Ignition failure; vaccuum pump - leaky diaphragm? Is this right or wrong? - PeachParts Mercedes-Benz Forum

Blevinsax · #1 06-01-2007, 01:26 AM

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!

Motorhead · #2 06-01-2007, 01:51 AM

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?

rs899 · #3 06-01-2007, 07:31 AM

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.

Blevinsax · #4 06-01-2007, 08:33 AM

Quote:

Originally Posted by Motorhead

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?

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.

Quote:

Originally Posted by rs899

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 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.

Biodiesel300TD · #5 06-01-2007, 09:38 AM

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.

Stevo · #6 06-01-2007, 11:57 AM

Quote:

Originally Posted by rs899

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.

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.

Brian Carlton · #7 06-01-2007, 12:05 PM

Quote:

Originally Posted by Blevinsax

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!

Yes and yes.

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

Anytime........

vstech · #8 06-01-2007, 12:25 PM

Quote:

Originally Posted by Brian Carlton

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

Brian Carlton · #9 06-01-2007, 12:31 PM

Quote:

Originally Posted by vstech

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.

rs899 · #10 06-01-2007, 12:57 PM

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

Brian Carlton · #11 06-01-2007, 01:18 PM

Quote:

Originally Posted by rs899

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??

arew264 · #12 06-03-2007, 12:42 PM

I've only worked on a 617 but I assume the system here is similar - someone can correct me if I'm wrong.

If the A/C vents went out at the same time, it COULDN'T be the shutoff diaphragm because there is NO VACUUM to that diaphragm when the car is running. If the A/C vents stop when you try to turn off the car (with the key) it could be the shutoff diaphragm, but if they are dead when the car is running, it's a leak or the pump.

Check the pump - you should be getting 15+ inches at the main line. Since your brakes were fine, it's probably not that.

That leaves another subsystem messing things up.
You said the locks worked? I'm not sure if you have an electric pump that is only for the locks, but if you do - good for you, you have no door lock leak. If not, it was leftover vacuum in the storage tank in the trunk (it lets you operate the door locks 5 times between recharges).

That leaves the climate control as the main suspect for the leak. Try shutting off the ACC completely and waiting about 30 seconds. Then turn off the car with the key. If it works, you know one of the climate control vacuum pods has a bad diaphragm (also possibly a bad vacuum line, but probably a vacuum diaphragm).

If it doesn't work, use a mityvac to see if the climate control system main line (on my 300D with a 617 it is green) holds a vacuum with the ACC off. If it doesn't you have a bad ACC switchover valve that is leaking in the off position. Not sure where those are in your car.

Hope this helps, it takes quite some time to firmly grasp the logic behind vacuum troubleshooting. If I was unclear, let me know, I'll try to repost.

Also, this is how things would work on a 617. I have noted all the places I think the 603 could be different - let me know if I missed anything.

EDIT:
This would help you find your leak if it's not the engine, and while I believe this is useless because it is definitely engine related (because of the oil in the lines), I'll leave it.

Blevinsax · #13 06-03-2007, 01:17 PM

I'll have to check on the specifics with the A/C, and I will try what you said about turning off the ACC completely, then waiting to shut off. I have been driving in 'Econ' mode - just fresh air, no A/C - and the car still fails to shut off with the key.

However, I now realize that perhaps I have left out some important details...

When using the key to shut off, the car does act as if it is trying to shut off. It definitely slows down and spins down as if it is trying to shut off, but just does not finally stop running. Also, for the last several months my shut off has been longer than it should have been - it would take 2-3 seconds for the motor to spin down and shut off.

Brian Carlton · #14 06-03-2007, 01:34 PM

Quote:

Originally Posted by Blevinsax

When using the key to shut off, the car does act as if it is trying to shut off. It definitely slows down and spins down as if it is trying to shut off, but just does not finally stop running. Also, for the last several months my shut off has been longer than it should have been - it would take 2-3 seconds for the motor to spin down and shut off.

Test the shutoff diaphragm with a Mityvac. It should shut right down if the diaphragm is working properly. If it doesn't, then you know the diaphragm is NG.

arew264 · #15 06-03-2007, 01:48 PM

About the EC mode - in terms of vacuum, it's the same as normal. You're still using the same flaps, just no compressor and A/C.

I may be right or wrong with my post, but even if there is an ACC leak, it won't account for the oil. I'm with Brian, get the line to the shutoff and pull a vacuum on it directly with a MityVac (you do have one, right?). It should shut right off and not leak.

If it's not the shutoff, procede with that ACC test I outlined.

There is a third possibility I didn't mention that seems like it may apply.
If you get to the ACC tests and it doesn't turn off with the ACC off, and the ACC main line is not leaking, it may be a clogged restrictor.
There are restrictors on the main vacuum line where the other systems branch off. These are basically plastic circles with tiny pinholes in the center, the idea being to severely restrict airflow to the accessories. The air can compress enough and flow enough that you still can get good vacuum pressure, but when an accessory leaks, the restrictors keep it from interfering with the brake booster.
Occasionally a restrictor can become clogged. When this happens, you will find that nothing leaks but your engine still will not stop and the A/C flaps either don't operate that you can see or operate very very slowly.
The solution is simply to take the accessories off of the main vacuum line (with the engine off) and use a MityVac to pull air out and blow air in, alternating several times. This will free any dirt that cold be clogging the restrictor and will allow for better air flow.

This would fit with the fact that you have had a 2-3 second shutoff for a few months, but that could be either this or the diaphragm going bad.

Test the diaphragm. If it's good, you know how to procede. If it's bad, you have the problem right there.