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:

http://prevoman.com/Pages/Gen%20Fuel%20Pump/pump_2885.jpg

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.

[rfoster]

Hector. If you had a bigger hammer, it would run longer.v

[truk4u]

Harsh, but I believe there is merit!:p

[flloyd]

I'm still having a problem with my generator losing prime in the fuel system. The symptoms are consistent: When I perform the fuel line purging procedure which involves running the fuel pump while cracking open the bleed ports, the engine starts and runs fine. It seems to run indefinitely. Then, when I shut it off and leave it off for a few days, it won't start and the same problem returns - air in the fuel lines.

There are no visible leaks anywhere. I knowledgeable friend had a look the other day and suggested that it might be the Backflow Preventer valve. The construction of this valve looks suspicious. My friend said that it looks like it was added as an afterthought. It looks more like a valve designed for water rather than fuel use.

My hypothesis is that when the generator is shut down hot, the fuel expands (vaporizes) in the line, pushing liquid fuel backwards, back into the tank and leaving vapor in the line.

Can anyone else tell me if they have the same valve in their installation? I've looked at fuel check valves online and none are of the "flapper" style construction like this one. Most are much smaller, stainless or aluminum, with an integral spring loaded ball stopper.

http://prevoman.com/Pages/Gen%20Fuel%20Pump/pump_2885.jpg

[BoaterAl]

Fred,
After reading your posts the first thing was fuel line, ply separation.
Is it possible the fuel lines are old and should be replacement time ?
Are there mis -matched hose lines where a line was replaced and maybe not compatible with diesel fuel ? Is there a clamp not fully installed to grab the metal barb.
With this completely frustrating problem the idea of replacing all fuel lines may solve the problem, hopefully.
Back in the boating days fuel lines were an issue as the engine room temp always an extreme heat area.

Just trying to help and throwing out some ideas.
AL
102 deg in KC...yikes

[Jon Wehrenberg]

Fred,

It looks like you took a photo of my generator. Our coaches are near each other in serial number (yours is newer) and I have the exact same check valve. My generator is a little lazy starting after sitting for several months but it always fires up within a few seconds of cranking. Maybe 10 seconds but that is a guess. Once it has been run, even if it was a few days ago it seems to fire up right away.

I am not sure I would rush to blame the check valve. That coach, like mine had a bad fuel pump and when it would stumble upon the addition of a heavy load after running for a while (such as turning on the microwave) I replaced the fuel pump and all issues with it went away. I think at the time I replaced my pump I learned that model had fuel pump issues. This is all speculation so don't run out and buy a fuel pump, but try to isolate the problem if you can by putting a "Y" in the circuit and rig up a cheap NAPA electric fuel pump in parallel with the Kohler pump. If it will not immediately fire up with the Kohler, switch over to the cheap one (feeding from a fuel can) and see if that works better. All the fuel pump has to do is deliver a small flow of fuel to the engine. It is not like you need high pressure or high volume.

[JIM CHALOUPKA]

Fred, read my post #5 above.

Your photo looks identical to my generator, I have had no issues with the check valve.

Just rig it up and pump into a can. At this point you don't need to know about the running of the engine, just prove out the pump, then move on to the next step if it is fine.

JIM, :)

[flloyd]

Jon,
You may recall that Mango replaced this pump a few years back. I still have the temporary auto-style electric pump that he used until he got a factory replacement. The OEM pump seems to work fine as long as it has fuel on the input side.

Thanks for the confirmation that you have the same check valve as I. The question remains as to what is the source of the line air. Either there is a leak (but no fuel is evident), or it is coming from vapors in the line. Something has to be allowing the air to form and the #1 suspect is the inability of the system to hold pressure between the check valve and the fuel cutoff solenoid. I do which I had a proper diagram of the fuel circuit. I searched all morning online and came up with zip. I did read a comment that suggested that even the most miniscule air leak would allow a system to backflow into the tank.

I'm a little surprised that these things can't auto-bleed air pockets on the pressure side of the lift pump. Yanmar made a big deal of the bleeding procedure by adding two very prominent bleed screws and by making the starter solenoid wire easily removable so that you can hold the START button to purge the lines.

Al, thanks for the tip on possible bad lines. They all look to be pretty supple, however, I'm not ruling out replacing everything in the motor compartment.

[JIM CHALOUPKA]

If the fuel filter has been changed recently, that is simultaneously with experiencing this trouble, suspect that the new filter is not seating/sealing correctly. The seal must be very tight and can suck air without exhibiting a fuel leak, check your hose clamps.

JIM

[Mark3101]

Which controller do you have? On mine it allows for you to run the pump to prime the system by holding down a button while turning the switch to the run position. Nice when changing filters etc. I do NOT have a check valve on mine, and it doesn't seem to need one so far.

