Does anyone have a copy of the vacuum schematics for a 1987 SEL? Car is running rough. Replaced plugs and wires, but didn't solve the problem. Shop narrowed it down to a vacuum leak under the fuel mixture control unit.. don't even know what or where that is, or how to go about finding the vacuum leak. Help!!

V8 or M103?

Dumb question - If the shop diagnosed the problem, why didn't they just fix it?

Vacuum leaks are easy fixes. But to tell the truth, if you're not familiar enough with working on cars to know what a vacuum leak is or how to diagnose it, then you are only going to get yourself in trouble taking things apart.

I'm not trying to insult you, just politely suggesting that you might get in over your head real fast..... And then you'll have to pay somebody to undo your mistakes, and that will get expensive real fast.

If you're determined to plunge in anyway, what you are looking for is any hose or fitting attached to the intake manifold that is leaking air in. There are a few ways to do this. First and most obvious is listen for the hissing of air leaking in. The second is by spraying carb cleaner on the suspected area, and watching for a surge in engine speed indicating that carb cleaner is getting sucked in through the leak.

Good luck.....

My advice is to let your shop fix what they diagnosed.

__________________
-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition

And the third way, and easiest way to find a vacuum leak is the smoke test.