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Thread: 98 tahoe fouling #3 and #5 plugs

  1. #1
    Junior Member
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    98 tahoe fouling #3 and #5 plugs

    hello to all i am new here .my 98 tahoe has all of the sudden started consuming oil and fouling plugs # 3 and #5 it has a 5.7 vortec . engine runs great untill it fouls plugs no smoking or rough idling . i did a compression test all cylinders are between 200 and 210 . did some more troubleshooting today and noticed my pcv valve wich i put in 6 months ago is clean as new this is where i noticed something really strange when i pulled the pcv valve out of valve cover while engine was running engine started to die then idled rough plugged the end of it with my thumb still idled rough . i put it back in valve cover then noticed engine was building up a vacum at the oil fill tube then when i took my hand off of the fill tube engine wanted to die agian the idled rough
    heve never encounterd a problem like this before . could i have a leak in the plastic intake or at the base of the intake . any help would be greatly appreciated . also the check engine light does not come on and there are no trouble codes
    baffled in maryland
    steve
    Last edited by chandler; 03-13-2007 at 04:38 PM. Reason: forgot some info

  2. #2
    Senior Member junior3382's Avatar
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    two questions, How many miles does the engine have? Does it have a timming chain or belt?

  3. #3
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    truck has 98 thousand miles it has a timimg chain smallblock V8 gen 1. just to test i drove truck with the oil fill cap off it has a slight hesitation now at takeoff but has a lot more power and gets way better gas milage. engine has no knocks or noises in the valve train and runs 55 lbs of oil pressure after warmup

  4. #4
    Junior Member Browndog350's Avatar
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    Sounds like an internal intake manifold leak. Running with oil filler cap off might be allowing cylinders to pull enough crankcase gas/air mixture to actually run O.K. This also explains the oil consumption and plug fouling. Vacuum created with hand on oil fill tube is further evidence especially when engine wants to die when you pull your hand off. Hope this input helps with getting that Chevy running good again.

  5. #5
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    hey browndog just got finished putting engine back together it was the manifold gaskets engine runs great now thanks for reply

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