My 91 300D 2.5 Turbo runs *too* well! That is, it is so enthusiastic it runs on after I turn it off with the key.

Searching the site I realize that the problem is probably a leaky diphram in the shut-off mechanism. The red shut-off lever moves, but it stops a few cm short of activating the shut-off correctly. When I nudge it down just a little more, the engine shuts down promptly.

As everything else vacuum-related works just fine, I figure I just need to have either the diaphram or the whole solenoid replaced. The CD doesn't seem to explain how to do this, and a previous post said "The part is about $19.00, but it can be tricky to replace". The question is, *how* tricky?

I see that inviting bolt head on top of the shut-off solenoid, but it has yellow paint over it (DIY beware?).

What are the steps involved in replacing the offending critter?

There are two bolts that hold down the shut-off valve. the hard part is getting a socket on the far bolt. Take a moment and try it, you will what I mean. After you remove the two hold down bolts and remove the old valve there is another tricky part. When you install the new valve, you will see a little piece of metal with a hole in it sticking down from the new valve, that hole is made to catch a littile hook inside the pump. When you are shutting off the car, the hook is pulled up and that is what shuts off the car. The way I tested mine to make sure it was hooked up properly BEFORE starting the car, was to hook up a little vacuum hose to the nipple on the valve and apply vacuum and make sure the STOP lever engaged. I say to do this BEFORE starting the car, because if it is not hooked up you will not be able to shut the car off and it may run and increase speed up to 5,000 RPM.

If you have any other questions, let me know. It is easy to do, but it can be time consuming and it does test your patience, so just be patient and make sure you have good tools. I used a 1/4 drive socket on a small universal with a 6 inch extentioin, to get to the bolts. I think the bolt is an 8mm, but I may be wrong.

The easy way to do this, assuming the same layout as the 603 engine, is to remove the electrical connection just in front of the shutoff by rotating the locking collar, removing the plug, then rotate the collar some more and lift it off, too.

Then unscrew the lower nut on the ALDA -- the big square can just behind the vaccuum can. The nut is captive on the top part. Unscrew off the IP, then tilt toward the engine and wrestle out from under the mainfold. This is necessary to reach the second bolt -- at least on the 603 is isn't possible to use a swivel, the one I had at any rate.

Remove the two holddown screws, lift off the old servo, remove the seal from the old one and put it on the new one, then install the new one. Make sure the shutoff lever is engaged and moves up as you put the new servo in place. This isn't difficult. Don't forget the seal -- there isn't a new one with the servo.

Please have a vaccuum source handy when you do this -- as stated above you need to check function. You can also just push the lever down and put your finger over the vaccuum connection and see if it stays down! Better to use vaccuuum.

Re-install the ALDA , vaccuum line, and electrical connection and you are done. Very nice to have the engine shut off with the key, particularly when it is raining!

Also, have a 14mm wrench handy, and have someone else start the car -- if it runs away, crack the injection lines at the injectors to stop it. Fuel will be everywhere, but the engine won't blow up!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

PSFRED,
You way of doing the job would make life a great deal easier. I wanted to use your method, but I am not that familiar with the ALDA and did not want to remove it. If it is a simple as just pulling it of the engine, then your way is the path to go.
Thanks!!!!!

CJ:

This one just sits on top of a pin in the IP. The captive nut holds in it place.

Adjusting it would be a pure pain -- there is only about 5 mm clearance between the adjusting screw and the bottom of the manifold!

The servo replacement is very easy if you take the ALDA off -- I had to use two Cresent wrenches on the ALDA, and clearance it tight. You may also need to take the windshield washer reservior off -- it just pulls up and out. Spills all over, as I remember, so you might want to empty it first.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thanks!!
You learn something new everyday!!!

Many thanks for your advice PS and CJ! You are what makes this site so great! In less than a few hours I have the advice of pros who've been there. Now I'm ready to dive in.

One question, though, I see you use the term "servo" to describe the errant part; I have seen other posts refer to the "solenoid". Am I correct in thinking that while a solenoid involves current, a servo doesn't?

Also, will I need to replace the whole thing (servo) or is there just a diaphram to replace? I'll need to tell the parts person at the dealer exactly what I need, and, in my experience, they're not all of equal expertise, not to mention cooperativeness.

I noticed too, that after I push the red shutoff lever down a few cms, and the engine quits, the lever returns happily to its original position. Does this help diagnose the cause of the problem. Could something be sticking rather than ruptured or leaking. (Yes, I'll look, but before I unscrew things and go buy more tools...)

Naturally it is raining today in Atlanta, so I'll wait before taking the plunge. You cautions are very helpful.

It's not that I particularly *mind* jumping out, popping the hood and nudging the shutoff lever, it is just that my girlfriend seems unexplainably amused, and mumbles something about just leaving the hood off like in the '50s... (Not to mention her allusion to my actions amounting to a "hooptie move" --or Southern for the stuff I used to have to do to get my "61 VW started in the old days).