[BoaterAl]

I will second Jim's advice on the fuel filter. During the NAPA day's every so often we would get a call about new filter replacement. For what ever reason new fuel filter installed and now a issue. No questions asked send out another filter.
On the service side when we had fuel delivery issues, first thing new fuel filter. The one taken off examined for contents other then fuel. Would not hurt to pull that filter and open it up.
Fred, we love spending your money.

[flloyd]

The filter is new and yes, it was changed recently. I put a thin coat of oil on the gasket before hand tightening per normal procedures. Also changed fuel/water separator at the same time. Bled the system and it ran just fine. that was in April and the generator has had less than 100 hours since then.

I guess its just going to take a lot of fiddling and experimenting to figure out. The tough part, as usual, is that each test cycle takes a run-up to full temperature and then a shutdown and storage period of a few days. Summer might be over before I find it....

[travelite]

Fred, Tap a fuel sight glass into various places along the fuel line to see if you can spot air bubbles. Check out the following link, bottom of page:
https://secure.k9bytes.net/~monacoto/cgi-bin/k9bytes.pl?command=listitems&pos=0&type=search&search=mack

[Jon Wehrenberg]

I made up a little device that I use to check plumbing before turning on the water. I have a pressure gauge and a Schrader valve mounted on a plumbing fitting that I can adapt to just about any line I want to check. I pressurize the system via the Schrader valve and then let it sit. If the pressure does not change over night I know the system is leak free and I can run water or air or coolant through it. Is it possible to temporarily mount a gauge in the system, and monitor it to see if you do lose pressure back through the check valve?

On my Kubota powered generator in the previous bus the generator would not start unless I primed the pump. I would open the valve near the injector manifold and with 24 volts to the fuel pump listen as the ticking sound became labored indicating it was moving fuel and the fuel system had some pressure. Then the Kubota would start almost instantly. Starting was never an issue, even if it was a week before we ran it again, but after sitting for a month or two I had to go through the process of reprining.

[BoaterAl]

Fred,
Is this a new-new fuel filter or a new filter with less then 100 hours run time.
AL

[JIM CHALOUPKA]

Fred, I repeat, jump the pump and make a flow test.

I had a similar situation to what you are describing and it turned out to be an intermittent supply of voltage due to bad crimps in several connectors in the wires supplying the pump. Don't know why they were there. Making up a new one piece wire harness fixed the situation.

If that is not your problem at least you have ruled it out and can look elsewhere.

JIM :)

[flloyd]

Fred,
Is this a new-new fuel filter or a new filter with less then 100 hours run time.
AL

I was a brand new filter.

Yesterday I went through the priming procedure per the Kohler manual and tightened the hose clamps on a couple of lines. The lines could be turned over the nipples by hand so I figured that the hose clamps should be tighter. The motor started as expected and I ran it for about half an hour with all 4 cruise airs running - all OK.

A detailed inspection did reveal that the turbocharger outlet hose is cracked and leaking slightly where the hose connects to the turbo. Does anyone have a recommendation as to where I might get a replacement hose and/or whether something from a typical car parts store might work? I realize that I might have to order direct from a Kohler supplier and have it FedEx'd to my next location, which will be Birch Bay, WA. Hitting the road today, outbound from Columbia Falls, MT.

[jack14r]

I had a clamp that was not installed on the turbo oil return properly and it cut the hose,I found the exact hose with a 90 degree bend at NAPA,I think that it was for a PCV valve.

[BoaterAl]

Fred,
If you contact a local NAPA store stocking hoses with a "warehouse classification" in hoses they will have in there store every hose a distribution center will have. As another idea calling NAPA to locate the nearest dist center to you. There are 53 dist centers in North America. They should be helpful to let you cruise the hoses back in the warehouse, as it won't be in any application the books.
AL

[dreamchasers]

Fred, I repeat, jump the pump and make a flow test.

I had a similar situation to what you are describing and it turned out to be an intermittent supply of voltage due to bad crimps in several connectors in the wires supplying the pump. Don't know why they were there. Making up a new one piece wire harness fixed the situation.

If that is not your problem at least you have ruled it out and can look elsewhere.

JIM :)

Fred,

It is clear to see you have spent much time in troubleshooting the generator issue. And my comment is solely offered to indicate experiences I have had with my generator. Jim stated that the electric diesel lift pump should be checked. My experiences are that I have replaced the electric lift pump twice, in the last two years. The first was in Washington DC in Cherry Hill RV Park. The second replacement was this year, last week, in a New Mexico Walmart parking lot. I have noticed that Powertech has changed the electric fuel pump design and does not offer the electric pump that was original on my generator. You might consider replacement of the electric lift pump as a troubleshooting event.

If you put your hand on the pump with power applied to the generator(either running or starting), you should feel it "clicking" as it is running. On both pump failures the generator would run for a while, then shut down for no apparent reason. The suggestion of installing a temporary pressure gauge to monitor discharge pressure of the pump sound very reasonable. It would involve a few fittings changes for the temporary gauge, but would be definite. It might be easier to simply replace the pump.

Good Luck,
Hector