Generator fuel lines sucking air

[flloyd]

I've been having problems with my gen set, the Kohler 20KW. All of last year it gave me troubles with difficulty starting, and occasionally dropping out under heavy load. Basically, the engine would slow down and sometimes quit.

This year I'm having the same trouble. It recently got so bad that the engine would not start at all and since I had recently changed the fuel filters I figured that I'd check to see if there was any air in the fuel lines. Sure enough, there was plenty of air in them. I went through the bleed procedure and the unit started and ran fine, under load.

Today, two days later, same problem. Somehow, air is getting into the fuel system. There are no visible leaks in the generator compartment. Where do I start looking?

[Reagan Sirmons]

If air can get in, fuel can get out, Do you have the correct fuel filters? A diesel 60 can run for a few moments and then die if the fuel filter is not the correct one. I am not a diesel mechanic but had the experience of having the wrong fuel filter placed on my engine once. It took forever to solve and then we checked the filter and it was the wrong model.
Pres

[joelselman]

This is an interesting one. I haven't thought about this long (I do my best thinking early AM in the bathroom), but I would probably start by isolating some of my systems. If this condition can be replicated on a regular basis, I would probably establish a new fuel source to the gen, like a 1 gallon can with fittings, etc. If the problem persisted, I would know it was downstream of the intersection (ie filters, pumps, etc.) or, if gone, upstream (ie fuel lines or tank). Just thinking out loud.

[johnklopp]

Floyd,

Typically diesels have 2 fuel pumps and 2 fuel filters. The first pump is often referred to as a lift pump since its job is to lift fuel from the tank and supply it at low pressure to the high pressure fuel pump. Most lift pumps are electric and may operate when the pre heat is on as well as any time the diesel is running.

Each pump should have a fuel filter on the suction side of the pump. The first filter on the lift pump is intended to catch the big chunks. The second filter on the high pressure pump will be a micron level filter of around 10 to 15 microns. Small micron level screens will plug easily with a huge pressure drop causing a lack of flow.

The suction side of the lift pump will have no more than the pressure head of the fuel above the level of the pump. What this means is that if the fuel supply level is 2 feet above the inlet pump, the pressure will be approximately 1 PSI since pressure head is equal to approximately 2.2 Ft per PSI. This is a static condition and does not take into account pressure drops due to flow restrictions. Depending on the way the fuel is removed from the tank, at the top or close to the bottom the suction line may be at a negative pressure and will never leak fuel, however it may leak air. If air is in the suction line, the pump will lose suction and stop pumping.

The suction side of the high pressure pump will have a pressure equal to the discharge pressure of the lift pump. Typical lift pump discharge pressure is 5 to 10 PSI. The discharge pressure of the high pressure pump will always be in metal in metal lines at thousands of PSI.

Best bet to quickly determine if you have a problem is to permanently install a 10 or 15 PSI gauge on a T in the rubber line between the discharge of the lift pump and the inlet to the high pressure filter. You could also install a second gauge on the inlet of the high pressure pump.

The two gauges above would eliminate any questions on leaking suction lines, dirty low pressure filters, failed lift pump or dirty high pressure filter at a cost of less than $50 if you do it yourself.

If you have the pressures noted above, you will probably need to replace the high pressure pump or have a problem with injection timing.

[JIM CHALOUPKA]

Fred, Get a piece of lamp cord and jump the pump to see if there is good flow.

Check the fuel hose that is in the shape of a U and be sure it is not sucking shut in the bend.

When replacing that hose use heavy wall special fuel injection hose, available at better auto parts houses.

JIM

JIM

[flloyd]

I have some more information today. This morning I had to dry camp for a while and started the generator. It failed to start at first and after resetting the control unit, it cranked on the second try. Then, after about 5 minutes, a load kicked in and it slowed down and died. I went out to the unit and performed the bleed procedure. The engine started promptly after that and ran fine for several hours, until I manually shut it down. A couple of hours later, I restarted it and again, it ran fine for a couple of hours until I manually shut it down. It powered all four A/C units, full load, no problem.

My hypothesis is that when it is given a chance to rest for several hours, perhaps overnight, air gets into the lines. Fortunately, the coach's previous owner, Mango Mike, documented a fuel pump problem that he had with this same unit and it's mentioned on his prevoman.com website. His account includes several useful photos, including this one:



The item that draws my attention is the "Backflow preventer", or check valve. Could it be that this valve has failed and thus allowing fuel to empty from the lines after an extended sit? What purpose does the check valve serve?

I see no evidence of any fuel leaks. Since I've bled the lines a few times now, the smell of diesel is omnipresent, however, it should retreat once I get a chance to do a thorough cleanup.

Just wondering now...

[Jon Wehrenberg]

FWIW I believe the low pressure fuel pump on thiese generators (just below the vertical fuel filter on the left) has had issues. Mine exhibited similar running symptoms with the generator losing RPMs under load and stalling. I changed it several hundred hours ago and the generator hasn't missed a beat.

Kohler is quite proud of that fuel pump and pices it accordingly.

John's suggestion of monitoring fuel pressure on the suction side of the injector pump is a good one, but if the pump is acting like mine was its performance was intermittent and the stumbling and stalling was not always predictable so it may take a while before seeing the fuel pressure fluctuate or diminish. For just a few dollars an electric fuel pump available at NAPA or any decent auto parts store along with a few fittings can be carried as a back up to the Kohler pump to keep the generator going assuming the issue is the fuel pump. I'll let the Trukman or JDUB explain how easy it is to swap pumps in the cold rain.

[dreamchasers]

The electric fuel pump for my generator faulted last year while in Washington DC. All the symptoms describes fits my scenario. I noticed when I would tap the electric fuel pump, it would run for a few minutes, then stop. All is well since I replaced the new fuel pump (easy to replace). I now carry a spare (thus assuring it will never fail again).

On my generator, if the electric fuel pump is not running, the generator will not run.

Hector

[Jerry Winchester]

"I'll let the Trukman or JDUB explain how easy it is to swap pumps in the cold rain."

A1 = A Hole

[Jon Wehrenberg]

Some POG members have no sense of humor.