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TBI hesitating BAD!!

Discussion in 'The Garage' started by muddysub, Sep 12, 2002.

  1. muddysub

    muddysub 1 ton suburban status Staff Member Moderator GMOTM Winner

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    when i get on it from a stop light it will just kinda die and idle for a few seconds then all of a sudden VRROOOOMM!! it's hesitiating really bad what is wrong? it does it when it's cold but it's not cold out at all like 80-85deg right now. i plan on replacing a fuel filter and rebuilding my TBI will that cure it? /forums/images/icons/confused.gif
     
  2. dammit32

    dammit32 1/2 ton status

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    sounds like a vaccuum leak
     
  3. heavy4x4

    heavy4x4 1/2 ton status

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    Mine will kinda do the same thing. If, from a stop or while driving, I press down on the accelerator quickly, the engine will bog for a second and then really go.
    Anybody else have this happen? What'd you do to fix it?
    If I had to guess, I would say that the opening of the butterfly valves so quickly, either chokes the engine with air (not enough fuel mixed in), or too much fuel enters and the engine bogs. I couldn't begin to tell you how to fix either of these situations though.
     
  4. HarryH3

    HarryH3 1 ton status Author

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    My S-Jimmy was doing this last year. It was driving me nuts. Then I was taking the factory air cleaner off for something and noticed that the little return spring for the thermostatic air valve in the snorkel had broken. I fixed the spring and the truck hasn't hesitated since. /forums/images/icons/cool.gif

    I think that without the spring, the valve would just flop open and closed as the truck accellerated. When it slammed closed, intake vacuum would rise, causing the MAP sensor to send back a high vacuum signal, confusing the heck out of the computer. Just one of those odd things to check. /forums/images/icons/cool.gif
     
  5. muddysub

    muddysub 1 ton suburban status Staff Member Moderator GMOTM Winner

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    i have a 14x4" open K&N air cleaner, so i'm getting plenty of air. a vacuum leak?! aw man!! /forums/images/icons/mad.gif
     
  6. muddysub

    muddysub 1 ton suburban status Staff Member Moderator GMOTM Winner

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    did i mention it only does it at certain times? like i start it up and leave it does it on the way out but after it's been driven for a few minuites it's fine. like i said it's not cold. /forums/images/icons/confused.gif
     
  7. ftn96

    ftn96 1/2 ton status

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    So its when the computer system is in "open loop".

    I'm no emissions pro, but that thermistatic flaper thing that HAIR-E was talking about could possibly causethat if it is staying open. It's supposed to stay closed while cold so the exhaust heat can help warm up the intake.

    Another thought would possibly be a faulty throttle position sensor maybe.

    A thought.... Even if you aren't getting any codes, go ahead and jumper off the diagnostic port and see if the computer is storing a code in memory.

    Good luck!
     
  8. muddysub

    muddysub 1 ton suburban status Staff Member Moderator GMOTM Winner

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    thermostatic flapper thing??? /forums/images/icons/confused.gif /forums/images/icons/confused.gif where is that?
     
  9. jc71355

    jc71355 1/2 ton status

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    It's in the snorkel of the origional air cleaner. It has that metal hose that goes down to the exhaust manifolds.
     
  10. 2BLAZERS

    2BLAZERS 1/2 ton status Premium Member

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    I have had the same issue before. What cured mine was a new cap and rotor with new spark plug wires. The cap and rotor were diffently warn. This is only a 30 dollar fix and anyways when was the last time you changed them.
     
  11. Sandman

    Sandman 3/4 ton status Author

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    I agree a bad TPS could do this. Easy to check with a voltmeter or even an ohm meter depending on which way you went.
     

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