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1983 truck 350 engine, kaboom! out exhaust every once in a while and on dec

Discussion in 'The Garage' started by R72K5, Nov 5, 2003.

  1. R72K5

    R72K5 Banned

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    and during deceleration in gear coming to stop using tranny to slow up truck it makes a really super loud KABOOM liek gunshot going off out the exhaust, sometimes during idle for no reason too. sometimeswhen revving it upand slowingit back down, kaboom!

    cam shaft lobe wiped ? exhaust valves jammed ?
    lifters stuck pumped up ?


    what would this be ?

    otherwise engine will rev up not too bad and such,

    thanks
     
  2. Sandman

    Sandman 3/4 ton status Author

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    Sounds like an occasional misfire. Bad plug wire or cap and rotor loose maybe? When was the last time you did a tune up?

    I guess it could be a sticky valve train. I had a similar problem and it turned out the timing had slipped really bad.
     
  3. R72K5

    R72K5 Banned

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    trucks been sitting not fired up for at LEAST five years- if not even longer, he said it had an oiling problem or some junk, it did blue smoke for about five minutes after i got it to start and run, just had to dump gas down carb about four times and keep trying to crank her over, finally got it to start and stay running after second time it started up

    what you think ?
    change oil and run her harder and see if clears up, or ?
    run some kerosene in the oil ? this is only thing wrong with entire truck, once this i fixed then it be a daily driver /forums/images/graemlins/laugh.gif

    thanks
     
  4. Thunder

    Thunder 3/4 ton status

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    I would do a complete tune up: Time it, plugs, wires, cap, rotor,
    Run some carb cleaner thru it.
    Maby do a quick engine flush and Change oil.
    If the problem isn't fixed it may be the timing chain going out on ya.
     
  5. R72K5

    R72K5 Banned

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    [ QUOTE ]
    I would do a complete tune up: Time it, plugs, wires, cap, rotor,
    Run some carb cleaner thru it.
    Maby do a quick engine flush and Change oil.
    If the problem isn't fixed it may be the timing chain going out on ya.

    [/ QUOTE ]


    good point, timing chain, hummm


    its just funny that it idles fine and all but every once in a while big KABOOM out the pipe, doesnt kill engine or anything, it keeps right on running

    cuz more i think about it i think a wiped klobe causes constant and even pop out carb and not exhaust, at idle mainly but also speeds up with engine acceleration


    or no ?



    thanks
     
  6. MEPR

    MEPR 1/2 ton status

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    yeah a flat cam lobe will probly give you a constant back fire and will come up through the carb most likly.
     
  7. camok5

    camok5 1/2 ton status Premium Member

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    The first thing I would do is check the timing. Just to make sure its not detination. I had an old chevy truck with the same problem.
     
  8. R72K5

    R72K5 Banned

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    [ QUOTE ]
    The first thing I would do is check the timing. Just to make sure its not detination. I had an old chevy truck with the same problem.

    [/ QUOTE ]

    more than just simple detonation, unless its doing it in the exhaust pipe such as like with extra unburnt fuel from the electric Q jet. cuz it does only kaboom inside pipe when are getting off from a rev up, and also in gear slowing up using engine to slow truck down.

    hum... interesting..

    oh and stretched timing chain would cause crank to be ahead of cam im thinking and i can see how that can cause kaboom to slip past the exhaust, or am i thinking correctly on this ?
     
  9. justhorsinaround

    justhorsinaround 3/4 ton status

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    Also since the motor sat for so long dump some Marvel Mystery Oil down in the crankcase to help loosen up the innards. Good luck to ya.

    Allan
     
  10. the cork

    the cork 1/2 ton status

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    a friend of mine had an older nova that did this, turned out he found a loose wire that would connect and disconnect
    from vibration, causing the ignition to turn on and off ,
    the cylinder would fill up with unburned gas then suddenly
    fire as the power came back on,
     
  11. 99firehawk

    99firehawk 1/2 ton status

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    Does your truck have all the emissions tiff still.......ie air pump manifolds ect?
     
