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Old 11-01-2011, 09:36 AM   #1
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Onan 8DKD Strange Behavior

I have an ONAN 8DKDFJ/Spec-C in a 1994 American Eagle. It has the Kubota D950 3 cylinder engine.

It has its own onboard alternator to charge a dedicated battery. I noticed the problem due to what turned out to be a cooked battery. The voltage regulator on the alternator had failed and was throwing between 17 and 19 volts at the bat...when it was producing power at all. No wonder the battery failed. Rather than replace the voltage regulator; I just popped a brand new alternator it its place. Nothing else was changed or disturbed except a new battery, of course. The new alt charges perfectly.

Now for the spurious fault..........The gen cranks and runs beautifully......but, it will not shut down when I push the rocker switch to the stop position. I have to shut it down by removing power from the fuel solenoid. I have searched online, reviewed the Onan tech manual, and talked to folks who should know. Apparently, Onan used two relays for the start/stop services. I know what they look like and even where they are in a sense....if I could actually get to the box they should be located in. I am of the opinion that this should be in the box under the front TV behind the swing-out door. I can get to the front of it but AC really confined this thing in there. I have been told the relays act as breakers and are manually resettable so I should be able to open the box, find the second, red relay on the board and push the port side of it with a dowell to reset it. A few I have talked to gave me the idea that powering up a brand new alternator may have thrown some funky current for a few seconds while the diodes burned in and possibly tripped this protective relay/breaker. I can't get the beast open, though.

Any ideas out there as to how I can access the guts? Is this reasoning even sound? Onan gen controls are kind of like modern automatic transmissions to me. I love them when they work properly but they remain mysterious black boxes to my brain.

Thanks,
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Old 11-01-2011, 06:43 PM   #2
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I have a '95 7.5 DKDFJ with the Kubota 3 cyl diesel engine that had a similar symptom. A short time later it developed into a situation where I could momentarily start the generator, but it would immediately shut down. I was able to see the fuel solenoid pull while cranking to start it, but when the engine started, the fuel solenoid would drop out when I released the start button. I could manually hold the solenoid and the gen would continue to run until I released the solenoid. The solenoid has both a pull and a hold circuit controlled by a circuit board located above the generator in a metal box on my set up. .

Onan has a service manual that has the theory and sequence of events that occur during startup and shut down. This will tell you what happens first and where the signal comes from. With this I was able to monitor input and output signals on the circuit board with a volt meter and determine that the board had failed.

If you need a circuit board, I found the board I needed on the internet for about half of what Onan wanted for a replacement.

I thought this may help if your 8.0 is similar to my 7.5.

Good luck.
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Old 11-02-2011, 03:05 AM   #3
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Check the 7.5 amp fuses behind the radiator coolant pressure cap access door.
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Old 11-02-2011, 03:39 PM   #4
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Thanks for the responses. In looking for these 7.5amp fuses; I came up with nada. I have no door to open to access the radiator cap. It is t'ed into the coolant hose up near the front, right of the engine in clear sight. The radiator is side mounted and accessed by a locked door on the side of the coach. Where else might I look to find these fuses? I haven't seen anything of the sort while troubleshooting so far.
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Old 11-02-2011, 04:11 PM   #5
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Quote:
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Check the 7.5 amp fuses behind the radiator coolant pressure cap access door.
You are thinking of the quiet diesel. This is the old "shakey" diesel.
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Old 11-03-2011, 03:03 AM   #6
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You are thinking of the quiet diesel. This is the old "shakey" diesel.
Ah, yes indeed I am. Not sure where it is fused but thought that it may be screw cap type.
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Old 11-03-2011, 08:29 AM   #7
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Indeed, it is the old "shakey" diesel. Only on shutdown, though....I've had a spilled drink or two because of it

I sure do like the fuse idea. Given the chain of events; that sure seems likely if I could only find them.

Anyone out there with another example of ole' shakey that has run into this?
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Old 11-03-2011, 01:29 PM   #8
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Is this a 8.0DKD without a local control panel that looks like this?



