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Loss of power and stalling

Tiny
BSBOY
  • MEMBER
  • 1981 PONTIAC GRAND PRIX
  • 3.8L
  • V6
  • 2WD
  • AUTOMATIC
  • 68,000 MILES
Once vehicle is warmed up when stepping on the gas it loses power and stalls. Pumping the gas does not help, but at idle car runs fine. Replaced the fuel pump and carburetor. Vehicle ran fine for about a week now it's stalling, hesitating and losing power. Distributor is new. Replaced plugs and wires still no change.
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Saturday, May 30th, 2020 AT 5:01 PM

23 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

When I hear of power loss, I always thing of a plugged catalytic converter. Have you checked that? Next, is there any black smoke from the exhaust when this happens?

Let me know.
Joe
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Saturday, May 30th, 2020 AT 7:26 PM
Tiny
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The catalytic converter is eliminated. Also I have like grey smoke coming out when this happens I noticed my transmission fluid was low so I topped off and smoke got worse and hesitating and stalling got worse. Could it be a bad radiator causing the problem?
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Tuesday, June 2nd, 2020 AT 10:16 AM
Tiny
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Hi,

Have you noticed any loss of engine coolant? Also, with the cat eliminated, it is hard to know what the computer is doing with fuel trims (air/fuel mixture).

Do me a favor, I'm not sure why topping off the ATF would have caused this, but the idea that you have the white/gray smoke is a concern. That could be related to coolant getting burned in the combustion chamber via a bad head gasket. Take a look through this link and check as much as you can following it. Let me know what you find.

https://www.2carpros.com/articles/head-gasket-blown-test

Let me know.

Joe
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Tuesday, June 2nd, 2020 AT 7:47 PM
Tiny
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I'm not leaking coolant. The smoke smells like oil burning. I checked all plugs i'm getting good readings on all of them. Checked the combustion chamber it stayed blue. No oil leaking. After replacing radiator topped off transmission fluid again and it has not gone down. Checked fuel flow to the carburetor that's okay. Checked timing that's all okay. I don't have a clue unless the re-manufactured carburetor is bad. Any other suggestions would be greatly appreciated.
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Friday, June 5th, 2020 AT 9:12 PM
Tiny
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The only thing I can think of related to the ATF causing it to get worse is the old vacuum modulator on the trans. However, if this is the original transmission, I don't believe it had one. Was the transmission changed (different model)? The ones that had the modulator valve would allow ATF to be sucked into the engine via the vacuum hose when they failed.
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Friday, June 5th, 2020 AT 10:15 PM
Tiny
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It's the original transmission no vacuum pump on it. The car is all original but sat for a while and did not run at all when I purchased it. I did change the radiator and i'm not losing transmission fluid anymore, but the car still wont run under load.
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Sunday, June 7th, 2020 AT 9:17 AM
Tiny
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Hi,

Do you know what model the transmission is? Is it a turbo 350? It could also be a 200. Are there any vacuum hoses going to the transmission? My manual shows several different possibilities. One is a turbo 350 that does have a vacuum modulator. It is a valve that simple identifies engine load (via vacuum) to determine line pressure and shift points. In it is a diaphragm which can go bad and allow ATF to enter the combustion chamber and create odd shift patterns.

Joe
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Sunday, June 7th, 2020 AT 8:31 PM
Tiny
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I will check tomorrow to see if I see any vacuum lines going to the transmission and try to determine what transmission I have and get back to you. Thank you
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Tuesday, June 9th, 2020 AT 8:13 PM
Tiny
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Sounds good. That is the only thing I can think of that would cause the engine to smoke when you added ATF.

I will watch for your reply.

Take care,
Joe
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Tuesday, June 9th, 2020 AT 9:08 PM
Tiny
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I do have a vacuum modulator on my transmission I ordered a new one and waiting for it to come in and see if that helps with the problem. Thank you ill get back as soon as I know something.
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Friday, June 12th, 2020 AT 10:59 AM
Tiny
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Not a problem. If you disconnect the vacuum hose at the transmission modulator valve, is there any ATF in it?

Joe
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Friday, June 12th, 2020 AT 11:12 AM
Tiny
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Yes, there was a lot of ATF that came out. That's why I ended up ordering a new one hopefully this is the all end cure.
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Friday, June 12th, 2020 AT 12:43 PM
Tiny
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That's the cause of the smoke and likely the cause of the driveability issues. When you said adding ATF made it smoke more, that is the first thing that came to mind.

If you have the chance, let me know if it takes care of the issue for you.

Take care,
Joe
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Friday, June 12th, 2020 AT 11:00 PM
Tiny
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I changed the vacuum modulator and ran the car no more smoke car runs good except if you just step on. The gas the car bogs down and stalls or it kicks back up. If you lightly step on the gas you here a vacuum noise from the air filter area but the runs fine was able to drive it for about 15 plus miles and ran good except for that bogging down when not lightly stepping on the gas.
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Sunday, June 14th, 2020 AT 2:13 PM
Tiny
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When you press the throttle and hear the vacuum sound, is that only when driving or can you hear it if the vehicle is parked and you hit the throttle? Have you checked for other vacuum related issues?

Here is a link that explains how to check:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Joe
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Sunday, June 14th, 2020 AT 5:53 PM
Tiny
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The car is running perfect except for you have to lightly feather the gas to go or its stalls from to luch vacuum can't find any vacuum leak at all its like the air filter is taking too much air and its original air filter housing.
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Friday, June 19th, 2020 AT 12:23 PM
Tiny
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If there are no vacuum leaks and the carburetor and fuel pump are new, the only other thing I can think of is ignition timing. When you installed the new distributor, how was timing set?

Here are the (sad) directions from the manual:

___________________________

1981 Pontiac Grand Prix V6-231 3.8L
Ignition Timing Adjustment
Vehicle Powertrain Management Ignition System Ignition Timing Adjustments Ignition Timing Adjustment
IGNITION TIMING ADJUSTMENT
Set timing at slow idle and Before Top Dead Center, unless otherwise specified.

Disconnect and plug distributor vacuum hose at distributor.

On 4.3L (265), 4.9L (301) engines, ground distributor bypass pigtail (blue connector).

On others, carburetted, disconnect 4-wire connector at distributor.

Timing must be set to specifications on emission label. If "Check Engine" light comes on during procedure, remove ECM fuse to clear.

________________

Let me know.
Joe
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+1
Friday, June 19th, 2020 AT 7:37 PM
Tiny
BSBOY
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I replaced the EGR valve because that was failing checked all vacuum lines found a couple are crushing with vacuum. I had not had time to replace them yet. I will get back to you soon.
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Tuesday, June 30th, 2020 AT 2:52 PM
Tiny
JACOBANDNICKOLAS
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Hi,

What you mentioned can certainly be the problem. If you have a chance, let me know how it turns out for you.

Take care,
Joe
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Tuesday, June 30th, 2020 AT 9:40 PM
Tiny
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I replaced the vacuum lines and it still is bogging down and stalling. When you do give it throttle it sounds like carburetor is sucking in too much air causing it to bog down and stall. What could be the cause of that? How do I fix it? I have put 3 gaskets on for the carburetor still no change.
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Wednesday, July 1st, 2020 AT 3:00 PM

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