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Old 10-19-2018, 02:25 PM   #43
30 Closed Cab PU
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Join Date: Aug 2018
Location: Wisconsin
Posts: 1,402
Default Re: Terriable backfiring

a 12 LB difference when all other 3 are at 60 looks like a problem. Could be head gasket, could also be a valve issue. Not sure if it would cause backfiring, others may know.


Sticky valve, carbon under valve, bent valve, etc.


Take the plugs out.


Crank the motor with ignition off or hand crank and you may be able to view the valve operation through the spark plug hole


Or take the valve cover off, crank engine and view valve operation


Or use a borescope through the spark plug hole.


Or perform a leak down test.


To see if you have a head gasket leak into the coolant - look for bubbles in the radiator coolant with the engine running, also load the engine down and recheck. As a final check you can purchase a NAPA Block Test and test the coolant for exhaust gas (the test kit is about $45).
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