Onan 4k Microlite runs 10 minutes, quits, will start later.

[F-20_Tigershark]

Hey all you Onan experts out there,

I have an Onan Microlite 4000 genset in a 1999 Winnebago. It starts and runs fine but quits after about 10 minutes, under load or no load (maybe a couple minutes less under load). Just before it quits it will sort of miss once or twice and 5 seconds later it shuts down as if on command.

This problem has manifested itself in only the last hour or two of operation time.

Pertinent info:
Model KY-FA/26100H
1250 hours on the Hobbs meter.
Oil is changed regularly. There's less than 50 hours since the last change. Oil level is carefully monitored.

For the last three years I've driven this RV to work out of town and stay in it four days a week and run the genset three nights a week to cook dinner in the summer. In the winter it's run for a couple of hours so the furnace doesn't drain the coach batteries.
The fuel is shared with the chassis engine. The RV is driven 75 miles a week so the fuel is always fresh.

The fuel pump is working verified by disconnecting the hose and starting the unit. It's putting out about an ounce a second. I don't think it's a fuel supply issue. After it quits, disconnecting the hose shows there's fuel in the line and some also drips back out of the carb. nipple.

I changed the spark plug and set the gap to .025".
Recently (before this shutdown problem) there was more than the usual rpm fluctuations along with the voltage apparently since the lights would flicker once in a while. But after changing the plug this seems to have gone away although it's hard to say when running during the day.

From what I have read on the interweb this model doesn't have a low pressure/level sender but I haven't verified this yet. One guy on youtube (who really enjoyed hearing himself talk) said to take a half pint of oil out to trick the sender. This didn't make sense to me but with trepidation I tried it anyway. No luck.

I did find a dead mouse in the bottom of intake side of the cooling system that looked like it died fairly recently. Because of the limited access I can't see if there is a nest blocking air flow. I seems like there isn't very much air flowing out the exit but I don't know how much it should be because I've never had reason to check it before. I think I read that the unit will shut down if the windings overheat. Or does the engine have a sensor to shut it down if it's too hot? After the last shutdown I measured the cylinder near the head with an infrared thermometer and the highest reading I could get was 244 degrees. That seems kind of hot for ten minutes of running in 60 degree ambient air temp.

How long do the brushes last? Is 1250 hours on the clock a lot?

How is that for a data dump?

Does anybody have any clues or advice? HELP! PLEASE!

Lance

Update:

My wife suggested that I use compressed air to back-blow the airway to see if mouse nest stuff could be dislodged (she's a pretty danged smart woman, I don't know why she married me).

Sure enough, a couple bits of mouse bite-sized foam came out. I looked harder and that little bugger had chewed an area of the foam insulation. It looks like I might have to take things apart to clean it out.

[F-20_Tigershark]

It's getting fuel. After it quits I've pulled the fuel line off and operated the starter. It pumps plenty of fuel. I'm pretty sure that's not the problem.

I got a new job and won't need to stay in my rig anymore so I'm not so anxious to get this working properly. Nonetheless, I'll want to have it operational for when we go camping.

I'm looking forward to going camping next year. For the last few years the last thing I wanted to do was go camping. I just wanted to be home.

[cgmartine]

1. Disconnect the fuel line that comes from the tank in the motorhome. Connect a new fuel line from the generator fuel pump to a gas can with a mixture of one part Sea Foam to two parts gas. Let it run until it runs smoothly.

2. Replace the fuel filter.

3. Replace the fuel line between the fuel pump and carburetor.

4. Replace air filter.

[F-20_Tigershark]

I went to check if there was spark. There wasn't. I pulled the park plug out and it was totally wet with fuel. My wife was out in the garden and I showed it to her and told her to smell it. She asked, "Is it urine?" Hahahaha. (That wasn't the word she used) Maybe she's not so smart after all! OK, maybe she can't be expected to know what a spark plug is.

Anyway, it is definitely getting fuel.

I checked if there was a spark across the gap and there wasn't.

Then I noticed that the white wire had come off the blue ignition module. The connector is getting loose. I plugged it back on and of course it started right up with a lot of smoke from too much fuel.

It ran exactly 10 minutes and then there was the little hiccup, and sure enough, about 30 seconds later it died. It won't start now.

At least it's consistent.

[F-20_Tigershark]

Well, gentlemen. This week I tried to use the genny to run the microwave. It ran for about a minute (I had to eat my falafel lukewarm). The next day I pulled the fuel line off and there was fuel in it. But it would not start.

I'm starting to suspect the control board. But I suppose I need to pull the thing out so I can clean out the mouse nest. ****.

First, I'll check if there is spark.

Edit: Sorry about the language. I didn't think it was that bad of a word.

[bounder39zman]

ONAN discontinued using low oil level switch on the KY gen before yous was made. Bad idea to run less oil....keep it at full mark...only holds 1.5 qt, no oil filter or oil pump, so does not have low oil pressure switch either...so change it often...oil way cheaper than parts and labor bills. No high temp safety switch on these...make sure you run with service door installed, or it will overheat. Your spec is also just before Onan started putting diagnostics into control board, so no help there, either. I would check fuel delivery..OP stated fuel pump may be getting hot and quits pumping....happens a lot on these units.
Also voltage reg. may be heating up and failing. Also verify thaty 12+ battery voltage is being supplied while running. These sets do not have integral batt. charger...so depend on RV charger converter to keep bat volts up. If voltage drops too low, control board and fuel pump quit working...and shut down!! 1250 hrs not too long for brushes...but have
seen them worn out with much less hours. I think if brushes were problem, would not run even for short period of time

[maillemaker]

I had this problem with our older (1990) Onan.

It was a problem with a control board on the genset. It would run about 10-20 minutes and shut down. Some internally-detected fault.

Steve

[eHoefler]

Replace the fuel pump. Gets hot and shuts down. Been there done that.

[F-20_Tigershark]

I tried disconnecting the white wire from the blue ignition module. It does not run. I tried grounding the white wire. The engine does not run.

I'll have to try checking for spark.

If the ignition is breaking down would it suddenly stop? Wouldn't it start missing a lot and then die?

I have to drive up to work now so maybe I can mess with it after work tomorrow.

Thanks guys.

[pappy437]

If it's not a mouse problem,check for spark as soon as it shuts down.It may be the ignition breaking down when it gets warm.

[darsben1]

Yes it can be bypassed but it could be one of 2 ways
Onan made some models with a normal open switch and others with a normal closed switch.
So either you just disconnect the wire or you have to ground the wire which is which I cannot remember

[F-20_Tigershark]

Thanks for quick reply darsben.

It says oil level switch though. I think that stupid thing is inside the oil pan. What a pain. Can the switch be bypassed? I don't need that safety feature since I am very diligent about checking the oil level because of the tiny oil capacity.

Moderator, I didn't mean to block images. How do I change that?

[1492]

[darsben1]

Service manual can be found at
http://www.trekdocs.com/Onan%204000%20Parts%20first43.pdf
Page 33 shows an oil pressure switch. But the genny should not run that long if there is no oil pressure.