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Old 07-09-2015, 05:54 PM   #1
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Generator Problem

Hi Folks, hope someone has advice.

My generator is an 8 KW Onan with a Kubota engine. It's model MDKD. It's been running great until this weekend when it stumbled and stalled. It restarted easily enough and ran for several hours. The next day it repeated that sequence. Now it won't start at all. When it was running the temperature was normal, oil pressure normal with no signs of anything amiss.

On further inspection, I noted the stop solenoid was not retracting. Holding it in by hand allows the engine to start but the plunger won't stay retracted. The solenoid works fine if I attach it straight to a battery. A meter on the terminals of the solenoid shows no voltage when I try to start the engine.

This model has a small generator that I assume charges the start battery. The gauge indicates that its putting out over 13 volts. Any thoughts will be appreciated. Thanks, Howard
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Old 07-09-2015, 06:10 PM   #2
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If there is zero volts on the terminals, how can it start?


Sounds like you might have one of several possible problems:


1. Bad solenoid
2. Poorly adjusted linkage
3. Bad connections in start/run circuit


David
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Old 07-09-2015, 06:14 PM   #3
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Obviously it can't start if there is no voltage to the stop solenoid as the plunger won't retract. My problem is finding where the bad connection is and I can't figure it out. The linkage is set perfectly and the solenoid itself works if I apply 12 volts directly to the terminals.
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Old 07-09-2015, 06:17 PM   #4
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Have you checked the shoe box?
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Old 07-09-2015, 06:18 PM   #5
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Quote:
Originally Posted by hmason View Post

On further inspection, I noted the stop solenoid was not retracting. Holding it in by hand allows the engine to start but the plunger won't stay retracted. The solenoid works fine if I attach it straight to a battery. A meter on the terminals of the solenoid shows no voltage when I try to start the engine.

T
Quote:
Originally Posted by djmarchand View Post
If there is zero volts on the terminals, how can it start?


Sounds like you might have one of several possible problems:


1. Bad solenoid
2. Poorly adjusted linkage
3. Bad connections in start/run circuit


David
You may have answered your own question. I helped a guy with a Lehman 120 get started this weekend with similar issues. A good cleaning of the sloenoid contacts solved the issues. I'd start there..
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Old 07-09-2015, 06:19 PM   #6
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I threw the box away. It made me sad to look at it.
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Old 07-09-2015, 06:20 PM   #7
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Hmm. I cleaned them but will try that again.
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Old 07-09-2015, 06:20 PM   #8
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My lynchpin connection is the oil pressure switch. it is hot from there to the solenoid when things are normal.


Check around there.


Mine had similar symptoms but actually was the exhaust temp sensor connectors were rotten and my genny would be all over the map from running great... then throttling down and eventually stopping.


On mine, it was shutting down the fuel pump...the plunger was getting good juice through the main oil pressure switch.
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Old 07-09-2015, 06:44 PM   #9
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If you have plenty of wire, try running a new hot wire from the switch to the solenoid. Sometimes these go bad due to contacts or splices.

Just place it down the ER aisle to see if it works. If so, you can thread it properly in a wire bundle. If it doesn't change anything, you'll be that much closer to finding the true cause.
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Old 07-09-2015, 08:22 PM   #10
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On a generator, unlike a main engine, the stop solenoid is also part of a safety shut-down system that will stop the generator if it senses a failure in any of a number of sensors. They are commonly:
  1. Low oil pressure
  2. High coolant temperature
  3. High exhaust mixing elbow temperature
  4. High cylinder head or block temperature
  5. No A/C output
Items 1-4 are often on the same circuit where if any of the sensors or switches close (normally by shorting to ground) while the engine is running, the controller will disconnect the power to the shut-down solenoid. Item 5 will do the same thing if the unit stops generating A/C volts.

When the generator is started, voltage from the starter solenoid circuit typically energizes a relay that in turn powers the shut-down solenoid whenever the starter is engaged. Once the controller senses that the engine is running, and producing A/C voltage, it disconnects the starter circuit and provides power to the shut-down solenoid relay. It keeps it powered unless either a fault is detected in items 1-5 or the stop button is depressed.

The first place I would look is items 1-4, any of which will cause the shut-down solenoid to stop the engine. Item 1. the oil pressure switch will be closed (grounded) when the engine is stopped and open when it is running. Items 2-4 should be open (not grounded) when the engine is at or below normal operating temperature, stopped or running. Look for any loose wiring connections, corrosion, broken wires etc. and correct.

Issues with item 5 or the controller will be more challenging to troubleshoot and will require a service manual.

