Fuel Pump & FPR Didn't fix!HELP!!!!

Discussion in 'General Chevy & GM Tech Questions' started by tahoe freak, Oct 12, 2008.

  1. tahoe freak

    tahoe freak New Member

    Did the pump didn't fix the sputtering. Did the FPR, didn't fix...What gives? It is acting like a misfire. I had the cat's cut as well. I'm lost!!!!!!!!!!!I do a test an O2 sensor?
  2. dwill3015

    dwill3015 Epic Member 5+ Years ROTM Winner 1000 Posts

    Maybe we covered this befoe but id it throwing any codes at all?
  3. MrShorty

    MrShorty Epic Member 5+ Years 1000 Posts

    Could be an O2 sensor. 1st step in testing O2 sensors would be to pull codes as suggested. Now that you've changed those fuel system parts, is fuel delivery up where it should be?

    It might also help to know what year/engine we are talking about.

    From PM, I'm guessing before FPR change:
    This suggests fuel delivery was normal before. Fuel pressure has a vacuum connection that lowers the fuel pressure a little when engine vacuum is high, so ~55 psi while running is normal.

    Still would suggest pulling codes. If you can get a scanner, you might see if the ECT or IAT readings are "off" while cold. Still might put a fuel pressure gauge back on it to see if fuel delivery is still normal. Did you see signs of fuel leaking from the FPR vacuum port when you changed it?

    Also would suggest putting year/engine in this new thread, so readers will know what we are talking about and won't have to go searching through your past posts to find it.
    Last edited: Oct 13, 2008
  4. tahoe freak

    tahoe freak New Member

    no codes. The last code it gave was about the gas cap being loose.
  5. tahoe freak

    tahoe freak New Member

    99 Tahoe 5.7 4WD 2door

    Fuel is around 56 to 58psi. Checked Engine coolant temp sensor. It's fine. Check'd O2 sensors there fine. Voltage in and ohms out. I just caught up to a buddy of mine who has a scanner. I'll check it tomorrow and check back in. Anyone had Mass Airflow issues before?

    Again, thanks for all of the help. Didn't realize my posts were getting sent to my email account. I've been checking threads to see if anyone replied...
  6. tahoe freak

    tahoe freak New Member

    By the way, When I turn the key to the on position. The pump cycles. When I turn the key off it cycles again. Is this normal?
  7. jim1958

    jim1958 Member

    Try this before you throw all kinds of money at it. Had same problem with a 1998 Suburban replaced pump assy with Napa one worked for awhile and then took it to Chevy garage they said it was junk pump they replaced it , did it again. To make a long story short, drop tank and check the connector where it plugs in, thats what mine was. Pin connector was only making contact part of the time.
  8. JMoney02

    JMoney02 Epic Member 5+ Years 500 Posts

    FPR/FP readings are normal and in specs. Appears that the problem is Air mix, due to the fact that when it warms it clears, so fuel is not issue at this point. Posted was to Check IAT/IAC and also check MAF. You have already solved the fuel problem, even before you changed parts, readings from your post appear to have NOT changed since swapping parts...

  9. daddytech

    daddytech Epic Member 5+ Years 500 Posts

    the cycling it does when you shut the truck off is normal on a fuel injected system that is the fuel pump attempting to charge the lines again for an easier start up. I don't know what all else anyone has suggested but I have to ask have you changed out the fuel filter yet??? we had that same issue with our 2000 Astro van with a 4.3 in it after filling up at a gas station that had watered down gas. I had to change out the filter and it started right up and ran normal after that. The problem returned because water floats on top of gas and it wasn't until we had run the tank completely dry and changed out the filter again that the problem went away. Our van was acting like it just wasn't getting enough fuel to the motor for it to actually start and I almost burned up a battery trying to make it go. another thing too when we had a bad cell in the battery it wouldn't start either. it would crank just fine and act like it was going to turn over and fire up but never would. once all the bad gas was gone and the battery replaced the issue has stayed gone. This may not be your issue but it sounds suspiciously familliar. Also your MAF sensor could be part of the issue that or the TPS sendor and those ocassionally have a habbit of having issues and not throwing a code also.... just some other food for thought.

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