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Old 07-23-2017, 12:09 PM   #1
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ONAN 7.5kW Generator No Start

Hello boaters! I need some help diagnosing my no start issue with my Onan MDJE 2 cylinder diesel generator. I recently had it running flawlessly and then trouble hit. First the fuel shutoff solenoid that closes the injection pump armature wouldn't activate with voltage put to it. So, luckily I had a spare shutoff solenoid aboard and replaced it immediately. The generator started and ran as it should. Then I came back to the boat and the stop solenoid wasn't activating. I checked for voltage at the High Water Temp Switch and had none. I traced the wire back into the control box on top of the generator to a terminal on a buss bar. There are multiple connections after this point that I have questions with.
I have both the Onan Service and Training Manuals, but the wiring diagrams are a bit difficult to read. I'm wondering what kind of "over-current" protection the circuit offers. If maybe voltage from the control box to the HWTS may have grounded out and tripped a breaker or fuse. There are two circuit breakers on the generator control box that have power on both sides of contacts. I'm in desperate need of some help! I've sunk a ton of money into rebuilding the injection pump and various other things and don't want to condemn the generator if I can help it. Hopefully, I left enough information for someone to offer some insight. Any help would be greatly appreciated!
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Old 07-23-2017, 01:18 PM   #2
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Greetings,
Welcome aboard.
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Old 07-23-2017, 02:41 PM   #3
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Admittedly I have no Onan experience, I have Westerbeke, but, I remember that the solenoid on my genny has to be adjusted so that it does not remain activated full time, by having the proper inplay in the linkage. The solenoid will burn out quickly if left in the energized mode. if that did happen, I could believe that the power supplying wire could have burned too. You should be able to manually hold the fuel shut off open to check it.
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Old 07-23-2017, 04:18 PM   #4
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Quote:
Originally Posted by Capn Craig View Post
Admittedly I have no Onan experience, I have Westerbeke, but, I remember that the solenoid on my genny has to be adjusted so that it does not remain activated full time, by having the proper inplay in the linkage. The solenoid will burn out quickly if left in the energized mode. if that did happen, I could believe that the power supplying wire could have burned too. You should be able to manually hold the fuel shut off open to check it.
Thanks Capn Craig! I know the shutoff solenoid operates as intended when I jumper 12V to the terminal. It's getting it to do so on its own, haha! From what I've discovered in the manuals and online, the shutoff solenoid receives power immediately upon cranking thru a "pickup" coil and then when rpm is achieved the voltage supply transfers to a "holding/hold-up" coil to HOLD the plunger UP. I replaced the wire from the control box to the HWTS (High Water Temp Switch) and the wire from HTWS to shutoff solenoid. There is NO voltage at the HWTS when cranking. Nor running, when I manually hold the plunger to the shutoff solenoid in the UP position.
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Old 07-23-2017, 04:20 PM   #5
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Not much to add but to go through the schematic and go point to point with a volt meter. Not a terribly complicated control system, but there are some relays, etc, that can fail.

If schematic is hard to read, get the drawing number off the bottom right and google it, might find something more legible.
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Old 07-28-2017, 05:29 AM   #6
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Had the same, among many, problem with mine. I'm not at the boat now so I don't have the drawing. But there is a relay at the start of the safety shutdown circuit, check voltage from it's contacts. Mine were burnt and caused all kind of headaches till I changed it. Replaced it with a modern sealed relay.
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Old 07-28-2017, 01:56 PM   #7
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I don't know if this would help you with your specific problem, but I used to continually have problems like this with my MDJE generator off and on. Finally I replaced the entire YD regulator board with a Flight Systems aftermarket replacement. Best $200 I ever spent. It's mostly sealed components and designed to survive in the marine environment. Other than replacing the raw water gear driven pump with a Jabsco belt driven pedestal pump, no problems since and that was 15 years ago.

Time flies when you're having fun!

https://www.flightsystems.com/standb...-controls.html
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Old 07-28-2017, 02:41 PM   #8
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What does "YD" in "YD regulator board" stand for? I have same genny with the same no shutdown issue, trying to gather info before digging in.
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Old 07-28-2017, 02:56 PM   #9
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The "DJ" series of Onan generators used the "YD" generator end, which was a tapered shaft unit.

The regulator for those was a PC board with discrete components. As a FYI for allot of years I used to fix those boards and sell them on Ebay. I quit when demand dropped off.

Regarding the no-start ssue. If the plunger on the solenoid pulls in, allowing the fuel to go to full throttle the DJ generator will start if nothing else is wrong. Troubleshooting would be to first make sure that is happening.

This is an easy test. If you push the glow plug switch up (or down or in) as the case may be you should see and hear the solenoid operate. If it does not, this is a simple series circuit. Yes it goes through a relay or two, but in the end it is just a series circuit. Start at the selonoid and look for 12 volts. If it is not there, work backwards until you find the open.

Best of luck!
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Old 07-28-2017, 03:01 PM   #10
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Yep, the printed circuit board is an AC voltage regulator and that is all. Start/stop is unrelated to the board.
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Old 07-28-2017, 03:21 PM   #11
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Correct, the relay I'm referring to is in the compartment under the compartment the PCB is in. Totally different issue. But like sanders said, it's a simple series circuit. Start at the solenoid and work your way back. There is only three components in that circuit; HT, Over speed, and oil pressure.
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Old 07-28-2017, 03:22 PM   #12
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I believe that's Flight Systems designation for the board. But if you get the Onan part number for your generator, which will be like six numbers, you can pick out the correct replacement for your generator.

Once again, the component failure you're experiencing may not be on this board. Could be something else. Needs troubleshooting before you buy new components.
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