Possible Head Gasket Failure

[boyhonda5]

2003 GMC Sierra 2500HD with 6.0 gas V8. MIL on with p0300 stored (random misfire) #5 cylinder misfiring severely. swapped injectors, coils, plugs and plug leads from good cylinders, no change in misfire location. cylinder compression is much lower than others (140-150 psi) while others are 170-185 psi. cylinder also has excessive leakdown (31%) has been run hot while towing, and has signs of external coolant leak, but not constant leak.

[gmtech4]

sounds like it to me ,anyone else?

[minibike132]

The compression doesn't sound low enough to indicate head gasket to me. I would be thinking more like valve not seating correctly especially with the leak down #s. Either way you are pulling the head on this one assuming the leak down test was done correctly.

 

You can check for a cracked head/head gasket with a combustion leak detector like THIS ONE.