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Chevy stalls during acceleration

Tiny
ALBINASBOY
  • MEMBER
  • 1991 CHEVROLET LUMINA
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 15,000 MILES
Hi. My 3.1 Lumina (car)stalled yesterday at about 30 mph, (engine was warm). It restarted fine and I drove slow home. Next day discovered that while engine was cold, it will start fine, but when you throttle up fast it dies. If you throttle up slowly it will stay running.I was doing this in "park". Didn't want to take a chance of breaking down.I replaced the cps about 6 mos ago when I had a no-start deal and it corrected the problem. For the last few months when the engine was warm it would idle rough, but I think it needs a new tps or and iac valve. But it ran good enough, I didn't attempt to repair. When the engine is cold it is in open loop, it doesn't use the sensers does it? So the tps wouldn't have anything to do with it? Fuel pressure was 45 psi at the schreader valve. SO. My engine always strts up goog. Hot or cold. Doesn't idle well when hot. But will stall on fast acceleration hot OR cold.
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Wednesday, August 5th, 2009 AT 7:55 AM

26 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Has the check engine light come on? Also, have you checked to make sure the catylatic converter isn't plugging? If all of these things are fine, have you checked fuel pump pressure?
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Wednesday, August 5th, 2009 AT 6:47 PM
Tiny
ALBINASBOY
  • MEMBER
  • 17 POSTS
. No check engine light or stored codes, converter is new, and like I said.F.P. Is 45psi.I wanted to know if when this engine is in open loop could the throttle position sensor, if it was real worn. Shut the engine down as I described?
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Wednesday, August 5th, 2009 AT 7:53 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
I would have to say no. It would cause idle problems or maybe surging, but I can't see it shutting it down.
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Wednesday, August 5th, 2009 AT 10:57 PM
Tiny
ALBINASBOY
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  • 17 POSTS
Well?//
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Thursday, August 6th, 2009 AT 12:34 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Does he ehicle have the 3.1L V6? If so, I would check for an intake vacuum leak. They are common on this engine.
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Thursday, August 6th, 2009 AT 8:23 AM
Tiny
ALBINASBOY
  • MEMBER
  • 17 POSTS
Yes, like I said.3.1. Intake vacuum is 17. Gm had trouble with intake gaskets when they put dexcool in the engines. It rotted stuff. This engine doesn't use. It's a 1991.
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Thursday, August 6th, 2009 AT 9:50 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Honestly, this is a tough one. If the TPS is bad, I would say it wouldn't shut it down, but I'm at a loss.
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Thursday, August 6th, 2009 AT 9:01 PM
Tiny
ALBINASBOY
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  • 17 POSTS
I expected a little more than this for an answer. How long have you been a mechanic?
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Friday, August 7th, 2009 AT 9:10 AM
Tiny
ALBINASBOY
  • MEMBER
  • 17 POSTS
Is anyone going to answer my question I donated for?
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Friday, August 7th, 2009 AT 4:26 PM
Tiny
ALBINASBOY
  • MEMBER
  • 17 POSTS
Response deemed inappropriate by buddycraigg
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Saturday, August 8th, 2009 AT 1:10 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Sir:
I have been a mechanic for 29 years. Everything you have described to me indicates there is a vacuum leak or a shortage of fuel to the engine. I will repost this so others can answer it.
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Saturday, August 8th, 2009 AT 4:36 PM
Tiny
BUDDYCRAIGG
  • MECHANIC
  • 2,262 POSTS
To answer some of the side questions you asked.
Yes, the computer is still using the TPS and the MAP while in open loop.
The ECM is just using a predefined table for fuel delivery and spark timing.
After it goes in to closed loop, then the ECM gets to make it own adjustments.

Your fuel pressure is at 45, but what does it do when it's running?
It should be down to about 37 at idle, and then when you blip the throttle open quickly, it should jump up to 42-ish.
If you dont have these numbers, then the pump isn't able to supply enough volume, or there is a restriction in the fuel lines.

