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Old 05-18-2016, 09:27 PM   #1
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Onan 7500 Diesel gen problem

2003 Onan diesel 7500 with 250 total hours. The generator was serviced by Cummins 2 months ago including oil, both filters, and coolant. It was running just fine before and after service and would fully power coach. After running for approx 1 hour only powering one A/C a few days ago, it quit. Will restart and run smoothly for about 45 seconds and quit - about the time it actually picks up a load. If I start it with the breaker in the off position, it runs fine but when I turn the breaker on, generator quits. Oil and coolant levels are right on. Any ideas?
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Old 05-18-2016, 09:50 PM   #2
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Quote:
Originally Posted by MikeandJan View Post
2003 Onan diesel 7500 with 250 total hours. The generator was serviced by Cummins 2 months ago including oil, both filters, and coolant. It was running just fine before and after service and would fully power coach. After running for approx 1 hour only powering one A/C a few days ago, it quit. Will restart and run smoothly for about 45 seconds and quit - about the time it actually picks up a load. If I start it with the breaker in the off position, it runs fine but when I turn the breaker on, generator quits. Oil and coolant levels are right on. Any ideas?
MikeandJan,
Well, the very first thing you need to do is, when that generator quits, the start toggle switch, located on the generator itself, will "blink" in a code. It will blink in a series and, have a pause, then it will blink a second series. It will present something like this:

Blink-Blink-blink...........Blink-blink-blink........ start all over again.

That series of blinks is, 3....pause, 3.

The code is, "33".

You then need to look up, in your Onan Generator manuals (service and owners) to find out what that code represents.

Now, this is an example. It could be any code. So, try and read what that switch is telling you.

Scott
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Old 05-18-2016, 10:31 PM   #3
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If it's a 36, it's fuel. ( plugged gas filter or fuel pump). 33 means coolant temp
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Old 05-18-2016, 10:50 PM   #4
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How much fuel do you have in your main tank?


Low fuel will shut the gen down so you don't run out by accident....


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Old 05-19-2016, 07:42 AM   #5
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Quote:
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If it's a 36, it's fuel. ...
Maybe, maybe not. Good odds it might be but Per may 7.5 QD circa 2006...

Code 36 is "Engine stopped without command by controller"

Corrective Action:
1. Check fuel level. (Note: The genset fuel pickup is probably higher than the vehicle engine pickup.)
2. Prime the engine fuel system by holding the control switch down in its Stop position for at least 1 minute.
3. Check the engine air filter and remove any blockage (Page 16).
4. Check for mechanical damage.
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Old 05-19-2016, 08:00 AM   #6
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Quote:
Originally Posted by MikeandJan View Post
2003 Onan diesel 7500 with 250 total hours. The generator was serviced by Cummins 2 months ago including oil, both filters, and coolant. ...
When you say "both filters" you have 3. Fuel, air and oil. Which 2 were changed?

How old is your coach? 250 hours is not a lot of hours if your coach is over a few years old. While I don't think a 33 code is directly related to lack of running it would be something to look into for the long term health of the generator. The only direct connection might be the fuel filter if it has been in there a long time.
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Old 05-20-2016, 07:17 AM   #7
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99 national trade wind diesel pusher, with propane generator. generator not turning over, slide not working. seems like an electrical problem. any ideas
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Old 05-20-2016, 07:17 AM   #8
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Thanks for the clear explanation of how to get the error code. I was only getting the first digit - 3. Full code is 31, which I believe is engine overspeed. Engine sounds normal to me, in fact it shuts off when the engine bogs down slightly when it picks up the load. Only corrective action I can find in the manual is to take it to authorized Cummins/Onan repair. I'm actually sitting at Alliance in Wildwood but they no longer do generator repairs. Go figure - Cummins is only 30 minutes away but I can't drive there because I'm missing a window that is out for repair until next week. Thanks everyone - I'm amazed how much you guys know about these things.
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Old 05-20-2016, 11:06 AM   #9
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You apparently have a speed governor problem - the engine goes overspeed under load, when the governor tries to open the throttle to maintain the rpms as the load increases. For most of us, that means a visit to a Cummins/Onan shop. You can get an Onan7500 service manual if you want to tackle it yourself, though. I picked up an inexpensive CD version on Ebay.
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Old 05-20-2016, 05:35 PM   #10
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Take a look at the transfer switch box. I had a similar issue and found melted wires in the box.
Fixed the wiring and the generator was fine.

Mike
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Old 05-21-2016, 10:23 AM   #11
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I have a onan 7500 like u.It has 1600 hours run fine last year and sit over the winter and wouldnt start got it started run wide open.Took it to a local guy and shouldnt!He had it a month.Picked it up yesterday and it not fixed now charged me 680.00 for labor and he said that it is governor actuator?Got to pull gen out of camper to fix,He said!!but he sure ant going to do it!! A$$ hole.But that is where iam at!!Ifigured a month he could have it fixed plus iam going to missouri had to pick it up or not go!! and ant no telling what the damn bill would have been!
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Old 06-11-2016, 11:24 AM   #12
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I wanted to followup with everyone who tried to help with my generator problem. The generator was throwing a 31 code - engine overspeed - and the corrective action is to see an authorized Onan dealer. I took it to Register RV in Brooksville, FL, where I already had an appointment to have StoneVos slide toppers installed. In addition to the 31 code, their tech also got a 28 code one time. The corrective action for both is to replace the controller/inverter on the generator - $1,850 for the part and about 4 hours labor. When the tech removed all the covers on the way to the controller, a large part of a magnet was laying there stuck to the frame and small bits of magnet were all over. The cooling fan, rotor, and stator were all damaged and had to be replaced. No one had any idea why the magnet came loose - they are "bonded", i.e., glued in place. Total cost parts and labor came to $3,000. The good news is that the controller/inverter was good and we didn't have to install a new one.

The folks at Register were super and the tech took a lot of time explaining the system to me. The controller senses the generator load requirement and adjusts the power output of the engine by adjusting fuel flow. In my case the generator couldn't produce power so the controller would ask for speed up to the max of 2100 RPM at which time it would shut down the engine. After the repair, they ran it for 5 hours with no problem I also ran it 10 hours all the way back to North Carolina and it performed just fine. Thanks again for your ideas.
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Old 06-11-2016, 11:35 AM   #13
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Thanks for the update !!
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Old 06-12-2016, 10:29 AM   #14
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Very educational,
Thank you for the update.


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