If so, does the remote DC Control box you are reffering to look simular to this?



Dave
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Old 11-04-2011, 09:11 AM   #9
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Dave,

The Generator is quite similar to the one you posted...excepting the side mounted radiator, its associated plumbing, and the presence of a charging alternator. I also have a remote start on the gen slide in addition to the ones on the DC control box and dash.

The remote mounted control box is under the front TV and I was able to get at it last night. The only thing that differs from the picture above is a lack of a DC Charging Breaker. It has just the Start/Stop Switch, DC Control Breaker, and Fault Breaker. I removed the cover and took a peek inside to test whatever I could with my trusty fluke meter. All connections are solid and the two relays are functional. The fault breaker is OK.

I did figure out that switching the DC Control breaker off shuts down the gen. Also, when either of the stop rockers are pressed; the glow function does indeed work. It just fails to remove power from the fuel solenoid and pump.

I'm now looking for fuses and/or a loose connection and so far; I'm coming up with nothing
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Old 11-04-2011, 12:01 PM   #10
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Thanks for providing that level of detail because now that I have better view of what components you have, I think I can provide a bit of help.

MKD Service manual 981-0502: http://www.cumminsonan.com/www/pdf/manuals/981-0502.pdf

Basically, you have the wiring diagram Marine version of the generator. The wiring diagram looks like this:



When the engine is running, +12VDC is supplied to the K12 Run relay (located on the circuit board located in the Remote Box) from VR1 (alternator regulator). Thats the "Yellow" signal path on the drawing above. Return side of the K12 relay is via A11R1, S-6, anf K-1 (P coil). A bit odd but works.

When the STOP switch is depressed, this applies +12VDC ("red" signal path) to the Return side of K12. With +12VDC on BOTH sides of the relay the K12 relay deenegizes removing +12VDC from the K1 Fuel relay (A12 contacts that open are up by the START/STOP switch; They are closed when running and provide 12VDC to K1)

So, what is not happening is when you depress STOP, +12VDC is not getting to the Return side of the K12 relay (red signal path) OR the K12 Relay contacts (by the START/STOP switch) are fused together.

That should simplify your trouble shooting efforts.

For reference, I also listed the location of the 30 amp fuse from page 2-2 of the manual.

The different DKD wiring diagarms that use a circuiot board, all work on these basic principles. While there are variations, in general they follow the same concept especially for the power down process.

I highlighted the green portion to indicate the STOP switch is dueal function. Not only used to shut down the engine but is also used to energize the K13 relay for glow plug preheat

Dave
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Old 11-05-2011, 08:37 AM   #11
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Dave,

A million thanks for that diagram. I had been able to uncover online scans of that schematic but they were of such poor quality that I coudn't read them..especially the text markings. Not to say that I fully understand these kind of technical drawings, though. Your color coded circuit paths helped tremendously.

I have not yet found the root of the problem but I have a bit more information that may spark the mind of someone so vastly more expert than myself.

I found, where it looks like the 30 amp fuse should be, a 40amp cycling circuit breaker. It was zip tied beneath the starter and had gone unnoticed until this morning. It is inline directly between the B+ terminal on the alternator and the starter solenoid. It was fused shut thus providing no protection to the downline systems. I'm still looking for a 30amp fuse, whether static or cycling, down the line but have not yet found one. Since the 40amp breaker was continuously closed in and amongst an alternator dying a fitful death, it very well may be fried...or constantly cycling like Greg Lemond mid Tour De France.

AC did a fantastic job stringing out the components of this gen system ...probably due to it being on a slide requiring long wire runs and such. It might be logical from that perspective but it is nearly impossible to follow a wire from start to end.

Could this failed 40amp breaker have been an improper replacement for the 30amp fuse? If so, I may be looking at a new control board. If not, there might still be a dead 30amp fuse down the line....somewhere. I have tested the board and its components, including the relays and everything in there tests solid. The traces on the board are near a quarter inch wide and every run tested for continuity was golden so I'm hoping a new board is not in my future and there is indeed a 30amp fuse somewhere that found itself cooked by the awol alternator. I'll keep looking.