You can check the TPS, you have 3 pins in the connector.
Resistance between 1 and 2 will be high and should go down smoothly as you open the throttle.
Pins 2 and 3 should have low resistance and go up smoothly as you open the throttle.
If the resistance fails to change, or jumps around then you have a problem.

Finally, check for a weak spark.
I've seen failing ignition modules that don't ground the coils enough for them to get a full charge, so when the magnetic field collapses, there's not enough to make the plugs have a good hot spark.
And thus the spark is not enough to ignite a rich fuel mixture.

Hopefully one of these suggestions will lead you to your problem.
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Saturday, August 8th, 2009 AT 4:48 PM
Tiny
BUDDYCRAIGG
  • MECHANIC
  • 2,262 POSTS
One more thing.

as an added test to see if you are starving for fuel.
unplug this line and spray starting fluid in the hole in the big rubber tube while opening up the throttle.


https://www.2carpros.com/forum/automotive_pictures/281878_grand_am_1.jpg

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Saturday, August 8th, 2009 AT 5:10 PM
Tiny
ALBINASBOY
  • MEMBER
  • 17 POSTS
Thanks for the professional answer. Really appreciate it. Fuel pressure was checked while the car was running, and it was as you described. Also kept good pressure after it stalled.I will check tps sensor and do spray test anywys. It sure seems like it is an electrical thing. It doesn't stumble. Just a real fast quit. Will reply soon. Thanks again
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Saturday, August 8th, 2009 AT 6:09 PM
Tiny
ALBINASBOY
  • MEMBER
  • 17 POSTS
Hi Buddy. Well, I re-checked the fuel pressure with it running and it was as you said it should be. It even has good pressure in the rail after it stalls.I cleaned the iac valve and the throttle plate. It wasn't really dirty, I had cleaned it 6 mos ago when I changed the air filter, but I did notice quite a bit of oil in the air pipe for the air cleaner. The engine is good, so I'm gonna change the pcv valve. One thing.I had a digital olm meter hooked up to the tps.I didn't get any flat spots while checking, but it sure jumped around alot. Like started at 1.4 then jump to 1.8 then go down to 1.5 then 2.0 etc. And then sometimes it was a pretty smooth, gradual transition.I'd say 3 out of 4 times it jumped alot.2 of us checked it several times. Should I change it. Thanks
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Sunday, August 9th, 2009 AT 1:55 PM
Tiny
ALBINASBOY
  • MEMBER
  • 17 POSTS
I had to move the engine forward and take the map sensor bracket out just to get to the pcv valve in the back valve cover. It has a hose that goes under the plenum. Do I replace the whole thing. What an idiot place to put that
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Sunday, August 9th, 2009 AT 2:09 PM
Tiny
BUDDYCRAIGG
  • MECHANIC
  • 2,262 POSTS
If you are sure you had a good connection on the terminals when it was jumping around, then yes I recommend that you replace it.
Although I will be surprised if it is the root cause of your problem.
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Sunday, August 9th, 2009 AT 5:45 PM
Tiny
ALBINASBOY
  • MEMBER
  • 17 POSTS
Hi. Well, I haven't put the new tps in yet.I re-learned the computer. Then after while it was idling, it stalled.I had a fuel pressure gauge on it and it said 40 psi. It re-started and I noticed when I rev it up, the pressure gauge will bounce up to 45psi just for a sec. Then go back down. Then it stalls. Is it normal for the fuel pressure to bounce up like that?I also tried spraying in starting fluid while revving. It just stalls
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Monday, August 10th, 2009 AT 8:20 AM
Tiny
ALBINASBOY
  • MEMBER
  • 17 POSTS
.I have a "known" good module and coils. Should I put those on?
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Monday, August 10th, 2009 AT 8:25 AM
Tiny
ALBINASBOY
  • MEMBER
  • 17 POSTS
One more thing. After it stalls. It has 40 psi f.P. But if it sits for a min it looses pressure. It's not leaking. Maybe just my gauge. Also after letting it idle for 10 min, and it's still running. The vacuum gauge dropped from 20 to 14. Gauge says "late ignition timing". It always runs rougher at idle when hot
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Monday, August 10th, 2009 AT 8:51 AM

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