Hi upod,
If you can replace shut-off valves and delivery valves I'm certain that you are capable of checking a pneumatic governor for its ability to hold a vacuum. And in the case of a leaky pneumatic governor I think there's a good chance that you are capable of diagnosing the problem and making the proper repair yourself, including replacing a diaphragm and/or adjusting shaft and the related parts. There's no danger of throwing off the pump's basic calibration, that which is determined by adjustments made between the rack and the elements deeper inside the pump.
Do you have access to the factory service manuals associated with these cars and their engines? If not, the information is available here in this and other forums, found after a bit of searching. In them you will find procedures for checking the pneumatic governor, and also for making the necessary adjustments and repairs. There are no highly specialized tools required. However, if you believe your customers are better served by having an injection shop check for problems and make those repairs, then I respectfully suggest you continue practicing under that model. It is good to know one's limitations!
In W123 240Ds, you will find the pneumatically-governed M type injection pumps on OM616.916 engines. When they went to the OM616.912 engines, I don't know what year model that was, they used the MW type injection pumps with internal mechanical governors. You will find this ID stamped into the engine block casting on the LH side, near the top rear corner (you probably knew that). If the engine has a throttle body on the intake, with a steel or hard plastic tube running to the rear end of the injection pump, then you know you're looking at a pneumatically-governed pump.
Yes, I could make a video, but I'm not going to. I am happy to add more photos to this thread, though. I'm also happy to provide more information related to specific questions you and anyone else might have.
Here's a shot showing the ID tag on a PES4M injection pump with pneumatic governor as used by Mercedes-Benz:
Here's a shot of the rear end of the pump. I've drawn a red ellipse around the rear-most housing, and added a green arrow pointing to the outer end of the adjusting shaft:
And here's a shot of the housing removed and disassembled (and cleaned!):
For more information I suggest going through the threads I've linked to in posts #1 and #3. Next time you see a car in your shop that seems to be over-fueling, and that has this older style, pneumatically-governed injection pump, check the governor's ability to hold vacuum. You might be able to fix it yourself, and save your customer the time and money involved in pulling the pump and having an injection shop check and repair it for you.
Thanks again!
