Shut off valve testing. - PeachParts Mercedes-Benz Forum

#1 12-23-2003, 04:26 PM

I just installed a new shut off valve (in the IP, not on the key switch) on my '84 300D turbo. The car still is not shutting off properly (it slowly winds down then shuts off, takes up to 10 seconds sometimes). In my testing, I pulled a vacuum on the shut off valve, and it takes a few pumps before actually climbing up to the 15-20 inch range, and then holds. I have a feeling it winds down that way because, like pumping it by hand, the vacuum pump on the car needs time to increase the vacuum, and as the engine slows down, it just lengthens the necessary time, does this make sense?

Is my new valve faulty, or is it supposed to take that amount of time to build up? Would anyone be kind enough to pull a vacuum on their known good shut off valve and see if it's the same? Thanks!

Rick Miley · #2 12-23-2003, 04:57 PM

It should shut off right away, not wind down. It's telling you there is a leak somewhere else. What is your vacuum measurement at the brake booster line?

Fisherman · #3 12-23-2003, 05:37 PM

Pull the line from the key switch out of the back of the shutoff valve. Try to build a vacuum there with the key in the on position and then in the off position. If you can't build vacuum in the on position then you have a leaking line from the key switch down. It has rubber fittings right at the switch side accessable via the kick panel and contortionism...

if you get vacuum on the on position but not in the off position then you have leaks elsewhere. Try disconnecting and plugging lines under the hood until you find the one that is leaking. Remember that you might have to pump up the vacuum tanks so it may build vacuum very slowly.

All this with the car not running of course.

#4 12-23-2003, 06:30 PM

NOTE!!! CAUTION!!!! WARNING!!!!

It sounds like you are lucky. Whenever removing and replacing the shut off valve you should ALWAYS draw a vacuum on the valve and ENSURE that the Stop lever moves upon actuating the diaphragm. If it does not move, DO NOT START THE ENGINE. The engine will run away to top RPM with no way to kill it.

Been there, done that and spoiled a freshly rebuilt engine.

The only way to kill it is to listen the injector lines. You have less than a minute to get this done before the engine is damaged, or possibly destroyed.

Keep a 17 MM open end wrench in your hand whenever starting an engine after such IP work.

As Rick said, you have a leak somewhere else. The most common thing is for one of the vacuum lines to get knocked loose when changing the oil filter.

Merry Christmas,

russb · #5 12-23-2003, 08:49 PM

Larry.
The best and fastest way to kill a diesel engine is to cut off it's air intake supply!
I changed a vacuum shutoff valve on my 300D and had a small piece of plywood to slam over the air intake on the air cleaner in case of a "run away".
Been there many times, I used to rebuild Detroit Diesel 2 cycle engines, 71's, 53's, 92's, as well as a lot of trouble shooting them, 100's of them, usually stuck injectors!
Takes to long to cut off the fuel!
Kill the air supply, and they will die fast.

#6 12-23-2003, 11:57 PM

Larry--

No need to worry about that. I've already had the valve replaced and run the car several times since with no problems with running away. My question is about pulling a vacuum on the valve, and how immediately it should be coming up.

Fisherman--

I tested the line going from the key switch to the shut-off valve. I kept it connected to the key switch and tested from the engine compartment. I cannot pull a vacuum with the switch on, but I can with the switch off. I then tested the other line (from the vacuum booster to the key switch) in the same fashion and can pull vacuum with the switch on or off.

Rick--

I've got between 20 and 25 inches at the booster line.

Any other suggestions? Thanks!

Rick Miley · #7 12-24-2003, 08:08 AM

Ok, since your pump is making good vacuum, there is a leak somewhere else. Disconnect all the other vacuum consumers (locks, climate control, trans, egr) and plug the rubber connectors with golf tees. You should then be able to start up and shut down properly. If that works, then use your MityVac to track down the leak.

#8 12-24-2003, 09:37 AM

russb,

I've spent my time around Detroits over thirty years ago and we always kept the piece of plywood handy. Don't expect this to work on a runaway 617 engine. Believe me! Been there, done that.

