Compression in intake manifold - PeachParts Mercedes-Benz Forum

abuzar1 · #1 04-04-2015, 10:23 PM

So I took off my intake manifold to track down a fuel leak on my 97 E300 Diesel. I fixed the fuel leak and as I was cranking the car to move fuel through the shut off valve (so I could check if it was still leaking) I noticed out of ONE of the valves air was coming out with pressure. It's the intake manifold so air should be going in right, not coming out. Any ideas on what this could be? I'll take a picture of the valve tomorrow morning and post it also.

GregMN · #2 04-05-2015, 12:01 AM

How many miles on the engine ?
How many miles since you have blocked off the EGR port ?

The intake valve no longer seals. Start the car with in intake manifold off and shine a light down each intake port. The weak ones will have combustion gases in them at idle. Watch them as you accelerate.

abuzar1 · #3 04-05-2015, 12:04 AM

I have done nothing to the EGR port and not sure on miles maybe 200k. Cluster was changed before I bought it so I don't know for sure. One of the cylinders intake valves are coated in black slimy carbon though, one of them is worse than the others. It was dark so I couldn't verify if it was that one.

GregMN · #4 04-05-2015, 12:15 AM

While I disabled the EGR flapper when I first got the car at 170k, I did not block off the port. At 325k the valve stems had so much soot on them that they would not close. Now at 341K, it really needs a valve job. The valve guide seals are shot, it smokes on closed throttle on long down hills.

abuzar1 · #5 04-05-2015, 12:17 AM

Well I'm pretty sure the old vacuum lines have leaks in them so maybe the egr line was leaking and it did the same thing as disabling it? Can I dissolve the crud off it? Maybe spray something in there?

SD Blue · #6 04-05-2015, 01:20 PM

A diesel producing vacuum? I thought that is why they are outfitted with an external vacuum pump.

barry12345 · #7 04-05-2015, 01:53 PM

Probably needs a valve job unless sludge or whatever has limited the movement of the valve stem. If you felt the light blast of combustion chamber contents getting by the valve.

I was also wondering about a head gasket failure in that cylinders area as well or a head crack. I certainly would try to check it out..

Not the best thing to observe. For example a breech between cylinders could produce pressure in an an adjacent cylinder When the intake valve was open.

I suspect I would apply air pressure to that cylinder to attempt to establish what exactly is going on. With both that cylinders valves closed and the piston at top dead centre.

GregMN · #8 04-05-2015, 02:25 PM

Quote:

Originally Posted by abuzar1

Well I'm pretty sure the old vacuum lines have leaks in them so maybe the egr line was leaking and it did the same thing as disabling it? Can I dissolve the crud off it? Maybe spray something in there?

Lack of vacuum may disable the flapper but it does not prevent EGR soot from entering the intake.

What I did on mine was to spray some MMO on the valve stems while the engine was running.
I did this over 30 minutes with the engine running from between idle and 3500 rpms. I probably used a total 3oz.
After doing that the valves closed better, less combustion gas coming up the intake runner. But, the deposits on the stems was what was sealing the stems in the guides and guide seals. So, now the guide seals do not seal around the cleaner stems and it sucks oil down them. It needs a valve job, or least new guide seals. But, it has 341k and rust and doesn't owe me any more miles. When started, it runs fine. Just keep oil in crank case. I drove it to AZ and back in Jan. and Feb.

Stretch · #9 04-05-2015, 05:51 PM

Quote:

Originally Posted by abuzar1

So I took off my intake manifold to track down a fuel leak on my 97 E300 Diesel. I fixed the fuel leak and as I was cranking the car to move fuel through the shut off valve (so I could check if it was still leaking) I noticed out of ONE of the valves air was coming out with pressure. It's the intake manifold so air should be going in right, not coming out. Any ideas on what this could be? I'll take a picture of the valve tomorrow morning and post it also.

So you felt air was coming out of the valve during cranking?

If so =>

The first thing I'd do is check valve clearances. The clearance could be so tight the valve stays open allowing air to come out of the cylinder during the compression stroke.

If the valve clearances are correct and the valve still leaks then you will probably have to remove the head to check for a correct valve seating and or cracks in the head.