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Thread: Fuel Pump Issue (I think)

  1. #1

    Fuel Pump Issue (I think)

    Weirdest thing just happened.

    My dad's out from Alberta and I decided to take the car for a spin in the cul-de-sac where I live to show it to him in action. I turned over the engine, she spun over, no problem, but she just wouldn't catch.

    I did it again, but this time paid attention. Usually when I turn the key to the "on" position, I hear the fuel pump prime and then shut off. Nothing this time. I tried turning over the engine. It took about ten to fifteen seconds, but she finally caught.

    The engine is a 350SBC, carbeurated. No idea what fuel pump is in there. The car ran perfectly after it fired (video to come tomorrow morning), but I'm concerned at the lack of prime. Too late in the day for more experiments, but does anyone have any ideas what's going on? Is the fuel pump going? Is there a relay just for the prime that went on me?

    What's up!?!
    Meddle not with the affairs of the Dragon, for you are crunchy... and taste good with ketchup.<br />http://www.rc-sub.com/resources/grap...ni/avatar2.jpg

  2. #2

    Re: Fuel Pump Issue (I think)

    I'm no expert, and it's hard to know what was actually done on the car with the SBC swap. With mine, I've got a stock fiero pump with a pressure relief and regulator that limits the fuel pressure to what the carb likes.
    With that setup, I've retained the stock fuel pump test port. Offhand, I'm not sure which one it is, but if you attach one of the pins in the ADL to power, it will directly run the fuel pump.
    You could be lucky and simply have a bad fuel pump relay. However, on my car at least, the oil pressure sensor will power the fuel pump also. If you have the fiero oil pressure sensor used on your engine, you may have the same setup. Basically, if you have oil pressure, the fuel pump will also run. So, unless you ran the car lean on fuel last time, and the car hasn't sat too long, there should be enough fuel in the lines to prime the system, and at least get it to turn over enough to get oil pressure, thus priming the pump.
    One other thing you could check is the fuse. If that's bad, no fuel pump. However, then you'll have to track down what blew the fuse, which could be tricky.

    Changing the fuel pump isn't too big a deal on Fiero's fortunately. The worst part is where the 5 hoses attach to the tank. They are awful to get apart, and worse to get back together. Aside from that it's just 2 bolts for the straps, and 4 for the bracket that hangs below the tank. I'm not sure why, but I've heard people say not to install anything but an AC Delco brand. I didn't do so, and the pump didn't last 6 months :-\ Not sure whether it had anything to do with the brand name or not.

    Of course, if you have anything other than stock fiero, forget all of that Good luck with it!

  3. #3

    Re: Fuel Pump Issue (I think)

    Bob, another way to test the relay is to disconect it and bridge the conector with a short peace of wire... When bridged the pump will come on.... If it don't... then it's your fuel pump. Felix

  4. #4

    Re: Fuel Pump Issue (I think)

    Thanks guys, but the really confusing part to me is that the car runs just fine! It just won't prime the lines when I turn the ignition to "on". Here's a video of the car running after I got it going last night:

    http://www.rc-sub.com/resources/grap...rnoondrive.wmv

    You can see that it runs just fine... after it gets going. Usually when I turn the key "on", there is a period of about four seconds or so where the fuel pump runs and primes the fuel lines (I am supposing), so that when I kick in the starter the engine catches immediately. The fuel was low in the tank, however I added gas.. and would that explain why the pump doesn't kick on with the key initially? What would have changed so that it won't prime, but it does run? I'm baffled.
    Meddle not with the affairs of the Dragon, for you are crunchy... and taste good with ketchup.<br />http://www.rc-sub.com/resources/grap...ni/avatar2.jpg

  5. #5

    Re: Fuel Pump Issue (I think)

    Beautiful car; nice work on it

    The initial prime that you are talking about is driven by the Fiero Computer. The computer turns the pump on for 2 seconds when the key is turned to the on position.
    What I'm guessing is happening is that when you shut the car off, you still have fuel in the lines. You turn the key, and it turns over with enough fuel to get the engine running and get oil pressure. The oil pressure sensor will make the fuel pump run whenever it sees oil pressure, so whenever the car is running, the oil pressure switch makes the fuel pump run.

    The good news is that the fuel pump does run. I would start at the fuel pump relay. Check if it's getting the signal from the computer for the 2 seconds after the key is turned. If not, the computer could be bad, or it may not be getting the signal from the ignition switch. If your relay is good and is getting power, the problem is in the wiring from the relay to the fuel pump. Hope that helps; good luck with it.

  6. #6

    Re: Fuel Pump Issue (I think)

    The fuel was low in the tank, however I added gas.. and would that explain why the pump doesn't kick on with the key initially? What would have changed so that it won't prime, but it does run? I'm baffled.
    Even if the fuel was low, the pump should still run 2 seconds after the key is turned. The only difference may be that it may be louder/quieter if the pump isn't totally submerged in fuel. It may sound different then, and you may not hear it as well. I doubt that is what is happening though.

  7. #7
    Moderator FunnyWheels's Avatar
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    Re: Fuel Pump Issue (I think)

    It sounds like the pump is bad to me. My car ran great once it was primed because of the vacuum created by the engine pulling the fuel into the engine. I tried the jumper to see if the pump would function doing anything else, it was not pushing fuel. So I had to knuckle down and fix it. I dropped the tank and pulled the fuel pump. It was a long and messy process but not to hard to do physically. The hoses were the hardest part in my opinion. Since fuel weighs in at 6 pounds per gallon I did the job with an almost empty fuel tank. Anyway, the pump was FUBAR, full of an accumulation of crud form 1986 to 2003. I replaced it with a pump from a 1999 Pontiac designed for a 3800 engine since that is what I have in the car. (By the way, side by side the pumps are identical.)

    Today all is well, the engine fires as soon as I tap the key, fuel pressure is set at 35lbs for now but I can bump it up to 45lbs once the turbo is functional.
    If you're not confused, you're not paying attention.

  8. #8

    Re: Fuel Pump Issue (I think)

    Quote Originally Posted by RHK
    I would start at the fuel pump relay. Check if it's getting the signal from the computer for the 2 seconds after the key is turned. If not, the computer could be bad, or it may not be getting the signal from the ignition switch. If your relay is good and is getting power, the problem is in the wiring from the relay to the fuel pump. Hope that helps; good luck with it.
    Great... where is the fuel pump relay located? I'll check the computer connections to make sure that they're all secure.

    Thanks for the info!!
    Meddle not with the affairs of the Dragon, for you are crunchy... and taste good with ketchup.<br />http://www.rc-sub.com/resources/grap...ni/avatar2.jpg

  9. #9

    Re: Fuel Pump Issue (I think)

    Bob,I'll stop by this evening if your around... Felix

  10. #10

    Re: Fuel Pump Issue (I think)

    The fuel pump relay is supposed to be on the driver's side firewall, right around the decklid hatch hinges. It should have a black, green, a couple orange, and maybe a pink(?) wire going to it if I remember correctly.

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