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Car Forum / Mercedes-Benz Cars / July 2006Electrical/vacuum/shutdown relation- 83 300D
Help me figure this one out: Car suddenly would not shutdown, PLUS the headlights would not shut off, and the wiper/sunroof/turn-signal curcuit was dead. I jumped a wire from a life fuse to the nonworking one and got the sunroof to close in the rainstorm and the wipers on the get me home. But still no shutoff and lights stay on until engine is manually extingushed. Any ideas? Pop the hood the pull that Stop engine level >Help me figure this one out: > [quoted text clipped - 4 lines] >But still no shutoff and lights stay on until engine is manually >extingushed. Almost certainly not related. First of all the best thing I've found for emergency wipers is Rain-X (or equivalent). With a *scrupulously clean* windshild squirt it on douche it around, then wipe dry. It's bloody magic and I frankly almost never use my wipers any more. Non-shitdown of a diesel engine of that wintage is usually always the muchroom shaped shitoff valve on the back of the injection pump. There's a vacuum circuit thatgoes through the ignition switch and in the off position it allows full (about 15-20 lbs) vacuum to the shutoff valve. Inside the shutoff valve there is a diaphragm and when vacuum is applied it pulls a lever inside the injection pump that shuts off the supply of fuel to the motor. Check to to see if the vacuum hose is still attached to the shitoff valve. If it is, see if it holds vacuum. You can use a vacuum test gauge or (and it tastes very very bad) you can just suck on the hose yourself. Prepare to eat oil if things are really ugly in there you don't want and shouldn't have oil in that line that could indicate vacuum pump failure and that would need to be addressed also. The most common cause of failure in cars of this vintage is a defective shutoff valve, they're cheap and fairly easy to replace. Last week somebody here had the vacuum hose fall off - an even easier fix so do check that first.  SignatureNeed Mercedes parts? http://parts.mbz.org Richard Sexton | Mercedes stuff: http://mbz.org 1970 280SE, 72 280SE | Home pages: http://rs79.vrx.net 633CSi 250SE/C 300SD | http://aquaria.net http://killi.net I believe you have either a bad ignition switch and / or combination switch or a (water caused) short in one or the other of these. Rain leaks can cause shorts and sun roof drains rust out so that's a possibility here, given the car's age. The motor is normally shut down by a vacuum bellows inside the rear of the injection pump. The vacuum to that shut down device is controlled by the ignition key. Since you don't mention power brake failure the car's vacuum is basically OK so one can surmise the shut down problem is in the controls - unless its been shutting down slowly for a while - kind of trailing off, not cutting off, in which case the shut down device is worn out or there's a vacuum leak elsewhere - in a door for instance. all these replys make sense - except - this morning everything started working correctly, shutdown AND electrical stuff, so, tho i realize one is vacuum and one12v, there is SOME connection somewhere between the two and both going at the same time and coming back up at the same time is a bit more than coincidence. The only connection with both systems would seem to be the key ignition. Any new ideas on what to start looking for? Yes, its working now but we all know its gonna go out again..... > all these replys make sense - except - > this morning everything started working correctly, shutdown AND [quoted text clipped - 10 lines] > Any new ideas on what to start looking for? > Yes, its working now but we all know its gonna go out again..... I'd suggest first determining for sure how the shutoff system with the ignition key works. On my car 116 300SD 1980, the ignition switch has two entirely seperate components. One section is electrical. The other is a vacuum switch to which vacuum lines running to vacuum source and the bellows on the injection pump are connected. So, in my car, the behavior you are seeing would be impossible. However, does anyone know for sure how the system in your car works? For example, if MB went with a totally electric ingition switch that then works the shutoff vacuum through some other element, then the ignition switch could be the problem. One of the more intersting symptoms to me was the fact that the lights would not turn off, granted, they will stay on anyway with the car shut off if the light switch is on - but with the switch off, the headlights would be on til the engine was cut off. Now how would THAT connected to the ignition switch?.... One of the more intersting symptoms to me was the fact that the lights would not turn off, granted, they will stay on anyway with the car shut off if the light switch is on - but with the switch off, the headlights would be on til the engine was cut off. Now how would THAT be connected to the ignition switch?.... >> all these replys make sense - except - >> this morning everything started working correctly, shutdown AND [quoted text clipped - 22 lines] >then works the shutoff vacuum through some other element, then the >ignition switch could be the problem. The 126 ignition switch is the same as your 116 switch. And it's the same engine and the vacuum bellows shutoff switch is even the exact same part. You can spend a lot of time trying to find out why they're related, but they're not. Just fix the freaking shutoff then worry about the headlights after. SignatureNeed Mercedes parts? http://parts.mbz.org Richard Sexton | Mercedes stuff: http://mbz.org 1970 280SE, 72 280SE | Home pages: http://rs79.vrx.net 633CSi 250SE/C 300SD | http://aquaria.net http://killi.net It must have stopped raining! >Any new ideas on what to start looking for? Time to get a vacuum tester and chase down the vacuum leak. There really is no place where 12V and vacuum mingle. SignatureNeed Mercedes parts? http://parts.mbz.org Richard Sexton | Mercedes stuff: http://mbz.org 1970 280SE, 72 280SE | Home pages: http://rs79.vrx.net 633CSi 250SE/C 300SD | http://aquaria.net http://killi.net >The motor is normally shut down by a vacuum bellows inside the rear of >the injection pump. The vacuum to that shut down device is controlled by >the ignition key. Since you don't mention power brake failure the car's >vacuum is basically OK Don't count on it. I've seen power brakes work even with a myriad of vacuum woes. SignatureNeed Mercedes parts? http://parts.mbz.org Richard Sexton | Mercedes stuff: http://mbz.org 1970 280SE, 72 280SE | Home pages: http://rs79.vrx.net 633CSi 250SE/C 300SD | http://aquaria.net http://killi.net
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