93 Northstar 4.6 hodrod high idle

[BodybyFisher]

I cant wait to see your results, that would explain the high idle if you have a vacuum leak

Did you ever hook up a vacuum gage on this engine?

[crackerjacc]

On Wednesday, December 14, 2016 at 1:51 PM, BodybyFisher said:

On Wednesday, December 14, 2016 at 4:39 PM, BodybyFisher said:

 

What is the idle speed suppose to be for theae motors?

[BodybyFisher]

I would say 625 in drive.  

[crackerjacc]

5 hours ago, BodybyFisher said:

I would say 625 in drive.  

Bah, darn this car.   Time to light a match and end the suffering.

Geez the hits keep coming with this car.  So I was told today that apparently this is a 1996 motor that the previous owner install the 1993 throttle body and electronics, ecu on.  My understanding is at the time he though the 1993 ODB1 ECU would be easier to setup.  I had a good laugh.    Anyone foresee any issues with this arrangement?  Is a 93 throttle body going to function ok on a 96 intake manifold.  It looks like they changed out every sensor to the 93 stuff.  I'm just wondering if there was different air flow characteristics between the 93 and 96 setup causing the higher idle. 

MAP is around 1.1volts at idle (9 inHg).  Manifold Air Temp 64 deg (closer to 80 deg F at operating temperature), Baro Pressure 29 inHg (4.16volts).  TP sensor 0.51volts (0% angle).  900~1000 RPM idle.  EGR pintle position 0.71 volts (EGR actual position 0 volts).  Left and Right injector pulse width each at 3msec.  System in closed loop.

Well the intake fix didn't do much for taming the idle.  I'm at a loss as to what to check next.  I guess fuel pressure, what should that be?  What about the coil packs, would a faulty coil pack cause higher than normal idle?  How do you check them?  Also, although it doesn't sound like there is a leak I understand the backfire plastic valve thing on the end of the plastic intake is known to cause vacuum issues?  I reached my hand and felt around it but I can't feel any obvious leaks nor am I able to change the idle pitch by pushing in to see if it seals and leaks.  It's a bit of a pain but I guess it's worth removing and inspecting.

[BodybyFisher]

13 hours ago, crackerjacc said:

Bah, darn this car.   Time to light a match and end the suffering.

Geez the hits keep coming with this car.  So I was told today that apparently this is a 1996 motor that the previous owner install the 1993 throttle body and electronics, ecu on.  My understanding is at the time he though the 1993 ODB1 ECU would be easier to setup.  I had a good laugh.    Anyone foresee any issues with this arrangement?  Is a 93 throttle body going to function ok on a 96 intake manifold.  It looks like they changed out every sensor to the 93 stuff.  I'm just wondering if there was different air flow characteristics between the 93 and 96 setup causing the higher idle. 

MAP is around 1.1volts at idle (9 inHg).  Manifold Air Temp 64 deg (closer to 80 deg F at operating temperature), Baro Pressure 29 inHg (4.16volts).  TP sensor 0.51volts (0% angle).  900~1000 RPM idle.  EGR pintle position 0.71 volts (EGR actual position 0 volts).  Left and Right injector pulse width each at 3msec.  System in closed loop.

Well the intake fix didn't do much for taming the idle.  I'm at a loss as to what to check next.  I guess fuel pressure, what should that be?  What about the coil packs, would a faulty coil pack cause higher than normal idle?  How do you check them?  Also, although it doesn't sound like there is a leak I understand the backfire plastic valve thing on the end of the plastic intake is known to cause vacuum issues?  I reached my hand and felt around it but I can't feel any obvious leaks nor am I able to change the idle pitch by pushing in to see if it seals and leaks.  It's a bit of a pain but I guess it's worth removing and inspecting.

I don't see any issues as long as he changed the CAM, CRANK, KNOCK and ECT sensors to a sensor that was used with OBD1 engines or at least confirm that the part number is the same.   We recently had a member successfully swap OBD1/OBD2 engines recently see this thread.

Did he use a 96 intake and 93 throttle body?, I didn't think that was possible, please confirm.  Make sure there is no leak behind the throttle body to intake.   Have you checked vacuum, it should be 18 to 22 at idle, what did you find?

With the ignition switch ON and the fuel pump running, the fuel pressure indicated by the fuel pressure gage should be 333-376  kPa (48-55 psi). (from manual)

I don't believe the coil pack could cause this.   If the backfire valve were leaking you would hear a whistle, we have seen them leak, but its obvious.   You don't have lean codes so I don't think fuel pressure or vacuum leaks are responsible.

Can you see any timing parameters at idle?, do you know if Westers messed with the timing tables?

