Car starts then stalls instantly --- Help! - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1987-1991 Parley with regards to your 1987 to 1991 Bonneville, Olds 88 or Buick Le Sabre Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 08-18-2005, 08:58 PM   #1
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Default Car starts then stalls instantly --- Help!

I have a 88 bonneville. I can not get it to run after I start it. Turn the key, it fires right up, then dies almost instantly. If i give it a little gas it will run, but it will die once I let off. I have changed the IAC, no luck.

The car ran just fine the day before, no problems what so ever. BTW, it only has 48,000 original miles. Can not pull any codes from it. Also, it has a strong smell of unburnt gas, or so it seems, maybe even some back fireing? The IAC that i pulled out was covered in black soot. Is that normal?

I need help! I just bought this car about a month ago from grandparents, who kept it well maintained.

Thanks!
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Old 08-18-2005, 10:09 PM   #2
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It still sounds like an IAC problem. The car starts using the ignition module only and a priming shot to the injectors from the ECM. After it starts the timing switches over to ECM control, but that circuit must be somewhat functional or it wouldn't run with the throttle opened partially. If you have no codes, it may be possible the wiring to the IAC is a problem and wouldn't be cured by replacing it. The black color on the IAC is normal, and most get really gummy after extended operation. When you replaced it, did you clean the passage inside also? Does the engine run normally if you use the throttle to keep it running? I know you mentioned a possible backfire but does it run smoothly if you keep it running "manually"? If you have tried repeated starts, it will load up on fuel as the ECM will give it a priming shot from all six injectors every time you try to start it.
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Old 08-18-2005, 10:33 PM   #3
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Check the fuel pressure regulator. See if fuel is getting into the vaccum supply line.
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Old 08-18-2005, 11:10 PM   #4
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It seems to run smooth when I keep it running, unless i try to keep it at a speed just above idle, then it hesitates and tries to stall. How would I check the wiring? Is that something that happens normaly?

I did not, however, clean the passage inside. Would that prevent it from functioning properly?
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Old 08-19-2005, 12:09 AM   #5
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Lets get a little more detail...

When you start the car how long will it run? Should be for a few seconds if its what I think it is...

Just as stated, the ECM will rattle the injectors to prime for the start... The car can run off this initial primbe for a few seconds... I think this sequence is called module mode, at 400 rpms the ECM should take over the reigns of control...

If it doesn't, you'll start the car with that initial pulse of fuel, usually( if you have a tach ) the tach will go to 1500-1800 and then drop to 1100 or so... If the ECM is not taking over control the car will usually just die... At time if you try to keep it running you may just get a series of backfires and the car may still die anyhow...

Is this car backfiring through the intake? The unburnt fuel you are smelling makes me wonder if you are having ECM issues...


I will reccomend that you first do a fuel pressure test to see if the fuel system is within the proper pressure range, and holding pressure...

Also being that this is an 88, is this a Vin 3 3.8 V6 or is this a 3800 Vin C V6( if its a 3800 the top of the manifold or the injector sight shield will have 3800 in red )..

Being that the car does start for a brief time, we can say you have spark, and evidentally fuel... But do check the pressure and get back to us... You'll be looking for 37-41 or so PSI..

Good Luck

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Old 08-26-2005, 12:16 PM   #6
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Update

Sorry it took so long for a reply, I live in an apartment complex that doesn't allow anyone to work on cars, so I had to wait till no one was home.... Anywho

The motor is a vin C.

the car will only run if I pump the gas pedal. If i try to hold it at a constant (higher) rpm, it will die just as fast as if I let it idle. It only back fires if I try to keep it running when its at a low rpm or while its stalling. Its usually just does one pulse back through the manifold (as it sounds), sort of like when you cut off a lawn mower and right before the motor stops spinning, turn it back on and it will make a pop sound.

I have not tested the fuel pressure, as I do not have a gauge. I am currently trying to find one to borrow, and if I can't I have to wait until I get paid to maybe rent one from autozone, or just buy one.

I have not smelled the unburnt fuel since the first day that I had the problems. Also, I did clean the area where the ica goes just to be sure.

hopefully this is helpful....
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Old 08-26-2005, 12:20 PM   #7
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Sounds a lot like the ECM is not taking over timming control...

I want to say bad ECM, but without being there to look at it, its difficult...

Check the Fuel pressure.... If the pressure is good with the ignition on, start the car and see if the pressure is still good... also listen to the Pump as the ECM controls the pump... Sounds stupid I know..

Once you figure out the fule pressure get back to us..

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Old 08-26-2005, 12:36 PM   #8
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Have your checked for codes? Water in fuel?
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Old 08-26-2005, 12:53 PM   #9
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No codes, except 12.

not sure about water in the fuel, not even sure how to check that.
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Old 08-26-2005, 01:12 PM   #10
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I'm skeptical about this being it... but perhaps a vacuum leak? Since you cannot really keep the car running, it'll be hard to prove this. But It has happened to me a couple times where the car just won't stay running with a very large vacuum leak. It'll fire right up, then die within a second. Sometimes with the perfect amount of throttle the car will stay running, then the rpms will drop then raise, drop, raise.. and even with consistent throttle the engine'* RPMS will be all over the place.

Only two vacuum sources can be that big of a leak. The brake booster line [blocked off if on an ABS car, used if on non-ABS], and the PCV Valve. Or the entire engine vacuum distribution block. If that is completely missing, but i think you'd notice a big gaping hole eh?
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