Quote:
Originally Posted by Mark123
My 240D has good compression, properly adjusted valves, and rebuilt injectors. then a year or two ago mileage dropped to 21 or 22. After reading the fuel pressure threads, I made a gauge and tested the pressure per the FSM. Way low. I was lucky enough to buy the overflow valve and a rebuilt lift pump from Greazzer. The overflow valve put the actual operating fuel pressure well above factory minimums. Mileage moved up to 26 to 28. And much more power. Even at 70mph.
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Good post of what is possible. A system that checks out marginally at idle. Will further decline under engine load. Starving the engine for the fuel it could deliver if in decent shape further. Another issue is the 616 lift pump by design has a weaker pressure output regulating spring than the turbo lift pumps.
Not the relief valve spring but the spring in the lift pump. My feeling for what it is worth is that over time a pressure differential increases across the secondary fuel filter. This has an effect of lowering supply pressure further in a system. The weaker the lift pump the worse the possible effect. Also as that differential increases dirt that would be stopped by the filter may get forced through.
Since the 616 lift pumps output pressure is weaker than the turbo engine 300d.It may be prudent to change out the secondary fuel filter from time to time. If you fuel at high volume outlets as much as possible the fuel is pretty clean. Small volume places will give you trouble eventually unless you are very lucky.
I live by a simple rule with cars. With any reasonable preventable road breakdown. It is better found and rectified before it creates one. Always far cheaper and you do not also lose a day or more in the process. There will be those breakdowns that you cannot expect or avoid of course.
This poster purchased hopefully a 0-30 or 0-60 pound liquid dampened pressure gauge and used it. This is the right way to do it but you can still get around using that gauge.
This periodic check incidentally is in the Mercedes engine tune up check list of that period. They want a gauge used. The gauge was about 10.00 at harbor freight but might be a little more now.
I have suspected for years that low fuel pressure may be the cause of a very serious problem with the 616 engine. I am not sure I can prove it as the effect I suspect takes place over a long time period very gradually..
So I just decided instead why risk it? Just keep my 240d engines at or above the minimum acceptable fuel pressure. There are also many other benefits in doing so.