they would get a stall and or a difficult to start symptom. I have not had those, but who knows.

Think I'll stay on the top of the engine for now and buy a coil pack and swap it around. To change the TPS I know I need a volt meter. I have the tap connector for and 86 Corvette that I used to tap into the TPS and set it to .45 volts. I need to see if it will fit the Northstar as well as the procedure for setting the TPS position. Will buy gas from a different gas station(BP or GATE) and change the filter just to see if it has an affect. I have a laptop and 4 GM cars. I think the Autotap or Protech with the bluetooth look like the way to go !

Will keep knocking things off the list until we get to the root cause.

The TPS bolts on there is no adjustment. You might do a resistance test of your TPS using an ohm meter and sweep it up and down a few times and see if you get any anomalies in the sweep also tap on it. Have you ever seen a bad volume control where it was noisy because of a bad contact to the carbon rheostat?, the TPS can act the same when its bad. AGAIN however, I think you would set a code, and in this case, I think it would happen throughout the range.

http://en.wikipedia.org/wiki/Potentiometer

Do you ever have long cranking? I wonder if your year has the dual fuel pump feed where it is fed by a relay, and also fed by the oil pump switch?, if the relay fails, the oil pump switch acts as a back up so that the car does not die on the middle of the highway. What if your fuel pump relay is kicking OUT, and the system kicks over to the oil pump switch to run the fuel pump?

I think you need to do a few things

Fuel pressure test and if possible watch it taped to the windshield

Swap in a known good Fuel Pump Relay

Check your coils and ICM grounds and bolts

Check your ICM plugs, there is a plug on the ICM that if you disconnect it, it allows you to crank the engine without it starting, what if that connection is intermittant or corroded?

Check your fuse center for corrosion for the injectors

Have your battery load tested, next time you get the chuggle watch your charging rate to see if it takes a dive

Check the connections to your TPS, Crank Sensors, and CAM Sensor for good positive connections

Do a compression test

Check your engine grounds

[kens96]

Thanks Mike,

Appreciate the offer for the use of the Autotap. I think I'll work through the list you provided and do some more checking to eliminate the easy items (plugs, grounds, relays, coils). Will look to get a fuel pressure gauge and see if fuel pressure is dropping out. I like the idea of seeing if the voltage drops using the DIC. More sensitive meter than the analog RPM and Tach gauges on the dash that have not show any drops or spikes.

[BodybyFisher]

Thanks Mike,

Appreciate the offer for the use of the Autotap. I think I'll work through the list you provided and do some more checking to eliminate the easy items (plugs, grounds, relays, coils). Will look to get a fuel pressure gauge and see if fuel pressure is dropping out. I like the idea of seeing if the voltage drops using the DIC. More sensitive meter than the analog RPM and Tach gauges on the dash that have not show any drops or spikes.

Ken you and I have the same year engine. Take a look at these photos, this is the seal behind the throttle body spacer, just a thought, I just saw this photo that I took looking for something for jeezy112, this seal did not look good to me and I replaced it.. Just a thought, keep in mind that you are getting a lean condition, it might only be a momentary lean condition, if it was a serious lean condition, you would set a code (171&174)

close up (I don't think I would fly into space with this o-Ring), you can see oil looks like it was leaking out, my question at the time was, could it have been leaking unmetered air in. Do you see the black carbon kind of 'torn' or disturbed just inside the intake above the o-ring, I think that is evidence of air leaking IN... what do you think?

[kens96]

Now that is some carbon buildup! I sprayed around the vacuum lines and outsides of the TB with TB cleaner looking for a surge and or stall to see if something was cracked or leaking. Didn't get a response so I guess the lines and seals are tight. I have been thinking about the EGR valve. It was replaced about 70K ago. I was getting a very poor running condition with hard starts and stalling. It happend instanteneously with a service engine soon and check emssions. From what I have been reading the EGR does most of its work when the car is in a cruising or light load condition. This is when I get the tug or stutter. Could it be I just need to pull it and clean it?

[BodybyFisher]

Personally I believe you would get a pindle position code, when you are doing 41, you should be flowing EGR fully. If you were not, you would get a code.

