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Old 03-31-2014, 07:38 PM   #1
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Onan trouble

Hi folks,
Having trouble with my Onan 6.5 emerald gen set. Last trip I had the following scenario play out.

Outbound trip, gen ran great, right up to the moment we made the turn into the site wherein it cut off. The restart produced a backfire, then the unit cranked and ran fine for the next ten minutes until I shut it down.

Return trip, on the way home it ran fine for 2 hours before shutting down.

What I presently have:
Gen oil checked fine.
Is getting fuel.
Will start and run as long as I'm holding the switch in the START position, and as soon as I release it to the RUN position the gen dies.

It will start each and every time, but dies as soon as I release it to the run position.

I am wondering if the start sequence has an electric "boost" pump to prime for run, and when I release to the run position it's defaulting to a mechanical pump that has failed?

I have no literature on the genset, and I'm having trouble getting any helpful info from my local RV shop.

Opinions and ideas. Anyone had this issue?

Tim in NC
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Old 03-31-2014, 08:24 PM   #2
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I had a no run problem too. It turned out to be a ground wire between the generator case and the MH chassis. It had vibrated loose.
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Old 03-31-2014, 09:22 PM   #3
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Engine starts but stops when start switch is released is usually a control circuit problem.
Low oil pressure switch not opening
Due to: Low oil level or low pressure, defective pressure switch

No output voltage from generator or a defective control board. (Ac output is required for the genset to continue to run).

Backfire may be a fuel problem, dirty filter. Gasoline model does have electric fuel pump.
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Old 03-31-2014, 09:55 PM   #4
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Thanks for the hints, clues, facts folks. That should give me a path to begin trouble shooting. I appreciate it!

Tim
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Old 03-31-2014, 11:36 PM   #5
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Mine did same thing. I would bet its your fuel pump. Onan had a rash of them. Mine was brand new and did the exact same thing as yours. Replaced fuel pump and no more problem. I keep one on hand in case it goes bad again. They will run fine for 10 minutes or a couple hours and then done, gen dies. They may or may not start after a few minutes and then run for an hour and die. No rhyme or reason.
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Old 04-01-2014, 04:47 AM   #6
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Please post your exact model # - many things are different amongst the various models and Spec series.

There is only 1 electric fuel pump, and if the genset is running when holding start, the fuel pump is not your problem.

If it's an older BGE or NHM series unit there are generally only 2 common reasons they will stop when the start button is released - brushes worn out (or slip rings dirty), or Low oil pressure switch. Once you post your model # I can help you much better. These units are very basic and easy to troubleshoot/repair if you have a volt/ohm meter and are comfortable doing some troubleshooting.
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Old 04-01-2014, 07:19 AM   #7
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I'm not familiar with the Emerald but I have all the shop manuals for BGM and NHM Onan gen sets.
If anybody knows if these apply to his unit I have them in PDF FILES
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Old 04-01-2014, 07:50 AM   #8
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What code is it throwing 6.5 diesels are know for leaky antifreeze tanks it's not over heating.
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Old 04-01-2014, 03:10 PM   #9
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Model #: 6.5 NHEFA26100E
Appreciate it.
Oil level checks perfect, but was first thing I checked when it stalled the first time.
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Old 04-01-2014, 07:28 PM   #10
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Originally Posted by RamblinOn View Post
94-Newmar
Model #: 6.5 NHEFA26100E
Appreciate it.
Oil level checks perfect, but was first thing I checked when it stalled the first time.
Private message me your email address and I'll send you the service manual for the NHE series. Usual suspects that cause these units to shut down when you release the START button are any opens or shorts across the quadrature (stator), or lack of excitation namely the brushes.

If the problem is brushes: When you are pushing START you are using the coach's 12v to power to excite the unit, when you release it a process takes place through the brushes which create the DC voltage necessary to excite the quad, thus keeping the unit running. Using the manual, I would skip right to checking the brushes... they're very easy to access and they're the most common item to fail - especially with age and hours on them. It could even be something as simple as cleaning the slip rings (what the brushes ride on the rotor). They do get dirty and corroded over time and in many cases a simple cleaning with some emory cloth solves the problem.

If the problem is in the stator: Using the manual, it will guide you on doing the ohms checks across the quad - you do not have to remove the unit to perform either test, just unplugging 3 connectors.
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Old 04-01-2014, 08:54 PM   #11
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while holding down the start switch. the 12V that the generator needs to run is supplied by the battery. When you release the switch, the 12 volts is supplied by the generator. You probably have a bad board. It is not switching over to the running 12 volts. Most large dealers have a board tester. All Onan factory stores have a board tester.
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Old 04-01-2014, 08:57 PM   #12
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Originally Posted by ga traveler View Post
while holding down the start switch. the 12V that the generator needs to run is supplied by the battery. When you release the switch, the 12 volts is supplied by the generator. You probably have a bad board. It is not switching over to the running 12 volts. Most large dealers have a board tester. All Onan factory stores have a board tester.
the NHE series does not have a control board.
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Old 04-29-2014, 04:33 PM   #13
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I just fixed my HR with my Onan doing the same thing . What I did was plug a DVOM into an 110 outlet and set it to hertz , cranked the engine over and had the wife monitor the HZ reading. you should see 60-62 hz . If you do not see that reading it will not run when you release the start button. On mine the return spring had popped off the carb linkage causing my HZ to go out of limits. I know this sounds crazy but I read all the online diagnostics for the Onan with these symptoms and the first test fixed mine. Hope this helps, Mike
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Old 04-30-2014, 06:02 AM   #14
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I just fixed my HR with my Onan doing the same thing . What I did was plug a DVOM into an 110 outlet and set it to hertz , cranked the engine over and had the wife monitor the HZ reading. you should see 60-62 hz . If you do not see that reading it will not run when you release the start button. On mine the return spring had popped off the carb linkage causing my HZ to go out of limits. I know this sounds crazy but I read all the online diagnostics for the Onan with these symptoms and the first test fixed mine. Hope this helps, Mike
Impossible. There is no way to read hertz from the genset at cranking/turnover speed. First, the transfer switch wouldn't be closed/energized and 2nd, even if it were, a cranking speed of 500 rpm would never show 60 HZ. Perhaps you meant that your unit would start and stay running, transfer switch energized, then you could read hertz at the outlets. In the case of the original poster here, the unit will not stay running after releasing the start/stop switch - a completely different problem than just setting the hertz, which on this model, is based purely on engine RPM. Additionally, the NHE series will continue running at any RPM and hertz as there is no logic in this unit to prevent it running under voltage or under speed unlike the newer PC controlled units, such as the HGJAB series units, which you probably have.
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