Generator problem (onan micro 4000)

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skydivemark

skydivemark

Well-known member
Joined
Oct 3, 2015
Posts
479
Location
North East Tennessee
2015 class C thor Four Winds 31L. It's 2 years old and we've had it about a year. Recently the Gen (onan micro 4000 with about 175 hours on it) is acting up. It cuts off after 45 minutes or so and will not re-start for several hours. When it quits, I press the start button to the stop position the pump clicks loud (much louder than usual). After i let it set a while (usually til the next day) it sounds normal - can barely hear it.  I'm pretty sure this noise is the pump cavitating (not getting fuel). I checked the fuel cap and no rush of air or vacuum heard.
It has been parked a few months and I keep stabil in the fuel whenever I know it will be parked more than a few weeks. I do run the gen an hour or so every few weeks.
Any suggestions where to start looking or what to look for?
 
That was my first guess. Yes the fuel tank is nearly full - probably 9/10 full, barely under the full mark. I have a filter on the way. Just find it a bit odd the filter may be clogged with less than 200 hours on it. I haven't crawled under the rig yet to inspect all the lines for dry rot or possible rodent damage. The gen on my previous rig (same onan model but of course more current spec #) had close to 1500 hours on it when we sold it and I had never replaced the filter. If the filter cures the issue i guess I'll need to keep a few on hand in case it acts up on the road.
thanks for the input.
 
Have you removed the fuel line from the carburetor yet to make sure gas is flowing? Place the end of the hose in a gas can or glass jar and crank the engine. If you see a steady flow of gas, then you know gas is coming thru ok past the fuel filter and fuel pump.  If your carburetor has the solenoid with the screw that you loosen, you can also do that to see if any gas comes out. Place a rag under the carburetor, but make sure the engine is not extremely hot. This will you will make sure there is gas in the bowl. The next thing to do is check for spark if there is no gas.
 
I was having lots of trouble with mu Onan 4000 starting. Long primes and several attempts to start. I installed a fuel shut off on the gas line, every time I shut the genny down I shut the valve and run the fuel out of the carb. Since I installed the shut off it starts on the first time after priming a few seconds.
 
Preparing for Irma so i won't  have time for more troubleshooting for a few days.
A lot of good info shared here. The thing that makes me most curious is after i let it sit over night it works fine - again with same results. I wonder if its getting too hot causing vapor-lock?
 
I had the same problem, Mark......run about 20 minutes or so and quit.  I installed a new fuel pump and filter and that cured it. YMMV, of course.  Some guys have moved the pump outside the Onan enclosure and mounted it to the MH frame.....some have even insulated it!  Good ideas, methinks.  Access to the pump in the future would be MUCH improved, for sure.

A couple of reviewers (on Amazon IIRC) said their new pump was short lived.  Mine has been fine, but it is only about a year and a half old. My Onan has 400 hours on it now and the pump I removed appeared original.....no wrench marks or whatever, just lots of grime.

Good luck with the fix.............and more importantly, with Irma.  Be safe.
 
Putting the pump outside the gen compt sounds like a great idea especially if the cause is vapor lock, hadn't  thought of that. Plus like you said, it makes future access much easier. I've  heard the airtex pump is good quality. 
Thx for the info.
 
skydivemark, I just need to get one thing straight in my mind. You say that after it quits, you press the stop/prime side of the start switch.  The stop/prime side is used to prime the carburetor, which is usually done when it is cold and it is the first start of the day. Is that what you are trying to do, prime it, because it shut down? Is that because you think there was a vapor lock and you are trying to get additional fuel to the carburetor?  When the generator is working well and is already warmed up, there is no need to press the stop/prime side of the start switch.  You should be able to tell if the carburetor bowl has gas by opening the carburetor float bowl drain valve. I just moved my fuel pump and filter outside the generator. When I get a chance, I will post photos.
 
