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Thread: 1995 Silverado 5.7 rough idle with pops during acceleration

  1. #1
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    1995 Silverado 5.7 rough idle with pops during acceleration

    1995 Silverado with 168K miles, recently had new head gasket installed. Truck now has a rough idle and has recently added pops and bangs (sounds like backfire during mid RPM (1800-2000) acceleration) Have changed plugs, cap, rotor, fuel filter and egr valve (heavy carbon build up on egr). Have run seafoam thru gas and cleaned injectors (carbon all over injectors). Could the rough idle, carbon build up and acceleration problems be caused by one issue or many issues?

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    leolkfrm's Avatar
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    who did the head gasket
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    is it popping and banging through the exaust or the intake

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    vacuum leak comes to mind.

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    Mech did the head job and gave me lots of headaches afterwards which is another issue all together.
    Seems like popping is coming from exhaust, but cant be sure.
    Another issue I found on todays ride was at 1200-1500 rpm around 40-50MPH, the engine has a vibration felt throughout the vehicle.
    I will work on checking for vacuum leaks, but am also thinking about new plug wires and timing? I dont know if my ace mech even checked the timing when he put the engine together.

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    Senior Member Oldmech's Avatar
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    usually when it pops like that when you accelerate its because the cam has a rounded off lobe. It can be hard to detect doing a compression check depending on how bad the lobe is.
    if you have done everything else (which it sounds like you have.) pop hte valve covers off and check the travel on your rocker arms.. I would bet you will find at least one that is barely moving, if at all.

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    oldmech i had cam in mind but i never had one to pop threw the exaust i'ts allways been back threw the intake carb or throtle body

  8. #8
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    I'm going to say its a lean issue. either a vacuum leak or fuel delivery..
    Joe
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  9. #9
    Senior Member Oldmech's Avatar
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    I've had em do both, but the intake side is usually the most noticeable and obvious. when the exhaust lobe wears off it pops through the intake, when the intake lobe wears off it just gets less fuel, and eventually no fuel, so it isnt really POPing, but more or less WOPing through the exhaust Its really rather easy to tell if its the cam. I know the sound all too well, and its unmistakable.
    Vacuum leaks, and other issues usually create misc/random backfires, but the cam bad, will make a rapid fire unmistakable pop,Pop,Pop,Pop sound, about as fast as you can say popopopopopop... and usually only when you accelerate.
    if it isnt doing that, and is more random then your cam /lifters/rockers/pushrods etc should be ok. The other things could be... a wire on wrong? You dont have some joker of a friend that switched a couple wires on you?

  10. #10
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    I know it's stupid, but check your firing order. Simple and would cause the rough idle with popping. It definately sounds like a valve timing issue. Mebbe with 168K the timing chain stretched or jumped a tooth? Put the engine at TDC on the compression stroke, pop the distributor cap. Is the rotor pointing at the #1 plug wire? If not that's a pretty good indication. Then I'd check the compression, the worn cam would have similar symptoms too.

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