Need opinion on intake valve condition.

[cdavidson]

I'm presently replacing the injector lines on my 94 S350D (yes I know, the rod bender). When I removed the intake manifold, I noticed that 5 of the 6 intake chambers and valves had the usual coating of carbon (thanks EGR valve).


However, the #1 cylinder intake chamber was wet and there was very little carbon buildup at the back of the chamber.


Does this mean the valve is leaking? Is this a serious condition that demands repair? If so, I assume the only way to fix this is to remove the head.

The engine was rebuilt recently (and not very well) and has been very rough at idle ever since. Could this be the cause?

Any opinions would be welcome.

[Diesel911]

Since you have the Manifold off a Leak Back Test Might really tell you if the Valve is not seating well as you could feel the Air coming out past the Valves and you could compare them to the other Valves in the Cylinder.

Another indicator could be a Compression Test.

The Harbor Freight Leak Back Tester does not cost much but does not have adapters for Diesels so you would need to buy a Compression Tester kit for the Adapters or make an Adapter yourself. You also need a source of compressed Air.

Do you know if the Valves on your Engine have Rotating Valves? If so it may be some of the Rotators are not functioning OK.

Lastly leaking Valve Stem Seals can cause wet Valves.

Also I would expect the area and Intake Valves next to where the Crankcase Breather Hose goes into the Intake Manifold to be wetter than the Valves further away.

[cdavidson]

Thanks for the advice. I have everything you mentioned. I've heard of a leak down test but never knew exactly what it was. Now I do. I performed the test and found that the valve did not leak. I was surprised at the amount of air that came out of the PCV hole in the valve cover. I tried the same test on the #2 cylinder and got similar results but with much less air flowing past the piston. I'm thinking that cranking the engine to get the valves closed for the second test, got oil up on the cylinder improving the rings seal.

As long I was pretty much set up to do a compression test, I compared the #1 and #2 cylinders. Both read just under 400 PSI. Earlier this year I ran a compression test and got similar readings on all 6 cylinders. I think I can assume my rough idle is not due to poor compression in one or more cylinders.

I'm currently replacing the injector lines (one developed a leak from abrasion and others are worn) and as long as I have it torn down this far I've pulled the injectors and will have them inspected and cleaned at a local diesel injector service shop. I should have it put back together by the weekend.

I'm hoping this will cure the extremely rough idle.

Thanks again for your advice.