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A few TBI questions...

Discussion in 'The Garage' started by kp texan, Dec 5, 2005.

  1. kp texan

    kp texan 1/2 ton status

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    I've had my '88 K5 for awhile now but I was wondering if some of the things that it does are normal.

    The first thing is that, in order to start it, I have to crank it over about 2-3 seconds before the engine will actually start. Is this typical? The reason I'm asking is because both my LT4 Corvette and my Dad's '04 Sierra fire off right when I turn the key. It's really not an issue to me but just wanted to know if this could be an indicator of something wrong.

    The other issue I have with my TBI is that, under a very small amount of throttle, the engine kind of runs rough and acts like it wants to bog down. When I say a small amount of throttle I just mean like when I'm leaving an inclined driveway and I just barely give it enough throttle to cause it to move up the hill. Whenever it begins to run rough and then I immediately let off the gas, it causes the RPMs to drop almost enough to stall the engine but then it always automatically brings it back up to idle. It has never died on me from this but acts like it wants to for a split second. Whenever I give the engine more than a small amount of throttle, it runs perfectly and doesn't seem like anything is wrong. What could cause this? Possibly a bad TPS or EGR valve?

    The engine has 69k original miles and I just did cap, plugs, wires, and fuel/air filters.

    Thanks so much for the help,

    Wes
     
  2. bluehen

    bluehen 1/2 ton status

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    I had the same troubles a little while back. I changed the EGR valve and adjusted the timing and the probs exist no more.

    2-3 seconds is all it takes you to start? Nice!
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    That might be your fuel pump relay.

    Once oil pressure gets up far enough to close the oil pump switch the fuel pump will work. You can test all this, I'd force the fuel pump to run before trying to start, and see if it starts quicker with the fuel pump forced to run.
     
  4. kp texan

    kp texan 1/2 ton status

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    Okay, so I'm guessing that might be fairly normal for TBI start time? I'd really rather it have full oil pressure before firing off anyway so it sounds kind of like a good thing to me??? I suppose I'll just change out my EGR valve and then check my timing. Can the EGR valve just be rebuilt or do I need a new unit? I remember reading on here to only go with the Delco unit and not one from Auto Zone, correct? Thanks so much for the help!

    -Wes
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    It's not really a good thing, using the starter to crank the engine over longer is hard on the starting system, and is just prolonging what happens anyways. GM has the system as they do for a reason.

    I'd make sure the relay works. The oil pressure switch is redundant, if your relay is bad now, and your oil pressure switch fails, you are dead in the water unless you know how to force the pump to work and have the stuff to do it.
     
  6. kp texan

    kp texan 1/2 ton status

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    How can I force my fuel pump to run? Do I need to use a jumper wire where the relay is or something? Where exactly is the fuel pump relay and how much will a new one cost? I know that's alot of questions to answer but this forum seems like the best place to find the answers. Thanks again for the help!

    -Wes
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    post #7

    There are more out there, I searched "fuel pump relay test" and there was also a result with the wiring diagrams which can also be used to deduce how the relay can be bypassed for testing.
     
  8. beastofablaze

    beastofablaze 1/2 ton status

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    Can you hear it run before you start it? You should hear it as soon as you turn the key on.
     
  9. kp texan

    kp texan 1/2 ton status

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    Yeah, I can hear the fuel pump come on as soon as I turn the key. Does this mean the relay is alright or is that totally separate (i.e. pressurizes the system, turns off, and then won't come back on until oil pressure is high enough)? Thanks.

    -Wes
     
  10. yagsinairod

    yagsinairod Banned

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    it means your fuel pump relay is fine.
     

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