QuestionQUESTION: 97 Grand prix GTP supercharged 3800 w/124000 miles. Will start every time but dies within 2-3 seconds. This problem used to be intermittent but now happens almost all the time. The fuel pump pressure is good and the computer diagnostic doesn't show any problems. Problem seems electrical. If I pull the fuel pump speed control relay halfway out so the top two connectors barely touch (or maybe not at all) the plug but the bottom connectors are still plugged in then the engine doesn't die. I've tried switching the relay with the fuel pump relay since they are the same but I get the same results with either one. The car will run while the relay is in this position. If I plug the relay in correctly the engine dies. I changed the resistor found behind the right headlight but that didn't solve the problem. I am considering buying a new wiring junction box for under the hood. Do you think the that would solve the problem.
ANSWER: Just a couple of questions:
After the vehicle dies out after 2-3 seconds does it start again immediately and run fine? Does it do this continuously? Have you tried monitoring fuel pressure when this happens? Did you remove the vacuum line from the fuel pressure regulator to see if it is leaking fuel out of the vacuum port? When it is running is there any thumping noises coming from the supercharger and does it build good boost? Have you removed and cleaned the IAC and throttle bore? Have you noticed any problems with accessories being intermittent like the blower and door windows etc? Did you jump the relay female pins to run the pump continuously to see if this still happens? (the diagram for the pins is on the relay 85 86 87 30) Is the vehicle equipped with passlock(R)? Have you tried the valet key? Does the security light blink when this happens? Are you using a generic code scanner or do you have access to the datastream?
Sorry for the questions just need to narrow this down a bit....
Wayne Howie
---------- FOLLOW-UP ----------
QUESTION: Let me give you some more history and info. After it dies it always starts right back up but dies again within 2-3 seconds if I don't push the accelerator. When this started happening last summer the only way I could get the engine to run correctly was to keep it at 3000 rpm or more or it will die again. I could rev the engine and put it in gear (not good for the transmission i know) and I could get it rolling. Then it would die again... I would put it in neutral and restart it/rev the rpm/put in in gear and get up some speed before it died again. I did this to get it home after the first occurrence and several times since. After I got on the freeway and had it up to 65 or 70 the problem would usually quit and it would start to run fine. After I got home and parked it the next time I drove it the problem might or might not occur. Oh the other hand, I might drive it two blocks to the store and when I try to start it to come home it would start but die again. I had my mechanic try and repair it when but the problem wouldn't occur while it as in the shop. He thought it was bad fuel or something...
The problem didn't reappear until Dec. 07. It happens almost everytime I start it now. I put it back in the shop and he was able to rule out the fuel pump. It has good pressure... it just seems to quit pumping. I don't know if he removed the vacuum line from the fuel pressure regulator. I will ask him. I don't hear any thumping noises from the supercharger and it has excellent boost. I don't know what and IAC and throttle bore are... sorry. The back drivers side window hasn't worked correctly for several years. It will go down using the master control or the one on the rear door but will not go back up unless I repeatedly push the rear door control... sometimes it goes up after just a few tries... sometimes it takes as many as 20 or so tries.
The fuel pump relay and the fuel pump speed control relay are the same. They are side by side in the wiring junction box under the hood. I read about a similar problem in a Grand Prix forum that suggested I bend the bottom left pin of the fuel pump speed control relay out to the side so it doesn't plug in then reinsert the relay. The car started and ran fine when I did this... (I think this put the fuel pump in high pressure mode). The forum said this indicated a bad fuel pump resistor which I then replaced but it didn't resolve the problem.
The security system and remote keyless entry have been out on the is car for at least 4 years. I don't know if it has passlock(R). I haven't tried the valet key but I will if you think it would help. The scanner my mechanic used had the datastream. It didn't give any definitive information about why the voltage to the fuel pump was dropping.
I've been driving for a couple of weeks with the fuel pump speed control relay plugged in the way I described. Could the wiring junction box have a bad plug or short or something like that? Thanks for your help.
AnswerHey,
Its tough to do drivability diagnosis without a vehicle in front of me but it is starting so sound like you are having problems with the IAC valve and fuel pressure is not an issue. There is always the possibility that the computer is shutting off pulse width of the injectors due to a lost crank senor signal that is intermittent but your description sound suspiciously like an IAC valve that isnt retracting.
Wayne
