Well my 408 started running like . It is pulling a STRONG vacuum from the crankcase. I think it has been doing this all along ('bout 1500 mi since install), but now it is MUCH worse. I originally noticed it from the pcv breather port on the passenger side. I thought it was just vacum from the pcv valve through.

Motor started running rough w/ no power. While doing an initial diagnosis I pulled the pcv valve from the valve cover and the motor ran up to about 3000 rpm at idle. It is pulling vacuum through the valve cover hole. I pulled the crankcase breather tube also and plugged the pcv hole in the valve cover. The engine is pulling a strong vacuum through the breather at the driver's side valve cover.

Anybody have any ideas? I'm gonna run a compression test tonight and look into it further.

 

When you plug the pcv hose or port, does your engine run better? Your crankcase is supposed to be in vacuum when you PCV is hooked up. It can act as a vacuum leak if your seals are torn, ex. leaky valve cover gaskets, dipstick tube seal, leaky engine cover gaskets, etc.

 

Wow.... Thats A Tough One. Do You Have Any Crankcase Vent Lines Hooked To Direct Manifold Or Tb Vaccum Possibly By Accident??

 

NO vacuum lines hooked to the valve covers, valley cover, or oil pan.

I wonder if an intake runner in one of the heads could have been damaged while porting or cracked somehow?(stage III 317 heads).

 

Damn Thats A Tough One.... Any Codes To Help Light A Path??

 

When heads get ported the rocker arm bolts do go into the intake runner. Never heard of one causing crankcase vacuum though. Try putting some teflon tape or other thread sealer on the intake rocker bolts.

 

No codes either. Runnin SD w/ LTFT disabled. Idles real rough and dies. Smoothes out some at higher RPM but no power. The truck is running extremely rich 9:1 AFR wideband reading.

*EDIT* I haven't put the supercharger on the new motor so I've ben running NA since the install.

 

I used teflon pipe thread sealer on the rocker arm bolts. This is not a slight vacuum either. I am planning on running a compresion test tonight and possibly tearing into the motor. Just hoping someone will come up with something I missed.