The reason i pressed the stop side of the button is because it seemed like it - for some reason - ran out of gas even though the tank is nearly full. The first time it did this i also had the main engine running which made me thing it was drawing a vacuum due to possible bad gas cap but when i loosened it i didnt hear any air release. Yes I am familiar that it doesn't  - or shouldnt - need primed once warmed up (when initially troubleshooting always do the easy things first). Under normal operation like when its cold and fuel is available the pump makes a barely audible sound, the sound is much louder after it quits, like a clicking type sound. When cooled back down (the next day) it again sounds normal - barely audible.
We do run the generator while traveling in warm weather to keep the coach (and dogs) comfortable so maybe with more air movement while driving that's why it hasn't acted on the road.
I'll  have more time to actually mess around with it once this weather clears and clean up (if any) is done. Looks sort of like I'll  be mounting the pump outside the compt and probably also insulating the fuel line. I still work for a living (not retired - yet)  so my time to work on this is a bit limited - i wish this was my only project, then it would likely be fixed already.
 
I just took these photos of my pump. I got the box from the Home Depot. It is about the size of a shoe box. When I get a chance, I will be drilling a bunch of holes to allow it to breathe. The box has a door with a hinge, so it makes it convenient when I want to change the fuel filter, and to check on the pump. It is located almost next to the generator, but not in direct contact. I replaced all fuel lines and re-routed them away from any heat. I do hope this resolves the heating and vapor lock problems, but just in case, I will be getting braided fuel lines to further isolate them from heat.  at about $2.94 a foot, it is not too expensive.
 

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That's  pretty slick. How much$ was the box? What dept did you find it in?
Yes, drilling vents (&drains) is a good idea, but not big enough to invite rodents.
 
skydivemark, the box has to be ordered on the Internet via their web page, and can be picked up at the store or be delivered. They do not stock it at the store. It sells for $12.29.  The store sku# is 1001528577, the model is 75-005, and the description is "1 gal. storage box in metallic." The door has hinges and it can be locked.
 
P.S.  Due to the way they manufacture the fuel pumps, with the metal fuel outlet pointing down, (they should make it point straight out instead) it will require that you install two plastic supports feet to raise the pump from the surface of the box about 1/4 inch. This will also prevent any vibration (I got those at my hardware store). In addition, you will have to drill two 1 inch holes to insert the fuel lines. Each hose should have a rubber grommet so that the metal opening does not cut into the hose. I mounted my box to a nearby storage area, which is made of hard plastic, and which was within 10 inches of the generator.
 
Great lookin' install, cg.  And thanks for the description and the info on the hardware you used from HD.  I've got it all archived for my "round to it" list. :^)

BTW- Be sure to let us know the outcome on the "frozen" flywheel.  Hope it is a relatively minor fix.
 
I had time yesterday to mess around with it. It was close to being due oil change(due in about 25 hours) and a little overdue for air filter change so I did both (changed oil & air filter). I started the gen and ran it for about 2&1/2 hours with no problem. The only thing I can think of is it may have been a little over full on oil, where I usually park it is not nice and level ground. This time I made sure it was as level as I could get. The air filter was dirty but no more than I would expect for around 200 hours (I've seen much worse).
Anyway, I bought all the hardware for mounting the fuel pump external of the gen compartment like CG did but - at least for now - it looks like I don't need to be in a hurry to do that.
 
I'm a bit late to the thread.  I hope you've solved it with that.  I have the same 31L model, just a bit older.  We have really liked the floor plan.

I had lots of intermittent genny problems.  I feel confident it's heat related vapor lock.  I've done a variety of things and I feel very confident that it has been solved, since my trip this summer through the desert to the Grand Canyon....

I do think that moving that filter and pump out of the plenum is a good move.  I had been thinking about trying that but didn't get to it.

