Engine falters

[jbd3]

A few times while motoring, I've had the engine falter and drop in RPMs seemingly starving for fuel. Quickly placing the lever in idle/neutral restores a normally idle to the engine and I can again put it in gear and resume operations for a wildly variable amount of time ranging from many hours to a few seconds. Fuel lift pump appears to be working (clicks while key is held in start position). Figuring clogged filter after a fairly rough Lake Michigan crossing I noticed a fair amount of air in the Racor filter cannister with maybe 3 inches of diesel in the bottom by the drain. I believe the lift pump needs to exert a vacuum in the fuel line to draw fuel from the tank. So here are some questions:

1. Should there be passive fuel flow from the tank to the Racor? Might it vary with tank fullness?
2. Should one make sure the Racor cannister is full of fresh diesel to avoid introducing air in the fuel lines, i.e. prime it when changing filter?
3. How to distinguish a "lines need bleeding" problem from a "clogged fuel filter" problem? Any different behavior in the engine?
4. At fuel tank half full in rough conditions, should one expect sloshing fuel to cause an introduction of air into the fuel system? If so, what is a safe lower fuel limit?

I'm stranded in Leland, MI at the moment awaiting a new lower alternator bracket to replace one that cracked completely through in 2 places..

[AynB]

The following answers are just MY understanding of the system..
1) From the fuel tank to the Racor should be a direct line - no pumps or other fittings.
1A) You should NOT have air in the Racor - if you do, then you WILL get air in the system. Look for an air leak upstream i.e. towards the tank.
2) When you change the Racor Filter, you should fill the bowl with fresh diesel. I carry a 1 quart fill just for that purpose. I also replace the gaskets ( plural ) with every fuel filter change. Same goes for the on-the-engine fuel filter.
3) Line need bleeding versus clogged fuel filter... hmmm... a clogged fuel filter will allow flow at low levels but prevent high rpm. A line that needs bleeding ( I am going to make an assumption here that you are talking about one of the high pressure lines feeding the injectors ) , you will get rough running as you'll be running on three of the four cylinders. If you have air getting sucked into the fuel lines, usually the engine will just die, not sputter unless the leak is very small. Once the fuel has entered the high pressure pump, unless the pump is beginning to fail, you will eventually purge all of the air from the four injector lines. You can easily just put an open end wrench on the eight high pressure line fittings and make sure that they are just tight enough. Then backtrack towards the on-the-engine filter then back to the Racor and check each end of the line.
4) The answer will really depend upon how clean your fuel is ( and has been taken care of ) and how rough "rough" is. I have been out in a pounding five foot square wave swell with half a tank without problem, the tank design is such that there will be a minimum chance of introducing air.
Finally : from your description, I would start chasing down an air leak, after changing out the on-the-engine fuel filter and the Racor filter.

[jbd3]

Thanks for your response.My plan today is to inspect the interior of the tank and make sure no debris is in there that might occasionally be blocking the fuel pickup. I will be filling the racor cannister as you suggest. The part that confuses me is the fact that the engine runs fine, sometimes for hours but not dependably. Possibly a failing lift pump? Your response is much appreciated!

[jbd3]

Just to put closure on this topic, the problem was a loose engine mounted (secondary) fuel filter that permitted air to enter the system. Glad it was simple but being unexpected it took some time to figure out. Also, if upgrading to Balmar alternator, make sure the lower alt. mount is properly shimmed or it can crack when tightened. Apparently the Balmar is slightly less wide than the oem..Thanks for the reply. If nothing else, I'm getting more familiar with my engine!

[russp]

Closure to closure. Just wanted to emphasise to anyone reading this who has, or is about to, upgrade alternator to a Balmar, exactly as stated above the spacing on the Balmar adaptor is wrong and it has to be shimmed. Mine failed in exactly the same way and it cost me hundreds of dollars to get a replacement bracket. Real failure on the part of the supplier to provide properly built parts.

[jbd3]

Yet more closure...

After this series of posts last year my engine ran fine for the rest of the season. Second trip out this spring, same thing with faltering and limping along at about 2K rpm. I replaced the lift pump assuming (wrongly) that there must be some sort of intermittent failure as the filters had 5 hours on them having been replaced at fall layup. Still wouldn't run properly after the new lift pump so I gave up and called in the experts. Blockage thru the secondary filter assembly. The mechanic assumed it may even be a defect in the casting as there was no visible sign of fuel contamination but it was, in fact, the virtually new filter. I think mine is 2 microns. Really wondering about this we hack sawed the old secondary filter element and the fuel had a viscous mucous-like quality on the upstream side of the element with no discoloration. Operating hypothesis is 'algae' (really bacteria) that gave absolutely no visual clue as to being present in the tank or lines. Kinda like cold weather gelling in 100 degree F temps ?? More if warranted but beware the possibility of bad fuel that looks fine. I really hope this is my last post on this topic.. Any thoughts on additives? We had used biocide and Stabil pretty regularly..

[wolfe10]

Doesn't sound like algae. Algae would be black and kind of stringy.

Do you have a "Fuel Polisher" in your area? They clean/polish diesel fuel for a living.

Brett

[jbd3]

We opted to dispose of the fuel and start over with fresh. I've been in contact with multiple diesel specialty shops and technicians and as you say, this is atypical of 'algae' but no one had a solid idea as to what it was. We'll see how it runs this coming weekend.

Jack
Esperance #394
Marinette, WI

[digitalvillager]

There is a parallel conversation regarding this topic going on under "Engine dies - after hard sailing, not during" that has some additional ideas. You might want to check out that string as well. Make sure your vent lines are not clogged and that they are routed to remain above the the level of the tank. Mine were rerouted slightly lower due to the placement of the Genset lines and caused the lift pump to have to overcome the vacuum that the clogs created in both vent lines which it is not designed to do as well as trying to pressurize the supply line at the same time. Easiest way to check the vent lines is to slowly remove the diesel fill cap and if you hear a sucking noise, then you have clogged lines. I re-positioned and cleared the vent lines, replaced what turned out to be a dead lift pump and life is good!