Interesting to compare engine compartment geography in 'MBenzi 1 ('79 300SD, 360Kmls), and 'MBenzi 2 ('91 300D 2.5 Turbo) --which has the run-on problem. Seems one needs smaller hands and various universal/extension permutations to fix things.

The part I replaced is labeled on the reciept as "shut off valve". It was not serviceable, only a one piece unit. The way I tested mine was I pulled off the vacuum hose and put in a piece of tubing. I then sucked out the air out and the lever went down to the stop position, it then would lift up, I knew I had a leak.

Check to make sure the vaccuum lines aren't shot before changing the servo (aka shut off valve) -- I always call these a servo rather than an solenoid because a solenoid moves a piece of iron with a magnetic field (Physics 201, 1978) while a servo moves an actuator via some kind of a motor or diaphram, not restricted to movement of a iron rod in a magnetic field.

You will want to take the windsheild reservoir out for room.

If the screw was a few degrees counterclockwise of where it is, you would leave the ALDA on and save a bunch of time.

I couldn't find a short swivel (the kind were the socket is part of the swivel), and my brother's little Snap-on set was too long to get under the ALDA. If you can find a short swivel, you won't need to take the ALDA off. This will save some time!

The diaphram has a small hole in it. It is not repairable. Mine would actually hold off the car, but not on -- wouldn't pull down hard enough to shut the car off, just had to touch the stop lever to kill it. Not like a W115 or W123!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Right, Peter; I used to have to really lean on the stop lever on my 79 300SD to get it to shut the beast down.

I'm off to suck tubes. I'll report progress.

Sorry, but what's an ALDA? And an IP? I can locate these from the description, but I'm curious.

I have observed that the shut-off valve seems to last about 100k mls, and the belt, tensioner and pulley mechanisms about the same (my 91 300D 2.5 Tbo has 110K miles) on these great cars. I'm observing, not complaining.

Do the newer Diesels shut down electronically rather than by vacuum-servo?

Thanks, Simon

Simon:

ALDA = altitude adjuster = boost pressure senor -- adds fuel as the barometric pressure and/or boost pressure goes up. Present on MB injection pumps since the late W115 chassis.

IP = injection pump, I'm lazy and use shorthand when typing! Fairly obvious, hard to miss the injection lines!

On the 601/602/603, the ALDA is a squarish box at the rear of the pump, sitting on top of a short stem. Has the boost line connected to it and a captive nut on the bottom and a hex collar so you can unscrew the captive nut. Made of aluminumn.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

The 1/4" with 6" extension and a 10mm swivel socket worked on my 91 300d 2.5 Turbo. I got mine at the local Sears.

Don't be surprised when you get a white, ceramic (I think) shutoff valve from MB; it does fit in place of the original metal one. The vacuum line nipple is on the top rather than the side, but you can just use a longer piece of tube --it clears OK.

While I was picking up the part, an MB mechanic wandered over and warned me (see above postings) of the danger of "run-on" ; he suggested removing the intake manifold and standing by with a suitably-sized piece of plywood with which to cut off the air sucked in should run-on occur. Sounds better than cutting fuel lines.

Mmm, sure is nice to stop with the key...

MB must have recently substituted the plastic one for the metal one -- either that, or there is some confusion in parts numbers as I got the plastic one first and returned it -- correct part number, wrong part (the white plastic is the power steering vaccuum servo). Interesting.

It is cheaper, though ($18 vs $40!), and if it works, you're done.!

Very nice not to have to get out of the car in the rain to open the hood and push the lever.....

Opening the injection lines (NOT cutting them, you probably can't by hand, anyway, without a bolt cutter) is safer -- the engine will certainly stop. I don't like covering the intake, especially the turbo intake, for fear of what will happen if something falls in. I'd rather spray fuel everywhere rather than bend a rod.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I have read the appropriate threads and in in the midst of attempting the replacement off my shut off valve. It has been recommended to remove the electrical conection and ALDA in order to achieve clearence for the removal of the difficult nut.

Thanks CJ and psfred for the great thread: "Fixing '91 300D Shut-off solenoid: how tricky"

My problem: the retaining nut for ALDA has been consistently very difficult to move. It has not, like most nuts, become progresively easier with each turn. I feel like I am stripping something. Is this normal? Secondly, does the base of the electrical conection come off, how? If I can completely remove this, I might be able to get my 10mm socket elbow in there. Any help is appreciated. Thanks in advance.

1992 300D 2.5 Turbo 174,000 miles

Sloemoe:

The nut on the ALDA is captive -- it stay on either the ALDA or the IP, ALDA I think but that was last year....

It will be a bit hard to turn for the first round or two, but should be free after that. You must use a backing wrench on the other nut -- again, I dont' remember if it was on the ALDA (flats on the bottom) or the IP -- if you don't, you are just rotating it around rather than unscrewing it. I really think the nut stays on the ALDA -- the ALDA must not rotate while you unscrew the captive nut.

The base of the electrical fitting says there. Just pull the plug.

Do you have a 10 mm nut or a cap screw? I had torx cap screws, what a pain. Use some antisieze on them going back in so they won't be so stuck next time.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!