Any thoughts on a possible hiding place for the 30amp fuse?
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Old 11-05-2011, 10:40 AM   #12
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You did notice I provided a link to the manual that came from I hope The picture above came from that file (Page 2-4).
Now, given the MDKD wiring diagram is you closest match, the best version of that is in the MDKD installation manual (981-600): http://www.cumminsonan.com/www/pdf/manuals/981-0600.pdf on pages 8-6 & 8-7.

My "guess" is someone most likely replaced the 30amp fuse with the 40 amp circuit breaker. Becasue of it's placement in the circuit (Battery output), the generator would not start if the fuse was blown (or breaker reset).

Now for troubleshooting.
From what I see the A11 Engine Monitor Board is the same for all configurations. Now my understanding is that you have the remote DC control box which looks basically like the one on 981-502 page 3-8a (fig 3-5a) minus the DC Charging CB (CB-13 in the drawings). That shows A11 board inside the remote DC Control box.
Because the A11 board is the same across configurations, we can use any of the drawings as a reference in order for us to communicate this way. I am going to refer to the 981-600 page 8-6 & 8-7 since they are the easiest to read. Now that we have got past the confusing documentation part, we can get to what is the simple actual troubleshooting part.

Looking at bottom of page 8-6 on 981-0600, when you select STOP (switch S11) that shorts pin 30 (B+) to pin 20. That sends B+ to pin 8 (I think that is what the drawing says) on the A11 board. That is the pin that the CR1 diode and the J3-3 lead (from the dashboard mounted panel) also connects to. The signal goes through the CR1 diode to stop pin on the A11 board. So, when you select STOP, you should see B+ at A11 pin 9 AND the pin labeled Stop (other end of CR1 diode). If no B+ at A-11 stop pin then diode is bad. Now the magic on the board happens which de-energizes K12 which removes the the 12VDC voltage from the A-11 CB-12 Line pin that provides B+ to the K1 fuel solinoid. So, if you hit STOP and B+ is at the A-11 Stop pin but B+ is not removed from the A-11 CB-2 Line pin, then the board is bad.

Dave
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Old 11-07-2011, 09:19 AM   #13
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I have arrived at a resolution. Odd, it is, but very simple. The 40amp cycling breaker that was inline from alternator B+ was a known fault but no one at Onan or Kubota could help with as it wasn't supposed to be there. It was fused shut thus cancelling itself out and providing no protection. But... no harm no foul. As the unit was designed; there was indeed a 30amp fuse downstream. I'm having a hard time finding the words to describe where it was located. As the wires leave the starter solenoid and join up with a few stragglers; they enter a nice, protective sleeve that routes between the AC control box and the heat blanket over the injector lines. In this unviewable void; the bundle is folded back onto itself over and over to shorten its length. It looks like a solid run of flexible conduit until you cut the zipties and unfold it. There's stuff in there ...namely the 30 amp fuse I was looking for

When the old alternator went south; it must have put on a spectacular show. It welded the 40amp breaker closed and current made a run straight for this lowly 30amp fuse. You would think it would be blown into next week...but not completely. It took the jolt for however long and as the solder joints on the ends of the fuse plate were melting; it was bowing to gravity and finding a new home laying on what was the inside,top of the little fuse box. In and amongst the mess of melted metal and plastic; that thing was actually passing a little bit of juice. I could see about 3volts on the meter.

Anyway, I slapped a new 30amp fuse in there and everything works very well. One modification was made, though. The fuse is now out where I can easily see it

Thanks to Dave78Chief and all who offered advise. I've learned so much from this board and this sort of friendly help is why it's so sucessful, IMO.
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Old 11-07-2011, 11:30 AM   #14
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Glad to hear you got it all figured out even with all the not so obvious modifications.

Dave
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