Thread: Misfire when car warms up and no boost

I have a 97 GTP with 148,000 miles. It's been a great car until about a month ago. It will crank up when cold perfectly and runs great, the problem starts after you get to your destination and it sits there for 20 minutes or so. when you try to start it will misfire and rpm's go up and down until it shuts off (check engine light goes on), you now have to wait for it to cool down (about an hour) for it to crank up again. Mechanic said it was the fuel pump and I just had it replaced with an A/C delco. Same problem, and now I noticed the boost is not working. Any ideas what to look at? Sensors etc?

The codes that are coming up are P0171 and P0300. I just had a tune-up done about 2 months ago, new wires, plugs, air filter, fuel filter all A/C delco parts. The weird part is that in the morning it starts great even the check engine light goes out after it runs for a few miles. Runs great all the way to the first destination, then you are out of luck. To start it back up you have to accelerate it quickly to about 3000 rpm's and hold it there for about 2 mins until it will not shut off when in idle, of course by then the check engine light flashes a few times and stays on.

Thanks. I am planning to attack the problem tomorrow. I will let you guys know what I find. Thanks again for all your help.

Know this is a few days old but....PO171 is Bank 1 Lean. Had it before my tune.

Hello everyone. I am sorry that I have not posted in the past two weeks, I have been working on my GTP every chance I get.
I did find a meltted vacuum line going from the manifold to the MAP, replaced it. The air intake tube from the air filter to the TB had a crack and I fixed that, also cleaned the TB and the honeycone screen and replaced the gasket and MAF sensor. Replaced the gasket and cleaned the EGR, checked the gap(.060) on the 3 month old sparck plugs (a/c) and the new delco wires. I even plugged the vacuum line going into the cabin for the A/C just in case the a/c system had a vacuum leak. I have inpected all the T's, the rubber connectors and vacuum lines. Car works great when you first crank it up in the morning or when engine is cold and will drive great (no check engine light) but when you turn the ignition off and let it sit for about 20 min. it will not start if you get lucky it starts and then stalls.
What else can I check for or focus on?
Replacing the MAF seems to have fixed my lean condition but when at the working temp you can't turn it off or you will wait until it cools to get going again.

Originally Posted by 99pgpgt

Also check your fuel pressure if you haven't.

Just checked my fuel pressure at the Schrader valve, it reads 20psi even with the regulator disconnected. I just replaced the fuel pump with a brand new a/c delco and the fuel filter is also brand new (not even a month old). Is there a way to check pressure at the pump? I also jumped the fuel pump resistor wires but no change.

Going crazy the car will run great until it gets to about 210 degrees and then power loss and the p0171, p0300 codes come up. Then will stall and shut off. HELP!

Did you check fuel pressure in the morning or when it wouldn't start? With the car ideling the fuel pressure should be between 45 and 55 psi.
You may want to check the fuel pressure while it's acting up like when you have to give it pedal to keep it running. This will tell you if there is a fuel issue.
Is this what you've done?..cause 20 psi will not only cause a lean condition, it's not good for the engine.

If the pressure is in fact 45 to 55 psi when running then move on to what these other guys have suggested.

20 psi while running:
I understand why you asked about pressure at the pump but check the voltage at the pump first. It should be over 13 volts. If it's only 8 or 10 volts then you'll probably have to install a fuel pump rewire kit.

If the voltage is correct then I would suspect something wrong with the regulator. Did you remove the vacuum line when you "disconnected" the regulator?
I don't think this a sure-fire way to eliminate the regulator as a possible suspect.

Heat soaked electronics:
When you park the car the latent engine heat can wreak havok on many electrical components, ICM, CPS etc.

Hope this helps.

Hey guys I am back. I finally got it fixed. It was actually the new A/C Delco fuel pump. I whent to the local junk yard and bought an entire A/C Delco fuel pump assembly for about 31.00, and once I put that baby in all problems solved. Pressure is at 48 psi when ideling and I have been driving it know for about 4 days with no check engine light and my mileage has gone up from 11 mpg to 17 mpg city driving. Thank you all so much for all the help. I should have never assumed that a new pump would not have been defective. Again thank you, and hey now after all this I know for sure that I have no vaccum leaks at all!!