REALLY need help! Please?

Tiny
XXXTINA63
  • MEMBER
  • PONTIAC GRAND PRIX
I have a 1990 Pontiac Grand Prix, 3.1, overdrive, and about 200k. Recently, it has developed a problem. It will die and is impossible to restart untill it cools down, mostly when under load or at operating temperature. Here's a list of what I've done/checked:

1. Replaced spark plugs
2. Checked wires-OK
3. Replaced dirty air filter
4. Replaced clogged fuel filter
5. Replaced howling fuel pump
6. Checked for fuel leaks-none found
7. Replaced all 3 coil packs.
8. Fixed numerous vaccuum leaks
9. Checked MAP sensor. Held vaccuum. Replaced with a known good one-no change.
10. Cleaned IAC motor. No change. Unplugged IAC. No change. Replaced IAC. No change.
11. Checked IAT sensor. Passed
12. Checked coolant temp sensor. Failed. Replaced. No change.
13. Checked crankshaft position sensor. Passed.
14. Cleaned digital EGR. No change.
15. Cleaned throttle body and passages. No change.
16. Replaced ignition control module. While it runs better, the problem still persists.
17. Replaced TPS sensor. No change.

The car will start and run fine when at idle and cold. However, as it approaches operating temp, the more grumpy it becomes. When cold, you can increase throttle, but only to a point, and then it will die. Also, if you increase the throttle too fast, it will die. When the engine reaches operating temp, the slightest touch of the throttle will cause it to die. In any case, you can not restart until it has cooled down. Almost acts like it's flooding out. Pressure regulator? Any help would be much appreciated.
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Monday, April 16th, 2007 AT 2:00 AM

11 Replies

Tiny
MMPRINCE3000
  • MEMBER
Check the fuel pressure at the fuel rail test port with a mechanical gauge. Should be around 40psi and hold it when engine is off.

The pump could be bad.

If the FP regulator diaphram is ruptured, you would see gas in the vacumm lines.
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Monday, April 16th, 2007 AT 6:32 AM
Tiny
XXXTINA63
  • MEMBER
Thanks. Was actually going to head in that direction today. Have not found any evidence of fuel in the vaccuum line pointing to a ruptured FP diaphram. However, I wonder if it could be stuck in position? Also, although the fuel pump is new, I too have questioned if it's faulty. When not running and key on, all seems normal. But, when you turn the key off, you can hear what sounds like the fuel pressure releasing back through the lines.
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Monday, April 16th, 2007 AT 9:07 AM
Tiny
COOLCB
  • MEMBER
Is not the first time a new fuel pump was bad. Also check injectors, I have a car like yours, with about 300,000 miles on it, have replaced all 6 now! First time I thought of injectors and that was the problem that I replaced 3. Second time about 10,000 miles later acted differently that I thought was not injectors, but ended up it was. I then had one bad one, and one pretty good and other good that had not replaced before, but I went ahead and replaced all those 3 so was in short period of time or miles have 6 new ones!
Bought them on ebay and saved a bunch! Lol
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Tuesday, April 17th, 2007 AT 12:30 AM
Tiny
XXXTINA63
  • MEMBER
Ok, today I got a fuel pressure test tool. Book says with key on and not running, it should be 40.5-47 psi. Was about 40.5-41 psi. With key off, it was about 40psi, but would lose about 4 psi in 5 minutes. When the engine was running, pressure stayed at about 38-39 psi, regardless of RPM's. I don't think this qualifies as a fuel problem. Also, people have told me a partially clogged cat can build up pressure killing the engine. So, I removed the cat, but had no results, although it did run smoother longer.

