Intake manifold vacuum leak

[Dieselman966]

Finished up installing my headers and running new exhaust on the galaxie today. Checked for vacuum leaks around the intake and found some by the intake bolt holes.  Seems weird that it can suck it in that far with the gaskets being under the valve covers. How are you guys checking for intake manifold vacuum leaks leaks? Do you pull valve covers off to check them?

[fastf67]

Possibly the carb is getting some of the vapor from your aerosol cause its a little lean? Is it hard starting or vacuum gauge low? Disconnected PCV would have a suction and intake would be pulling in air/oil mix causing smoke out tailpipe if gaskets leak from under the covers or in valley area.

[Dieselman966]

It could start raiser. Cranks over 4 or 5 times to start after its warm. Vacuum is at 14.5 at idle and goes up to 20 when revved up to 1500 rpm. PVC is capped of on the carb and no smoke out of the tail pipes. I'll have to spray again and try to keep it away from the carb this time.

[winr1]

With mill idling, slowly close choke or a 2 folded shop towels over the primary entrance

Mill will idle faster if there is a vacuum leak



Ricky.

[C6AE]

Could be PCV?

[Dieselman966]

I forgot I put a new pcv in along with new line to it. The motor slows down when I spray at the 4th intake bolt on the right side. I put up some cardboard to shield the carb from the aerosol.   Seems weird that it would pull enough air from around a bolt. I dont get an rpm change anywhere else though.

[fastf67]

Strange. Does rpm drop instantly or seconds afterward? Pull the pcv and see if problem still exist, that may tell you if its pulling in the valley area possibly. Hard to believe it would go all that way with out smoking out the exhaust. I'm sure you have checked rear block off plate and everything around there so and lose the aerosol, use a brush or Q-tip with fluid on it to pin point the problem. See if it will pull fluid in around the bolt. If it does you can back the bolt out to make sure the top of the bolt hole is flat and making good contact all the way around for proper torque and sealing of manifold and no cracks leading out of it. If it checks good and think it leaks, put some rtv around it and re-torque. let dry and see if problem still exists.

[C6AE]

copper washers?

[cjshaker]

If you're pulling vacuum around one of the intake bolts, sealing the bolt is NOT the answer. You've got a gasket sealing issue that needs to be dealt with. There could be one of several causes, but sealing the bolt won't fix any of them.

[fastf67]

Yes, Doug you are correct! The surfaces need to be checked and gasket needs to be changed if it truly is leaking at the bolt. I'm not so sure that's the problem until proven threw process of limitation. Odd that it would leak that bad at a bolt with a intake runner (1 1/4"?) away not sucking oil in? It is possible, and by no means was I implying to live with sealer on it. I've just had better days at work then pulling a FE manifold. LOL

[67428GT500]

I don't see how they could have an air leak. What I have seen a couple times was them wet with oil.  If I remember correctly the issue was lack of a functioning PCV valve or excessive blow by.

[C8OZ]

Wondering if I'm the only one who's taped over the airhorns and blown a few cigar puffs down the PCV tube chased by a little shop air...
Not that there aren't better ways. Generally just a trickle of propane will pinpoint the spot.

[Dieselman966]

Pulled the intake. The intake gaskets looked ok from what I could tell. I kept going and pulled the passenger side head off to check some things for a low power issue. Found out I have a compression ratio in the high 7. So I'll fix that and see where that leaves the vacuum leak.