Author Topic: Onan generator 7500  (Read 3257 times)

Randy Keaveny

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Onan generator 7500
« on: April 20, 2024, 10:20:50 PM »
Hi all. Back at  the motorhome working on genset.  Showing a code of 3 flashes. But will not start. It fires.  Like it wants to.  But will not grab.      Plenty of fuel.  Is there a shutoff accessible.      Or way to get to injectors.     The rapid flashes for pre heat  glow plugs is working.   And I can hold button down to hear it prime.   Any help ???
1998 Patriot

David T. Richelderfer

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Re: Onan generator 7500
« Reply #1 on: April 21, 2024, 10:29:20 AM »
Our generator is a different model but I believe the fault codes are very similar for all their models.  I found the following.  It indicates you should be able to get a second-level fault code which would more precisely define the generator's issue.

"• Three blinks indicate a service fault. Press Stop once to cause the two-digit, second-level fault code to blink. (Pressing Stop again will stop the blinking.)The two-digit code consists of 1, 2, 3, 4 or 5 blinks, a brief pause, and then 1 to 9 blinks. The first set of blinks represents the tens digit and the second set of blinks represent the units digit of the fault code number. For example, Fault Code No. 36 appears as: blink-blink-blink—pause—blink-blink-blink-blink-blink-blink— long pause—repeat"
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Randy Keaveny

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Re: Onan generator 7500
« Reply #2 on: April 21, 2024, 04:08:49 PM »
Thx.  I got it to run.  But does not sound right.  As it surges.   Starts up.   Runs.  Takes the load. Then ki da struggles to keep running.  No codes now.  But. Something is still not right.  Internal fuel filter that I cannot see ??   Is what I am wondering now.
1998 Patriot

Eric Maclean

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Re: Onan generator 7500
« Reply #3 on: April 21, 2024, 09:06:56 PM »
Randy
How long has it been since you saw it run properly?

It may still be a fuel issue .you may still have air or a restriction.
The first thing I would do is turn off the breaker/s on the gen set and then let it run for an hour or more to warm it up well and see if it doesn't smooth out then turn the breaker back on and load it with about a 2k watt load to see how it responds.

Eric
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2009 Chevy HHR
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Randy Keaveny

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Re: Onan generator 7500
« Reply #4 on: April 22, 2024, 04:07:02 PM »
Thanks.  Yes. I thinki will try that.  Let it run its little heart out.  Wondering if I ran somebody fuel thru it when I replaced fuel filter last winter ??   But. Really have to crank on it to get it to start.  Then she purrs.   Takes load.  Runs for about a minute or two.   Starts surging. 
Hmmmm
1998 Patriot

Richard Davis

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Re: Onan generator 7500
« Reply #5 on: April 22, 2024, 10:59:17 PM »
It really seems like you are getting air in your fuel.  I would carefully check the supply and return fuel lines for any issues. The only way I found the issues in my fuel lines on my QD8000 was to disconnect them, pressurize them with air and spray the lines with soapy water.  Boy, did I create bubbles, the supply line was sucking air, but not showing leaks.  Replacing both lines made it run much better. 
Good luck.  Richard
p.s. If you have not replaced the fuel filter, do that also.
06 Monterey Ventura IV, C9 400 hp

Eric Maclean

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Re: Onan generator 7500
« Reply #6 on: April 22, 2024, 11:38:18 PM »
Randy
I believe Richard is right  on .
To verify you can do as Richard suggested to check the supply line.
You can also use the fuel can trick to eliminate the fuel supply line altogether to see if that is where your problem is.

Eric
1997 Patriot Yorktown
3126-B
2009 Chevy HHR
Roadmaster falcon tow bar
Demco Air Force one tow brake.

David T. Richelderfer

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Re: Onan generator 7500
« Reply #7 on: April 23, 2024, 02:56:11 AM »
Yes, you could have an air leak allowing air to get sucked into the fuel flow.  How long has it been since you filled the diesel tank?  If a long time, then you could have water or algae in the fuel tank, or got filled with a bad load of fuel, in which case your fuel filter could be plugged... even after you recently changed the filter.  Remember, the generator pulls its fuel from the very bottom of the tank.  Have you driven the coach recently at highway speeds up any hills, and if so, did the engine run properly?
2004 Beaver Marquis Sapphire

I had a dream... then I lived it!