General Maintenance & Repairs - Fuel Pressure - Troubleshooting

I'm trying to diagnose a several month old intermittent (mild, but usually present) hard start condition and poor gas mileage. I've already done:


Fuel filter
Air filter
PCV Valve
PCV hoses
Sea Foam gas tank
Power Foam intake (removing oil from bad PCV)
All O2 sensors
Cleaned MAF
IAC replaced

Currently, I'm checking the fuel pressure and it goes to a tick over 60 PSI when priming and when running. I have '98, so keep in mind that the fuel system is a bit different from '99-'02 cars. I've read on some pages that it is a return-style system, unlike the later models, but I'd always thought it was returnless. When priming, the pressure goes to ~61 and then almost instantly begins to fall back to zero which takes another few seconds. When using the bleed-off valve in the test gauge for a clean disconnect, no fuel even comes out.

I pulled the rail and left all the injectors on and primed it looking for leaks. I couldn't find a single one. Tried with and without the harness attached. For now I am soaking the fuel injectors in Sea Foam as long as they are out of the car.

Could this mean a bad fuel pressure regulator? Is this behavior normal? What else should I check for? (For the record, I don't recall having a fuel cutoff at the top end.)

Put it all back together, checked again for leaks at several stages of reassembly, still no leaks. I paid closer attention to the lines this time and I'm quite certain it is return-less just like the later cars. There is only one line feeding the fuel rail. Pressure still drops precipitously when the pump shuts off. I noted 59 PSI this time (may have been the angle I was viewing the gauge from before that made it look over 60) and it barely shakes the needle when I rev the engine, so the pump seems to be good. Perhaps the fuel pressure regulator is bad? I'm hoping this is not on the tank, but somewhere near the fuel filter.

Side note: the O-rings for the fuel injectors all stayed behind in the fuel rail, and since they are as black as the rail itself, I didn't realize that what I was looking at was rubber and not metal. I had real trouble re-inserting the injectors into the rail this way and when I put them back on the car, they leaked profusely. I couldn't figure out how to insert them any further until I extracted the O-rings. Since some were damaged, possibly from attempting to seat the injectors against them, I replaced them all just to be sure. Once I figured that out, re-assembly was a piece of cake.

If I remember correctly, one of the sending unit components blocks off the return line to maintain proper pressure to the rail. When that fails, the symptoms you're experiencing can occur. A clogged filter would stop the rail from getting any pressure. As far as a bad fpr, that would do more of leaking fuel into the intake and causing a miss.

So you're saying the faulty part is on the fuel pump. Can anyone else confirm this?

So I need to drop the tank and replace...what? Anyone?

Just an update to this thread. I bit the bullet and bought a new fuel pump (complete assembly) for $220 off Amazon. They're really expensive on the 1998 cars, but at least this one is a Bosch unit and not Airtex. Anyway, I installed it this weekend and it finally fixed my problem. Completely.

The car once again fires up with enthusiasm if you so much as look at the ignition, which is the way it behaved since I bought it 8.5 years ago until the end of 2011. I'm hoping that the fuel economy will come back as well, as that started to dip just before the hard starting began.

The pump part may still be good for all I know. It ran just fine and never cut out or hesitated no matter how hard I drove it. It’s just that the fuel pressure would drop if the pump wasn’t running, which as was said above, could simply be a check valve in the pump return. Being that this is my daily driver though, I didn’t have time to experiment with the old pump, so I just put in a new one. Maybe I can sell this one for parts?