Is the throttle open at idle or being held open by the ISC?

 

[crackerjacc]

On Wednesday, December 14, 2016 at 1:51 PM, BodybyFisher said:

On Wednesday, December 14, 2016 at 4:39 PM, BodybyFisher said:

 

Going to check fuel pressure today.  Yes the ISC is holding the throttle plates open a bit at idle.  I belive Westers play a bit with the tune, calls it a hot rod tune i believe but he doesnt rhink it would affect anything.  I'm flying blind when it comes to what he did.

[BodybyFisher]

Fuel pressure wouldnt cause this.  

Remove the ISC or wind the plunger back till the plate is closed and see what the RPM is.

Also, deposits in the throttle body throat and on the throttle plate edges can hold it open.  You want to see what it idles at with no idle compensation from the isc

Close the plate and see what it idles at, by eliminating the ISC.  You need to isolate what is causing this.  

[OldCadTech]

Why the reluctance to check the basics???           Fuel - Air - Compression - Spark

Check engine vacuum !!! Engine vacuum alone and the action or lack of action of the vacuum gauge needle will speak volumes. Ohm check the coils, pull all the plugs, Lay the plugs on the engine or on the bench as they are in the engine are coil pack "pairs" all the same? is the spark plug carbon tracking? Are they rich? Are they lean? Ohm check the spark plug wires. look at the connector that connects to the spark plug is it corroded - burnt?

A systematic approach beats random checks - even though it is a morph it still needs the basics to run. If you're using used parts - expect "used" inconsistent results.

Look back over this thread, in the beginning you stated the increase was 100 rpm from open to closed loop, any new readings on this? As long as the engine IDLES when the throttle plate is closed take the darn ISC off of the engine and just let the TPS talk to the ECM. The ISC was designed to increase idle speed under load conditions such as A/C compressor engagement and P/S bypass loads AT IDLE. The engine doesn't care as long as the driver doesn't and the driver doesn't care as long as the engine doesn't stall. Use the ISC as a STOP, adjust it so the engine doesn't stall on snap throttle releases. What is idle in gear, brake applied, sitting still? To me that would be the most important engine RPM to deal with.

My old 70 Chevlle SS-396 idled around 950-1000 rpm until you dropped it into gear! IT didn't have an ISC motor on it........... AND it ran GREAT!! Get BACK to the BASICS

[crackerjacc]

6 hours ago, BodybyFisher said:

Fuel pressure wouldnt cause this.  

Remove the ISC or wind the plunger back till the plate is closed and see what the RPM is.

Also, deposits in the throttle body throat and on the throttle plate edges can hold it open.  You want to see what it idles at with no idle compensation from the isc

Close the plate and see what it idles at, by eliminating the ISC.  You need to isolate what is causing this.  

The screen in the FPR was toast but not the issue.  Replaced and still getting 45psi at idle and under load.  All good there.

Reading back I guess I didn't mention that the first thing I did when the ISC seemed to be causing issues was pull it and idled the motor.  It will idle down low without the ISC fine but the owner doesn't like short cuts and wants whatever causing the ISC issues resolved.

So far nothing.  Plugged every possible vacuum port except the MAP sensor.  I also recently changed out the intake gaskets, cleaned and inspected the back-fire flap (or whatever you call it), removed and inspected the injectors and their o-rings.  I did a couple vacuum checks and so far nothing.

How many inHg should the MAP sensor have at idle? (generally)

 

 

 

The only thing that I haven’t done is remove the 93 throttle body from the 96 intake and inspect it for issues internally or for compatibility issues.  I'm wondering if running the 93 MAP on the 96 intake manifold would have different flow characteristics and issues?  I'm beginning to think this could be a problem.

  Something to add to the list.

Currently at operating temperature it idles around 850~900 and in gear drops to 750~800.  He would like it to be about 100rpm less in both cases.

 

 

 

 

Anyway, I will test for vacuum leaks again and manifold vacuum again on Thursday when I'm back at their shop.  Third time's a charm, lol.

 

 

 

 

[BodybyFisher]

The reason for me is because his problem is a racing idle.    I agree that checking vacuum is important and have asked what it is.   I didn't think that low fuel pressure  or coils could cause a racing idle.

I am looking to see if the ISC is holding the throttle open, if the plate is hanging open, or if an unmetered air vacuum leak is causing the racing idle. 

This is what I was trying to say above, and I agree @OldCadTech  lets eliminate the ISC from the equation.