It really seems to be a temp issue. You can start cold fine. Will idle perfect as temp increases. When up to operating temp, the themostat will open, the temp drops, and all is still good. However, once it starts to really reach operating temp again with thermostat opening and coolant flowing. That's when it will stumble and die. Any ideas?
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Tuesday, April 17th, 2007 AT 12:59 AM
Tiny
COOLCB
  • MEMBER
I have not seen on your list or ever mentioning checking fuel injectors, injectors will work fine when cold, as warms up they will fail, they will act in different ways. You could have two week ones, or one bad one or two! One can check them with out taking fuel rail off, it is a little hard to do so that way, but it can be done. Also is by wiring harness on passenger side, but need wiring diagram. It is not that they have high readings, but if is one really lower than the others, is bad. I would about bet u have a bad injector! Check the ohms, resistance on them. Mine did the very same thing, and also I replaced some things like u did, crank sensor, Map sensor, coil packs which one was cracked and needed replaced which I also got off of ebay for about $14 for 4 brand new ones! Sold one and paid for the rest I needed! LOL But ended up it was fuel injectors!
Til I have seen u have checked the fuel injectors, I would not recommend checking anything else or doing anything else!
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Tuesday, April 17th, 2007 AT 10:14 AM
Tiny
SERVICE WRITER
  • EXPERT
Have you been able to verify what is being lost when it quits? That is is there still spark present, is fuel pressure lost. You HAVE to do the testing when it isn't starting. I'm not refuting the possiblity of an injector problem, But I have seen more that lose spark.
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Tuesday, April 17th, 2007 AT 5:06 PM
Tiny
MIRADA_75
  • MEMBER
Just wondering how this ended? What was the final solution to the problem?

I am wondering because this sounds exactly like what my 1990 3.1 MFI grand prix is doing right now. I have been through the list of repairs and the shop and I have pretty well narrowed it down to a problem with the injectors or the circuit that gives them a signal.
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Saturday, October 27th, 2007 AT 4:19 PM
Tiny
XXXTINA63
  • MEMBER
Sorry to keep you hanging. Yes, it turned out to be a faulty injector. As a recap, it started out dying every once in a while, but would restart. It gradually got worse and harder to start as time went on. In the end, it would only start when cold, but would run beautifully, that is, until it reached operating temp, at which point it would to cough, stumble, and die with no hope of restarting until it cooled off.

While my car has close to 300k on it, a lot of things were worn and tested out of spec, but ultimately, it was a single injector going bad and would short out when at operating temp, shutting it down.

When testing, all injectors tested between 12.1 & 11.9 ohms resistance except one, which was around 7.8 if I remember correctly. I replaced the odd injector with a remanufactured one and the problem is gone and the car runs like it has 80k on the clock and pulls 30-33 mpg on the highway.

Keep in mind that this was a painful experience for me since I replaced most everything that was worn or tested out of spec. Counting the axel shaft and ball joint replacement also, I've put around $550 into the car total, which is more than it's worth. Good thing I got it for free. Still yet, it's a nice running car to drive in the MN winters as a beater.
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Wednesday, October 31st, 2007 AT 12:45 AM
Tiny
SERVICE WRITER
  • EXPERT
Aside from the anguish, $550 ain't too bad. A couple car payments would top that. Thanks for the update, Knowing the solution can help others.
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Wednesday, October 31st, 2007 AT 5:40 AM
Tiny
MIRADA_75
  • MEMBER
Thanks for the helpful replies. While I was waiting to see if anyone had an answer from various online auto sites the garage that had the car came to the exact conclusion that you guys did.

The injector on cylinder #6 was causing the car to have a lean miss when it did run ( as opposed to an ignition miss) and when the shop pulled off the connector to do the 'bulb' test on it, as soon as they plugged it back in the car died immediately. Also, unplugging the harness from injector #6 didn't really make the car run any worse which was another indicator that it wasn't contributing properly.

I am in the same boat as you, I spent approximately $700 on it but I still don't have a car payment.

Thanks again for the help from your site. I still need to know if there is some way a 'Canuck' can donate to the site?
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Wednesday, October 31st, 2007 AT 6:28 PM
Tiny
SERVICE WRITER
  • EXPERT
Yes Canuckish money is welcome!

Paypal is one way or a check to :

2carpros
341 W. Whittier Blvd
La habra, CA. 90631

PLEASE Include your user name!
And thanks for the follow up.
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Wednesday, October 31st, 2007 AT 6:34 PM

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