Fuel flow 'phantom' problem

[claiborne]

Captains, I have a mysterious, occasional problem with my Universal Model 25 (21hp) diesel engine. Have any of y'all heard of or experienced a problem where fuel flow seems to be disrupted, either by air entrainment or blockage or pump failure or ??? This occurs rarely, and is usually when the boat heels or rocks. It's as if someone has their hand on the throttle add just pulls back. Sometimes it revs down, then fluctuates up and down and slowly returns to previous RPM. Other times it will rev down and die, but easily restarts. There is plenty of fuel to rule out slosh factor.
I have replaced the fuel pump, filters, and all the lines, pulled the fuel tank and scoured it, pressure tested everything, checked the uptake tube in tank for pinholes, checked external overfow for obstruction + replaced screen, removed fuel cap during problem to check for vacuum, soldered a tube onto fuel return line (from injectors to tank) so it couldn't siphon air back to engine.
My last thought is to replace the recommend fuel pump with a slightly stronger one. While running, the current pump does get hot to touch. Any ideas or suggestions are much appreciated.

 

[Brent Wright]

Hi Claiborne:
I do not know if diesel fuel pumps are different, but they make liquid cooled gasoline pumps (the liquid is fuel). If the pump gets pretty warm you will probably notice a loss in performance. Electric fuel pumps push better than they pull and once warm they pretty much won't pull at all. If you could install a fuel pressure gauge inline it would tell you really quick if it is the pump. Hope this helps some.

 

[Loren Beach]

My M25XP engine is similar, with the external Facit brand electric lift pump. Since some many Universal (& Westerbeke) engines have been built with similar lift pumps, I feel it must be sized correctly. OTOH, maybe your particular pump is on the verge of failure...
There is a related thread in the searchable archives one this server and over at the various list servs @ Sailnet.com on finding an auto parts store replacement for your pump at a modest price. I have not checked my pump for heat while in operation -- perhaps I should!

(Most of my boat's engine stuff dates to the year of construction, 1988.)
So far, we have (in order of occurance) replaced the exhaust riser, replaced the heat exchanger, and rebuilt the alternator, starter, and injectors... [the last 3 were preventative maint. items].

Your symptoms sure sound like air is getting in somewhere --- even tho you have done many many things to rule this out. I admit to being puzzled.
Keep us posted,

Loren
Portland, OR

 

[Tom Plummer]

I had the same problem with my Yanmar 3GM30F. I did every thing I could think of. Replaced the fuel feed pump, changed both filters several times (I have a Racor prior to the fuel feed pump and the factory one between the feed pump and the injection pump), took the filler cap off when it all of a sudden lost power. Had the tank scrubbed, I even did a vacuum drop test on the fuel line from the tank to the fuel feed pump.

This went on for two and a half years I was getting ready to replace the injection pump when quite by accident I found the culprit. On the top of the factory fuel strainer which remember is between the feed pump and the injection pump there are two plugs one is the bleeder I still don’t know what the second plug is for but it was loose and when the engine would work a little harder like when it tries to maintain rpm in a sea it would suck a little air. The power would drop off and then in about 5 minutes she would come back up to full power. I hope this helps.

The reason it took so long to find was because it was between the feed pump and the injection pump. I had assumed that the feed pump would pressurize the line between it and the injection pump, which would include the fuel strainer and that because the area was pressurized that it would not suck air. I also assumed that if air could get in then the fuel would drip out. This was not the case; I found it while changing the fuel strainer element quite by accident it is a bit of a stretch to reach the strainer and as I was feeling around to find the bleed screw I accidentally found the second plug which turned when I touched it.

All of this goes to prove that when you assume it generally makes an ass of u and me.

 

[Geoff Johnson]

Maybe it's not the fuel. A few years ago my M25 would occasionally start to lose power. When I shut off the engine and started up again, everything was fine. Turned out that the flapper gate in the exhaust line (between the mixing elbow and the muffler) had broken loose and would sometimes block the exhaust. The increased back pressure would cause the engine to slow down dramatically.

 

[sailingdeacon]

word to the wise

Word to the wise. Keep a cheap auto fuel lift pump on board as a backup. My lift pump died in a very remote area. Symptom was a on-and-off engine slow down for a few hours before failure. You can tell for sure by turning the ign key and listening for the clicking pump. If only one single click, then it is dead. I was told by a mechanic a pressure of 7 lbs would work. Also, when I wired a auto lift pump in, for some reason the starter would not work. Had to hot wire the temporary pump to the battery. So I later had to replace the pump with a genuine (and pricey) pump.

 

[roger hinds]

my loss of power was plugged riser

I had an occational loss of power also. I changed the filters and the problem seemed to clear up. Later in the off season , I could'nt restart the engine. A mechanic finally discovered , after several hours , that the riser was plugged tight, preventing ignition. That was about 4 or 5 years ago (87 Ericson 34, C'est Si Bon).