As long as the engine IDLES when the throttle plate is closed take the darn ISC off of the engine and just let the TPS talk to the ECM. The ISC was designed to increase idle speed under load conditions such as A/C compressor engagement and P/S bypass loads AT IDLE. The engine doesn't care as long as the driver doesn't and the driver doesn't care as long as the engine doesn't stall. Use the ISC as a STOP, adjust it so the engine doesn't stall on snap throttle releases

 

[crackerjacc]

41 minutes ago, OldCadTech said:

Why the reluctance to check the basics???           Fuel - Air - Compression - Spark

Check engine vacuum !!! Engine vacuum alone and the action or lack of action of the vacuum gauge needle will speak volumes. Ohm check the coils, pull all the plugs, Lay the plugs on the engine or on the bench as they are in the engine are coil pack "pairs" all the same? is the spark plug carbon tracking? Are they rich? Are they lean? Ohm check the spark plug wires. look at the connector that connects to the spark plug is it corroded - burnt?

A systematic approach beats random checks - even though it is a morph it still needs the basics to run. If you're using used parts - expect "used" inconsistent results.

Look back over this thread, in the beginning you stated the increase was 100 rpm from open to closed loop, any new readings on this? As long as the engine IDLES when the throttle plate is closed take the darn ISC off of the engine and just let the TPS talk to the ECM. The ISC was designed to increase idle speed under load conditions such as A/C compressor engagement and P/S bypass loads AT IDLE. The engine doesn't care as long as the driver doesn't and the driver doesn't care as long as the engine doesn't stall. Use the ISC as a STOP, adjust it so the engine doesn't stall on snap throttle releases. What is idle in gear, brake applied, sitting still? To me that would be the most important engine RPM to deal with.

My old 70 Chevlle SS-396 idled around 950-1000 rpm until you dropped it into gear! IT didn't have an ISC motor on it........... AND it ran GREAT!! Get BACK to the BASICS

Thanks for the advice.  Air check , fuel check, spark check although I didn't ohm check the coils.  It's a new coil pack, new spark plugs etc but never say never I suppose.

Vacuum is an on going issue I'm currently figuring out.  What should be the idel engine vacuum at idle for this motor?

[OldCadTech]

If the owner was worried about modifications the vehicle would still have the original engine in it

[BodybyFisher]

Vacuum should be about 18 to 22..

I am glad to see with the ISC backed off, she idles down.

If you were getting a lean code can you retrieve it?

Does the throttle linkage sit on the stop (not ISC stop) when closed?

[crackerjacc]

3 minutes ago, OldCadTech said:

If the owner was worried about modifications the vehicle would still have the original engine in it

Haha, the number of times I told him he should chuck this motor for a crate engine are many!

Last resort come last Thursday is probably a ISC elimination.

[BodybyFisher]

I cant help but think that the 93 TB is causing this......on the 96 intake.

Keep in mind that the 93 intake was VERY different with the phenolic spacers and EGR ports..  So the 93 TB could be calibrated differently, upping the Idle

[crackerjacc]

2 minutes ago, BodybyFisher said:

I cant help but think that the 93 TB is causing this......on the 96 intake.

Keep in mind that the 93 intake was VERY different with the phenolic spacers and EGR ports..  So the 93 TB could be calibrated differently, upping the Idle

To be honest this has been my thought the whole time.  The TB and intake manifold on these cars are designed hand in hand.  So far no one has said this won't work so I've kept my mouth shut.  I'm wondering if the MAP from a 96 would respond differently?  They are totally different sensor styles though.

To answer your other question I can get the throttle plates to rest on the throttle stop and idle it down but I do have to manually adjust the throttle stop alot.  That's why I was asking before where the throttle plates should sit in stock form because I've been messing with the adjustment screw on the bottom so much I don't know where it should sit, lol.

There are no learn codes but at one point the scanner was reading the O2s as stalled (not cycling) and in a lean state.  I was not able to confirm this again before leaving today.  I'm hoping there isn't an issue running this setup and the 93 fuel tables etc.

Anyway I'm off for the night and will touch base Thursday with results or pictures of the fire after lighting a match to this thing.  I appreciate all the help and advice guys.  Cheers.

[Logan]

2 thoughts....

The '93 should be using a ISC solenoid.

A '96 should be using a IAC valve.

2 different monsters there.

Also some years use a large O ring between the throttle body and the intake. If removed....impossible to put back together without a new O ring....they swell up.

 

 

[crackerjacc]

12 minutes ago, Logan said:

2 thoughts....

The '93 should be using a ISC solenoid.

A '96 should be using a IAC valve.

2 different monsters there.

Also some years use a large O ring between the throttle body and the intake. If removed....impossible to put back together without a new O ring....they swell up.

