Ignition Key OFF ... Engine still runs? - PeachParts Mercedes-Benz Forum

BIG Doug · #1 02-21-2009, 10:01 PM

The other day my 85 300SD started a new trick.

I switched off the ignition, removed the key, and the engine kept running normally.

It did not appear to want to stop, or slow down. The bright red Battery Idiot light came on.

After opening the hood, I couldn't see anything unusual, so I pushed the stop tab on the linkage above the Injector pump. That seemed to take more than the usual travel before the idling engine came to a stop. Once it stopped, the Battery IL went off.

Is there a solenoid or vacuum diaphragm that pulls the linkage to the kill position. Where should I look for a loose of disconnected link?

kerry · #2 02-21-2009, 10:22 PM

Vacuum shut off valve. Check your vacuum level with a Mity Vac. Cause could be a bad diaphragm in the shut off valve or low vacuum because of a leak somewhere else. Pulling a vacuum on the brown line coming from the back of the IP controls the shut off valve while the engine is running should shut the engine off if the shut off diaphragm is intact.

mplafleur · #3 02-22-2009, 12:51 AM

Yup, right on the back of the injection pump (IP), is a vacuum operated shut off valve with a vacuum line attached to it. Sometimes the diaphragm inside gets torn or the vacuum switch at the ignition switch gets a leak. usually much more the former than the latter.

You can test the shutoff valve easily. It doesn't take much vacuum to make it shut off. You should be able to disconnect the line to the shut off valve and suck on it yourself and have the engine shut off. But first look at the line and see if it looks like there is engine oil inside the line. If there is, there is a leak in the shutoff valve and the oil is evidence of this. The oil is coming from inside the IP.

TchTchr · #4 02-22-2009, 01:55 AM

A leak in a door lock actuator caused mine not to shut down properly.

mplafleur · #5 02-22-2009, 02:47 AM

Yes, I forgot the general "you have a leak somewhere in the vacuum system".

toomany MBZ · #6 02-22-2009, 05:41 AM

Quote:

Originally Posted by TchTchr

A leak in a door lock actuator caused mine not to shut down properly.

The 126 chassis, an SD, has a separate vac pump for the door locks. When my SD failed to shut down, I pulled, with a mity vac, 10 Hg, it stopped. I did have oil in the brown line going to the ignition. I replaced the shut off valve, problem solved.

BIG Doug · #7 02-22-2009, 06:04 PM

Thanks for your suggestions.

I suspect the vacuum system must be causing more problems than the shut off function I mentioned initially. I discovered today that the transmission is shifting with a jerk going up or down in gears, and the door locks are not working as usual.

I'll start tracking down the stopping problem with a hand vacuum pump first.

Then I need to learn where to look for the major leak, or vacuum pump failure.

BIG Doug · #8 02-24-2009, 01:49 PM

I tried to follow up on the vacuum leak problem by looking at the back of the Injection Pump. I found a thin black "tube" coming out of the top of a white plastic hexagonal fitting. I followed the line to a fitting near the firewall, that has electrical wires going into a quick disconnection.
Low and behold, there was black oil at the top of the white plastic fitting, suggesting that engine motor oil may have gotten into the line. The outer shell of the "tube" appeared to be broken. I tried to tug on the line, and found that while the outer part was loose, there was something inside that kept it from pulling free of the shut-off-valve-diaphragm.
I tried to unscrew the white plastic fitting to loosen the tube, but it disintegrated before my eyes

In order to get a socket wrench on the white plastic fitting, I cut off the line coming out of the center of it. At that point, I found that there were three small wires inside the tube, saturated with black oil. I still have not been able to remove the white plastic fitting.

I drove the car after cutting the above line, and find that the shut-off does not work when the ignition key is turned off. The transmission is still acting jerky. However, Door locks are working OK, in contrast to my earlier comment.
How Now to proceed?

I appreciate your insights and suggestions.

mplafleur · #9 02-24-2009, 05:27 PM

If you have oil in the vacuum line, it is getting pulled in probably from the injection pump at the shut off valve. Try pulling vacuum at the shut off valve. It should take little vacuum to pull the diaphragm and it should hold it.

Toblin · #10 02-24-2009, 09:16 PM

Are you absolutely sure? This is the first time I've ever heard of anybody having this problem.

mplafleur · #11 02-24-2009, 09:30 PM

It's happened to me. The diaphragm tears in the shut off valve. Instead of pulling the diaphragm, the vacuum pulls oil from the IP.

Oil does not belong in the vacuum lines and shouldn't be there. It has to be coming from somewhere. Where else is there oil?

kerry · #12 02-24-2009, 11:43 PM

It sounds to me as if you have been messing with the lines that go to the vacuum control valve and not the line to the shut off valve. The VCV is a white plastic fitting on top of the back of the IP. The shut off valve is at the back of the IP down between the IP and the oil filter housing. It has a brown vacuum line going to it.

Your door locks are on a completely separate vacuum system powered by an electric pump in the trunk so you can ignore them.

BIG Doug · #13 02-27-2009, 07:57 PM

In a previous post, I told how I cut a bundle of three wires going to what I thought was the shut-off valve.

That was not the shut-off valve at all, but a diaphragm actuated switch of some sort on the engine side of the injector pump, IP. I suspect that this may be the reason for the jerky shifts.

I read in some other threads that the shut-off valve mechanism is between the IP and the oil filter, . Sure enough, I was looking at the wrong thing. Now what to do about the wires I mistakenly cut?

I am happy to report on the troubleshooting test I did. A hand vacuum pump plugged in to the nipple on the "shut off valve" caused the running engine to stop cold with just two squeezes of the hand pump! The vacuum gage showed less than 10" of Hg. Also, there was no sign of oil in the vacuum line, it was dry. I think that means the next step is to look for a problem at the ignition switch/vacuum valve.
Any other suggestions on how to proceed? Must I drop the cover from under the dash near the ignition switch? Thanks for your help!!

kerry · #14 02-27-2009, 08:20 PM

Vacuum leak can be anywhere, not just related to the ignition switch. So, you need to do general diagnostics to narrow it down. Could be in the climate control, brake booster, or transmission vacuum control system.

Don't know what to do with what you cut, apart from reconnecting it.