Fuel Pump or possible CCRM issue?

[doctorj357]

So I purchased my 95 GTS back in July. One of the very first things I noticed, or lack of, was no sound of fuel pump priming when ignition was turned on. Didn't think much about as the car still starts and drives. But always had a nagging suspicion in the back of my mind its not right. But it had to be working, right? I mean the car runs and drives.

Fast forward a couple months - I'm now running into a cold start issue (Michigan weather) where the it barely can idle for the first couple mins until warmed up. Once warmed up its fin but requires me to give it some gas to stay alive until then. I believe this to be strictly a tuning issue with my heads/cam setup. Happens on both the stock ecm + BAMA tune, but I'll get that sorted out later.

Meanwhile, as I was doing some basic troubleshooting, I decided to inspect the fuel pump/pressure. As I recalled it still wasn't making any sound when it should have been priming, was that maybe contributing to my cold start issues? Doubtful, but worth checking it out. First I checked the fuel rail pressure. I didn't have a gauge on hand, but to make sure there was pressure at least, I pressed on the schrader valve. With a rag and a quick press fuel shot out. Next I just checked the regulator by disconnecting the vac line. No fuel leaked out. Next I checked the inertia switch in the trunk and appeared to be fine. Just for grins I released it, and pushed it back back down just to be sure. Next I jumped the ECC ping for the fuel pump to ground to trick the pump into running. As I hoped, the pump continuously ran while the key was turned on. Could also hear to relay click nice and loudly with each key turn.

Now, here's the odd part. After I took the jumper out, every time I turn the key to IGN, the pump primes 3-5sec just like its supposed to. I must have tried this 10-12 times and I can hear it prime every time. I'm also hearing the relay click each turn of the key. So the question is, what changed? Only two real changes was playing with the inertia switch and the ECC pin for the pump. Could have one of those reset something in the process? Better yet, how was the car running at all if the pump wasn't turning on/priming at startup?

 

[General karthief]

You need to get a fuel pressure gauge, just a few lbs of pressure will squirt fuel out the valve. Next understand computer controlled systems, you may have a sensor that is not doing the job any more, check for codes. As for the fuel pump noise there may have been a connection issue that made the pump run slow because there was low voltage and fooling around with things like the inertia switch made a better connection so now the pump is getting more power.
Of course this is just the rantings of a 'back yard mechanic'. I will refer you to the technical/how to forums, the surging idle checklist will show how to test sensors and the differences in the 94-5 stuff is highlighted.

 

[jozsefsz]

Check the condition of the wires at your test port - where you probably jumped to ground. It's most likely that your working with that has temporarily helped an issue (broken wire, corroded connector) which was causing an intermittent ground for the fuel pump relay. If everything looks to be perfect with the wiring, it's possible you had a sticking relay in the CCRM which temporarily improved after you gave it a solid ground connection. The intertia switch is generally shielded from corrosion, and it's pretty much on-or-off so I'd consider that less likely. Wiring at the test-port, followed by a CCRM about to head south would be my first two guesses. Agree that you'll want an actual guage that you can monitor next time it's acting up. Driveability can suffer with just a few PSI of lowered pressure, and you can't finger-push diagnose that.