GM 6.2 engine running issues after rebuild

Sadel Owner/Technician Ohio Posted   Latest  
2008 Cadillac Escalade 6.2L (8 L92) 6-spd (6L80)
P0300 — Random/Multiple Cylinder Misfire Detected
Hard Start
Blowing Rear Main Seal
High Crankcase Psi

I had this caddy come through the shop, and I was asked if I could look to see what was going on with it. It had a complete engine rebuild done to it and they said it would still run rough and would continue to blow multiple rear main seals and leak out of valve covers and out of the intake etc… I really didn't know where to start , but I started with basic relative compression and boy was I glad that I did, because it gave me a result that I had not seen yet based on how it ran. And from there it was just a matter of trying to make sense of the whole thing and finding multiple problems causing the issues at hand. I hope it yields some interest to some and maybe gives some tips along the way, thank you in advance.


Mark Technician

I think that there is an issue with crankcase venting possible wrong valve covers does it have a pcv valve or just the orifice on left valve cover make sure correct for year of vehicle is the vehicle stock or does if have some power add-ons does not look like stock by the intake hose best of luck

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Sadel Owner/Technician

Mark, the vehicle is able to “vent” …. the issue is that it cannot vent all the extra positive pressure put upon the pcv system due to the exhaust not being able to evacuate spent gasses. meaning with there being clogged cats on both banks, raising exh psi under load to close to 30psi per bank…. that otherwise spent gas that would have left the tailpipe is now backed up in the cylinder as now…

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George Technician

You say it was rebuilt however the rebuild is trash. Head gasket blown or damaged during rebuild. Talk to the rebuilder. The engine may not have been assembled and torqued correctly using new fasteners.

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