Another Onan that won't stay running.

CapnDirk · September 24, 2017, 08:41 PM

Low on oil, fixed. Plugs fairly black but also found them gaped to .035 (spec is .025), fixed. No fuel pump but manually filled float bowl through vent. Will run with starter engaged. Jumped battery positive to coil and it runs fine and continuously.

On my BGE I fixed this by cleaning the slip rings since the AC has to generate the DC after start. This however is a different setup, and not sure how to proceed to find where the 12V is not happening after start.

Any help appreciated. Medel Onan 6.5 NH-3CR/14004P

CapnDirk · September 27, 2017, 03:58 PM

Thanks Ralph for the link. It seems though that it is for newer models with a control board where this one has relays in the box with the solenoid. I should though still be able to follow the flow and maybe get lucky.

When running, I do see 120V on the circuit breakers.

legomybago · September 27, 2017, 04:27 PM

Either a broken wire, or one of your relays ainta workin. We just had the exact issue with a newer model 4000, it turned out to be mice damage on top to the unit, they ate some wires...

CapnDirk · September 27, 2017, 05:14 PM

Thanks Lego. That was my thought to.

I found that the wire to the oil pressure switch has been cut. However, I'm getting mixed info (different model functions) on the switch. Some were closed with no oil pressure, and some were open so it's hard to test it not knowing its normal state.

My first assumption would be normally open on this model and when oil pressure builds it sends a ground signal to the relay to trigger the relay coil closing the circuit.

legomybago · September 27, 2017, 06:40 PM

I believe the relay closes too in order to complete the run circuit. You need to look at some schematics of your model. You could jump the oil pressure switch wires and fool the relay?

Rickf1985 · September 27, 2017, 07:18 PM

Just check your oil pressure switch with it not running and see if it is grounded or open and that will tell you which way to go. I would just hook the wire back up, or did you and still no go?

DaveVA78Chieftain · September 27, 2017, 08:14 PM

Model Onan 6.5 NH-3CR/14004P
Thats Spec P

The Onan Service manual is 900-0337. Description of operation and schematic is on page 35 (pdf age 37) "Operation and Description BFA, BGA, and NH (Spec K - P)"

Oil pressure switch closes when oil pressure builds up. If the oil pressure switch is disconnected, then the K3 run relay cannot be not energized to supply B+ to the ignition and fuel pump. In this implementation, the charging voltage via CR1 charges the battery as well as supplies the run voltage to the ignition and fuel pump.

Onan Parts manual is 940-0222.

Both manuals are in the members area.

CapnDirk · September 28, 2017, 12:20 AM

Thank you all. I just a short time ago found the schematic and could see that the relay would not close without a ground signal from the pressure switch. I'll jumper that line tomorrow to see if it will stay running and if so see if I get a ground signal from the pressure switch.

Odd that someone would cut the wire. Assuming a faulty switch the wire to the relay would have to be grounded for the relay to work. But then, how many odd things have we seen done by PO's.W%

Thanks for the part numbers and direction Dave. I'm going to give myself a spanking on this one for not looking in the members area sooner.

Will update this with what happens, it's a pretty simple setup.

CapnDirk · October 02, 2017, 11:09 PM

To trouble shoot I put my 12 volt ice pick light on the battery positive and had it ready to check ground from the oil pressure sending unit when the genset was running (keep in mind the wire from it to the relay had been cut inside the control box). I stripped back the wire on the end going to the relay and jumpered it to ground. The genset started immediately and probing the wire to the sending unit showed ground. Hitting the stop button shut of the light in the probe in a moment when oil pressure faded.

To sum up, the genset seams to have been deliberately disabled by

1. Cut wire to sending unit.
2. 5 amp fuses were missing the fuses and caps.
3. No fuel pump (if anyone knows what to use in an aftermarket, would like to hear it).

Lastly. There are two 30 amp circuit breakers on this. I remember a "Dave" post that was very descriptive of the larger gensets having two 110 output circuits. The cable coming out of the genset is only three wires. Copper ground, and a 12 gauge black and white. How does one wire the two output circuits on only those two wires? Or is the black and white 110 each?

Thanks.

Rickf1985 · October 03, 2017, 08:59 AM

Sounds like someone sabotaged that unit. The power out is only 110 volt and not 220 so only 2 wires and a ground. The wires are black=hot, white=neutral and copper=ground.

CapnDirk · October 03, 2017, 10:05 AM

Thanks Rick. Sabotage was why I was thinking to, but why disable a perfectly good genset?

Refering back to Daves post on generators, the 4K had one circuit of 20 amps, the 5K a large and small of 20 amp and 15 amp I think (working from memory). And the 6.5K and up had two circuits with equal output. That's how the 6.5K could run both AC as they were separate circuits. This would also account for the genset being able to output 240V as two 120v legs.

Will dig into the wiring schematic, and installation manual for more info.

Warren · October 03, 2017, 12:34 PM

Electric fuel pump that was on my Onan from a previous owner, and it works fine.

Listing of fuel pumps, I would go with a low pressure, not sure what the carb needle / seat can handle.
This listing is from Aircraft Spruce a good supplier to work with. I could not find them on the FAcet web site.

http://www.aircraftspruce.com/catalog/eppages/facetpumps.php

Or rebuild the fuel pump, some old school carb rebuild shops like this one, Carb Refactory, Richmond, CA.
https://www.carbkits.com/
They rebuilt my Onan carb, which had sat for years, I could not get it to idle, it was loaded with el crapo crud,
and they cleaned, repaired stripped threaded holes, etc. Wow, what a huge difference.
(72 D18)

Rickf1985 · October 03, 2017, 03:12 PM

Quote from: CapnDirk on October 03, 2017, 10:05 AM
Thanks Rick. Sabotage was why I was thinking to, but why disable a perfectly good genset?

Refering back to Daves post on generators, the 4K had one circuit of 20 amps, the 5K a large and small of 20 amp and 15 amp I think (working from memory). And the 6.5K and up had two circuits with equal output. That's how the 6.5K could run both AC as they were separate circuits. This would also account for the genset being able to output 240V as two 120v legs.

Will dig into the wiring schematic, and installation manual for more info.

My guess on the sabotage would be that someone was buying it and cut the wire so it would not run to get a better price on it. Possible the seller said no so there it sat with the cut wire. I have seen that type of thing on cars many times.

CapnDirk · October 03, 2017, 03:29 PM

Oh yea. Used to work for wreaking yard (DB programmer) and shopped many auto salvage auctions. At the auctions they would steal the keys to the car so nobody could tell if it would run and the price dropped for the person that had the keys in their pocket at the auction.

Waren: From my research it looks like the Onans take about 3-5 PSI depending on model.

RCND · August 24, 2018, 11:15 PM

Howdy All:

I know this is an old post. The OP said the generator would run when the starter is engaged. He also said it would run when he ran a wire from battery. to the coil.

This means that the ignition voltage drop circuit (ballast resistor) is not supplying power to the coil. I do not have a diagram for this genset, but would assume that the run circuit is part of the control board. It may be as simple as a bad relay or a burnt resistor on the control board.

Take care.
Robert