Could a bad IAC cause a lean cond.?
03-02-2002, 10:03 AM
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Could a bad IAC cause a lean condition?
I am in the process of hunting down a part throttle/WOT knock,
I have tried to eliminate as many causes as possible.
I believe that it may be caused by a lean condition.
The Performance Resource Chip that I originally thought
was the culprit ended up as a dead end.
I switched the chip back to the stock piece and set the timing
1 degree below the factory setting @ 5'. New plugs and new
wires. Have also ran 3 cans of GM Top Cylinder cleaner through it.
This is with 93 Octane in the tank.
Still have the same spark/pre-det. knock at the same places as
before.
Back when this test was made, I was able to borrow a TECH1
briefly to verify this. No longer have access to it though.
The Plenum, Lower Intake and TB have fresh gaskets, vacuum
hoses have been replaced, brand spanken new EGR Valve, MAF,
and FPR checked at approximately @ 43 PSI at WOT. TPS@.54
...and still no change.
No codes stored.
Does anyone know if a bad IAC can cause a lean condition?
Any other ideas would be greatly appreciated.
I have tried to eliminate as many causes as possible.
I believe that it may be caused by a lean condition.
The Performance Resource Chip that I originally thought
was the culprit ended up as a dead end.
I switched the chip back to the stock piece and set the timing
1 degree below the factory setting @ 5'. New plugs and new
wires. Have also ran 3 cans of GM Top Cylinder cleaner through it.
This is with 93 Octane in the tank.
Still have the same spark/pre-det. knock at the same places as
before.
Back when this test was made, I was able to borrow a TECH1
briefly to verify this. No longer have access to it though.
The Plenum, Lower Intake and TB have fresh gaskets, vacuum
hoses have been replaced, brand spanken new EGR Valve, MAF,
and FPR checked at approximately @ 43 PSI at WOT. TPS@.54
...and still no change.
No codes stored.
Does anyone know if a bad IAC can cause a lean condition?
Any other ideas would be greatly appreciated.
Last edited by whiteroc; 03-02-2002 at 10:11 AM.
03-02-2002, 10:31 AM
#2
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Re: Could a bad IAC cause a lean condition?
Originally posted by whiteroc
I am in the process of hunting down a part throttle/WOT knock,
I have tried to eliminate as many causes as possible.
I believe that it may be caused by a lean condition.
The Performance Resource Chip that I originally thought
was the culprit ended up as a dead end.
I switched the chip back to the stock piece and set the timing
1 degree below the factory setting @ 5'. New plugs and new
wires. Have also ran 3 cans of GM Top Cylinder cleaner through it.
This is with 93 Octane in the tank.
Still have the same spark/pre-det. knock at the same places as
before.
Back when this test was made, I was able to borrow a TECH1
briefly to verify this. No longer have access to it though.
The Plenum, Lower Intake and TB have fresh gaskets, vacuum
hoses have been replaced, brand spanken new EGR Valve, MAF,
and FPR checked at approximately @ 43 PSI at WOT. TPS@.54
...and still no change.
No codes stored.
Does anyone know if a bad IAC can cause a lean condition?
Any other ideas would be greatly appreciated.
I am in the process of hunting down a part throttle/WOT knock,
I have tried to eliminate as many causes as possible.
I believe that it may be caused by a lean condition.
The Performance Resource Chip that I originally thought
was the culprit ended up as a dead end.
I switched the chip back to the stock piece and set the timing
1 degree below the factory setting @ 5'. New plugs and new
wires. Have also ran 3 cans of GM Top Cylinder cleaner through it.
This is with 93 Octane in the tank.
Still have the same spark/pre-det. knock at the same places as
before.
Back when this test was made, I was able to borrow a TECH1
briefly to verify this. No longer have access to it though.
The Plenum, Lower Intake and TB have fresh gaskets, vacuum
hoses have been replaced, brand spanken new EGR Valve, MAF,
and FPR checked at approximately @ 43 PSI at WOT. TPS@.54
...and still no change.
No codes stored.
Does anyone know if a bad IAC can cause a lean condition?
Any other ideas would be greatly appreciated.
Have you checked/replaced your knock sensor? Seems if you are getting a knock it should be sensing it and retarding timing to account for it...............
03-02-2002, 01:52 PM
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Re: Re: Could a bad IAC cause a lean condition?
Originally posted by BlazinOR
I am far from an expert on this stuff, but you want ideas, so I'll try.............the IAC only affects IDLE mixture, not WOT or even part throttle, *from my limited education on IAC*. If you don't have a scanner, and it sounds like you don't, I'd suggest getting one...............Auto Xray's are about $150 and worth every penny. Or go with a Craig Moates type hookup to your ALDL through a laptop, either way it is rather important.
Have you checked/replaced your knock sensor? Seems if you are getting a knock it should be sensing it and retarding timing to account for it...............
