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Old 06-15-2014, 12:00 PM   #1
james schaechter
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Default Onan Diesel Generator gurus?

We have a 7.5 Onan diesel genset inour 93 Monaco. This year, it has been finicky. It always starts right up and makes electricity. It randomly runs rough and will almost die, then recover and run fine, but it seems to cycle like that randomly. Sometimes it will run fine for a minute or an hour before it does it. At first, I thought it was the AC unit, but it is affected by smaller draw units also.

Air filter and fuel filter are good, the oil and coolant level is good.

I have my suspicions about the governor but am not sure even where it is or how to check it. Fuel pump or?

The genset is an ONAN 7.5 model 7.5DKDFJ SERIAL A943117785 SPEC 660440
Any ideas? Thanks, Jim
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Old 06-16-2014, 02:50 AM   #2
Don Higgins
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Default Re: Onan Diesel Generator gurus?

I tell everyone with an Onan diesel generator that they *may* need to run a second 12 volt wire to the fuel pump because there are so many board failures on the fuel pump circuit.

Mine would do that and eventually quit. Ran a second power wire attached to a switch and it works perfectly. Much cheaper than $800 for a circuit board and works forever.
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Old 06-16-2014, 07:52 PM   #3
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Default Re: Onan Diesel Generator gurus?

Jim a DKDF is not one like I generally see.....but I do recall the DKD series as being an open style unit....a 3 cylinder diesel.....with a radiator out front.....

The only reason a diesel runs rough is a fuel problem....or air being drawn into the fuel system.....

I would go over the entire fuel system.....lines....filter.....etc.

After that it could be an injector or pump problem...

I will look that model up for you and see what it looks like......tomorrow....
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Old 06-16-2014, 11:07 PM   #4
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Default Re: Onan Diesel Generator gurus?

Thanks Rich. I turned it on today and it ran for about 30 minutes before acting up. It sounded like it had a lean roll to it before it really starts to die. It never quits, but almost. I did hit it with a temp gun, and it was 189 degrees.
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Old 06-17-2014, 06:22 AM   #5
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Default Re: Onan Diesel Generator gurus?

James,
I have a DKDFJ - 8.0 in my old Eagle and they are the most reliable Gennys I've seen.
If your stumbling begins to get worse it's most likely the Fuel Pump beginning to fail. Easy fix for less than a 100 bucs for a new one. Its a Facet 6 psi- I have the part number if you need it.
In order to check the Governer and engine speed (and it should be 1800 RPM Constant)
Go to Lowes and buy a Kilowatt Meter ( about $25).
I keep mine plugged into the bathroom outlet, it reads constant voltage and Hertz.
The numbers should be 120 volts/ 60 Hertz constant under load.
I have all of the manuals and quite a few part numbers if you need them.
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Old 06-17-2014, 06:52 AM   #6
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Default Re: Onan Diesel Generator gurus?

Jim if it has the original fuel pump on it there may be a fuel filter built into that pump.

I have seen those pumps with a twist off lower section and there is a filter in there that never gets changed. They get plugged. Just a possibility...

Kubota engines and yes very reliable.... they just need a good clean steady fuel supply...
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Old 06-17-2014, 08:11 AM   #7
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Default Re: Onan Diesel Generator gurus?

Here is your Fuel Pump and How to maintain it.
>http://www.pbase.com/mainecruising/f..._filter&page=1
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Old 06-17-2014, 08:17 AM   #8
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Default Re: Onan Diesel Generator gurus?

That's the filter I was talking about ....good post Chuck....

It gets ignored as most people don't know it's in there....
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Old 06-17-2014, 08:25 AM   #9
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Default Re: Onan Diesel Generator gurus?

Rich,
Don't mean to steel your Thunder on here, I completely rebuilt mine a few years ago after it had 14,000 plus hours.
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Old 06-18-2014, 05:26 AM   #10
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Default Re: Onan Diesel Generator gurus?

Thanks guys! I will get some parts and try it out. I will let you know how it goes. Jim
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