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Old 02-20-2014, 09:14 PM   #1
Join Date: Oct 2013
Location: Newbury Park, Ca.
Posts: 48
Onan gen blowing fuel pump - auto choke fuse

Hi All
My Onan gen just started blowing the Fuel Pump/ Auto Choke fuse.

Model is Onan BGE series, 4KV. 1996 vintage. Was working perfectly last time I used it ( 3 weeks ago) Now it cranks but wont start. I Noted the 10 Amp Fuel Pump/ Auto Choke fuse was blown. I replaced the fuse and that one blew too. Any ideas what I should check would be very appreciated!
Thank you again.

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Old 02-21-2014, 03:09 AM   #2
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Join Date: Nov 2009
Posts: 2,043
Can you please post the exact Model# ?

How quickly is it blowing the fuse? Immediately upon hitting the START button?

The choke assembly on these units units 12VDC to operate the choke pulloff after it has started and roughly 25V AC (of it's own AC power being generated) to heat the bi-metal coil inside the choke housing. If the fuse is blowing immediately upon cranking, never starting, then I doubt the trouble is in the choke circuit.

The fuel pump is initially energized at the same time the start solenoid is energized using the very same house or chassis 12VDC battery power as the starter and starter solenoid. Once the unit starts the fuel pump relay is de-activated the fuel pump gets its 12VDC directly from the 12V being produced by the generator itself. This is why it's important to know when the fuse is being blown.

Unplug the fuel pump connector, replace the fuel pump fuse and attempt cranking it over again (without the fuel pump being connected). If the fuse does not blow, then we can direct attention to the fuel pump OR somewhere within the fuel pump control circuit. I have wiring diagrams to post for you, but need your exact model #.

94-Newmar Kountry Star 40-KSDP
Spartan/Cummins 8.3C-300HP/Allison 3060 WTEC-II/25yr RV Tech RVIA Certified/Onan-Cummins Certified
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Old 02-21-2014, 10:06 PM   #3
Join Date: Oct 2013
Location: Newbury Park, Ca.
Posts: 48
Hello Newmar
Thank you for your reply. The fuse was blowing as soon as it was installed into the fuse holder.
Using your advise (and several fuses) I was able to find the problem.

I disconnected the wire to the fuel pump and the fuse still blew.
I traced the wire from the fuse back to what appears to be some kind of relay behind the choke.
I disconnected the wire from the 'relay' and the fuse did not blow. The output of the relay had several wires. One goes to the fuel pump and one went to the choke and I could not find where the other went.
I disconnected the wire to the choke and reinstalled the wire from the fuse to the input of the relay. The fuse did not blow. I figured the choke was the problem and was getting ready to replace it.
For kicks. I reinstalled the wire to the choke and the fuse did NOT blow. So now all the wires were connected and no blowing fuse. Strange. I figured the problem was intermittent.
I started the genny and it fired right up. I let it run for a bit then I grabbed the wire from the fuse to the relay and gave it a shake. Sparks began to fly everywhere.
The problem was the wire was not properly shielded/covered and it has been rubbing on the chassis. The wire insulation finally wore away and the 12V was shorted to ground. When I was fiddling around disconnecting the wires I must have moved it so it was no longer grounded. Problem Solved. I rewraped the wire and put it in a plastic wire loom to protect it.

If the offer still stands I would really like to have a schematic for future problems. My model is 4BGEFA26100M.
my email is bicyclejames@yahoo.com

Thank you again for you help.
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Old 02-22-2014, 05:45 AM   #4
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Posts: 2,043
Ok glad you got it going.. now to the service manual...

You have a Spec M Gasoline unit which is a California "ULGE" emissions compliant engine. This particular Spec build from Cummins/Onan is pretty much the same as Spec A-L with some exceptions such as the carburetor will have no mixture adjustments and the ignition timing is mechanically locked at 12 BTDC (Before top dead center), plus a few minor differences. This mostly is only important to you should you ever want to rebuild/replace the carburetor. Should you rebuild it then you'll need the proper Spec rebuilt kit; should you replace it they will rape you on price since it's a ULGE compliant carb. However, you do NOT need the Spec M carb. The other spec carbs will work on your unit - the only difference being fuel mixture adjustments - all for 2/3 the price of the ULGE compliant carb! :-)

With all that being said there IS a service manual supplement that would would be attached at the back of the service manual I'm going to send you via email. The addendum is only about 5 pages and specifically covers Spec M and forward with an emphasis on the emissions changes.

Unfortunately, I have never worked on or seen a Spec M unit (California emissions) nor do I have the supplemental manual. I am able to see from Cummins quickserve that the wiring is identical with an exception near the choke pull off assembly.

The supplemental for Spec M is 965-1060 which I do not have.

I have sent you via email the service manual:
965-0528 Covering BGE Spec F-K

Glad you got it going, good luck in your future endeavors!

EDIT: Aha! The service manual I had and sent to you does indeed have the Supplement 965-1060 already inserted into the proper places!
94-Newmar Kountry Star 40-KSDP
Spartan/Cummins 8.3C-300HP/Allison 3060 WTEC-II/25yr RV Tech RVIA Certified/Onan-Cummins Certified
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fuse, onan, fuel

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