Quote:
Originally Posted by vox_incognita
A very intriguing thread !
Browsed some docs and found a difference in where the place the measurement takes place:
-between fuel pump and fuel main filter(w116 om617.95x)
-between fuel main filter and IP.(w115,w123)
Incorrect translation maybe?
The values given are the same.However,other manuals suggest that a clean fuel filter restriction may amount to 0,2-0,3 bar difference.
No document decribes testing the fuel delivery pressure under load-only at idle and high idle(3k rpm)..
I`ve applied pressurized air (>2 bar)to the outlet port of the fuel pump,expecting at least some air loss at the roller follower side-nothing(but no fuel dilution in the oil sump either)...just slight air leak from the inlet valve(I don`t expect them to seal completely)...and one can feel how easier is to push the rear plunger when the main spring is compressed. Think it`s good to change the main spring after decades of operation. ..Has anyone checked the delivery end pressure?
|
The recommended tests with an unloaded engine do not absolutly indicate if proper pressure will still be present under heavy load or just cruising load. The strategic position of the gauge to read the actual base pressure present in the injection pump when cruising seemed far more important to me originally.
I disgarded the concept of the static tests for our needs. This was after Yellit a fellow member tried a dynamic test that proved it seemed a much sounder approach.
A solid side benifit was it alerted you when a filter change is really required. Or something less likely had occured to start dropping the pressure under load. It is really bad to just drive these cars until the effect of a partially blocked filter becomes obvious.
With a gauge permanatly installed this is not going to happen. The car will still be runing fine but you notice on the highway especially the base pressure is starting to sag. When it drops to a number you settle on change the filter.
This will and should occur far before any deterioration of performance is obvious. Also keeping your fuel milage at the individual cars higher end.
A dynamic load test will always be preffered to a static type test. Under very light feed conditions even with obstructions the pressure might seem adaquate. As soon as you up the flow rate it might impact things. This of course you never know without a gauge in the passenger compartent. .
I believe one of our members (yellit) had a real time getting reasonable pressure for highway usage. Ultimatly it was the lift pump I believe. If he had not read the gauge on the highway the true condition would have not been known. Unfortunatly he had the 616 engine. They just seem more sensitive to the rod issue. So it is wise in my opinion to get it right on them especially.
At the present state of knowledge the delivery end pressure of the lift pump seems to vary somewhat. This is understandable as the pressure relief valve on the injection pump releases any pressure higher than its output in operation..
Basically as long as the lift pumps output is higher than the minumin requirement under load there is no issue. Again the static test may fool a person on occasion. Far better than no test at all though.