Pardon me for asking, but why would one want to increase the pressure when Mercedes gives a specific value range of pressures that the pump should see? It would seem that the risk of damage to the fuel system would be very real if you increased pressures beyond the factory specified 1.0-1.3 bar.

The manual says that if the pressure drops below 0.8 bar to simply remove the spring, stretch it to 27mm and then check the pressure. If it's not within the specified range the hollow bolt assembly should be replaced with a new one and/or the lift pump should be replaced or rebuilt.

After all, the new part from Mercedes (000 074 72 84) is only $27.00 list from any dealer, probably less from some.

Just wondering....seems like a rather dangerous thing to be doing, not to mention a possible waste of money...

Mercedes did not design the fuel system. Nor did they produce it to the best of my knowledge. The designers of the system had concerns that perhaps have not proved to be justified. The minumin operational pressure has validity.


They did expect certain levels of maintenance that in general was never performed often if at all. They perhaps where also the first to produce a diesel fuel system with no water and sediment trap. At a time when this was far more important.


Increasing the base fuel pressure does result in better filling of the injection pumps elements. Producing more power if the rest of the fuel system is in good condition.


Mercedes does recommend periodically checking it with a gauge but again is seldom done. This very old fuel design system is both really durable and reliable if a general maintenance check is done every few years. Otherwise the chances of being stranded along the road somewhere are increased. Most maintance is also cheap to do.

In addition to the other replies ;

Because I personally have opened quite a few of these and _every_single_one_ has had a worn out spring ~ not only do coil springs have a finite life span but the check ball sits directly in the end of the spring and moves constantly, this wears the open end of the spring until it fails ~ many I have seen were paper thin and crumbled when I touched them .

As mentioned, older German cars/mechanics/engineers all assumed you'd be endlessly under the hood cleaning, adjusting and testing things .

A Mechanic I know was trained in Germany, by Mercedes but thinks they're '****' because of this aspect ~ he drives a Lexus and will trade it in long before it reaches 80,000 miles so he sees no point in doing the things we Diesel Heads consider normal .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better