Question about 1998 Chevrolet Tahoe

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1998 gmc 4x4 runs poorly and sounds like a vacume,air leak .

1998 5.7 vortec in my 4x4 sounds like i have vac/air leaking on driver side of motor and runs like it is out of time . ijust replaced spark plugs ,timing chain cover and took off injecter manifold to check for cracks .found some loose inj,manifold bolts but that was it put back together an runs better but not fixed pls help.

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The 5.0l and 5.7l all have this problem at some time.The lower intake gaskets are bad.and are sucking air which will cause the eng. to idle high and sound like like there is a cylinder or two that are not firing and you also may loose antifreeze.The upper intake is black/plastic and the lower is aluminum.Tightening the lower intake bolts may seem to help but once the gaskets are blown,they need to be replaced.If its sucking more air through the bad gasket than the TBI it will not get the right air to gas mixture.Check that all vacuum hoses are in good shape and the vacuum line that runs from the top of the upper intake to the brake booster is sealed good in the intake.Hope this gives you a better idea.

Posted on Mar 03, 2009


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Now I am not at all saying this couldnt me something much more difficult, however VAC leaks are also pretty easy to check. Get yourself a can of SPRAY CARB CLEANER from your local parts store, some times gas stations have it too, wal-marts and places like that have it. Start your truck and SPRAY the CARB CLEANER around places that could have a VAC leak. Like hoses, the intake manifold gaskets and those kinds of things. If your engine suddenly runs REALLY ROUGH or even DIES when you spray a certian spot you know thats where your leak is.

I hope this helps you as much as it helped me

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Here is the firing order diagram for that engine, and let me know if this does not solve your problem or if you require any further asistance.


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