Need Board Wisdom...Diesel Engine issue has me stumped

[Cathy Monaghan]

Hi Chris,

We had a similar problem (sounds exactly the same to me--happened nearly everyday until we went though all of the fuel!) this year. We found that the problem was with the fuel.

Our CD32 sat on the hard all last year and while she sat there her fuel gunked up. The symptoms were as you described with the RPMs dropping for awhile then coming back up again on their own. Sometimes they dropped to the point that the engine might actually stall, sometimes only a by a couple hundred RPMs. This happened to us on our way from NJ to Oyster Bay for the July 4th float-in there and my husband, with the help of Bob Emmons, changed the Racor filter and Bob gave us some biocide. When we returned to homeport Bruce had to change the Racor again along with the fuel filters on the engine and fuel pump.

We thought about having the fuel tank cleaned and the fuel polished professionaly then decided that since we have a Westerbeke and the pump moves more fuel to the engine which is needed then returns it to the tank after it's gone through the filters to let the engine polish its own fuel and Bruce would just keep replacing the filters until we had gone through all the fuel in the tank. Before making that decision we also had a mechanic look at it and he checked the fuel in the tank and said that it wasn't too bad (seen worse) and he recommended to keep changing the filters. He also checked the fuel pick-up tube to make sure it wasn't clogged. And neither Bruce nor the machanic thought it was the fuel pump (we do carry a spare). When the mechanic checked the pickup tube we discovered something else -- that the pickup tube could not be removed for inspection or replacement since it had been welded to the aluminum tank! So he drew some of the fuel through the tube with a little hand pump (kinda like a turkey baster).

Anyway, to make a long story short, Bruce changed the filters several times during our summer cruise from NJ to ME and back to NJ. During that period we did alot of motoring, purchased fuel from various sources and tried to fillup after we had really used up most of the fuel in the tank. (We carry a jerry can of diesel so there was no chance that we'd run out of fuel but it did make me a bit nervous and we kept checking fuel levels in the tank.) With each fillup he added biocide, fuel stabilizer and cetane booster.

Another possible cause is the Racor filter housing itself. After replacing the filter (and removing all the air) you really need to tighten down that nut on the top of the thing otherwise it will suck air into the system. Our mechanic recommends using a wrench on the thing (he says he hates the design) to tighten it, something Bruce is afraid to do since it's just plastic.

Hopefully your problem is just a bad tank of fuel like ours and you'll be able to deal with it by constantly changing the filters or you'll have to have the fuel polished and the tank cleaned.

Hope this helps,
Cathy
CD32 Realization, #3
Rahway, NJ
Raritan Bay

[tartansailor]

In my diesel engine days I installed an electric fuel pump
immediately after the fuel tank. This allowed me to recirculate
diesel through the fuel filters immediately after a fill up.

It is IMHO not too prudent to trust any marina to have "clean" fuel.

A set up like this allows you to be certain that there are no air or fuel leaks going undetected, and to state the obvious, you can be reasonably certain that fuel is getting to the injectors.

However:
NEVER switch on a push type electric fuel pump underway!!.

Dick