Ignition failure; vaccuum pump - leaky diaphragm? Is this right or wrong?
 

I just had the classic ignition failure - when I shut off the car, it continues to run until I pop the hood and shut it off manually. At the same time I believe it happened, I was driving and my A/C suddenly stopped coming from the center dash vents and went to the defroster vents - also a sign of vaccuum failure, I think.

I took it to my mechanic and after he showed me the vaccum line cap covered in black oil (I'm not sure whether it's motor oil, diesel, or WVO) he said that the air/vaccuum pump diaphragm has failed and is leaking into the vaccuum lines. He told me to go get a new pump diaphragm and he will install it for me and clean out the vacuum lines to the ignition.

Does this sound like an accurate diagnosis and solution? If so, where would be the best place to get the necessary diaphragm?

Thanks for the help!

If the vacuum pump fails, the engine won't shut off. The key switch ports vacuum to the inj pump diaphragm when the key is in the OFF position.
How do the brakes feel? Does it feel like you have no power assist? If you feel like the brakes are hard to push then the pump is Ka-Put. Which line does the mechanic see oil in?

There is no diaphragm in your pump, so I would question your mechanic's ability. If you have adequate vacuum, I would expect its the diaphragm on the vacuum shutoff on the back of the IP that has failed.

My brakes have felt fine - haven't noticed anything different. The vaccuum locks still work, too. My mechanic quickly found a cap on a vaccuum line at the top of the motor, driver's side, that was very loose - it came right off when he touched it, and it was wet with black oil; not sure if it is motor oil, diesel, or WVO - but it was black. He replaced the cap with a new secure one, but it did not solve the problem. Therefore he said there was too much oil in the line already and it would need to be cleaned out before the problem would be corrected. However, we need to address the oil in the line, otherwise the problem will come right back.

My mechanic is definitely not a Mercedes or diesel expert, but he is honest with me and has always worked to help me solve my problems with the car, despite his lack of knowledge. I would be happy to take it to a Mercedes/diesel specialist if I knew one who would be honest, straightforward, and wouldn't charge me an arm & leg just because it's a Benz.

If it is the diaphragm on the vaccuum shutoff on the back of the IP, how difficult/expensive is that to repair? What might have caused it to fail?

Could hot (too hot) WVO cause a problem like this? I am running a Greasecar system with a VegTherm Mega, so my WVO is pretty darn hot - add that to driving in stop & go traffic with A/C, so my engine temps were pushing 100C - the WVO is heated by the coolant plus the VegTherm, so I'm sure it was very hot.

If its black it's oil. Again which line has oil in it? If it is the main vac line and all the other lines then the check valve on top of the vac pump is bad. The check valve is right where the main vac line bolts onto the vac pump. If the oil is only in the ignition lines than your shut-off valve is bad, and you'll need a new one.

I don't think the pump is bad because if it were you would have hard breaks, and the door locks wouldn't work. And the oil in the lines definetly points to either the check valve in the vac pump or the shut-off valve.

There is a diaphragm in the pump if its an early (pre 80s) W123 which can be purchased from the parts dept here, they come in a "kit' which is not expensive.

Yes and yes.

Right on this site.......from Roy or or Phil. Click "buy parts" at the top of the page.

Anytime........;)

hey brian, I was under the impression that the 60x series vehicles had a piston style vacuum pump. do they have a diaphram like the older 61x motors do?
John

Never took either pump apart........but........his question was concerning the shutoff diaphragm on the IP.

From what I recall, you are probably correct.........the 60x pumps can't be easily rebuilt.

not really Brian- his mechanic told him to replace the diaphragm on the vacuum pump to fix a shutoff problem

Well, if that's what he meant.........then he's mistaken. Somehow, I think it's a terminology problem.........cannot fathom how he'd conclude you could replace a vacuum pump diaphragm on a 60x engine??

Photos of offending vaccuum line...
 

Here are a couple photos of the leaking vaccuum line. The cap is new because the old one was loose, soft, and covered in black oil - my mechanic replaced it hoping to correct the problem, but obviously it did not work.

The A/C venting also went out at the same time - while driving before the shut-off failure, all the A/C suddenly went to the defrost vents. Does that help diagnose the problem? Would a failed shut-off valve affect the A/C vents, too?

That's not a symptom of a failed shutoff diaphragm.........it's a sign of a large vacuum leak thereby depriving both the ignition switch and the climate control systems the necessary vacuum to function.

Vacuum
 

I thought that your model has an electric vacuum pump that takes care of the doors and the trunk and fuel door lock so you can't use those systems to judge your engine/ignition vacuum. The best test is really a mityvac and see if you have more than 18 inches of vacuum on any of the outlets on the main engine vacuum pump to brake booster hose... if you do then it is possible that you have a vacuum leak feeding your AC vents, ignition and maybe other problems with the shutoff.... check the main vacuum line to see if you have any oil in it

What about the check valve on the vaccuum pump? BioD300TD mentioned perhaps it is the shut-off valve or the check valve on the vaccuum pump. Might that be a possibility?

Otherwise, where should I start looking for the large vaccuum leak, and how?