Anyone have ideas about what could cause this behavior? After running for 20-60 minutes my fuel pressure drops and the car shuts off. After sitting for a while it will repeat this. Is this the FP going? Also, can the PCM cut power to the FP through the grey wire from the relay (FP signal from PCM) and why would it do this after running for a given amount of time?

Any suggestions appreciated,
Ferrell

 

Sounds like a pump problem. Symptoms can be like that because it heats up and then shuts down until it cools off. The pcm does have control over the relay, but has no reason to intercede when you are driving normally.

Relay wiring changed between 1995 and 1996. Don't know what year your car is.

 

Thanks for the reply Shoebox. I tend to agree that the pump is the problem. However, I have a EM Tec3 running the car. The relay has been rewired to accomodate it. The grey wire is the only one that is as it came. I thought it only went to the pump but now that I have a Helms I see that it also serves as the FP signal from the PCM. Can you think of any reason the PCM would decide to shut it off after running for a while? I thought this might be the result of problems with the ign cylinder / passkey but I don't think it would work this way if VATS was enabled, so probably not the issue. Do you agree? What I really need to do is rewire the whole thing and get rid of the factory PCM / wiring harness completely.

Thanks,
FL

 

I don't think VATS will shut the relay off, just the injectors. About the only reference I have seen where the pcm would kill the relay is loss of low resolution pulse from the opti. I am not totally familiar with your engine management and don't know if this could be an issue for you.

You could immediately check the voltage on the grey wire when it happens or maybe rig a temporary tell tale lamp on it to see. Of course, once the engine stops the fuel pump relay will disengage and will only engage for 2 seconds when the key is first turned on (priming).

 

ttt for you bud

Go ahead and replace the external and go from there. I agree with shoebox and dont think the vats has anything to do with the problem.

 

Hmmm. Shoebox, I think you just gave me some insight to the problem. There is no opti on the car anymore. I have full control over the relay until current leaves it via the grey (PCM signal) wire. I don't know why the PCM would suddenly start doing this after months though. I'll try to wire directly from the relay to the pump today to get the PCM out of the picture.

Mean: Part of the reason I haven't done the pump yet is that I have a hard time believing that both pumps would quit without the power being cut.

Thanks guys,
Ferrell

 

Ahh...I see, Good luck man