I am far from an expert on this stuff, but you want ideas, so I'll try.............the IAC only affects IDLE mixture, not WOT or even part throttle, *from my limited education on IAC*. If you don't have a scanner, and it sounds like you don't, I'd suggest getting one...............Auto Xray's are about $150 and worth every penny. Or go with a Craig Moates type hookup to your ALDL through a laptop, either way it is rather important.
Have you checked/replaced your knock sensor? Seems if you are getting a knock it should be sensing it and retarding timing to account for it...............
it from time to time rattling a little before the ECM compensates
with the knock sensor input. On the matter of the IAC,
if it is able to leak vacuum, then it would'nt matter if it was idle,
part throttle or WOT -or would it?
The long block is the stock factory set-up.
Thanks for the replies guys.
Last edited by whiteroc; 03-02-2002 at 01:55 PM.
03-02-2002, 07:41 PM
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The IAC has no bearing on part throttle and full throttle performance.
You may have a problem with you TPS. My car didn't knock bad, but it did knock. My ECM was bad, it was only sending 1.4volts to the TPS. So, check the TPS voltage at WOT.
You may have a problem with you TPS. My car didn't knock bad, but it did knock. My ECM was bad, it was only sending 1.4volts to the TPS. So, check the TPS voltage at WOT.
03-02-2002, 09:10 PM
#6
whiteroc,
I'll guess I'll take teh contrary point of view. The IAC could be causing a slightly lean mixture if it isn't seating fully or is stuck open. However, since you have a MAF, the ECM relies most heavily on the MAF input and considers the TPS as only a small part of the fuel calculations. You may be lean because of a stick IAC, but only just slightly. It's more likely that if the mixture is truly lean, you have a fuel delivery issue or leak in the intake. The ECM will only tollerate the lean condition for a short time before setting a '44', so I'm guessing the ECM doesn't think it's lean either.
You've got a good one there, for sure. I'll think on it for a bit and pop back in if I get any real revelations.
I'll guess I'll take teh contrary point of view. The IAC could be causing a slightly lean mixture if it isn't seating fully or is stuck open. However, since you have a MAF, the ECM relies most heavily on the MAF input and considers the TPS as only a small part of the fuel calculations. You may be lean because of a stick IAC, but only just slightly. It's more likely that if the mixture is truly lean, you have a fuel delivery issue or leak in the intake. The ECM will only tollerate the lean condition for a short time before setting a '44', so I'm guessing the ECM doesn't think it's lean either.
You've got a good one there, for sure. I'll think on it for a bit and pop back in if I get any real revelations.
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03-05-2002, 09:44 PM
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Originally posted by LS1thunder
My guess would be vacuum leak or fuel filter to start, or possibly a fuel pump relay. Then go for a scanner.
My guess would be vacuum leak or fuel filter to start, or possibly a fuel pump relay. Then go for a scanner.
leaks that I could find. The fuel filter is new.
I don't understand how the fuel pump relay could be causing
a lean condition. The fuel pump seems to be working fine.
Keep um' coming guys -thanks
03-05-2002, 09:47 PM
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Have you checked the voltage of the TPS at WOT?
Maybe change the O2 sensor(s)? If the computer isn't coming up with codes, then you may have a bad O2, because the computer should tell you that you have a lean condition, thats its job, right?
Maybe change the O2 sensor(s)? If the computer isn't coming up with codes, then you may have a bad O2, because the computer should tell you that you have a lean condition, thats its job, right?
03-05-2002, 10:17 PM
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TPS is at 4.0+ volts @ WOT, watched it climb with no faults.
The O2 Sensor has also been replaced. GM parts counter piece.
The spark/pre-ign. knock may very well not be caused by
a lean condition. I am just out of ideas as to why it is still
knocking after all that has been changed on it.
The O2 Sensor has also been replaced. GM parts counter piece.
The spark/pre-ign. knock may very well not be caused by
a lean condition. I am just out of ideas as to why it is still
knocking after all that has been changed on it.
Last edited by whiteroc; 03-05-2002 at 10:21 PM.
03-05-2002, 10:20 PM
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Have you tried replacing the Ignition Coil? If not... get a MSD GM Blaster coil, it wires up exaclt like stock, and you get some more power behind your spark.
03-05-2002, 10:39 PM
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Originally posted by nblanchard
Have you tried replacing the Ignition Coil? If not... get a MSD GM Blaster coil, it wires up exaclt like stock, and you get some more power behind your spark.
Have you tried replacing the Ignition Coil? If not... get a MSD GM Blaster coil, it wires up exaclt like stock, and you get some more power behind your spark.
made for this car. The plugs are AC DELCO R45TSs which has the same factory heat range. The gap is set at .035 back from .045
The wires have been checked for exhaust burns etc.
The engine idles smoothly, no uneven firing noticed.
