Onan MicroLite 2.5 LP series L

Final (I HOPE) update. After further diagnoses, they decided that it was indeed the magneto causing the problems. They replaced the magneto. They said they ran it under full load for 2 hours and it never missed a beat. They said it was ready and to come and get it. Went the 90 miles picked up the unit and brought it home. Installed it yesterday morning and to my surprise it would now only run for 2-3 seconds before it would completely die. Would start right back up, miss severely and die again in a couple of seconds. Not so happy now! Almost seemed like it wasn't getting fuel so I pulled the LP tank off the grill, with regulator and hose, and hooked it to the generator. Same thing. Called the service manager and expressed my anger and then calmly discussed the issues. He requested I bring the entire unit to them. Got up early this morning and took the Sprinter to them with the wife following behind in the car. They got it in and supposedly diagnosed the new problem to a bad spark plug! Replaced the bad plug and they said it ran fine. We went back to the dealer to pick up the unit. Started the unit and it sounded fine. However not all was good. Now the light on the microwave was flickering like the generator wasn't putting out "clean" power. Also noticed that the gen wouldn't supply enough power to run the A/C and the microwave at the same time, which it had been able to do in the past, although it would really load the gen to do it. I requested that they hook the unit up to their load bank and show me that it was putting out it's rated output. They said they would but it would be late in the afternoon before the generator tech could get back on it. The wife and I went bumming around till 4pm. Went back and they were just finishing putting the seats back over the transfer switch. He had taken a picture of the load bank gauges and it showed it was putting out fine. Still won't run the A/C and microwave at the same time, but I can deal with that since it is at the generators maximum output to do that. Curiously, the light no longer flickers on the microwave. Also noticed my torque marks on the generators mounting bolts were no longer in line. I think they removed the entire unit, and did something to it to cure it's issues besides just replacing the spark plug. I guess it doesn't really matter, at least it now runs.
Thanks for all the replies and suggestions, and sorry for the long post.
Bob

Sooo, I talked with the generator tech at Cummins in Grand Junction, CO. and he wanted to see the unit. I pulled the unit out and took it to them yesterday. Today they called and confirmed that it would loose spark temporarily after approx. 15 minutes of running under load. However, the tech doesn't think that it is the magneto/pickup assembly. They/he is going to do more testing and see if he can pinpoint the issue.
I'll post more as I find out what they say.
Thanks for the replies.
Bob

I have the same Microlite 2.5K LP
Last month I couldn't get the gen to run without hunting badly under no load, and when load applied it seemed to struggle. It only has 175 hours on it.

I found it was running lean.....carb spray while hunting cured it for 20 seconds.

I ended up pulling the demand regulator on the gen (Garretson SD regulator) and got a rebuild kit for ~$50 instead of ~$300 for a reg.
Started right up, no hunting, no dying, works great under load, holds rpms and HZ after small adjustment (I had tweaked it previously).

I probably saved about $600 doing it myself.


Edit, I just noticed the part about the spark not visible.
Sounds like either the coil or a crank pickup sensor is breaking down when hot.

Okay. Pulled the unit from under the Sprinter today and replaced the PCB (power control board) and the coil assembly. Reinstalled the unit and 12 minutes later it stated it's miss. It took over 20 minutes before it got so bad that it died. As always, it started right back up. I had inspected all the wiring and did not see anything. I decided to eliminate the propane supply system as a possible problem, so took my bar-b-que tank with regulator and hose and hooked it direct to the generator propane supply pipe. This also did not make any difference. I'm was still fairly sure it is spark related, so I borrowed a spark tester from a former co-worker. This is the type that plugs in-line between the spark plug and the plug wire. With this device installed, it is clear to see that when the unit misses, there is no spark. Contacted Cummins and they say there isn't anything in the system that could cause this issue besides the parts I've already replaced.
Does anybody have any other suggestions?
Thanks

Update! Last summer we didn't use the generator during hot weather long enough to cause the generator to start it's miss/dying issue.
This summer has been very hot early so it's doing its thing again. Onan has looked at it again and still have not got any ideas. I purchased a new PCB (power control board) and a new coil today. I will pull the unit out from under the Sprinter and replace these parts. Hopefully this will cure the problem. I will post the results.
Bob

When it gets hot enough to start it's dying thing, it appears to miss several times and then the RPM falls so low that it can't recover and then dies. It always starts right back up. It may do it's thing right away and sometimes it will restart and continue to run fine for a few minutes before it does it again. I have thought about buying one of those lighted spark plug wires, that lets you see the spark, to verify what is happening, but haven't yet.
According to Onan, this model of 2500 does not have a low oil level shut down. The model specific wiring diagrams support this. I have changed the oil but that didn't make a difference.
I took apart every connection and coated with "Stabilant 22A" which is an electrical connection enhancement (Google it. It really does work) but it did not help. That is another reason that I am leaning towards the controller and not a poor connection issue.
Thanks for the replies and ideas. I know we will figure this out.
Bob

it has a low oil level sensor. I bought a toy hauler that had a 2800 gas gen it did the same thing. Oil level was good but when it got hot the oil was so thin it thought it was out of oil. Changed the oil and all was well. When I drained it the oil was as thin as gas. The oil was either old or the wrong wgt. Kept it for a few yrs and sold it. Never had another problem. Sold it to a friend who had it for another 5 yrs and it was still running good. I change the oil every spring no matter how many hrs are on it. Just a guess.

Will it always restart immediately? If so, that argues against it being a heat-related. But if it requires a cool-down period, it may sell be heat-related. Both my failures on my current Onan 2800 required at least 5-15 minutes cooling in summer before they'd re-start (fuel pump, voltage regulator).

Another thing often overlooked is the spark arrestor being plugged, but your symptoms don't match mine when that happened (run fine no or light load, chug down and die under load).

Good luck with it.

Jim, "Trying to understand the behavior of some people is like trying to smell the color nine."

Just an update.
Since the weather has cooled off, I have had no issues with this unit running. It seems that the ambient temperature makes the difference. My guess is that when something (controller?) gets hot I start loosing spark. The Onan dealer suggested replacing the controller, but I hate to just throw parts at it. I may buy a controller to have on hand in the event it totally fails.
Thanks for all the relies!
Bob

I replaced the spark plug and gapped it to .020, as per the manual for LP. I checked the generator regulator vent hose that is secured at the lower left front of the generator. When it is running there is a slight pulsation on the hose. If it is plugged off the engine will die. If it has a vacuum pulled on the hose, it also dies. As per the tech at Cummins/Onan, all of these tests are normal since any change in the back side pressure of the regulator will create a change in fuel supply. Is there another regulator in the system? I don't think it is a fuel supply issue since I can run the furnace and the fridge and the generator does the same thing.
Anyone else have any ideas? Nothing I have tried seems to make any difference.
Thanks for the input!