Onan 7.5 Diesel Gen won't run

[C-PHartley]

I've got a 95 Newmar with a 7.5 KW diesel generator (7.5 DKDFJ) model that starts but then quits. I can hold the throttle open and it will run, but the governor/solenoid is pulling the throttle closed. It's got plenty of oil and coolant. Does any one have any ideas. I suspect the oil pressure switch, but I am uncertain how to check it out.

Thanks,

--Chuck

[Martind4]

On ours, when the gennie fails to start, a green light on the starter switch flashes in a sequence that indicate the failure. Our owners manual has the codes listed for troubleshooting.

Yours might be the same.

[Mike Canter]

Maybe the oil pressure safety switch is trying to tell you there is a problem. Just because it has oil doesn't mean it has oil pressure. Every time an oil warning light comes on in a car does that mean the light is bad. Martind4 has the correct procedure on reading the codes. i would highly recommend not bypassing any safety devices until you have read the trouble codes.

When was the last time the fuel filter was changed.
Is the fuel tank more than a quarter full because they will not run if it is below a quarter tank.

[C-PHartley]

This model has no lights that I can fnd and no flashing trouble indicators. I am not trying to bypass the switch, I want to see what voltage should be present at the various connections. Then I can back track to a possible source of the problem. I worked on this some this morning and found a broken switch connection on the middle connector of the start/prime switch. I will replace this switch Monday and let you know what happens. Thanks for your suggestions.

[wingman8]

Quote:

Originally Posted by C-PHartley I've got a 95 Newmar with a 7.5 KW diesel generator (7.5 DKDFJ) model that starts but then quits. I can hold the throttle open and it will run, but the governor/solenoid is pulling the throttle closed. It's got plenty of oil and coolant. Does any one have any ideas. I suspect the oil pressure switch, but I am uncertain how to check it out. Thanks, --Chuck

Don't laugh at this but when I had my Toyhauler the Gen did the same thing and boy was I feeling stupid when the RV service center found a mud dobber on the throttle so it could not operate. Removed the mud and took off just fine would be nice to have simple fix all the time

[C-PHartley]

I've looked for bugs, nests, etc. but I don't see anything that could cause this. It feels like a definite pull on the solenoid that is closing the throttle.

[gwtilley]

IF it is a slide out unit, check for kinked lines when you slide it back into position. Had that happen. Unit would start and run a bit the die.

[C-PHartley]

Thanks GW,

I do see a kink in the conduit running from the generator back to who knows where. It looks as though it kinks when the gen is slid back into position. I think I will pull that apart tomorrow and see if that could be the problem.

Thanks for your comment,

--Chuck

[C-PHartley]

An update for my diesel Generator problem. I checked both the low oil pressure switch and the High coolant temperature switch and both check out fine. Opening and closing at the correct times. It appears that there is a pull relay and a hold relay that will hold the fuel cutoff solenoid open when energized. The Pull relay works as it should when activating the start switch. The Hold relay does not seem to be latching at this time. The generator is making 240 volts AC at the output when I hold the fuel cutoff solenoid to the run position manually. I will switch this hold relay out tomorrow and see if that is the problem.

[C-PHartley]

Well, I found the problem to be a failure in the circuit board that controls the operation of the generator. After running both A/C units for 5 days while we traveled to Texas and back, I feel pretty certain that the board replacement fixed the problem. I also ran a crock-pot and microwave oven intermittently with no problems. I hope this helps someone else with a similar problem. The board can be found on the internet for approximately half of the price of what Onan charges you.

[KIX]

Thanks for the update info C-PHartley.
Glad you got it fixed