Volvo DI-30 diesel problem

[Toys_with_time]

Am a bit stumped on a diesel problem so appreciate any suggestions.

Had one diesel suddenly drop to idle revs only so replaced pre filter, engine filter and blew the fuel and return fuel line and bled it. Engine now runs fine.

Other diesel then did the same thing so did the same things to it. It now starts fine and runs for about 20 minutes then drops to idle revs and won't rev (it actually drops below idle revs and runs a little rough for a few seconds then comes back to idle properly). If I leave it turned off for about an hour it will then run ok for another 20 minutes.

Fuel in fuel tank is clear (one tank feeds both engines and have a polisher I run weekly) and pre filter didn't look particularly bad when I changed it, just a little gunk in the bottom of the bowl.

Only thing I have noticed is that the hand pump for bleeding the motor only comes back up really slowly unless the engine is running.

Any ideas appreciated.

TwT

[sailormed]

If running from the same fuel tank I would start and look at the fuel pickup and fuel lines before anything else.

[Captsteve53]

Sounds to me like you are sucking in air along the way in the troublesome engine system (especially since you have just had the system apart)

It could be an issue with the lift pump diaphragm but as above check first for minor leaks , quite often it will suck air but not leak diesel so easily,also if not pumping correctly it's fuel starvation (again the pump)

Cheers Steve

[Lepke]

Do you have a vacuum gauge after the primary filter but before the lift pump? Besides indicating a dirty filter, it can show low or zero vacuum - air leak, or high vacuum (with new filter) - plugged pickup tube or strainer.
Also, with constant polishing, there should be no "gunk" in the bowl and only a little water. I use a biocide every fueling and never get anything but clear water and no debris of any kind. I get so little water I only drain about once a month when running. I run 2 micron primaries and my tanks hold 2000 gallons.