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Old 07-21-2008, 07:26 PM
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1993 gmc 5.7 back fires tru ext and int

idels with a miss at part trottle back fires tru tbi and even sometimes tru ext i have new wires plugs timing is set new rotor and cap i did replace this motor in the truck a week ago and never had this problem before since i put this new engine in i have this back fire do i have a intake leak bad cam bent pushrod???????????

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Old 07-21-2008, 07:35 PM
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First off, are you certain you have the firing order correct? 5 and 7 on the plug wires are side by side and very easy to cross up. Go over the firing order 1 by 1 and make sure it`s correct. If the firing order checks okay then I would remove the valve covers and check the rocker motion, see if any rockers have little motion compared to others, this would indicate the cam is shot. It`s common now on flat tappet cam break in if you use basic motor oil the cam will go flat due to lack of anti wear additives that was removed from motor oils some years ago. If that checks okay check the rocker arm adjustment, you may have a few rockers set too tight. Lastly, check it for vacuum leaks. Is the check engine light on? if so what codes does it give?
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Old 07-21-2008, 09:30 PM
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firing order is right

i have more than triple chec ked the order as far as the codes i dont have way to check the engine never did this before again new wires plugs control modul in dis the velves have been rechecked over again it seems to be only on the driver side of thne ext that i hear this miss
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