wont shut off- separated underdash vacuum hose somewhere - PeachParts Mercedes-Benz Forum

bigblue · #1 08-26-2007, 07:57 PM

way back when I broke the mount off for the under dash duct

http://www.peachparts.com/shopforum/showthread.php?t=192443

so today I removed to bracket to rivet it back together. I realized the instrument cluster had to come off to reach the bolt. That's off, and I removed miles of aftermarket stereo/alarm/cellphone wiring to simplify things back to stock wiring

It was no surprise to me that when i packed up, the engine doesn't shut off using the key. I even suspected it because I can see a separate vacuum hose deep up there close to the firewall bulkhead that was probably upset by pulling out an aftermarket harnesss. I can't be 100% certain that is the culprit and had to close shop for the night.

There's quite a few electronic boxes of different type and I can't figure the best way to temporarily get them out of the way to further inspect this hose. It looks almost like I need to remove 2 brake pedal bracket nuts. Does that seem right?

hey_allen · #2 08-27-2007, 10:54 AM

On mine, the hose to the shutoff valve/servo thing was brown with a white stripe, I think..
There were two total involved in that system, and they should both connect to the back of the ignition lock assembly.

If it doesn't reach back to the lock, just barely clearing the firewall, it may be the vent hose I've heard some others mention. (I am not sure that is on the 126 chassis, though..)

If you do have two tubes attached to the back of the lock assembly, you can test with a vac pump and a gauge.
with the engine on, stick the gauge into one, then the other. Check if you have vacuum on either. If you do, then try applying vacuum to the one that didn't have vacuum present on it.

Assuming that the diaphragm in the shutoff thing on the IP is intact, the engine should shut off.

If you didn't have vacuum on either hose, try applying vacuum on each of them. You'll probably find that one will shut off the engine.

From my car, I found that someone hacking at the radio in the past had dislodged one of the many vacuum connections just to the right of the radio opening. Lack of vacuum in the system makes the shutoff valve a bit ineffective.

I hope this helps some.

kerry · #3 08-27-2007, 10:59 AM

There is a vent hose on the 123's so I wouldn't focus on that hose as the cause of the problem. I would first get under the hood and isolate the problem to either the ignition circuit, the climate control circuit or the door circuit by plugging the climate control and doors to see if it shuts off with those plugged. Once you isolate the circuit where the leak is occurring it will be easier to track it down under the dash.
Or, if you're like me, once the plug the circuits and it shuts off fine, you'll let it go for a few months before returning to find the problem.

bigblue · #4 08-27-2007, 11:53 AM

That's good advise. earlier this week I came to the conclusion that it is time to buy a mightyvac. Now I really need it. The 2 lines on the ignition switch are intact. They are weeping oil (probably from when the shutoff valve broke recently with the PO) but until I was working under the dash yesterday, still functioned normally. Hopefully this separate line is just a vent like Kerry mentioned but I feel grim about that possibility. In this case I don't believe in the coincidence and think it's probably one of the vacuum lines to the engine.

The stock wiring/ vacuum harness has definitely been hacked up quite a bit.
Prior to me removing the aftermarket radio it kept blowing the fuse for the instrument cluster/turn signals.

It is still blowing fuse 15 so I figured I should start with removing all the leftover aftermarket wiring. There was a LOT.

kerry · #5 08-27-2007, 12:00 PM

Quote:

Originally Posted by bigblue

In this case I don't believe in the coincidence and think it's probably one of the vacuum lines to the engine.

I don't believe it is a coincidence that your engine won't shut off after working under the dash either. I do believe that the chances that the line you are looking at that is disconnected is the problem are small. It doesn't take much pressure to disturb a vacuum fitting and there are tons behind the dash, including the switchover valves behind the radio. If it is the line you are looking at, the mating connector should also be pretty readily visible and you haven't mentioned it so I think it's likely you're looking at the vent.

bigblue · #6 08-27-2007, 12:51 PM

Quote:

Originally Posted by kerry edwards

I do believe that the chances that the line you are looking at that is disconnected is the problem are small.

Very well stated. I failed to mention that when I was pulling out an aftermarket wire that went through the firewall to the fusebox, I first noticed this unattached vacuum line was moving when I pulled. The wire must have wrapped around the tube, whether it was previously connected to something or not- I wont know until I test it. It isn't a soft hose, it's the harder neoprene type. It's very hard to see/reach/work on anything that far deep up under the dash behind all the wiring/ductwork/pedal/bracketry/control boxes.

