300td not shutting off...I've checked other threads... - PeachParts Mercedes-Benz Forum

johnrf · #1 08-03-2014, 09:35 PM

I recently acquired a 1984 300td for a song ($500). The car is in much better shape than my previous ones (1981 300d / 1983 240d), but it does have a few issues. The one I'm dealing with now is the typical not shutting off when the key is off. Previous owner said the vacuum pump works, and is pulling plenty of vacuum (I haven't checked this yet) All the hoses look good, connectors look new, its obvious some attention has been given to the system. On my 240d, a golf tee was in the line going to the door locks I believe, must have been a leak there because with the tee removed, the car wouldn't shut off. Put the tee in and the car cut right off. I tried putting tees in various lines, climate control, door locks etc...and nothing would kill the motor. Couldn't find my vacuum pump/guage, so I bought a new one, hooked it up to the fuel shutoff valve and after 2 pumps, the car shut off. So, for now because I really need the car to shut off without popping the hood, I have run vacuum line from the shutoff valve through the firewall where I can hook the pump to it and shut the motor off. Having said all of that, when I apply vacuum to the valve, after it shuts off I notice some red, oily liquid in the tube. Its not diesel, (Im not running off road diesel), it looks like transmission fluid. There was also some of this residue on the back side of the ignition switch when I checked it to see if the hoses were connected there. Anybody else have this happen, or know what this could be??

ichris93 · #2 08-03-2014, 09:50 PM

I think I have heard of the shut off valves leaking but they should suck motor oil and not transmission fluid. There is probably a valve in the transmission that can leak too but that would not be connected to the ignition switch so does your crankcase have transmission fluid instead of oil in it?

johnrf · #3 08-03-2014, 10:04 PM

No, theres no transmission fluid in the crankcase. I have my vacuum pump connected directly to the shutoff valve, I could see how some fuel may be sucked up through, unless the previous owner put some sort of oil in the vacuum pump if he had it off and that is what I am seeing...

ichris93 · #4 08-03-2014, 10:08 PM

Quote:

Originally Posted by johnrf

No, theres no transmission fluid in the crankcase. I have my vacuum pump connected directly to the shutoff valve, I could see how some fuel may be sucked up through, unless the previous owner put some sort of oil in the vacuum pump if he had it off and that is what I am seeing...

And the shutoff valve goes into the IP which has crankcase oil circulating through it. So the only liquid you should possibly see is motor oil.

snorider · #5 08-03-2014, 10:20 PM

Quote:

Originally Posted by johnrf

No, theres no transmission fluid in the crankcase. I have my vacuum pump connected directly to the shutoff valve, I could see how some fuel may be sucked up through, unless the previous owner put some sort of oil in the vacuum pump if he had it off and that is what I am seeing...

Does your brake booster work? Braking power would be poor if it doesn't. That should tell you a bit about your vac pump as well. Is it brake fluid? just a thought. I'd go ahead and start at the booster to vac pump line and kill vacuum circuits with a plugged piece of vac line. Add to the door lock actuators the climate control parts as possible culprits. Good luck.

johnrf · #6 08-03-2014, 10:20 PM

i see what you're saying...ill start checking the system tomorrow, hopefully I can pinpoint the problem fairly quickly. Right now things kind of are pointing to the pump, i guess we'll see...thanks for the tips

johnrf · #7 08-03-2014, 10:23 PM

Haven't checked what type of brake fluid, but I assume he used DOT 4. Door locks aren't working and the selector for the climate control won't switch the airflow. Doesn't look like those systems are getting vacuum either...I'll check it tomorrow and post a pic of the setup, maybe you all could see something not right

Zacharias · #8 08-04-2014, 08:58 AM

Three things before you do anything else:

1. You need to verify that you have decent vacuum coming from the pump. The brakes can feel normal even if the pump output is way low. Crack the large main line from the pump, where it enters the booster - the spec is 17-21 mmHg, IIRC. You need a vacuum gauge for that, they are dead cheap at any auto parts outlet.

2. Carefully examine every rubber connector and splitter on the vacuum lines. These crack and split with age and it isn't always apparent at first (and can be underneath). Also as they age these things get brittle and loose anyway, some folks put small zip ties on each outlet to prevent leaks. A couple of small leaks like this can add up.

3. Google a vacuum routing diagram for your car, sometimes you can luck out and find a photo or two as well online, and check that the lines are routed correctly to begin with. Over the years people work on these cars who have less than half a clue, and leave stuff in a mess.

If you can post photos of how your lines are arranged, people may have comments immediately.

As to the red fluid, pull some other vacuum lines and check if they have any of that present. And look for evidence when you pull the main vacuum line. A broken vacuum pump diaphragm will let oil into the lines. I don't know exactly what happens when the booster is defective.

vstech · #9 08-04-2014, 09:59 AM

Vacuum modulator on the transmission can leak transmission fluid into the vacuum system.

seo · #10 08-04-2014, 10:11 AM

I've had a problem with my 300d where if the doors aren't locked the engine won't shut off, and the transmission shifts abruptly. Lock the doors, and everything works fine. Apparently a vacuum leak in the driver's side door lock system? Anyway, try locking the doors and see if the engine will then shut off correctly, which would point you toward at least one of the sources of leaks. What fun!

Zacharias · #11 08-04-2014, 11:53 AM

Quote:

Originally Posted by vstech

Vacuum modulator on the transmission can leak transmission fluid into the vacuum system.

Yes but if the shutoff is properly hooked up (lines correctly routed), given the routing of the vac lines it would be a really serious infestation to get the trans fluid all the way in there... no?

johnrf · #12 08-04-2014, 11:01 PM

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I checked the vacuum at the pump and got 22hg. The valve in the picture is putting out very little vacuum that basically feeds everything else, it doesn't even show up on the gauge.