Question about GMC Sierra 1500

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I have a very noticeable engine knock in my 93 gmc 4x4 at idle after a few minutes of running engine, seems to lessen at higher revs. I just changed the crossover pipe and all piping on exhaust, kept same cat and muffler. It may have been there prior to exhaust work but didn't notice over noise. Checked knock sensor on lower engine seems ok and pulled plugs and seem fine, light tan colour no build up,good spark . the wires, dist and plugs just changed 5 yrs ago. Good power on engine exhaust is white etc. I don't drive it much as it doesn't have safety sticker yet, any thoughts

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  • Roy V Apr 11, 2011

    thanks, I will investigate further and let you know what I find.

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1. Remove the alternator & accessories drive belt out from the engine, and start again the engine. Listen the engine running regarding this very noticeable knock. If it will dissappear, check the crankshaft pulley, the belt tensioner, ... Replace bad pieces.
2. If the very noticeable engine knock still occurs, you need to use an engine stethoscope tool for carefully listening the engine block area & cylinder head area. It could be a valve rocker arm knock or a piston knock, depending of the noise area.

Posted on Apr 10, 2011

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