But you are correct about it being wrong to jump to conclusions when doing these types of diagnostics. Unfortunately I will not be back to see or work on this car for the next week and a half. The thing is all apart right now and it bothers me to think about what the problem could be. Thanks for the advise.

toomany MBZ · #7 08-27-2007, 04:03 PM

Can you determine the color of the hose? Kerry is correct about the vent line, most are black. If that, there will be no effect, so failing to shut off is still an issue. I think there is a brown line that has something to do with the ignition switch shut off. Have you checked the vacuum shut off valve by itself?

bigblue · #8 08-27-2007, 04:14 PM

Quote:

Originally Posted by toomany MBZ

Can you determine the color of the hose? Kerry is correct about the vent line, most are black. If that, there will be no effect, so failing to shut off is still an issue. I think there is a brown line that has something to do with the ignition switch shut off. Have you checked the vacuum shut off valve by itself?

I think I remember it being a dark colored line. Perhaps it is a vent.

what are the switchover valves? The vacuum controlled valves which open/close the HVAC flappers?

The PO of the car replaced the vacuum shutoff valve on the IP about a year ago. I would imagine the old faulty shutoff valve was what caused oil to enter the vacuum lines. The lines going to the back of the lock cylinder (is it appropriate to call it an "ignition" switch?) are very oily.

toomany MBZ · #9 08-27-2007, 06:18 PM

Yes, I think, ignition is OK to use. I am familiar with the switchover valve under hood, concerns the turbo overboost. On my CD, has been bypassed, no problems. SD works fine. The vacuum operated vent flaps (pods) are a different item, yet if there is a leak somewhere, that may be the culprit. Given the chance, clean out lines of oil to see if oil returns. New shut off valve may let you move on to other things. Does it shut off via the underhood lever? Are the locks working properly? Have you checked vac pump pressure? Questions, questions, questions I know.

bigblue · #10 08-27-2007, 06:59 PM

Quote:

Originally Posted by toomany MBZ

Yes, I think, ignition is OK to use. I am familiar with the switchover valve under hood, concerns the turbo overboost. On my CD, has been bypassed, no problems. SD works fine. The vacuum operated vent flaps (pods) are a different item, yet if there is a leak somewhere, that may be the culprit. Given the chance, clean out lines of oil to see if oil returns. New shut off valve may let you move on to other things. Does it shut off via the underhood lever? Are the locks working properly? Have you checked vac pump pressure? Questions, questions, questions I know.

i did test the power locks. They still work fine and the underhood lever works to shut off the engine. That's the only way I know how to get it off right now.

kerry · #11 08-27-2007, 07:19 PM

Stick a piece of vacuum hose on the shut off valve and run it out thru the cowl. Suck on it to shut if off. Saves opening the hood.

bigblue · #12 08-27-2007, 07:41 PM

Quote:

Originally Posted by kerry edwards

Stick a piece of vacuum hose on the shut off valve and run it out thru the cowl. Suck on it to shut if off. Saves opening the hood.

Thanks for the good idea. I can imagine many people on this board have been there before. I have the luxury of not having to drive the car until I get it right. The interior is in pieces anyway right now.

toomany MBZ · #13 08-28-2007, 06:53 AM

Quote:

Originally Posted by kerry edwards

Stick a piece of vacuum hose on the shut off valve and run it out thru the cowl. Suck on it to shut if off. Saves opening the hood.

Going around your elbow? Actually, you can hook up a mity-vac to determine if that new shut off valve is indeed working via vacuum.

kerry · #14 08-28-2007, 08:44 AM

Quote:

Originally Posted by toomany MBZ

Going around your elbow? Actually, you can hook up a mity-vac to determine if that new shut off valve is indeed working via vacuum.

I was thinking of it as a temporary measure to shut down the engine to avoid those embarrassing moments at the country club where he'd have to open the hood to shut it off.

bigblue · #15 08-28-2007, 11:44 AM

Quote:

Originally Posted by kerry edwards

I was thinking of it as a temporary measure to shut down the engine to avoid those embarrassing moments at the country club where he'd have to open the hood to shut it off.

I'm glad I'm not a member of that club

There is nothing more embarrassing I can think of than to pull up and have to suck on a small hose hanging outside my cowl to shut down my 22 year old rattling quarter million mile rusty benz.