help me narrow down my problem, 300sd vacuum - PeachParts Mercedes-Benz Forum

85drtysthbenz · #1 07-31-2004, 06:15 PM

well, ive tried to pinpoint the reason my 85 300sd wont shut off with the key and cant really come up with anything...

i checked all the lines that i can find, they all seem to be fine...no cracks in them or the connectors...also none of them had oil in them...i read that that can be a sign of a failed shut off valve

i dont have a mityvac, but i do have a vac/pressure gauge....is there any way i can troubleshoot and find out what the problem is with this? any help would be appreciated... and if anyone can point me to a thread with some pictures that would be a huge help

phantoms · #2 07-31-2004, 06:25 PM

I would check the vacuum at the shutoff valve itself (have a friend watch it when you turn the key off) and work backwards from there if there's a problem.

85drtysthbenz · #3 07-31-2004, 06:26 PM

just read a post that said if you suck on the line coming from the shut off valve while its running that it should kill the engine....i just tried that and it didnt shut off....just to be sure, the line going into the top of the white plastic valve on the rear of the IP is the right one?

so,if that is the right line...and it didnt shut off when suction is applied, does that mean that i should replace the valve?

engatwork · #4 07-31-2004, 07:11 PM

Don't think it is plastic. I think you are talking about the one that conrols vacuum for shifting purposes. The line you are looking for is brown.

85drtysthbenz · #5 07-31-2004, 07:19 PM

ok, the thing i was looking at is definitely plastic and a faded white...its on the rear of the IP, right behind the ALDA.....there is a brown line coming from directly under that plastic piece that leads into the cabin...it is connected to something under the plastic piece that is separate.....i would have to remove the plastic thing to be able to get in there to hook up my vac gauge....the plastic thing is held on by a couple of allen bolts and has two lines coming from it, one going into the cabin(black) and the other one(black w/ red stripe) leads to a switch located in the wheelwell....

now am i looking at the wrong thing? should i remove this to get at the brown line and check the vac pressure on it?

85drtysthbenz · #6 07-31-2004, 07:21 PM

the reason i thought it was the shut off valve is because it appears that the STOP lever is connected to it

engatwork · #7 07-31-2004, 07:30 PM

Quote:

it is connected to something under the plastic piece that is separate

That brown line is going to your shut off actuator. You will need to put a vacuum on that line going toward the injector and it should shut the car off. If it does then there is nothing wrong with it - you have a vacuum leak somewhere.

85drtysthbenz · #8 07-31-2004, 07:42 PM

ok,just went out and hooked a line up to where the brown line led...we'll call this the shut off valve from now on

....anyhow, i hooked a line up to that and was able to suck on it and kill the engine...so im guessing that means the valve is good.....also, i guess i have a leak somewhere between the shut off valve and the key switch? sound right? since everything under the hood looks to be intact, should i pull the gauge cluster and check for something amiss in there?

what should be my next step? is it going to be a leak in that brown hose somewhere along the line? or is there any other places i should check

now i took my vac gauge and hooked it to the brown line.....nothing...but when i turned the key it fluctuated just barely, i mean it barely moved at all......what kind of vacuum should i have when the key is turned to off....i guess i shouldnt have any at all while the car is running, that would just shut it off.....but when i turn the key back, how much pressure should i see?

85drtysthbenz · #9 07-31-2004, 08:18 PM

i just went and pulled the instrument cluster...the lines look to be hooked up just fine....also, there is definitely a leak...i sucked on the brown line and couldnt build up any pressure at all....so, does this mean theres a leak in the brown line somewhere between the shut off valve and the key switch? or could there be a leak elsewhere, in another line, that is effecting the shut off valve? the way it looks, the brown line just goes straight to the key switch without any other lines tapping into it....im just about at my wits end on this one....i feel like just taking it to the mechanic and saying," you deal with it"

engatwork · #10 07-31-2004, 10:02 PM

Quote:

im just about at my wits end on this one

Don't give up yet - you are almost there. What you need to do now is find the "supply" vacuum line going to the key switch. Should be teeing off somewhere around the brake master cylinder. You want to apply vacuum to the supply line (going toward the key switch) with the key in run position (it should not leak down) and then with vacuum applied turn the key to off to see if it shuts down. If it shuts down you will have to try to figure out why the vacuum "supply" is not getting to the keyswitch. You should have 16+ inches of vacuum going to the shutoff valve during normal shutoff operation. I suspect your leak is going to be in the vicinity of the master cylinder. Another thing to do to troubleshoot is to remove anything else that is teed into the vacuum source with the brown line and vacuum test those circuits. Leaks other than the shut off circuit will cause the problem you are experiencing.

85drtysthbenz · #11 08-01-2004, 02:13 PM

WOOHOOOOO!!!

i found the leak....it was on the numbered thing that holds a lot of vac lines...on the passenger side of the center console, right by the radio.....i installed a new cd player the other day and re-routed some wires through there....i guess when i pulled them out i knocked off a vac line.....it was a pain to get to, i ended up pulling the radio, ashtray, and the top wood piece to be able to see where the supply line led.....just slid the line back on, turned the key, and she shuts off like a champ

jim, thanks so much for the help....you are THE MAN

engatwork · #12 08-01-2004, 05:49 PM

Just glad I could help out.

Quote:

I suspect your leak is going to be in the vicinity of the master cylinder.

If you had indicated that you had installed a CD player just recently I would have suspected the leak in the area where you found it

.

85drtysthbenz · #13 08-01-2004, 06:07 PM

Quote:

Originally posted by engatwork
Just glad I could help out.

If you had indicated that you had installed a CD player just recently I would have suspected the leak in the area where you found it.

its all good...i learned some things along the way....i actually posted another thread like a week ago with the same problem and some of the guys told me i could have knocked something off back in there by the radio....i thought i checked it out pretty thoroughly, but i never saw the big distrobution thing on the right...i had to pull off the side of the console to see it.....live and learn, live and learn.....oh well, im a lot more familiar with the workings of my vacuum system now