90 Grand Prix starts, then dies

[Fishhead5]

I've got a 90 grand prix that is set up for the dirt track. It up and died and won't run. It fires, then dies. It will run on starting fluid. There is 30+psi fuel pressure at the rail. I checked one injector with the noid tester and it starts out fairly bright and then gets dimmer until there is nothing. You have to take off the manifold to test the rest. I replaced the ECM with no change. I checked for trouble codes and only got one, 12 which means there isn't anything wrong. I went through and checked all the grounds and cleaned them up.

HELP!!

 

[Blown97]

Alright, believe it or not you have already diagnosed your problem. You said that it runs on Starting fluid, that says it is a fuel issue - good diagnostic procedure. Then you said you check fuel pressure and got 30psi - good diagnostic procedure. That is where you should have stopped. You said that you got 30+ psi, not sure how much the "+" means in your description but 30psi is at best on the very low end of the range it's supposed to be. Your fuel pressure reading should be more close to 31-44psi. Moving on, you used noid lights to check to see if your injectors are getting a signal - good diagnostic procedure. From what you describe, your injectors are getting their signal correctly. The reason they get dimmer and shut off after a while is because the PCM will turn them off after a couple seconds if it senses a no start condition. If the engine started, they would stay on. This is a safety feature for in the event you wreck, the PCM will shut the injectors and fuel pump off when the engine quits.

My suggestion would be to see if your fuel pump it getting power. Remember, if the PCM senses a no start condition it will shut off the fuel pump as well after a couple seconds. So you're going to need 2 people to do the test. If your getting good 12 volt power to your pump, I would suggest replacing the pump as power would not be your issue.

Good luck! :th_thumbsup-wink:

 

[Fishhead5]

Thanks for your reply!

We got it running, but not good. The oil sending unit was bad which we found out by accident. We started looking for bad grounds and pulled the plug to the sending unit. When we turned the motor over to test it, it ran. We replaced it. I got ahold of a good computer scanner and tried that and it would pop some codes, sometimes. I replaced the ECM and we got a temp sensor code and IAC code. We replaced the temp sensor on the block and it didn't change anything. There is another temp sensor on the radaitor, not sure if that one is just for the electric fans or not, but it has three wires (fans are on a toggle switch)

As for the IAC code the sensor has been removed (the car ran fine without it before) I'm thinking about re-installing it.

Right now the car doesn't have any power until you get the rpm's up. When we ran it before you could hit the rev limiter in first, but when we went to second it was like shifting a manual transmission from 1st to 3rd, no power and took a long time to get to 4000 rpm's and it wouldn't go any higher. I haven't had a chance to get it out and run (other than 100 feet) it since we changed temp sensor and put the new computer in. We'll see what happens. We have another race saturday and it would be nice to get it running right.

This is a fun class. The cars have to be American made, front wheel drive, nothing over a 3.8 motor. There are 2 people in the car, the driver steers and runs the brake, the passenger runs the gas.

The 30+ psi reading was because the fuel pressure gauge leaked where the guage and hose hooked up. I got a better one and with the car at an idle we had 35 psi and with it reved up we had 41 psi of pressure.

This electrical stuff can drive a person up a wall!!!:th_sick1::th_sick1:

Thanks again for the help.