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Dead cylinder #4 - way forward?



Hello, I recently inherited a 1999 Tahoe LT 4x4, 5.7L Vortec, Auto, 194K miles. Codes are P0300 and P0304. 


cylinder 4 has no compression. Fuel pressure is 55psi, Spark is steady and strong on all wires as indicated with an inline spark tester and timing light. 120-125psi on all other cylinders to include 2 and 6.  No milk in the oil. 


I have not not taken off the valve cover yet to see what’s going on with valve springs yet. 


My question is “what sequence should I try to see if it’s springs, valves, seats, rings, pushrods, lifters, etc?”



Dave in Abq. 

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With 0psi compression you can rule out rings.  Sounds more like either a holed piston, or burnt valve, assuming no engine noise when running.  Take the valve cover off, and verify both valves open and close when cranking over.  If they are, then it is time to pull the head. 

If you have access to a compressor, you could back off both rockers to ensure both valves are closed and using your compression gauge hose connect airline to fill cylinder with compressed air. Listen at intake and exhaust to locate leak. 

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+1 on that - leak down test will tell the tale, then you can go from there. Either exhaust, intake, holed piston, head gasket, or the rare crack in either the plug or head. Follow the air leakage.

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