Download the service manual for your generator and follow the troubleshooting procedures, flow charts and schematics. You should soon find the culprit, and you will be really intimate with your generator too.

Good luck
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Old 07-09-2015, 08:26 PM   #11
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Larry,
Thanks for the input. Wouldn't the engine start from cold in items 1-4 and shut down after detecting faults?
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Old 07-09-2015, 08:53 PM   #12
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Quote:
Originally Posted by hmason View Post
Larry,
Thanks for the input. Wouldn't the engine start from cold in items 1-4 and shut down after detecting faults?
Normally that is the way it should work. If the oil pressure switch is defective or shorted it will prevent the engine from starting. A simple test is to disconnect it and try starting the generator. A warning here, if the switch is good and there is no actual oil pressure, the shut-down system is doing its job. Do you have gauges on the genset to monitor this?

If there is no voltage at the shut-down solenoid when you engage the starter, you likely have bad wiring, a bad relay, a tripped circuit breaker, a blown fuse, a loose connector or a bad controller board. The starter circuit, probably via the controller and a relay is what powers the shut-down solenoid when starting the generator. All of the other components kick in once it is running to keep the solenoid energized.

Again, the service manual will save you on this one. I just went through this with an older Kohler that had been jury rigged over the years and finally failed. I went through the systems step by step and finally restored it back to the way it came from the factory. It is happy now and so am I. It cost several hundred dollars in parts, and a couple of weekends of my time to complete, but I saved thousands when compared to a new unit.
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Old 07-09-2015, 08:58 PM   #13
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Good input Larry. Yes, the generator has gauges and when I hold the solenoid in manually and start her up all gauges are normal including oil pressure. I suspect it's a connection somewhere. Tomorrow the hunt begins again. Thank goodness I can almost stand in the ER.
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Old 07-09-2015, 09:15 PM   #14
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Agree with Larry M.

Had the same problem with my Onan and after replacing the start/stop solenoid, to no avail, and hours of messing around with it, it turned out to be an intermittent over temp. sensor.

One bad fault sensor, connector or wire will kill the circuit. My solenoid had two positive wires one direct from the box and one which followed the sensors back to the box. Follow the positive wire from the start/stop solenoid back thru the sensors to the source where you find 12 volts. Then while hitting the start switch, use a volt ohm meter to test each connection forward until you no longer find 12v, which will cover Larry M's list of 1 - 4. You might want to remove the wires from solenoid first so it doesn't start on you.
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Old 07-09-2015, 09:20 PM   #15
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Greetings,
Mr. hm. On my Onan there is a set of points to prevent over reving. They live under a small cover under the fuel solenoid. IF maladjusted they will prevent starting. The non-start situation can occur from one start to the next. REAL easy to check and adjust if so equipped. Take out the fuse in the control panel before you take the cover off if, in fact you have this mechanism. Takes less than 5 minutes.
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Old 07-10-2015, 10:20 AM   #16
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Thanks to all for your input. Tried my best to no avail. A friend who's really good with electrical stuff is stopping by this afternoon. Maybe he'll have more luck. If not, I will need to get the boat dollar ready. Positive thoughts will be appreciated, even from Oliver.

Howard
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Old 07-10-2015, 11:47 AM   #17
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I have the same genset. Mine did the same stumbling as yours does. I replaced the fuel filter and bled it and it ran for a week or so and then it repeated the same stumbling and fail. I hadn't thought of the fail safe circuits because the failure wasn't immediate, it stumbled. When I took the fuel pump off to check it out, it was totally full of fuel, the motor and points had been submerged by a seal failure. I solved the problem by buying an aftermarket Walbro (not Onan) electric pump and it now just hums.
I believe that if your genset stumbled first it is a fuel issue. Below a certain operating rpm the solenoid closes and I suspect that is what you are observing. Also, remember that you have a water lift muffler and excess cranking with no combustion can fill the muffler up and damage the engine.
Good luck!
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Old 07-10-2015, 12:18 PM   #18
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Onan MDKD has a bizarre control system. First thing I do is open up the box and gently snug all terminal screws on the printed circuit board. Screws often loosen and you get a erratic connection.

Otherwise, got to go through the schematic and takes what works and what does not and narrow it to a component.

CB12 little pushbutton breaker on front of panel can trip yet not pop the button out. A well placed whack of a screwdriver handle butt right next to button, not on it, can cause button to pop all the way out. Then reset by pushing.
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Old 07-10-2015, 02:50 PM   #19
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Ski,

I tried your advice with no luck. My electronics friend thinks it's the board. I have a generator guy coming on Monday. Thanks to all.
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Old 07-10-2015, 09:16 PM   #20
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Sounds like a bad fuel solinoid relay.
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