M117 Vacuum leak
 

Hey all, I own a 85 500sec (gen1) and im having a problem that is making my car unusable :-(
Im having a massive vacuum leak somewhere, the car is slow to start, it takes about 5 seconds cranking to get it running.
I think the vacuum leak might come from under the fuel distributor, I've heard there are some vacuum connectors there that is only accessible when you remove the plenum and distributor. When I give it some gas it starts to misfire slightly around 3k rpm, when I let go the engine goes down to very low rpm and then picks up, but sometimes it stalls. Do anyone have a picture of these connectors im looking for? Want to make sure before I start looking :-)

Sondrusen,
The problem as you describe it doesn't sound like a vacuum leak to me. Vacuum leaks usually cause problems at idle speeds and become less of a problem as RPM goes up. Misfires at 3K rpm and up are usually a fuel supply problem. The fuel accumulator located at the fuel pump/filter assembly can cause hard starts and low fuel pressure after the engine has been running.
Now to answer your question the best I can, there are some vacuum hoses under the fuel distributor but they usually don't cause problems. If one of them does crack and cause a problem you will probably have to replace all of them. I'm sorry, but I can't seem to fine a picture of the layout. There are also 8 seals between the intake manifold and plenum that can cause leaks. The manifold must be removed to get to these seals.

I wish I could be of more help but this is the only thing I can come up with, with the information I have.

PaulM

Hey, thanks for your reply :-)
I have been suspecting that the fuel accumulator could be bad. But it runs steady when it runs, and the misfire was worse when I had more leaks, to get it running i had to place a wrench opening the top plenum just slightly, and then the car would start right up without hesitation.
The car has been sitting for the last 12 years so there is probably allot of things in need of replacement, the fuel filter I changed a few weeks ago was from 1995 :-O
I found a vacuum line that went into the engine somewhere, most likely the one you describe, it's a bit larger then most of the lines around. It runs from that small tank looking thing on the front of the car, i disconnected it and found out that it did not hold any vacuum at all, like blowing trough å straw, so I found the leak, or at least one of them.
Tomorrow I will take a look and try to fix it,
Hopefully it will solve my problems :-D

Nope. That's just the canister for the fuel tank fumes. No vacuum there. Just a negative pressure caused by air flow through the air intake system.

On the M103, the 2 vacuum lines you are referring to are connected to the manifold
with the hoses sliding on from the front to the rear of the car.

The two connections are just bout under the fender side of the fuel distributor. They do come off ! Make sure your lines are long enough.

If you have to press the air plate down to get the engine to start then you may have a really bad vacuum leak. Do you know if the engine has an electronic idle control system? Some do and some don't and they are different.

PaulM

Hey guys, sorry for the late reply, I found the source of the leak,
that big rubber boot (116 140 06 18) that is under the plenum had a small crack at the rear side, that is also where the noise came from.
Im waiting for a new one in the mail :) I believe it's attached to a clip under the cold start valve, should be an easy replacement.
Hopefully this will make it run like it used to :-)

You would be wise to replace the eight rubber donut seals with OEM units while the CIS unit is off of the car along with the rest of the injector seals and such.

This is not a huge job, just time consuming to do it properly and clean everything.

I got the rubber boot today, hoping to change it tommorow.
Do anyone know what the bottom part of the boot is connected to?
I tried using a screwdriver to get it loose, but it did not seem to help.