I have an 87 944 turbo and it sounds like I have an exhaust leak coming from the exhaust manifold, however, I checked every gasket, checked every bolt for tightness etc....and still could not find the location of the "leak".

Instead, is it possible this "chh chh" sound is coming from a bad lifter? After about 7 minutes the noise goes away. I use 15-50 Mobil one.

Do these lifters go bad or do the passage ways get clogged and can be cleaned? If cleaning works, is there an additive for the oil or do I need to pull the cam tower and physically clean the passage ways. This is concerning since I change the oil after every track event, so the oil is replaced several times a year.

 

Have you been running synthetic oil for long? There's a lot of ongoing discussion about changing from petroleum based oil to synthetic causing rubber seal failures. I was just wondering if an injector seal was failing and as it heated up, it softened enough to temporarily seal itself.

 

are you sure the manifold isn't cracked - I don't know about the turbo, but the later (non-cast) mainfolds on the NA seem to all fail due to heat induced stress - I actually changed to the older cast iron manifolds to solve the problem once and for all.

 

Try using a piece of hose to pinpoint where the noise is. Going away after a few minutes sounds like a lifter but it maybe a small manifold crack closing as it heats up and the metal expands.

 

Try Seafoam. Connect a hose to the vacuum port on the throttle body then suck up about a third of a can of the Seafoam. Turn the engine off and wait about ten minutes. Lightly stuff a rag in the exhaust tip to create some back pressure. Start car and smoke from the Seafoam should start coming out of any leaking areas. Look at the exhaust manifold and any "Y" sections, also flange fittings for leaky gaskets.

 

Ah...the dread exhaust manifold leak....what a PITA to remove. Any suggestions for a replacement?

 

Probably some on ebay. I have stainless and a common area for a crack is at the manifold Y junction for the 1 and 4 exhaust. Look for a crack underneath the support gussett. I just had mine welded at a muffler shop that specializes in stainless exhaust. I mounted the two manifold flanges to a piece of wood so it wouldn't distort during welding and prevent re-aligning with the studs. Instead of removing the gussett to get at the crack, they just welded as much of the crack they could reach, then welded all around the gussett to seal off the Y junction. They tested it in water afterward to make sure it was completely sealed. Still no problems after 3 years. --Lizard

 

if you don't mind the extra weight, the cast exhaust manifolds are supposed to be much more crack resistant - that's what I used to solve the problem.

 

I swapped to the cast iron for the outside set after they cracked the third time. Havent had the problem with the inner set yet.

Michael