Engine runs rough under 2000 rmp and pressure in the crankcase builds up. If you get on the throttle too hard it will pop the oil cap off. Changed the crank and cam shaft sensors. Runs and idle rough with lack of acceleration. But does fine on the interstate. 2005 dodge durango hemi 168000 miles. Any thoughts? Please help

 

the egr valve popped up on the scanner also, along with the crankshaft and camshaft sensor that i changed . also something about multiple misfires.

 

The mechanic is telling me that its a cracked piston but he didn't look at it but for maybe 5 minutes. If that long. If the puston was cracked then wouldn't it run poorly at all rpm's?

 

It would. But, it would be less noticeable at higher RPM. Do a compression test. See what the numbers look like.

 

It's getting oil blown back into the air filter also. But i will try and get the pressure test done

 

Crankcase pressure tends to blow oil back thru the PCV system....... so, that doesn't really come as a surprise.

 

+1 for the compression test. do a dry, then wet test. this will rule out or confirm an excessive blowby condition that would overwhelm a normally functioning pcv system.

 

How hard is it to switch out motors?

 

Did you also change out the EGR valve? A stuck open one will cause the running conditions you describe....poor idle, misfire at speed, even detonation. If run long enough like that it can cause engine damage.