 

 

The 93 electronics/ECU/sensors/throttle body on a 96 intake which is designed for another setup like you say IAC and ODB2 etc etc make me think the flow characteristics of this intake are not setup for what the 93 had and the MAP is just not getting what it needs.  I do remember the 96 intakes have a huge o-ring setup behind the throttle body so perhaps it's worth the effort for me to take the TB off and inspect what's there.  Patching up any little leaks will help.

 

As far as ditching the ISC, it's a last resort option I suppose but I did try that route and you loose any cold startup, load idle bump, and any other higher idle based functionality right there since this is the only way in the 93/94 setup that this was achieved.  I'll have to make the call when the time comes.

[Logan]

The more I think about it...

The throttle bodies would have be different.....the IAC one would have bores cast in to it accommodate the IAC valve. 

There are likely other multiple ports that would be different. Kinda like different jets and vacuum ports on a carburetor. Different worm holes and grooves..

 

[crackerjacc]

8 hours ago, Logan said:

The more I think about it...

The throttle bodies would have be different.....the IAC one would have bores cast in to it accommodate the IAC valve. 

There are likely other multiple ports that would be different. Kinda like different jets and vacuum ports on a carburetor. Different worm holes and grooves..

 

Exactly my thoughts, what i was trying to say with regards to the flow characteristics etc.   This setup would work great if i had the ability like other projects to play in the code and manipulate MAP and fuel curve but that isn't going to happen in this particular case.  I respect Westers hard work in reverse engineering the code himself, must have been a lot of work.

[BodybyFisher]

So change the intake to a 93/94?

[OldCadTech]

On 12/12/2016 at 9:27 AM, crackerjacc said:

 

Since that is NOT a 93-94 intake or it would have the warnings about do not start without cover in place. The throttle body must be a 93-94 since it has ISC..... Change the T-body...Where is the MAF sensor? IAT sensor? If it has a MAF and IAT sensor what year are those from? Maybe the PCM is getting bad or skewed info - garbage in garbage out -

@BodybyFisher Mike, what do you say? Does your Eldo have MAF sensor?

[crackerjacc]

9 hours ago, OldCadTech said:

Since that is NOT a 93-94 intake or it would have the warnings about do not start without cover in place. The throttle body must be a 93-94 since it has ISC..... Change the T-body...Where is the MAF sensor? IAT sensor? If it has a MAF and IAT sensor what year are those from? Maybe the PCM is getting bad or skewed info - garbage in garbage out -

@BodybyFisher Mike, what do you say? Does your Eldo have MAF sensor?

It's a 96 motor with 93/94 TB and electronics.  In 93 they used a speed density setup which use a MAP (manifold absolute pressure) and not a MAF (Mass Air Flow) setup.  In 93/94 they used a ISC (Idle speed control, plunger motor that bumpers the idle arm) to vary idle.  In a MAF setup they used a IAC (Idle air controller, a solenoid that varies the opening to an orifice to vary air flow).

I can't change the TB without changing the entire ECU and wiring setup to something that is designed and calibrated for an IAC and MAF setup like the 96 was.

[crackerjacc]

So tested for ANY vacuum leaks for a third time just to be sure and there was none.  What I did find was the drastic differences in air flow to the different ports on the 96 intake.  I think the PCV port has more vacuum that the shop-vac in this setup, lol.  The FPR port is about the same and correct.  I can't say if the brake booster port is the same but it's not leaking vacuum so it's ok.  The MAP sensor port unfortunately is a little lower than it should be compared to the 93.  Probably design incompatibilities between mixing the 93 TB.  I was able to create a re-stricter for the PCV port which in turn bumped the MAP port vacuum just enough to get my idle down about 100rpm which is acceptable around 700~750, high sixes in gear.

What I'm seeing with this setup is a very touchy throttle which I now know is attributed to the mixing of the 93 TB and 96 intake.  As soon as the throttle is increased there is a rapid decrease in vacuum.  Decrease in vacuum is normal a operation in a SD MAP setup but not this rapid and as a result the idle revs very quickly and is a little slow to recover to idle.  I have some ideas as to how to manipulate the vacuum to the MAP port to resolve this but it's not unacceptable as is.  It's the middle of winter up here so no road testing until spring so the owner has decided to close up shop until then on all projects.  I guess I'll have to wait and see.

It's interesting, in the following photo you can see where someone went to the trouble of making or purchasing a spacer to make this setup work and have EGR function.  We removed the EGR code from the tune but left the EGR there and wired in so the computer wouldn't throw error faults with regards to it missing but I did removed the EGR tube from the TB and block off the port to clean things up.

 

[OldCadTech]

Okay, so you're mixing apples and oranges. The point I was trying to make is make it as close to a '96 as you can....