ONAN Generator mystery! Throttles up and down

[NWRVERNORCAL]

Can someone tell me if I cam going nuts!  I have a 2004 Itasca Class C with an Onan GenSet running at 57 hours total.  While on a trip boondocking the generator starting going all over the map with RPMs  up and down dimming the AC power and TV.  I get it home to the RV delaer he runs it for 3 hours no problem.  Our altitude has not changed drastically we went from sea level to 400 ft.  Then last week on our way toTahoe things are working great on our way back slight fluctuation but running solid.  I had it at the dealer before our Tahoe trip and he fond nothing.  I am headed to a northwest 10 day excursion and I am worried I will get stuck without a generator.  What could this possibily be

HISTORY of the coach before me not used too often and generator sat I added 20 hours to the generator.

Thoughts on what this could be and how to fix it in a bind?

Thanks

 

[RREngr]

Check the fuel pump on the Gen.

Rich

 

[teachers pet]

We had one do that.  An "expert" at a RV service center, couldn't get it to smooth out and his answer was "some do that with age"

A stop at an Onan Service Center in FL resulted in a $80 bill and a fuel filter that solved the problem.

 

[Mark R.]

I would doubt the fuel filter would be plugged as it does not have the problem all the time, and very low hours  in a new rig, same goes for the pump. I would suspect something as simple as the mixture jet on the carb could use adjusting, if it is too lean (screwed in too far) your generator will surge up and down like a roller coaster. As to the 400 feet altitude, that is your physical altitude ,you must also consider density altitude at the time the problem occurred , that is barometric pressure, you could have been way higher then you thought, if your gen. is running  too lean to begin with, the increase of altitude can put you over the line and off you go surging. Just an idea, good luck.

 

[Ron]

Sounds like the fuel filter needs replacement.  Filters do not cost that much and it is worth a try.  BTW I am aware of at least two cases where filter replacement corrected the condition you describe.

 

[Clay L]

Note that some of the Onans have two fuel filters. One just in front of the carburetor and one on the inlet to the fuel pump (on the left underside).

Also an air leak can cause similar symptoms. You might want to check all of the fuel connections.

Mine had a air leak at the clamp on the rubber hose to metal fuel line coming from the tank.
Two dealers and a Cummins shop diagnosed it as the fuel pump.
One of the dealers and the Cummings shop replaced the pump.
A Winnebago factory tech located the real problem.

 

[Master-Tech]

I agree sounds like fuel starvtion , Id start with a filter, check all lines going too the Genset from Coach ,may even remove bowl on Carb. may be full trash an getting up in the main jet ,also check solinoid that holds bowl in place may be sticking not lettig enough fuel through/  old gas does strange thangs too these small carbs if they set any at all, arule off thumb you need run Gen-Set at least every 2 weeks for bout 1 hour 30min. without load 30 with too keep fresh fuel an keep brushes an armiture clean an ready 4 Vacation , hope this helps good luck 

 

[NWRVERNORCAL]

Ok- I appreciate the posts everyone but where should a novice like me start?  Can someone give me a 1,2,3 list and the location of the engine area and what to look for.  I am nervous and we are talking a big trip soon.

 

[carson]

Sounds to me that a bit of professional help is required here. Perhaps a local garage mechanic may be able to help out here since we are not talking about serious engine problems. Show the mechanic this thread; that may help.

 

[scottydl]

Do you have the Onan owner's manual?  Mine was quite helpful when I was having problems, and pretty much illustrates where everything is located... I guess assuming that owners will be doing some maintenance themselves. 

I had a somewhat similar problem to yours once last year... here's the thread.  Mine was more of a power supply UP and DOWN vs. throttle revving.  But I had the revving too, which seemed to occur when the genset wasn't warmed up quite enough and I put a heavy load on it (both roof A/C's).

 

[busa]

A bad fuel filter will cause that symptom. Turn  the generator on and let it run for a bit with no appliances running. and then turn on as many appliances it can handle, and if it starts surging it is a bad fuel filter. Remember, a generator with no loads does not require as much fuel pressure and volume. And if you replace the fuel filter and still does the same thing, chances are the fuel pump is weak.