Alt Adjustment '75 240D Bosch PES4M55C320RS58 Inj Pump - PeachParts Mercedes-Benz Forum

Fisherman · #1 07-19-2002, 02:33 PM

Quickly I would like to ask if anyone is aware of a manual adjustment for this pump or if the altitude compensation is automatic and if so by what mechanism.
Driving at sea level the car runs very well with no smoke at all visible, even under heavy load.
At 3200 feet and higher the car smokes quite a bit while still performing well.
I understand that on the later models this adjustment is located under the ALDA on the top of the IP however this IP does not have an alda on the top so it is assumed that it is controlled by another means. perhaps the vacuum line connecting to the rear of the IP?
Any light you can shed on the adjustment mechanism would be greatly appreciated as I am certain it is not correctly setup at this time or is not functioning corrrectly

stevebfl · #2 07-19-2002, 06:16 PM

The 75 240D uses a pneumatic governor. Since this means it runs off manifold vacuum atmospheric pressure should be self compensating.

Likely the diaphram is poor and the full range of movement restricted. Limited calibration is made at the diaphram with shims.

Fisherman · #3 07-19-2002, 08:45 PM

Would you know if this part of the IP is repairable by a DIYer like myself or is this a bench type of job?
Also is there any availability of parts for this type of repair job?

stevebfl · #4 07-20-2002, 09:18 AM

This is really a job for a pump shop, but the adjustments are exact and undoable (not particularly easy though).

I would suggest replacing the pneumatic governor diaphram noting the shims. Don't change any till you have tried it with the new diaphram (that could be the problem). You will see that vacuum pulls the pump rack one way and the spring the other. Changing the shims changes this relationship in small quantities.

It would be trial and error and once you are good at it it will only take 15-30 minutes. The first time you do it you might swear it can't be done on the car; it definitely is.

Fisherman · #5 07-20-2002, 10:11 AM

And once again I thank you for your assistance. I will look into avaiolability of the parts as I live here in Central Oregon there are no shops around who can really help me on most aspects of repair on this vehicle. At least not within reasonable fees...

stevebfl · #6 07-20-2002, 10:57 AM

Reasonable..........

Actually, there are almost no reasonable job operations when the whole value of the product is low. I once started giving advise to a gentleman in the Ukraine about fixing a 115 body diesel. At first I didn't realize where he was. To him this was a piece of machinery to be preserved at all costs. To me I'd junk it, if it needed a rear wheel bearing. All a matter of priorities.

Fisherman · #7 07-20-2002, 09:51 PM

But thanks for being honest.
At the moment until I can get the vehicle that hit a deer last month fixed this vehicle is kind of important.
Also happens to be fun to drive...

stevebfl · #8 07-21-2002, 09:25 AM

They are, were, and can be fine transportation. As a seller of repair services, I am ever so aware that economics has more to do with reasonable prices than do technicians.