What I did....I started with trying to ventilate the door.  my first attempt didn't work well.  i think the vent was too small and it was still drawing most air from behind the door and from under the coach
So I ended doubling the vent opening and I rigged up a baffle to direct the air.  This is both the cooling air for the engine and combustion breathing air....so it helps x2.  here's a couple pictures of what I did

Next, just before my big trip, I insulated the fuel hose all the way back to the tank.  In doing so, I found that Thor had it hanging loose in the sliptream, not too far from the driveshaft.  I figure it picks up a lot of heat over that fairly long length.  Heat from the V-10 but also heat radiating up from the hot pavement...and even heat form the generator's cooling air and exhaust.  I used just regular pipe insulation from the hardware store.  I used the rubbery EPDM type, not the foam type, and sprayed a couple coats of undercoating from a rattle can on it before install in an attempt to help it last a bit longer.  I tied it up neat and tucked it into the frame so it's better protected.  If I'd had time I would have liked to replace the hose while I was at it.... oh well, another time.

The other two solutions that I had in my back pocket in case these fixes didn't work.... add a second auxiliary low pressure fuel pump back closer to the tank to pressurize the line.... &/or to install a re circulation fuel line from the genny's carb back to the tank.

The other variables I changed, but do not think it directly affects the solution...were the oil change and fuel filter change I did at the same time as the insulation.

Just the other week while running the genny for Irma, it started to surge.  Grabbing for anything, I found that if I turned the altitude adjustment screw to a higher elevation, it smoothed out.  I let it run that way fo a minute or so, then adjusted it back to sea level and it ran smooth for several hours after....  unrelated I think, but I figured I'd throw that out there for your future reference....
 

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blw2 said:
I'm a bit late to the thread.  I hope you've solved it with that.  I have the same 31L model, just a bit older.  We have really liked the floor plan.

I had lots of intermittent genny problems.  I feel confident it's heat related vapor lock.  I've done a variety of things and I feel very confident that it has been solved, since my trip this summer through the desert to the Grand Canyon....

I do think that moving that filter and pump out of the plenum is a good move.  I had been thinking about trying that but didn't get to it.

What I did....I started with trying to ventilate the door.  my first attempt didn't work well.  i think the vent was too small and it was still drawing most air from behind the door and from under the coach
So I ended doubling the vent opening and I rigged up a baffle to direct the air.  This is both the cooling air for the engine and combustion breathing air....so it helps x2.  here's a couple pictures of what I did

Next, just before my big trip, I insulated the fuel hose all the way back to the tank.  In doing so, I found that Thor had it hanging loose in the sliptream, not too far from the driveshaft.  I figure it picks up a lot of heat over that fairly long length.  Heat from the V-10 but also heat radiating up from the hot pavement...and even heat form the generator's cooling air and exhaust.  I used just regular pipe insulation from the hardware store.  I used the rubbery EPDM type, not the foam type, and sprayed a couple coats of undercoating from a rattle can on it before install in an attempt to help it last a bit longer.  I tied it up neat and tucked it into the frame so it's better protected.  If I'd had time I would have liked to replace the hose while I was at it.... oh well, another time.

The other two solutions that I had in my back pocket in case these fixes didn't work.... add a second auxiliary low pressure fuel pump back closer to the tank to pressurize the line.... &/or to install a re circulation fuel line from the genny's carb back to the tank.

The other variables I changed, but do not think it directly affects the solution...were the oil change and fuel filter change I did at the same time as the insulation.

Just the other week while running the genny for Irma, it started to surge.  Grabbing for anything, I found that if I turned the altitude adjustment screw to a higher elevation, it smoothed out.  I let it run that way fo a minute or so, then adjusted it back to sea level and it ran smooth for several hours after....  unrelated I think, but I figured I'd throw that out there for your future reference....
Click to expand...

Yes I'm also convinced it's heat related causing vapor lock.
I really like that fresh air intake mod.  I've seen others and this one not only looks good but looks like it should work well in addition to being easy to make, drawing the coolest air available instead of getting air that's already warmed up from underneath.
I'll definitely keep it in mind and if it's OK I'd like to save those pics for future reference. I think your mods along with mounting the pump external to the gen compartment will make a ton of difference.
I will also crawl underneath and inspect my lines for proper routing & security. I think Thor's quality control isn't quite what it could be (I'm sure they're not the only ones).


 
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