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Author Topic: onan 4000 starting problem  (Read 3098 times)


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onan 4000 starting problem
« on: July 31, 2005, 09:25:07 PM »
Hi all, new to motorhomes and to this forum.

My onan 4000 will start with either the inside or outside switch but will only continue to run if I hold the switch in the "start" position.  As soon as I release the switch, it dies just like I had hit the stop switch.  The oil and fuel levels are full.

I had it running for about an hour, shut it down for maybe an hour then this problem occured when I tried to restart it.

There is a soliniod or switch at the bottom of the carb bowl.  I took off it's ground and the gen would not start at all.  All fuses checked out. 

Thanks in advance,

Jim Dick

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Re: onan 4000 starting problem
« Reply #1 on: July 31, 2005, 09:35:17 PM »

Not sure I can answer your question. On your start switch outside is there a red light? If so it may show you a flashing code when it fails. Check your manual and there should be a list of each code and what it means. That might get you started in the right direction. I had a similar failure with mine and it showed an over current condition. I turned off the breaker and let it run for a few minutes and then it ran fine. Mine is a 7.5KW and I don't know if your 4000 has the same switch on the genset.


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John From Detroit

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Re: onan 4000 starting problem
« Reply #2 on: August 01, 2005, 03:36:50 AM »
How old is this generator? And, how many wires on the starter solonoid?

In days of old, when I was bold and all you needed to diagnose a badly running engine was a screwdriver, a bit of chewing gum, some paper,and a spark plug that had been modified a bit  (IE my 1977 Hornet) there was a part in the ignition circuit called a ballast resistor

If this went bad... It caused EXACTLY the symptoms you cite

Newer,electronic, ignition systems do not have that part

By the way...Re; said '77 Hornet... It chewed up 2 valves once (300 miles B-4 End of warranty) I saw two different mechinics hook up many hundreds of dollars worth of engine analyzer scopes to it (These things ran 1500 to 2500 back then) and both told me "Blown head gasket between cylinders 3 and 4" (or some such,, not sure which cylinders)

The dealer's tech then got out a spark plug,where the insulator and "Guts" had been, well, gutted, and an air chuch brazed in in place fo the spark elements.  Hooked up the air hose and on one of those cylinders blew the top off the air cleaner.

Said "Nope, burned intake valves"

And when he pulled the head and looked... Guess what he found... Yup, valves, 2 of them

Thousand dollar plus device out gunned by a about a dollar's worth of scrap part

Back to ballast resistors... When you are holding the switch in START, this  part is bypassed to give a hotter spark, however if you run it like this you will burn up the points (Traditional breaker point ignition systems) so when you release the start switch it returns the part to"Service" and if it's not working, shuts down the engine

I have seen a bad ballast resistor exactly once, in a class "B" MH, the owner had purchased it used,  there was a spare in the glove box so I'm guessing it was not the first time for that ride
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  • Posts: 4
Re: onan 4000 starting problem
« Reply #3 on: August 01, 2005, 01:28:21 PM »
Thanks for the replies guys..

The generator is in a 94 Tioga C.  It has no lights around the switches.  That ballast sounds like a good place to start.  So where is said ballast and will my local motorhome shop have one?


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Re: onan 4000 starting problem
« Reply #4 on: August 01, 2005, 01:38:25 PM »

I have a 93 Pace Arrow with an Onan 7.5 and it will do this occasionally too. Mostly though when it hasn't been run for a few weeks. One time I had exactly the same thing happen to me first thing in the spring and ended up taking it to Onan Service tech. They drained the bowl, bled a little gas from the line and put it back together and it ran fine. Their diagnosis was that the line had lost its prime and would not pump gas through except when start switch was held down.
Make sure your AC or other heavy load is turned off before you attempt to start the generator, often this will put too much on it before it starts to run smoothly.



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Re: onan 4000 starting problem
« Reply #5 on: August 08, 2005, 07:48:37 AM »
Turns out it was the voltage regulator that had failed.  I plugged in a new one from these guys:  http://www.partsfortechs.com/voltregulators.htm

Old 4000 fired right up and ran great all weekend after a little carb adjustment.

Thanks for the help ya'll.  I'm sure I will be back for more input.