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Mercedes Injection Pump O Ring Replacement


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All parts used in these pictorials are available at the diesel parts for sale page

Safety and security tips:

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! 



Mercedes Injection Pump O Ring Replacement

With the ultra low sulfur diesel fuel in all filling stations across the country, the may find your 1986 and later model Mercedes leaking fuel through the injection pump rubber O rings.  Fortunately the 1985 and earlier cars do not have the dreaded rubber O ring to deteriorate.  Doing the job is not that hard and it takes one special Mercedes tool to remove the stub pipe.

Your car hard to start after sitting overnight or it may be leaking diesel fuel all over the place.  Either one may point to bad O rings.

I did this job on a customers 1986 300SDL.  The DVD was also shot doing this job and has lots of extra tips and techniques.  The DVD will be available soon.

So lets not cry over the lower sulfur fuel lets just get your leak repaired.....


Here are the tools for the job and the gaskets.  You do not have to have the large manifold gasket if you don't want to remove the main intake body.  Notice the large serrated socket used to remove the stub pipe.


A leaky mess on the top of the injection pump.


Remove the 2 bolts holding the crossover pipe to the main intake body.....


Remove the 2 bolts and bracket holding the crossover pipe to the engine.


Swing away from the valve cover.


Loosen the fuel lines at the injectors....


....then push the off to the side.


Remove the 1st 3 lines on top of the injection pump....


Then remove the 2nd 3 lines..


Remove the locking bolts and securing tabs with a T-30 torx bit.


Remove only 1 stub pipe at a time.  When you remove the pipe a small spring will be underneath resting in the center of the copper crush washer.  Do NOT loose the spring.


Here is the stub pipe and the spring I was warning you about.  Note the O ring on the end of the stub pipe that you will be replacing.


New copper washer ready to receive the spring and stub pipe.  Do not drop the copper washer in the IP either.  Do NOT remove the assembly that the washer is sitting on!

If you want to torque the stub pipe then do the following.  First step is 22 ft.-lb. and break loose. Second step is again 22 ft-lb. and break loose. Third and final step is 26 ft.-lb. This should properly load the o-ring.

Now do this 5 more times and you are done installing the O rings.


Reinstall the lines on the injection pump....


...and on the injectors...



Reinstall the crossover pipe with a new gasket....


Reinstall the hold down bracket and bolts.

Now you must crank the car for a while before it moves all the air out of the fuel lines.  After a while it will start and run rough.              Keep at it and it will finally smooth out and run fine if you installed everything like you were supposed to.

You should now have a nice leak free injection pump!