Question about 1991 GMC G3500

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Dont know whats wrong !!

Ok to make a long story short my van (gmc 3500 vandura) has started to **** out on me. Skips/stalls/and boggs.. i have done a FULL tune-up. had my mechanic check the timing which he said was barely off and replace egr valve. Still runs like ****. Fuel pressure is suppose to be 9-13lbs with key on engine off but i only have 8Lbs. weak pump but still enough pressure for it to atleast run... My mechanic said he thinks it may be a blown exhaust manifold gasket?? He put his hands over the air intake where the injectors are and the engine smoothed out.. he also sprayed something on the valve cover where the gasket is and it would smooth out for a sec.. he seems to think there is an internal vaccum leak.... would that be a intake manifold leak or an exhaust maifold leak ?? anybody got any opinions or thought

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You may be right in thinking of a leak around the inlet manifold. by placing his hand over the intake, he restricted the airflow momentarily. try a small amount of shaving cream in the area you think its drawing air, don't use much, just a teeny amount. then if thats the problem, then you can fix it.

Posted on Oct 03, 2009

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Put a vucuum guage on it straight off manifold vacuum port, and monitor. A steady reading, but a lower than normal reading (lower than 17 hg) indicates an intake manifold leak. Make sure that the accessories that run on vacuum are disconnected, including the brake booster. Measure again to see if there is any improvement.

Posted on Oct 03, 2009


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