The air cleaner is NOT tight enough. I ripped off the intake hose and covered the hole to the air cleaner. It didn't lower the RPM by more than 30 or 40%. If the air cleaner were off, you could probably cover the top of the intake manifold and it would work.

BELIEVE ME. Some lessons are very hard learned. I am embarrassed to have to tell how I learned this one, but at the price of my own embarrassment I'm trying to save the same experience for whoever else will listen.

When this happened, I posted it and got a very long thread of discussion. Cutting the fuel line won't do it because there's enough fuel in there to run long enough to spoil the engine. Covering the intake while it is at max RPM might work if the air cleaner is not on the engine.

Merry Christmas,

#9 12-24-2003, 01:13 PM

I've gone so far as to plug the shut off system directly into the main vacuum line, so the only things hooked up were the shut off system and the brake booster (because I cant think of a way to block off that end of the line). Even then it didnt shut off properly (still wound down). I have replaced the shut off valves at the key switch and the injection pump, and both lines are good.

With the car running, I noticed pressing and releasing the brake pedal consumes quite a bit of vacuum (more than 5 inches), and the pump immediately compensates. Does anyone have any tricks to seal the brake booster end so I can test it or run without it to test? Thanks for all the help!

Larry----when i installed that valve, I had the air intake assy torn down to the turbo itself, and I did have a runaway, but placed a DVD case over the turbo, and it was shut off in less than 5 seconds. In that time, we got one injector line cracked, but by the time any fuel sprayed from there, the engine was off.

russb · #10 12-24-2003, 02:48 PM

Larry,
You know what I am talking about then.
Did not know covering the air cleaner on these would not work, good thing I didn't have any problems.
Sure gets the heart going in a hurry too. :-)
Like I always say "Takes a lot of money to train a mechanic".

Merry Christmas

Fisherman · #11 12-24-2003, 03:01 PM

One other thought struck me through all this.
have you pulled the rubber connectors at the switch? My car had oil travelling back up the vacuum line from the shutoff vavle that failed and had filled the lines with oil up to and through the key switch. There is the chance that the vacuum line/switch might be partially blocked. You could still draw vacuum but it might not be sufficient flow to pull the shutoff valve quickly hence giving you a slow shutoff.

I'm fishing now...

#12 12-25-2003, 04:03 AM

I have pulled the connectors, no oil.

I pulled the main line fromt he brake booster and plugged it. It shut off faster than usual, but still wound down a bit. I dont know that the booster is necessarily bad though, because I have had quick shut-offs like this even with the booster connected. I just cannot seem to isolate a leak, because everything is leaking at least a little bit!

What I have noticed however, is when I pull a vacuum on a particular line, it holds indefinitely, but when it stick it into one of those three way connectors (all of which I have replaced), it leaks. The connectors themselves hold when i use my fingers to plug it, but stick one of the plastic lines in there, and it leaks. Does this mean I have to replace all of the plastic now? Is there a way anyone knows to get them to seal better? Thanks for everyone's help and putting up with my questioning through this frustrating problem!

Ken300D · #13 12-25-2003, 09:44 AM

Did you buy those 3-way rubber vacuum connectors from MB or from K-Mart?

I ask because it sounds like they may be the wrong size. They should not leak.

Also, just for comparison, a properly running shutoff valve system should shut down a diesel so fast you'd think you'd cut the ignition on a gasser. Almost the instant you turn the key.

Now if you have something sticky INSIDE the injection pump, well.....

Ken300D

#14 12-26-2003, 05:02 AM

I got them from Fastlane. I've heard a properly working shut-off system, so I know when it's right, and I'm not there yet. Guess I just need to continue chasing leaks. Thanks for all the help.

kafer65 · #15 11-09-2006, 10:55 AM

O.K. I'm in a similiar situation. Since I had the car it takes about 3-4 seconds to shutoff. Now it takes 20-30 seconds. I've ziptied almost every rubber to plastic juction including the climate manifold to make a tighter seal. Doorlocks and EGR blocked off and I have a .5mm orific in for the tranny line. The center vent pod is bypassed. Engine stops immediately with manual linkage stop. I have about 22ish Lbs Hg vacuum from the pump. May be in the switch over lines in the engine compartment. Thats next.