84 300 sd Wont shut off.. - PeachParts Mercedes-Benz Forum

norcalwood · #1 09-07-2008, 03:59 PM

My 84 300sd keeps running when I turn off the ignition and pull out the key.. Where should I start with trouble shooting..

Thanks

kerry · #2 09-07-2008, 04:47 PM

It's vacuum related. Pull a vacuum on the brown vacuum line going to the shut off valve at the back of the IP down between the IP and oil filter housing with the engine running. If it shuts down, the vacuum problem is not in the shut off valve itself. You'll then have to trace it down.
If you don't have a Mity Vac, you'll need to get one. In the meantime, you can pull a vacuum on the shut off valve with your mouth to test it. Use a section of vacuum hose in place of the brown line.

toomany MBZ · #3 09-07-2008, 06:33 PM

I had a similar situation with my SD, replaced fuel shut off valve, problem solved.

norcalwood · #4 09-07-2008, 07:29 PM

I did as Kerry said, taking the brown vacuum hose off and attaching my own hose. I sucked to create a vacuum, the car then shut down. So That means its not the shut off valve.. I have no other symptoms everything is working fine..
Could it be the ignition maybe??

777funk · #5 09-07-2008, 08:09 PM

Quote:

Originally Posted by norcalwood

I did as Kerry said, taking the brown vacuum hose off and attaching my own hose. I sucked to create a vacuum, the car then shut down. So That means its not the shut off valve.. I have no other symptoms everything is working fine..
Could it be the ignition maybe??

Most definitely your shut-off valve. Ok just kidding about the most definitely part but I'd bet that it is your problem. That's a hard one to diagnose. Here's why...

At times a mityvac will shut off the car when the vacuum line in the car will not. I've had this. The vacuum shutoff valve was my culprit.

Check the vac line connections (rubber that looks like it won't hold vacuum) then if you don't find anything, Replace the shut-off valve. Easier said than done but I'd bet that's your problem.

also... if your vacuum level wasn't good you'd have problems like transmission shifts are hard etc.

kerry · #6 09-07-2008, 08:42 PM

If you can shut if off by sucking on the line, I think it is most likely that your shut off valve is good and the problem is elsewhere. Could be the ignition switch but your going to have to use a MityVac to do some more diagnostics. You'll need to T the Mity Vac into the main line to measure vacuum, then after into the brown line to see what happens when you turn the key off.

777funk · #7 09-09-2008, 08:29 AM

Quote:

Originally Posted by kerry

If you can shut if off by sucking on the line, I think it is most likely that your shut off valve is good and the problem is elsewhere. Could be the ignition switch but your going to have to use a MityVac to do some more diagnostics. You'll need to T the Mity Vac into the main line to measure vacuum, then after into the brown line to see what happens when you turn the key off.

Not necessarily in all cases. Again, I could slowly shut my car off with a mighty vac if I squeezed hard enough fast enough but the car wouldn't do the job itself. I put a new shutoff valve in and it was dead the second the key turned.

kerry · #8 09-09-2008, 09:29 AM

Yes, but in this case, the OP was using his mouth. I don't think his or her mouth can produce vacuum as quickly as pumping a Mity Vac, that's why I think the problem is probably somewhere else in the system.

Try pushing the far right button on the climate control system. This turns it off, excluding any climate control leaks as causes. If the engine shuts off with the climate control off, you know the leak is in the climate control system somewhere.

toomany MBZ · #9 09-09-2008, 05:58 PM

Quote:

Originally Posted by kerry

If you can shut if off by sucking on the line, I think it is most likely that your shut off valve is good and the problem is elsewhere. .

I also feel this not necessarily the case. I used a mity vac to shut the engine down, still had a bad shut off valve. Oil leaking from the ignition switch.

777funk · #10 09-10-2008, 08:40 AM

Regardless, if it is an original part, it's got a rubber diaphragm in it... Rubber that's 20 something years old is going to be in bad shape.

The original poster probably should do some elimination as Kerry said. That's wise.

But if it were my car not shutting off, I'd change the valve first. I already know that it's got to be in bad shape. Metal parts on these cars are machined well and last a long time. The rubber parts... no good machining can make rubber last much longer than it's lasted on our old cars. It's still rubber. It gets old and dry which means brittle and cracks or lack of seal over time. To bad they didn't use a metal cylinder with clearances so tight they wouldn't need a seal just a small amount of lube/or fuel from the IP. Oh well... can't ask for everything.

Old Dies · #11 09-10-2008, 11:38 AM

Be very careful when changing that shut off valve. Not only is it tricky to get out and back in, but if you install a new one incorrectly you will blow up your car.
Not a good thing to do.

toomany MBZ · #12 09-10-2008, 04:16 PM

Quote:

Originally Posted by Old Dies

Be very careful when changing that shut off valve. Not only is it tricky to get out and back in, but if you install a new one incorrectly you will blow up your car.
Not a good thing to do.

What he means is if you install it upside down, the engine will go to a full fuel situation.
Be sure to note the orientation of the old valve, it's not difficult to swap.
However, in the event you have a run away engine, have something handy to shut off the air supply.
Get two paper gaskets, they sandwich a metal one you reuse.

norcalwood · #13 09-15-2008, 07:39 PM

ok, so I'm going to start with the replacing the shut off valve. Doesn't seem so bad, as long as I don't put it in upside down.
I'll let you guy know how it goes..

Thanks