Spraying around the TB would NOT matter at idle, you are having the problem at 41+ when the engine is labored by the lock up OD.. when the problem becomes more apparent. I did not have any symptoms. Keep in mind that you are not getting codes, so it has to be something that won't throw a code.

BTW, that carbon build up is normal, according to the guru, when the engine is turned off, combustion gasses from the EGR settle in the intake, here is a photo that shows REALLY how THICK, the crud can get... This carbon peeled off like you were using a cheese grater..

Look at this build up, see the hole?

Close up

[kens96]

Have done all the checking I can do beyond blindly replacing parts. It is at the dealership now for a diagnostic check. Spoke dierctly with the service manager and he came out and went over the details of what has been done to date. Also noticed a coolant smell at start up today after parking the car to drop some thing off. It did it again at the dealership with the service manager there. They are going to look for a leak. If comes down to a timesert or big $$'s along with me having to replace the front bearings for around $250 we are contemplating trading out to something newer. Will keep you posted.

[BodybyFisher]

Wow I hope not, this was just a stumble.. Good Luck at the dealer

[kens96]

The dealer called back and is that they are positive the fuel injectors need to be deep cleaned. I have never had this done. Additionally they are saying the EGR ports on the intake plenum need to be cleaned out. They cannot find the a coolant smell or leak but will pressurize the system and confirm. I've asked that they go ahead with doing the work but made it clear I better see a significant difference. Sounds like we were on the right path with air fuel mixture under load. We will see. I really want to get another year out of this car. I believe we will start seeing some significant gains in 09 and 10 in the area of fuel economy technology and style ie. Camaro ; Volt, 2Dr CTS, and maybe the replacement for the STS/DTS

[BodybyFisher]

Hey Ken, I am really glad to hear that, we were right on the problem! Let me know how this turns out. I am sure that your diagnostics helped them focus on the problem faster and more efficiently! Good luck and let us know what happens

[kens96]

Well I picked up the car from the dealer and got to speak with the tech who worked on it. He cleaned the ports for the EGR, cleaned the EGR, and cleaned the fuel injectors. He lifted the intake plenum to clean something under it but realized this engine did not have port he was looking for. He told me the plenum seals were cracked and he did not have a new one so he put everthing back as tight as he could. He still sees ever so slight lean condition at idle. I went to the serrvice writer with the tech and got them to order new plenum seals and they will put them on next week for the cost of the parts and no labor.

As for the coolant smell he pressurized the system and documented there are no leaks. Glad I'm not if for a timesert and head gaskets but I'm either ultra sensative or I'm still getting a wiff of coolant inside the car after it has run awhile and shut it down for 5 to 10 minutes and then restart it. Could be the heater core but I'm not getting any film on the widows or gettting any wiffs when I run the heater or defogger on hot high.

Overall it is running much better but there is still a little fish bite there. Hope the plenum seals willl clear that up.

Got the wheel brearings and rented the puller and sockets from Advance Auto.Will start the job tomorrow.The 34MM feels loose on the nut. There is no 33MM avialable, Is it okay to use the 34MM or do I need to search for a 33MM?

Thanks as usual for the continued support and information

[BodybyFisher]

Hey thats great, if your intake manifold seals are bad, THAT would make sense..making your engine run lean which showed itself under load Cool

Yes you can use the 34 mm, I had the same 'problem'.

[kens96]

Thanks Mike,

Will let you know how the wheel bearings and plenum seal change go. As for the coolant smell if it does turn out to be a heater core I guess I should count my blessings that thats all it is. From what I've read they are not that difficult to remove and replace, but I don't have the FSM for this car so I will need to do some homework.

Ken

[BodybyFisher]

PM me if you want me to send you my cell number, in case you need any moral support during the hub bearing change.

If you are lucky, once you remove the big nut and the 3 hub to knuckle bolts, she will fall right out....

Here are a few photos that might help

[kens96]

Thanks for the pics Mike. Got both sides out and replaced within 3 hours. Passenger side literally fell out. Driver side needed a little convincing with a standard hammer. Amazing how much quieter the interior is and how much less vibration is resonating through the steering wheel.

[BodybyFisher]

HEY good for you! As I mentioned sometimes this job is a cake walk and they fall out... Glad to hear you are getting your car in good shape... Glad to help, Mike