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#8 cylinder misfire??? help!

Discussion in 'Chevy Trucks' started by RED_RIDERTB, Nov 9, 2007.


    RED_RIDERTB Junior Member
    Messages: 27

    My 96 chevy 1500 4x4 with a 5.7 350 automatic trans started missing a week or so ago. I hooked up a obd II scanner to the computer and it said cylinder #8 misfire. I replaced the plugs, wires, cap, and rotor. Still the same thing #8 misfire. Any ideas?? Thanks:dizzy:
  2. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Can you actually feel it mis-firing?

    If you can feel it, does it do it all the time or only under a load, like when climbing a hill or at a fast highway speed?

    RED_RIDERTB Junior Member
    Messages: 27

    Yes I can feel it misfiring. It gets worse under a load like climbing a hill. I can hear it in my exhaust too. I have true dual exhaust. There is a big difference in the sound on the passenger side. Thanks
  4. grandview

    grandview PlowSite Fanatic
    Messages: 14,609

    Timing belt?

    RED_RIDERTB Junior Member
    Messages: 27

    somebody correct me if I'm wrong but I don't think this truck has a timing belt. thanks
  6. grandview

    grandview PlowSite Fanatic
    Messages: 14,609

  7. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    A bad distributor cap is usually the culprit on the Vortec trucks but if you already did a tune up (with quality parts, like GM or a good aftermarket name brand) then more than likely it's either an injector (not too common) or a warped exhaust valve (very very common on the Vortec's). In fact, GM knew the exhaust valves were a problem on the '96-up 5.0 and 5.7's and changed a ton of exhaust valves under warranty on these engines.. What actually happens is under load, as cylinder temp increases the additional heat generated will actually warp the head of the valve ever so slightly..just enough for it not to seal against the valve seat, which the ECM pick's up as a mis-fire immediately. Once the load and heat are reduced (part throttle, light load) the valve will re-seal and will run fine..
  8. nicksplowing

    nicksplowing PlowSite.com Addict
    Messages: 1,226

    these trucks were known to have intake gasket failure in that area which results in antifreeze getting into the intake port or cracked a cracked cylinder head do yourself a favor and pull the top end off before the snow comes and then its too late your miss will only get worse and cause more problems good luck
  9. Newdude

    Newdude Senior Member
    Messages: 889

    Could a compression test help diagnose the problem?? Just a thought.
  10. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    If it is fact a leaking exhaust valve, not really. Since it needs heat and to be under load to duplicate the symptom..but 9 times out of 10 it's an exhaust valve.

    RED_RIDERTB Junior Member
    Messages: 27

    Someone also mention to me it may be the fuel injector spider assembly. Has anybody ever had to replace that? Thanks
  12. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    The poppet injectors in the spider assembly's do go bad, but they usually cause multiple cylinder misfires rather than a single cylinder, and they usually leak fuel into the cylinder after a shut down, which will make them smell rich on start up and may idle rough after a re start (which will usually set a P0172 or P0175 code also). If it doesn't have any of those symptoms, then I'd still suspect a valve problem.
    Last edited: Nov 12, 2007

    RED_RIDERTB Junior Member
    Messages: 27

    Well it was none of the above. It was the intake gasket. I guess the vortec engines are known for this problem. Not cheap to have done either. I was quoted anywhere from $350 to $550. Fel-pro makes an updated gasket that cost $60 but it is made out of metal instead of the factory cardboard. It is worth the extra $$$.
  14. Rangerman

    Rangerman Senior Member
    Messages: 148

    probably a distributor can you make very many rpm's?
  15. sechracer

    sechracer Senior Member
    Messages: 478

    I literally just replaced the intake gasket on my 97 with a 305 vortec (did it lastnight). I used the felpro gasket set that comes from advance auto parts. That gasket in NOT cork, nor is it metal. It is a plastic and rubber setup. If you are not decently mechanically inclined, I would pay someone to do it for you. It took me a little over 7 hours to do mine. The distributor has to come out and has to be put back in the exact way it came out. If you get it a tooth or 2 off, it will not run right. Plus the computer sets the timing for it.

    BTW, warning ig you do decide to do it yourself. The gasket kit for mine was $25 however, it does not come with a new distributor gasket. That had to be bought separate, and was under $2.

    Who told you it was the intake gasket? Usually, if that goes bad, it will use antifreeze. Does yours?

  16. AndyTblc

    AndyTblc Senior Member
    Messages: 681

    maby a bad fuel injector
  17. Rcgm

    Rcgm Senior Member
    Messages: 613

    PSSSTTT HELLO it was a intake gasket read the post before you reply LOL
    Glad you got it fixed.

  18. brian79z

    brian79z Junior Member
    from NW Ohio
    Messages: 13

    If you used Autozone parts... it could possibly be a problem.

    I learned my lesson after several AutoClone failures.. AC Delco or NAPA is all I buy now.

    Anyway, if you have a good intake seal and good ignition with all 7 other cylinders firing... I'd order up a compression check. Then a leakdown test. This will check your rings & valves for proper seating....

    Do you have valvetrain noise?