Engine will shut off when doors are locked - PeachParts Mercedes-Benz Forum

RML · #1 10-27-2018, 06:58 PM

In my 1985 300D, the engine was shutting off very reluctantly when I turned off the ignition. I knew it was a vacuum leak somewhere. Then I accidentally discovered that if I have the doors locked, the engine will shut down right away. So where should I start to look for the leak? I do not see any cracked connectors in the engine compartment. Should I start by taking off the door panel on the driver side door?

tangofox007 · #2 10-27-2018, 07:29 PM

Quote:

Originally Posted by RML

Should I start by taking off the door panel on the driver door?

That's the last place I would look. The other doors, along with the trunk and gas door, have actuators that are prone to leaking. If you have a vacuum tester, you can isolate the problem by accessing the vacuum lines in the cabin, many of which are under the carpet. Alternatively, you could plug one actuator at a time and see if the problem goes away.

RML · #3 10-27-2018, 08:06 PM

I do have a MightyVac. I'll pick up the carpet and start testing lines.

BillGrissom · #4 10-28-2018, 12:14 AM

The trunk lock is the biggest suspect. Just cap off the tubes and forget about it. Just use your key to open the trunk like in most classic cars, unless you care to pay >$200 for a new one (if you can find). The fuel door is another and you can just reach it from the trunk (fold back plastic side liner). You can get at both tubes under the front passenger seat outside. There should be 4 tubes going aft there, a set for the RR door and a set for the fuel/trunk. The rubber tees were still fine in my car.

Shern · #5 10-28-2018, 12:52 AM

Quote:

Originally Posted by BillGrissom

The trunk lock is the biggest suspect. Just cap off the tubes and forget about it. Just use your key to open the trunk like in most classic cars, unless you care to pay >$200 for a new one (if you can find). The fuel door is another and you can just reach it from the trunk (fold back plastic side liner). You can get at both tubes under the front passenger seat outside. There should be 4 tubes going aft there, a set for the RR door and a set for the fuel/trunk. The rubber tees were still fine in my car.

You know you can find these for between $30-60 bucks on eBay?

+1 on trunk actuator. Had the same issue, been good ever since.

RML · #6 10-29-2018, 09:45 PM

Thanks for all the input. Hope to check it out this week or weekend while waiting for a part for my 84 to come in. Always something to fix.

BillGrissom · #7 10-29-2018, 10:44 PM

Quote:

Originally Posted by Shern

You know you can find these for between $30-60 bucks on eBay?

+1 on trunk actuator. Had the same issue, been good ever since.

I see used ones for $30+ after shipping. I wouldn't trust those, nor a junkyard one, because they seem to fail due to age of the rubber diaphragm.

I find new ones starting at $60. Amazing they come w/ all the levers and springs for that price. Still, unknown manufacturer (General) and I would have to weigh the value since my key works fine and in comparison I only paid $400 for my 1984 300D.

OM617YOTA · #8 10-29-2018, 10:53 PM

I read the thread title as "Engine shuts off when I lock my doors" the first time around. Had me chuckling, thinking that's a pretty fantastic practical joke to play on someone. Re-route a couple hoses........

koooop · #9 10-29-2018, 11:24 PM

That’s funny, our 240D won’t shut off if the doors are locked.

Easy fix, we don’t lock the doors until the car is shut off.

Phillytwotank · #10 10-30-2018, 08:48 AM

Ok. From what you describe I would be looking for vacuum hoses connected wrong or some kind of weird hack Not just a simple leak. Each vacuum system should be completely separate from each other and if the proper check valves are in place severe leaking in the locking system wouldn’t effect the engine stoping system. Brown pipe for the engine stop is about the most simple of them all. Brown pipe from the vac to the key, brown pipe to the key to the IP.

tangofox007 · #11 10-30-2018, 09:37 AM

Quote:

Originally Posted by Phillytwotank

Each vacuum system should be completely separate from each other and if the proper check valves are in place severe leaking in the locking system wouldn’t effect the engine stoping system.

Great theory. It just happens to be incorrect. The check valve that isolates the locking system is necessarily open while the vacuum pump is operating.