I need to relieve the fuel pressure on my '89 IROC so I can begin work on changing the fuel injectors. Looking at the fuse box under the steering column, I found TWO fuses (one 10 amp, one 20 amp) that both say F/P on them. The 10 amp fuse says F/P/Injct2 and the 20 amp says F/P/Fan and something else I don't recall right now. So I pulled both of those thinking that would shut down the fuel pump but the car kept running for a long time.

After researching this a bit more on the site here, it sounds like there is a fuel pump fuse near the battery in the engine compartment. I did find a fuse there but it only says "P.E.D 5". It is screwed into a bracket to the right and more towards the front of the battery (looking at the battery standing in front of the car). My question: IS this the fuel pump fuse that I need to disconnect? Do I need to disconnect all THREE?

 

"P.E.D." is the company which made the fuseholder - Packard Electric Division (of General Motors). The 20A fuse near the battery powers both the fuel pump and ECM. Once you remove it, the ECM will not function, and the engine will not run. You can carefully relieve pressure at the Schrader valve along the right fuel rail, near the rear. Do this with a cold engine, with no ignition sources present, and in a ventilated area.

 

Ok, I found the Schrader valve. Do I just need to depress the pin needle to relieve the fuel pressure? Should I be prepared for any fuel to be released or will it just be mostly air?

 

Yes. It will be all fuel, but not much of it. A shotglass full or two. Wrap an absorbent rag around it/over it, press the stem and it'll all come out in about a second. It shoots out under pressure very briefly, so don't get your eyes or anything in the way of the spray. Having a rag fully wraped around it when you press the stem catches most of it, but don't take chances.

 

Well, I tried this the other day and NOTHING came out of the valve. I depressed the pin needle all the way down. Does that mean the fuel pressure has already been relieved? Am I safe to proceed here now?

 

You're safe. The oil pressure sending unit doubles as a fuel pump relay by-pass. When you pulled the fuses it kept running because the OP sending unit kept supplying power to the pump.

 

Ok, but I am still confused a bit. If the OP sending unit was powering the pump until I shut off the ignition, why wasn't there any fuel remaining in the fuel rail afterwards? I was surprised nothing came out of the Schrader valve. Did I need to depress the pin needle while the ignition switch was in the 'ON' position?

 

Your system is not holding pressure, could be the pump or the pressure regulator leaking fuel pressure back to the tank.