03-05-2002, 11:34 PM
#13
Hey, White,
You don't suppose you might still have some hot spots in your chambers, like a little carbon on some valves or chamber walls? A little incandescent chunk of carbon makes for a really nice "glow plug" to get the preignition going nicely. A little water injection instead of top cylinder cleaner might be worth a try if you haven't had the heads off for a while.
You might also want to make sure the EGR still works to keep that head temperature down a bit. I realize that the valve is new, but the solenoid needs to work and the intake passages need to be clear and flowing.
Forget about the O² sensor at WOT - the ECM basically ignores it at that point for fuel calculations. That doesn't mean that you can't still use the O² sensor at WOT to diagnose the situation or tune the fuel system, however. The O² is a good tool for that.
Spark energy isn't a problem either. A misfire would actually tend to cool a cylinder and deter any preignition on subsequent cycles. Spark timing is a different issue, however.
And back to your original question - it doesn't take long to remove the IAC, clean and lube the pintle rack gear, and clean the seat in the throttle body just to be sure it closes fully. If you want to test your theory then, jump the ALDL diagnostic request just as you would to set minimum air, unplug the IAC when it is fully seated, then start the engine ans adjust the throttle plates up a few turns to get a "streetable" idle. Drive it that way and see if the problem still occurs. If so, forget the IAC theory, but rest assured it's clean and working coprrectly.
Just a thought or two...
You don't suppose you might still have some hot spots in your chambers, like a little carbon on some valves or chamber walls? A little incandescent chunk of carbon makes for a really nice "glow plug" to get the preignition going nicely. A little water injection instead of top cylinder cleaner might be worth a try if you haven't had the heads off for a while.
You might also want to make sure the EGR still works to keep that head temperature down a bit. I realize that the valve is new, but the solenoid needs to work and the intake passages need to be clear and flowing.
Forget about the O² sensor at WOT - the ECM basically ignores it at that point for fuel calculations. That doesn't mean that you can't still use the O² sensor at WOT to diagnose the situation or tune the fuel system, however. The O² is a good tool for that.
Spark energy isn't a problem either. A misfire would actually tend to cool a cylinder and deter any preignition on subsequent cycles. Spark timing is a different issue, however.
And back to your original question - it doesn't take long to remove the IAC, clean and lube the pintle rack gear, and clean the seat in the throttle body just to be sure it closes fully. If you want to test your theory then, jump the ALDL diagnostic request just as you would to set minimum air, unplug the IAC when it is fully seated, then start the engine ans adjust the throttle plates up a few turns to get a "streetable" idle. Drive it that way and see if the problem still occurs. If so, forget the IAC theory, but rest assured it's clean and working coprrectly.
Just a thought or two...
03-06-2002, 08:34 AM
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Kind of a long story.....
I had a similar problem with light part-throttle ping years ago (I seem to recall there was a WOT knock on occasion).
Running top engine cleaner thru the engine per the instructions on the can would help for a short while, but the ping would return. A drivability tech at the local Chevy dealership told me to try using the cleaner per the instructions, then allow the engine to cool, remove the plugs and squirt the left over cleaner into the cylinders. Let it soak overnight, then run the engine. This was a lot more effective, but still the ping returned after a "longer" while.
Thinking I was on the right track; engine deposits, hot spots, etc. I did some research. I had started to notice the "blue tailpipe smoke on start up" and dug out a TSB which described a warped lower intake manifold allowing oil from the crankcase to be sucked into the intake tract. Was this where the deposits where coming from? Performing the inspections per the TSB, the intake manifold was indeed warped.
Bottom line is that after replacing the manifold, the ping/knock went away and has yet to return.
Running top engine cleaner thru the engine per the instructions on the can would help for a short while, but the ping would return. A drivability tech at the local Chevy dealership told me to try using the cleaner per the instructions, then allow the engine to cool, remove the plugs and squirt the left over cleaner into the cylinders. Let it soak overnight, then run the engine. This was a lot more effective, but still the ping returned after a "longer" while.
Thinking I was on the right track; engine deposits, hot spots, etc. I did some research. I had started to notice the "blue tailpipe smoke on start up" and dug out a TSB which described a warped lower intake manifold allowing oil from the crankcase to be sucked into the intake tract. Was this where the deposits where coming from? Performing the inspections per the TSB, the intake manifold was indeed warped.
Bottom line is that after replacing the manifold, the ping/knock went away and has yet to return.
03-06-2002, 10:38 AM
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I have a similar problem to what you describe. I'll have some pining under initial load (only once in awhile though, not all the time) but at WOT there's nothing. I also have a strange smell that comes from the car after I give it WOT almost like somethings burning. Then my RPMs will fall considerably, but shoot back up after driving around for a little while. The RPMs start going wacky especially if I give it WOT on the highway then decelerate off the ramp. I've replaced and reset the TPS, IAC, fuel filter, ignition coil, cleaned out the TB, replaced the air filters, full tune-up....but nothing helps. I'm not tripping any codes but the problem is definitely there. Let me know if you find out what the problem is.
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