andywear87

my buddy has a 91 lx with a recently put in 306 and it has smake coming out of the valve cover vents its not a lot but it is noticable. what is causing this and how do you fix it? he is running afr 165's

samseed101

I assume this is on a car with a carb? Or is it EFI w/o a PCV system? Either way, it sounds like he just has some crankcase gasses that are venting to the atmosphere. Probably got a little extra blowby in there, Just don't get on it until the engine gets past the break in period and everything seals nicely (I'm also assuming it's a new 306.)

ruger311

all new engines will do the "smoking" thing outta the breathers on the VCs when they are new b/c of blowby, if it continues to do it after you break the engine in do a compression and leakdown test to see if the rings really sealed up or not

andywear87

its and efi and yes hit was just rebuilt and should be out of the breakin period he has about 2000 miles on it its not much

samseed101

Did he eliminate the PCV system due to a supercharger / turbo? Just trying to figure out why there's an open-air breather on the valve cover of an EFI engine.

andywear87

hhits has aftermarket (cheap valve covers) from ebay and it just has a breather stuck in each side

samseed101

When he finalyl gets up and running, that's gonna cause problems if he hasn't completely eliminated his PCV system. It's going to cause a vacuum leak which will cause idle surge, cause a loss of power, hesitation upon accelerating, etc.

He can still run with the PCV system with the aftermarket valve covers. He just has to ditch the open-element breathers and run something like this. This style breather will allow him to hook up the required vacuum lines so that there is no vacuum leak.

andywear87

so if he just bought the efi valve covers from like bbk or ford racing would it be fine cause the chrome is chipping off of these and he wants new ones anyways. hhe has had them for 2 months and all the chrome has fall off except a tiny bit

samseed101

Yeah, he should be fine with those. The problems arise when the valve covers have breathers that allow them to vent to the atmoshpere. That allows unmetered air into the system which will cause problems. That's because of the way the PCV system works. So if you get aftermarket valve covers that have the openings (typically a 1.22 ID rubber grommet with or without baffles) then you need to make sure that you run the vacuum lines properly. Usually that involves simply capping off the driver's side so that it's no linger open. Then on the apssenger side, you's use the breather pictured above to run a vacuum line from teh valve cover to the TB. That would solve that problem.

But if he does switch to EFI covers, that should be taken care of.

andywear87

thanks alot man