  12. joez

    joez 1/2 ton status

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    does it have an exhaust? i know my toyota with open header likes to do this, it sounds like a shotgun every time i shift.
     
  13. mudjunkie 82

    mudjunkie 82 1 ton status GMOTM Winner

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    Change the cap,rotor.wires and plugs.Sound like a misfire.My Cousins Truck was doing the same thing but really bad, Blew the muffler clean off of it.Turned out to be bad wires
     
  14. Blazer1970

    Blazer1970 1/2 ton status

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    This is usually caused by a rich idle in combination with an exhaust leak at the manifold to head connection, or at the manifold to y-pipe connection. When the throttle closes, a bunch of unburned fuel goes right through the engine and out the exhaust. When it gets to the leak, it mixes with enough air to make the mixture correct for combustion, then BOOM! I had a Land Cruiser that would do that, and a new header gasket eliminated the problem.
     
  15. JRS2 75K5

    JRS2 75K5 Registered Member

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    Had the same problem with late 70's 350 blazer engine. Replaced carb, wires, cap, plugs, reset timing and still had same intermitant problem. Had to pull distributor and replace the pick up coil which requires removing the distributor shaft. Not a big job but the engine is still running great. Engine had set for 3 to 4 years also.I blew off two new new mufflers before problem was solved.
     
  16. R72K5

    R72K5 Banned

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    ill try HEI swap, whole dizzy with another one, then go from there, i checked at night with it running for any wire crossfiring or shorting to groundm and didnt see anything bad

    thanks
     
  17. R72K5

    R72K5 Banned

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    would still having original air injection reaction system on the engine somehow cause this maybe ?

    the outside shell of Y-pipe is peeling like a banana, i assume from past kabooms in the pipe, surprised it doesnt blow up the pipe like a muffler can

    i removed distributor cap a bit ago and found that the center contact button was severely arced and not even touching the contact on the rotor, so i replaced both, but engine does same thing as before, i fired engine up cold and tried ot rev it up cold and it doesnt want to and it makes KABOOM like gun shot going off once, its when extra unburnt fuel from revving engine makes it to exhaust pipe, somehow it is igniting in the exhaust pipe even with engine and outside temps really cold

    so new question would be: would stretched chain cause combustion chamber compresion and fire to not stop before exhaust valve begins to open ?
    it seems like exhaust valve is opening way too soon, this has to be it.

    no ?


    thanks
     
  18. mudjunkie 82

    mudjunkie 82 1 ton status GMOTM Winner

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    Did you check the wires and plugs?
     
  19. R72K5

    R72K5 Banned

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    [ QUOTE ]
    Did you check the wires and plugs?

    [/ QUOTE ]

    plugs will be going in with carb rebuild

    thanks /forums/images/graemlins/laugh.gif
     
  20. 99firehawk

    99firehawk 1/2 ton status

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    [ QUOTE ]
    would still having original air injection reaction system on the engine somehow cause this maybe ?

    the outside shell of Y-pipe is peeling like a banana, i assume from past kabooms in the pipe, surprised it doesnt blow up the pipe like a muffler can

    i removed distributor cap a bit ago and found that the center contact button was severely arced and not even touching the contact on the rotor, so i replaced both, but engine does same thing as before, i fired engine up cold and tried ot rev it up cold and it doesnt want to and it makes KABOOM like gun shot going off once, its when extra unburnt fuel from revving engine makes it to exhaust pipe, somehow it is igniting in the exhaust pipe even with engine and outside temps really cold

    so new question would be: would stretched chain cause combustion chamber compresion and fire to not stop before exhaust valve begins to open ?
    it seems like exhaust valve is opening way too soon, this has to be it.


    [/ QUOTE ]



    If you want you can swap in some headers and remove the emissions crap, or if you cant go to a junk yard or dealer and get a divertor valve. I would bet $$ on that
     

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