Happy New Year's everyone....hope everyone had a safe and happy holidays...

I have an issue that I could use some help with:
I recently installed the LS7 valley cover with integrated PCV valve, along with an oil catch can. The first time I drove my 'vette after this work, the engine stalled out at a stop sign. This condition repeated itself a few more times before I pulled back in the garage. I checked for codes via the DIC and did not find any "smoking guns." I talked to my engine tuner and he suggested that I had a vacuum leak on the intake manifold; he also suggested to check my STFTs and LTFTs. I did, and the LTFT seems ok, but the STFT confirmed his suspicion that I was getting "excess" air into the engine.

I removed the intake manifold and did some investigating. I found that the bolts for the new valley cover stick up higher than the old bolts by about 5mm. There are reliefs on the underside of the manifold that are about 4mm deep, so I concluded that was the issue and changed them out for the old ones (they only stick up about 4mm). I checked everything else and decided to replace the MAP sensor hose-connection because it was cracked. I also checked and tightened the hoses for the oil catch can.

I was very meticulous in re-assembly. Everything seemed to fit correctly, and I could not see any other sources of interference. Today I started the engine and drove around the block a few times. The first stop sign I came to, the engine stumbled a little but did not stall. Next stop sign, stall. Third stop sign, stall. Driveway, stall. I did a quick smoke-check to see if I had a vaccuum leak, but didn't come up with anything conclusive.

What could I be missing? Is there a known fitment issue with the FAST 102mm intake and the LS7 valley cover?

Any suggestions or advice would be greatly appreciated!

Thanks!!

 

With the manifold installed--start the engine and spray some brake clean or something similar around the manifold where it meets the heads--also around any suspected vacuum leaks- T-body etc---If there is a leak the engine will try to die or flare up--
Typically there is an interferewnce with the valley bolts--best way to check is before installing the manifold--put some typewriter white corrector on the bolt heads and install the manifold with 4-5 bolts--remove and se id any of the fluid transferred to the manifold---Most will use "button head allen bolts" for the valley cover--
Also make sure the PCV rubber lines/catch can lines aren't being sucked flat or closed--That will make it stall--Try removing the oil cap to vent the crankcase to atmosphere and see if it quits stalling--If so the lines are being sucked flat--

 

Thanks for the suggestions. The valley cover is bolted down with button-head allen bolts...those were the "old" bolts I mentioned.

More to follow....

 

OK...so I took the oil fill cap off...there was serious vaccuum behind it!! Drove around the block with the cap off...no issues. Seems that you are right about the PCV hoses.

Would putting a breather on the oil fill port be sufficient or should I get better hoses? Or both?

Thanks again!

 

Either or... The crankcase needs to be vented and the flow needs to be in one direction.
GM does it out throough the valley pan and in through the valve covers with clean filtered air.. SO yes putting a breather on the valve cover will do the same thing as the OEM clean air route.

 

GREAT--- I would do both and be 100% sure it won't happen again-- On my car--I bought a vented oil "fill cap" and after re routing the PCV lines for the new valley, they ask you to plug off or cap the driver's side valve cover PCV port---I installed a 2nd breather on this port as well---just any aftermarket breather from O-Rileys will do--

 

The way I have it set up right now is working. I'm going to re-think the "final" set-up but at least the problem is solved.

Thanks to both of you for your assistance!!