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I have a 2002 Winnebago Adventurer I purchase new which has a 5.5KW Onan Generator (original).  It sat in storage for 18 months unused.  The generator started fine when I got it out of storage and will run as long as the RV engine is running and I'm driving.  If I stop, say at a rest area, shut the engine off and leave the generator running, it will stall anywhere from 5-15 minutes later.  I can usually restart it but it will stall more quickly, 1-5 minutes.  As soon as I start up the RV engine and get back on the road, I can start the generator and it will run until I stop again 2-3 hours later.  Within 5-15 minutes it will stall.  I've repeated this scenario enough times to know it is definitely related to when the RV is not running at high rpm.  I have tried leaving the engine idling but that doesn't seem to be enough, I actually have to be driving (higher rpm) for the generator to not stall.  I am thinking this is maybe a fuel system pressure problem?  Maybe a new gas cap?  I can't think of anything else and so I'm seeking help on this forum.  When it is running, it runs fine, no missing or sputtering.  It will sometimes sputter just as it is stalling but that is all. 

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I wonder if the problem might be that the generator is overheating when sitting still? Onans have an over temperature shutdown. I would look for something that might be restricting air flow when the RV is not moving. Where is the generator located in the RV?

If you remove that air movement restriction it will likely resolve the problem. 

Edited by Kirk W

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Just now, Kirk W said:

I wonder if the problem might be that the generator is overheating when sitting still? Onans have an over temperature shutdown. I would look for something that might be restricting air flow when the RV is not moving. Where is the generator located in the RV?

If that's the case then the fuel pump needs to be replaced. When we had a 5500 it would only run 10-15 minutes in temperatures over 90F until we replaced the pump.

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I wonder if the installers just t’d into the fuel line for the engine. The fuel pump is probably I the tank. When you shut off the engine, the fuel pump stops working. Follow the fuel line for the generator and see where they connected it. To connect it to the tank the tank would have to be below 1/4 tank or you would lose fuel out the generator port.

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33 minutes ago, Ronbo said:

I wonder if the installers just t’d into the fuel line for the engine. The fuel pump is probably I the tank. When you shut off the engine, the fuel pump stops working. Follow the fuel line for the generator and see where they connected it. To connect it to the tank the tank would have to be below 1/4 tank or you would lose fuel out the generator port.

The generator fuel line cannot be 'T'd into the engine fuel line due to the pressure differences. The fuel injected engine in-tank fuel pump puts out 40-50 PSI, while the carbureted generator runs on 4-7 PSI. Motorhome manufacturers sometimes 'T'd into the fuel return line years ago, but most now use a separate port installed in the tank just for the generator.

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Usually there's just a seperate suction tube going 3/4 of the way into the tank that feeds the generator.  Engine mounted fuel pumps worked fine sucking gas out of the tank for many decades ... it's only been with the advent of reformulated fuel that automakers felt the need to put a pump in the tank to pressurize and raise the boiling point of the fuel in the lines.

I'll bet the same thing is happening with the Onan generator.  It has a fuel pump mounted on the generator that sucks gas out of the tank.  Since the generator's fuel line isn't pressurized, it's boiling and creating a vapor lock when the underside of the RV gets hot.

When you stop the engine, you stop the air from the engine's fan from circulating air under the RV.  Pavement heat percolates upward and vapor locks the generator's fuel line.

You might try adding a pump adjacent to the fuel tank and eliminating the one on the generator to pressurize the fuel line between the tank and generator, thus raising the boiling point of fuel in that line.

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All good suggestions and thanks.  The coach batteries are 5 years old but seem to be working properly, otherwise.  The air filter hasn't been changed in years so I'll check that too.  I am fairly sure this is a fuel starvation problem.  The problem occurs even with a full tank of gas.  I will research the generator's fuel pump system and call Onan for advice as well to see what they say.  If I decide to add a second fuel pump, how do I size it?  Where do I buy it and where do I install it? 

