vaccum issues......engine doesn't shut off - Mercedes-Benz Forum

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post #1 of 2 (permalink) Old 02-05-2006, 01:56 AM Thread Starter
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vaccum issues......engine doesn't shut off

I've got a '83 300d and when I first got the car the vaccum systetem was working ok....Although, it did'nt store the vaccum that long and if you didn't lock the door within a minuite of turning off the engine, the door would not automatically unlock and you would have to go around to each one to lock them....then, all of a sudden, I noticed the engine had a lot of trouble shutting I read on Diesel Giant that the car shutting off, also has to do with the vaccum I went back to my car an just started playing around with the brown tubing right next to the firewall and I think I must have done something, cause the car was shutting off better than ever.....then, a couple of days ago, again it had trouble shutting off, and now it doesnt shut off at all.......So I was wondering if anybody knows if there might be a fairly easy way to deal with this.....i.e. do I have to go out and buy a vaccum pump and test out all the connections or maybee replace the actual vaccum or might there be another way to go about it that may be a bit simpler? Thank you very much.
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post #2 of 2 (permalink) Old 02-05-2006, 09:07 AM
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RE: vaccum issues......engine doesn't shut off

i believe it is easier to troubleshoot problems if you understand how systems work[;)] m-b loves vacuum systems: lightweight, cheap, quiet etc. the 617 engine in your car has a plunger pump that is driven by the timing chain and is located at the front of the engine. follow the hard plastic line from the brake booster and you end up at the pump. you will need a test pump to troubleshoot this syetem. sears sells a good one, i don't like the mightyvac, but it works.
a few basics: brown line=fuel shut off circuit
yellow: door locks, (yellow w/green;unlock, yellow w/red;lock, yellow w/gray;reservior) green, climate control vents, blue (coupes only, seat back lock) black are vents to atmosphere, sometimes trans. modulator signal.
if your power brakes work good even after pumping the pedal 10 times, your pump and checkvalves are good. if not, reply and i'll tackle that.
if the car doesn't shut off, there is a leak somewhere, the vacuum signal is lost somewhere before the pump can recover.
step 1. visually check for cracked, loose, chaffed vacuum lines and connectors, repair as necessary.
step 2. pull brown line off shut-off plunger on back of inject. pump and :look for oil in the line, if not, pull vacuum on plunger with test pump. if it holds vacuum, plunger is good[:)] reconnect brown line, go to vacuum tees where brown line is connected and pull vacuum on that line. this will test the ignition switch part. oil in the sytem will cause the rubber to swell and pop off the switch. run motor, turn off ignition and pull vacuum on brown line, vacuum holds switch is good. if you are good so far, then the problem is either in the door locks or the dash vents. use a vacuum tee (pep boys etc) to tie into the system between the source line and the consumer lines. you should see at least 20" vacuum. if not, pinch the rubber connectors going to the different color lines until you see a rise in vacuum. if it is in the yellow, lock and unlock the doors to see which circuit is leaking. also try the yellow-gray since the reservior can leak. reply as to which circuit leaks and i'll help with finding the problem.
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