How to Repair Your Shutoff Valve

How to Replace Your Shutoff Valve

Please remember to recycle all your used fluids at an appropriate recycling center. Be mindful to not spill or splash fluids on yourself, others or the ground. Also as a safety tip please remember anytime you are working on, around or under your car, to wear safety glasses and secure the car with wheel stops and approved jack stands!

One of the most annoying problems that the old Mercedes diesels can have, is the shut off valve not working. You turn the key off and the engine keeps running. So out of the car you go and lift the hood to depress the stop lever. That whole operation is a pain, but Mercedes foresaw the valve failing, so they gave you a stop lever to use in a pinch. Replacing the shutoff valve is not hard, but if done wrong can destroy your engine.

Let me explain. Its a very simple design, using vacuum to pull a long arm with a tab that pulls on the internal linkage to stop the flow of fuel. The problem is, if you install the valve with the long arm on the wrong side of the internal linkage, then it is possible that when you start the car it will go full throttle. Since the valve is suppose to pull the linkage toward it, if installed on the wrong side of the linkage, it will push against the linkage. If this happens not even your stop lever will shutoff the engine. You would have to cut the fuel to the injectors by opening them, or even better cut off the cars air supply. The best way idea is to install the valve correctly, so a run-a-way engine does not occur. Installing the valve is best done when you can actually see what you are doing. Since the valve is installed in the end of the pump on US models, and the oil filter canister is only a few inches away, it is really impossible to see into the pump. You could pull the pump off the car, and change it out on the bench, but who wants to pull the injector pump just to do the valve. I found a better way. We can loosen the top ALDA plate, rotate it 90 degrees, and look inside as we line up the valve and linkage. So follow along as I show you how to do this job right.

The new shutoff valve and the 2 gaskets are needed. There is a metal ring that will come off the old valve with a gasket on either side. You will reuse the metal ring, and use the new gaskets. Notice the gaskets have a notch in them as will the metal ring. They fit on the shutoff valve only one way.

Vacuum pump that you will use to assist in removing the old valve and install the new valve.

If for some reason you get a run-a-way engine, this is the quickest way to stop it. A spray paint can top fits perfectly over the turbo inlet, to instantly cut the air supply and shut the engine. Just remember to remove the air boot from the turbo to the air cleaner, before you start the engine. If you have a non turbo car, just remove the air cleaner and get a piece of wood or cookie sheet that you can put over the intake manifold opening which also will stop the car instantly. Remember an engine needs three things to run, fuel, air and heat. Take away any one of them, and it won't run.

Now we need to remove the vacuum hose and stuff, blocking our way. If you have a non turbo car your layout will look a little different, but the principle is still the same.

I like to remove the master vacuum supply hose just so I don't break it. Be very careful when taking off the vacuum connections. They are usually very brittle. The screwdriver was used very gently to just assist me in pulling the hose off.

Remove all the vacuum hoses that are attached to the transmission switchover valve.

Don't forget the hose on the side. If you have a manual transmission car, you will not have this valve.

Carefully remove the ALDA line. Don't forget that there are 2 small washers on either side of the banjo fitting.

Then without disconnecting the linkage, just lay it over against the oil filter housing.

Remove the 4 bolts that hold the valve to the injection pump. Use a 1/4 inch drive ratchet to get in there. Its tight.

Remove the retaining cover and connect your vacuum pump to the shutoff valve. Since the clearance to pull the valve out of the pump is much less than the length of the shutoff valve in its extended position, we will need to apply vacuum to get the long arm to retract and essentially make the overall length of the valve shorter. This valve was leaky but still would hold a little vacuum if you kept pumping the vacuum pump. If your valve won't hold vacuum at all, then you will have to pull the valve out until it bumps the oil filter canister, and then try to compress the long arm on the valve to gain the necessary clearance.

See how much the long arm on the shut off valve is retracted and its still hard to remove it. The oil filter canister is just a few inches from the end of the pump. Be patient, you will be able to do it and it will come out. A long reach needle nose pliers may help you in compressing the long arm on the valve, if yours will not hold any vacuum.

Rotating the ALDA cover 90 degrees that we removed the 4 screws, we can now see how the lever is supposed to interact with the internal linkage. The shut off valve will pull the linkage toward itself. If you get the valve on the other side of the internal linkage, it would force the linkage to the full throttle position.

To install just take the new valve and install the new gaskets on either side of the metal disc that came off the old valve. (I forgot to take the pic). Then apply vacuum to shorten the arm and reinsert the new valve into the pump. There is a small notch in the pump at the bottom of the hole, that mates with the raised portion of the edge of the shutoff valve.

Bolt the valve into the pump and then apply vacuum to make sure the arm is pulling on the linkage correctly. Then just reassemble everything back just like you took it off.

After everything is back together, then BEFORE you start the car, remove the turbo air boot or the air cleaner on non turbo models, just in case. Better safe than sorry. Make sure you have a method to stop the air flow if it should run away. It won't if you did everything correctly. Then start the car and let it run a few minutes and shut her down.