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If it were me, I would start with the most simple and least costly thing first, then work my way into more complicated possibilities. For instance, if you have a large fan that you could place to blow into the generator compartment from under it to increase air flow while sitting still, that would soon tell you if it is a problem of air movement and cost nothing. There are also several fairly good videos on YouTube that deal with testing and replacing the fuel pump and filter that you will probably find helpful. I watched 3 of them and while a bit amateur, they should help with your problem.

You mention that the RV is a 2002. Is it correct to assume that the air and fuel filters have been replaced as part of periodic maintenance? If not this would be a good time to change both of them. The other question that I have is whether or not you have checked for an error code? If it happens to be a code 36 it is quite likely to be a fuel problem. 

From the Onan manual:

Quote

The genset controller provides extensive diagnostics by causing the status indicator light on the Control Switch to blink in a coded fashion. Following a fault shutdown, the indicator light will repeatedly blink 2, 3 or 4 blinks at a time. • Two blinks indicates a low oil pressure fault. • Three blinks indicates a service fault. Press Stop once to cause the two-digit, secondlevel fault code to blink. (Pressing Stop again will stop the blinking.)The two-digit code consists of 1, 2, 3, 4 or 5 blinks, a brief pause, and then 1 to 9 blinks. The first set of blinks represents the tens digit and the second set of blinks the units digit of the fault code number. For example, Fault Code No. 36 appears as: blink-blink-blink—pause—blink-blink-blink-blink-blink-blink— long pause—repeat • Four blinks indicates that cranking exceeded 30 seconds without the engine starting. • Note: Fault Code Nos. 3 and 4 are first level faults. Avoid interpreting them as second-level Fault Code Nos. 33 and 44, which have not been assigned as fault codes. Restoring Fault Code Blinking – The fault code stops blinking after five minutes (15 minutes, Series HGJAA). Press Stop three times within five seconds to restore blinking. Note that the last fault logged will blink, even after the condition that caused the shutdown has been corrected.

 

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If you have the exact model I might be able to post the service documents for your situation.

 I carry a spare low volume fuel pump for testing. It should be easy to install it with a separate gas supply for testing.

 

 Safe Travels,.   Vern

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Don't forget the basics. Check the oil level. If it's low the generator will stop. I assume you have more than a 1/4 tank of fuel in the rig?

Once those 2 basics are checked then move on to fuel filter. I seem to remember there is a fuel flow test measuring how much fuel the pump passes in a set time. That will tell you if the pump is bad.

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I think on the other RVing forum you pretty- well  were convinced to have the batteries load  tested by Interstate or another battery retailer.

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22 minutes ago, Ray,IN said:

I think on the other RVing forum you pretty- well  were convinced to have the batteries load  tested by Interstate or another battery retailer.

You must have me confused with someone else.  I have not posted this issue on any other forum. 

Edited by LSpecht
mistype.

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I have changed the oil and filter on the generator before this trip I took over 4th of July weekend.  I also had a full tank of fuel.  Basics, I've got covered.  One update, the generator now won't run for more than a few minutes even while driving.  The difference was the outside temperature.  The previous times I had driven it with this problem, were either overcast or early morning hours.  Today, while driving home the temperature was above 90 deg and the generator just wouldn't stay running.   I'll check for the fault code when I drive it tomorrow and see what it is giving me.

Edited by LSpecht

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1 hour ago, LSpecht said:

You must have me confused with someone else.  I have not posted this issue on any other forum. 

I apologize, I must be thinking of a different person.

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In my case the fuel pump on the engine didn't have enough pull to bring fuel up from the tank so a second one similar to the one WinnieView posted a link for.   I'm not sure of the pump volume.  My generator doesn't have a fuel return line  to the tank...not sure if yours does.

Mine was hooked into the same circuit as the glo plugs and onboard fuel pump using a mini blade type fuse.  The holders and fuses are available at Lordco or Napa.  A pretty standard item.

