Onan Marquis 5500 Genset-year 2000

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mudshark

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Nov 15, 2014
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Hi All
New day, new problem:
We have been on the road for 6 months now. Many places don't let you run a generator so it has been since September since I exercised ours.
I had a chance to run it here where we are. As usual, it took a few tries to get it to run but it started to run normally. I had two electric heaters set up so the genset had a load on it. It ran for about 3 minutes and I came in the coach and both heaters were running. The fridge had kicked over to AC so I know it was generating. Three minutes in it stopped. I had turned on one A/C unit at the time. Don't know if that was coincidence. Now it will kick over but will not run. There is plenty of oil in the pan so that is ruled out.

As a side, in September we were at a small RV park in California and their power went out on a day with temps in the low 100's. Their meter socket burned up. We are traveling with two cats so I started the genset to get the bus cooled down. It was surging badly from normal RPM's down to almost a stall. I ended up sticking an awl in the carb  linkage to get it to run at a normal speed. Don't know if the two incidents are related.
 
It sounds like the first step is to run it long enough for it to get some fresh fuel, depending on where it is mounted in your coach there may be enough fuel in the rubber fuel line between the gas tank and the generator for it to run for 10-15 minutes.
 
I'm guessing you have plenty fuel in your main tank, more than 1/4.

Sounds like it needs a good carb cleaning and maybe spark plug, or at least cleaned.  I would start with some Gumout Carb cleaner. 
 
Onan generators need to see adequate oil pressure and voltage from the generator to keep running after you release the Start button.

Two electric heaters on high @ 1800 watts each =  3600 watts.  Add 400 watts for the refrigerator and the converter and you're at 4000 watts, leaving only 1500 watts to handle the starting surge of the air conditioner.  Not nearly enough.

You may have tripped one or both of the circuit breakers on the generator.  Or fried the control board.  The first fix is easy, the second not so much.
 
I have the same Genny - 4 years newer. It will run fine with both breakers off.

I had a situation last year in Quartzsite where my Genny would run as long as I held the start button on. It immediately died when the button was released. That's when I found that it would run with the breakers off.

I found that the hot (black) wire had shorted to ground in the transfer switch. Note that the breaker did not trip. Fixed the short and all was back to normal.

Tom
 
Thanks Guys
I have some things to look at. Unfortunately, I have to wait until the couple beside me go out for the day. The exhaust from my genset can be obnoxious when it first starts. We are packed in pretty tight here.
 
OK, I went out again just now and tried the genny again.
Same as Tom, if I hold the starter down it runs fine. As soon as I release the starter it dies. Sounds good when it is running but stops.
Where was that short you found? Where is the transfer switch?
 
We had this problem with the Onan 6.2 kW generator in our 87 Suncruiser. It turned out to be a bad full-wave rectifier in the control box. The start switch supplies 12 volts to get it running, and then the rectifier is supposed to supply the run voltage. After the first time, I carried a spare, and once replaced it while on a trip.
 
If you turn off the breakers on the genny and it still dies then your problem is different than mine.
However, if it runs with those breakers off then the problem could be like mine i.e. the hot lead from the Genny to the transfer switch shorted to ground. Note that if this is the case, the coach will be fine on shore power.

My transfer switch is a cube shaped box mounted on the back of the AC/DC load center (the fuse & breaker panel). Mine is accessed by opening the cabinet door beneath the bathroom sink.

 
mudshark said:
OK, I went out again just now and tried the genny again.
Same as Tom, if I hold the starter down it runs fine. As soon as I release the starter it dies. Sounds good when it is running but stops.
Where was that short you found? Where is the transfer switch?
Click to expand...

Several things can cause that. Do you have an error code for us?

Onan generators do a bunch of "Sensing" and if things are not right they will shut down. The sensors are disabled while you hold hte start button however

Oil level/pessure
Temp
120 vac
Are all sensed. Not enough oil and it stops
no Power out (or a short that for some reason is not tripping the breakers) and it stopps
Too hot. and it stops

In all cases it will flash a code.. cryptic but we have cryptographers here who can decript some of 'em (That is not entirely a joke).
 
Where would I find the error code?
I have a code reader for cars/RV. Can I use it for this?
 
I bekieve you will find it is a sequence of flashes of the pushbutton light after it quits. Codes should be deciphered in the manual or list here and someone should have them.

Ernie
 
I just went out and checked again. I can see nowhere that a light would be flashing. Perhaps this wasn't a feature of a genset in 1999. (our coach is a "2000" but the stickers mention manufacture in September 1999).

A little more info: I just tried it again, from back where it sits and up at the instrument panel where the second start rocker switch is. From both locations the generator starts right up but stalls within 5 seconds. The rocker switch in the dash has an indicator light to tell you it is on but that goes out when it stalls. And it does not flash.
Any ideas?
 
The most common complaint is that the engine starts but will not keep
running when the START switch is released. This happens because the control board will not allow the engine to
continue running if the generator is not producing voltage or if the oil pressure signal is not present
 
Well, I have plenty of oil in the sump and I have never experienced an oil pressure problem, not that it couldn't be that, the unit is almost 20 years old. But it does generate power. I have had electric heaters kick in when it tries to run, and I can hear the relays snapping in the control panel. It does generate power in the short time it is running. At first I thought it was bad gas gumming up the carb. But today it started immediately but died within 5 seconds. I do believe it is electrically related. I just don't know where to look. I have nothing that flashes an error code.
 
From the dash (or the generator if it has an "I'm running" light. Tap the stop button  I'll need to fire up another computer for more info or you can google

Onan 5500 operating manual. and save the result to your hard drive (Recommended).
 
Thanks John
I did print out the owner's manual a long time before we started our trip. It doesn't mention anything about indicator lights, flashing or otherwise.
 
You say it has oil and voltage, but still shuts off. Unhook the wire that goes to the oil sensor. They do fail once in a while.
 
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