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Olds 88 (1998) Low fuel pressure

My 88 "Rosie" has been having problems for months. It hesitates, stalls, and sometimes backfires. This is an intermittent problem, though it is happening more often lately. I took it to local auto shop and their computer showed Rosie was throwing a misfire code as well as a lean code. I took it 3 months ago, and I took it last week, got the same codes. The lean code led me to check the fuel pressure. I did and while it should be healthy 48-55 psi, I got 48 for awhile then 15 PSI! Now I'm thinking fuel delivery. I started with the filter. Sure enough it was dirty. Weeks later, the problem persists. I replaced the fuel regulator (ok, mostly because it was cheaper than the replacing the fuel pump, which I really didn't want to have to do.) Still, no luck, so I finally caved and spent $200 and 12 hrs dropping the tank to replace the fuel pump. Guess, what? Still no dice. I'm still getting the hesitation and the misfiring. I haven't put the fuel pressure tester back on it (been busy) so I don't know if the pressure is still low or if these other things are even related.



I thought my logic was infallible. Let's face it, there's a finite number of parts that control fuel pressure. I'm running out of parts to replace. Where did I go wrong?



The only thing I can think of that could still do it is perhaps the fuel pump relay? I dunno. Would it work off and on or fail completely? I'd love to get some opinions on this.
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Comments

  • edited February 2011
    When chasing a problem like this, I always use an old sealed beam halogen headlight to make sure you have good power all the way to the pump. That way you're putting a load on the circuit. Voltage meters wont tell you if the circuit can carry a load. Of course you could go from the front to the back. I think you can go to the Zones website to look at diagrams and locations of components. Don't forget to check your fuel pressure to make sure you're still chasing the right animal.
  • edited February 2011
    was the engine running when you did the test ? Did you check the fuel pressure regulator ?
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  • edited February 2011
    Yes, turned the ignition (but not start) first to let the fuel pump "charge" the lines. The fuel pressure went to 55 then it drops to 48 after starting the engine. Then at some point it also dropped to 15 Psi While Running.

    Yes, I replaced the fuel pressure regulator.
  • edited February 2011
    You might be thinking along the right path about the relay. One thing I would try is to swap the FP relay with another relay not important to engine operation and see if it helps.
  • edited February 2011
    OK. I meant to check if there is vacuum at the fuel pressure regulator. If not you have a blocked vacuum port at the intake, just follow the line and use a can of fuel injector cleaner to clean it. Check the hose for cracks.
    There is not too much to say, assuming that the car is in shape, no accidents with body damage near where the wire travel to the fuel pump. The fuel pump is activated by the ecm trough a relay (fuse block behind the passenger kick panel, marked N) that receives power from a 20 amp fuse (#6 on the same block as the relay). You can try to remove the relay and bypass it to check if the pressure stays even, just be careful not to short the ECM.
    The attachment is a diagram and some more info. Just be very careful so you do not damage anything else. You could try a new relay, but what about if the problem is in wiring ? you will drive yourself crazy trying to find it. If you see that you can not guess just take it to as mechanic. Sorry to say that.
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  • edited February 2011
    Since I last posted, I did put the fuel pressure tester back on it. Sure enough, it was struggling at 18 psi. It is also still throwing a P171 code, which is lean bank 1, I believe.

    Thank you Pete, I'll check out the relay.

    Castironman, I did check the vacuum hose. It was pulling a vacuum. I also checked to see how the engine responded when I removed the hose. It checked out. (I can't remember off the top of my head, I suppose it would decrease the fuel pressure). No accidents or body damage, but I'll definitely take a crack at those diagrams and see if I can find this thing. Thanks so much for the great info!

    A guy today told me it could still be the fuel pump because I used the off the shelf one from autozone, not the manufacturers. I (politely) told him to take a hike, probably because I just would hate to admit I spent so much effort doing it wrong. Should I be listening to him? The probability of getting the exact same (somewhat baxar) symptoms 2 days after the brand new fuel pump goes in just seems astronomical to me. Open to thoughts, though, (and I promise I won't tell you to take a hike). ;)
  • edited February 2011
    Did you replace the fuel pressure pulsation damper when you replaced the fuel pump?

    It's a check valve located on the fuel pump assembly and if it fails it causes fuel pressure to bleed off.
  • edited February 2011
    I believe the pulsator was built into the new fuel pump. I'd feel like a doofus if it wasn't, but I'll tell you one thing, it would not fit. The new fuel pump was the length of the old fuel pump and the pulsator together. It had a plastic component on the top that the old fuel pump did not have. I had to assume it was the pulsator.
  • edited February 2011
    UPDATE:

    My fuel relay is hot. Not melting, but significantly hotter than it's neighbors.

    Been reading around on other forums, some guys are having similar problems and one symptom in particular caught my eye. They say their power windows don't work when it happens. Random. But Rosie has been doing this, too. They said they were going to buy the book and find a shared ground for the FP and power windows. Sounds smart to me. It does have all the earmarks of a loose/bad ground connection as far as I can tell. I'm a mechanical guy, though, not so much electrical. Does anyone know where I can find this type of diagram without buying the book? Castironman, I checked the ones you sent and learned a lot from them. I suppose the one that might answer my latest question might be higher level (that is, an overview of more systems and components). You guys rock. Thanks.
  • edited February 2011
    Find the return line to the tank from the fuel rail, pinch it off, recheck your fuel pressure after it sits and see if the pressure drops. If it doesn't drop then the problem is in the tank, more than likely the pulsator.
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