As I recall the fuel pump fittings were 1/4" OD and the fuel hose to my generator was either 5/16" or 3/8" ID and the original installer tried to squash down the hose to fit on the fuel pump fitting.  It didn't work, it sucked air so I needed to get an adapter to bush it up from the pump to the ID of the rubber fuel line.  The part was available at the parts store.

The pump just gets spliced into the fuel line somewhere it is accessible.  The can and do fail so don't bury it.

The inline fuse holder may have a heavy wire on both ends, may be 12g.  The circuit you splice into may be 16g so you may need a butt connector which will go from a bigger g to a much smaller one.  They are available in plastic packages.

 

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A few items to check:

Fan belt is still attached to the water pump.

Exhaust pipe dust clean out. 

Fuel line collapsing.

When I serviced mine I did all of the maintenance recommended, with the exception of the fan belt.

 

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On 7/5/2019 at 6:48 AM, LSpecht said:

I have a 2002 Winnebago Adventurer I purchase new which has a 5.5KW Onan Generator (original).  

image.png.2d1876e7b5c92077fa0933907fe12aec.png

This is a gas motorhome, right?  If so, and the generator is also gasoline powered,  then all the suggestions about glow plugs, water pumps, fan belts, etc. don't apply - these are for a diesel generator.

Vapor locking from reformulated gas in the unpressurized fuel line, or the rubber portion of the fuel line collapsing  are the most likely culprits. 

Edited by Lou Schneider

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Yes, this is a gas  motorhome.  If the fan belt was off the water pump, the RV engine would be overheating and it is not.  That would be the larger issue if it were.  I suspect a problem with the fuel flow and the fuel line collapsing is a good thought.  I will check for that.  The line is original and so 17 years old.  Before the 200 mile trip to TN this past week, I filled the tank at the same gas station I've used for years, a QuickTrip.   I also added 3 bottles of STP gas treatment (75 gallon fuel tank) in hopes that would help.  It did not.  I'll get the error code today and check the air filter to the generator only because it's been awhile since I last checked it, not that I think it is part of the problem.  I'll also get the model number and research the fuel system design to check the fuel line and fuel pump and also the overheat sensor.

Edited by LSpecht

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On 7/5/2019 at 12:18 PM, Kirk W said:

I wonder if the problem might be that the generator is overheating when sitting still? Onans have an over temperature shutdown. I would look for something that might be restricting air flow when the RV is not moving. Where is the generator located in the RV?

If you remove that air movement restriction it will likely resolve the problem. 

The generator is on the driver side in the most aft compartment (at the rear).  Nothing has been modified or added to alter air flow.  I will locate the sensor for the over temp shutdown and see if I can replace that.

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22 hours ago, Kirk W said:

If it were me, I would start with the most simple and least costly thing first, then work my way into more complicated possibilities. For instance, if you have a large fan that you could place to blow into the generator compartment from under it to increase air flow while sitting still, that would soon tell you if it is a problem of air movement and cost nothing. There are also several fairly good videos on YouTube that deal with testing and replacing the fuel pump and filter that you will probably find helpful. I watched 3 of them and while a bit amateur, they should help with your problem.

You mention that the RV is a 2002. Is it correct to assume that the air and fuel filters have been replaced as part of periodic maintenance? If not this would be a good time to change both of them. The other question that I have is whether or not you have checked for an error code? If it happens to be a code 36 it is quite likely to be a fuel problem. 

From the Onan manual:

 

Thanks for the error code description.  I probably have that in the generator manual somewhere.  I will see what the error code is today and post it.

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Today, as I drove the unit back to storage, I was able to get an error code.  36.  Fuel pump and or Fuel Filter are the most likely causes.  I will order new replacement parts and see if that fixes it.  I will report back on success or failure.  Oh and the model is HGJAB.

Edited by LSpecht

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