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jetmech85 · 10-08-2014, 12:02 PM

I have an "85 "M" code 3/4 ton. Does not have EGR, cat., charcoal canister, and able to run leaded gas, manual transmission, all from the factory. Point is that its most likely motor causing my problem. Runs good at idle and under no load. Compression check showed 160-170 on seven holes but 90 on number 5. Backed off both valves and applied shop air to that cylinder and it blew out of the exhaust port. Applied air to a good cylinder and it moved the piston to the bottom of the stroke. A compression tester is fairly inexpensive and can give you a good idea of your engine condition.
The port below your fuel filter looks like its an adapter for a spread bore(Quadrajet) to a square bore manifold so that is not the factory PCV port. I will have to look at my '85 to see where it goes. It may be fine where it is but is it capped off at the original location?

10-08-2014, 12:02 PM	#32
jetmech85 Registered User Join Date: Sep 2014 Location: Texas Posts: 215	Re: 86 GMC Sierra Classic 2500 questions I have an "85 "M" code 3/4 ton. Does not have EGR, cat., charcoal canister, and able to run leaded gas, manual transmission, all from the factory. Point is that its most likely motor causing my problem. Runs good at idle and under no load. Compression check showed 160-170 on seven holes but 90 on number 5. Backed off both valves and applied shop air to that cylinder and it blew out of the exhaust port. Applied air to a good cylinder and it moved the piston to the bottom of the stroke. A compression tester is fairly inexpensive and can give you a good idea of your engine condition. The port below your fuel filter looks like its an adapter for a spread bore(Quadrajet) to a square bore manifold so that is not the factory PCV port. I will have to look at my '85 to see where it goes. It may be fine where it is but is it capped off at the original location?