'87 300SDL won't stop running - PeachParts Mercedes-Benz Forum

thinkzingink · #1 11-10-2006, 05:08 PM

New guy here, thanks in advance for the help. 1987 300SDL, 240K miles.
Turn it off, take the key out, it still runs. Even with the battery disconnected. Put key back in , disconnected battery, still runs. Depressed some kind of lever on side of block ( hazard a guess that it's a manual choke override ) and it will immediately stop. Also tried taking a small red 10a fuse out that sits in the wiper motor area, the engine seemed to labor ever so slightly but kept running. Could not find alternator fuse in engine fuse block, did not check under dash block ( if there's one...).

What to do?

I did a search both by links that hunter put up and overall search function.
Sorry if this is stupid problem that's already been answered, couldn't find it.

Brian Carlton · #2 11-10-2006, 05:19 PM

You're chasing an electrical problem when you actually have a vacuum problem.

Your issue is likely one of two possibilites:

1) The shutoff diaphragm on the top of the injection pump is NG and won't pull the rack back to the closed position.

2) The shutoff diaphragm is working properly and the ignition switch is not sending vacuum to the diaphragm when you turn the key to the O position.

You'll need a Mityvac to confirm the problem.

Diesel Dan · #3 11-10-2006, 05:23 PM

Or... one of your vacuum lines has come undone or cracked, etc. Trace all your vacuum lines to be sure they are all connected and not broken.

thinkzingink · #4 11-10-2006, 05:26 PM

Super. Thanks.

Ara T. · #5 11-10-2006, 10:52 PM

For sure a vacuum problem, I'd probably start at the injection pump area. Remember diesels don't need batteries to run, only to start. This happened to me also, which stumped me for a couple hours till I noticed one of the 3 way connectors had broken. They get pretty brittle after a while.

dieseldiehard · #6 11-11-2006, 01:19 AM

Quote:

Originally Posted by Diesel Dan

Or... one of your vacuum lines has come undone or cracked, etc. Trace all your vacuum lines to be sure they are all connected and not broken.

I second that idea!
There are lots of hoses around the drivers side of the 603 engine and all should be tight and not leaking. One of them attaches to the shut off valve and is fed from the "ignition" switch.
If the car shifts really hard then its possible that a major vacuum line is loose, like at the vacuum pump. I've seen them come off at the pump's hose barb where there is a clamp on a short section of rubber hose that goes to several tees at a junction not far from the belt tensioner pulley.

Worst case is the vac pump is no good but thats very unlikely.

While poking around under there you should check the type of vac pump you have (on the front of the engine - not the one under the back seat that is for the central locking system). It should have 4 torx-head bolts holding the cover on, if its a crimped on cover then most mechanics suggest replacing it before it does your engine in (as in dead!)

Jadavis · #7 11-11-2006, 02:23 AM

If you are anything like my you bumped the brown vacuum hose loose on the driver's side of the engine compartment. It goes into a black connector on the edge of the compartment. I've bumped that sucker loose 2-3 times. Back on Friday the 13th fo October I broke the brittle vacuum line.

-Jim

thinkzingink · #8 11-11-2006, 11:45 AM

Again, great advice all.

Vacuum hose on top of injector pump was brittle. I also took out the switch that shuts it down, seemingly a diaphragm in a round case with a retractable arm assemmly that trips the "switch" ( attached to an external manual arm that when depressed does the job - pardon my ignorance, I don't have a repair manual and don't know the names or the detailed functions of this beast...yet ).

Replacing a bunch of brittle hoses, there are still many to do, solved the problem...once. Then, maybe on the other end of that "brown" tube may still be an issue, but that runs into the firewall, I have not checked under the dash yet to replace that end. It would "almost" work many times.

I ended up taping and wire tieing an old kitchen cabinet know on the depressor arm and...voila. Starts, stops, doesn't bind or catch. Just enough weight does it...for now, until I find and replace more hoses.

When it was still running in the "0" key position, pinching and releasing the hose "almost" did it, so I'm hoping that the brown vacuum hose to the ignition switch is accessible and the source of "not enough vacuum" to solve the problem.

This is a great forum, excuse my verbosity.....

firemediceric · #9 11-11-2006, 01:09 PM

Quote:

Originally Posted by dieseldiehard

I second that idea!
While poking around under there you should check the type of vac pump you have (on the front of the engine - not the one under the back seat that is for the central locking system). It should have 4 torx-head bolts holding the cover on, if its a crimped on cover then most mechanics suggest replacing it before it does your engine in (as in dead!)

Does this also apply to my '81 300 SD? I'm not having an vac issues, but should I fear the pump ruining the engine? Can you give a pic of the pumps location?

Thank you