Onan MDKAL with Kubota Engine trouble shooting

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ofer

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Joined
Apr 10, 2020
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545
Location
USA
Vessel Name
Unicorn
Vessel Make
1970 50' DEFEVER OFFSHORE CRUISER Timber
I have a couple of issues not sure they are related.

able to start the generator after a few tries. seems to run ok although lots of black smoke and what looks like diesel residue coming out of the exhaust.
gen will run for about 5 minutes and then will trip the check engine breaker.

if i restart immediately it will run for about 10s and rertrip the check engine breaker.

according to the manual three things can cause check engine.

low oil, high coolant temp and high exhaust temp. I am not sure how i can isolate what is causing the issue.

Thanks in advance
 
Oil pressure switch will be closed when running, high exhaust temp and high water temp will be open when running and closed when in fault so you can unplug both sides and see if they are closed while it’s not running. Verify you do not have any high temps. While running put a meter on ohms to the positive side of each of the high temp sensors (should find the end of the wire in the controller) and other to the negative on the battery see what closes or keep em unplugged on at a time see if it runs longer. Oil pressure switch if it opens when running then you either have low oil pressure check with a guage or that switch.

It also will trip for failure to produce any power, but that is part of the starter disconnect circuit that should be ok if it is running for a few minutes till shutting down.
 
Wires j5-5 and J5-4
 

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Does the genset produce power? A short in the stator could cause the output power to be very low or non-existent while also overloading the generator engine causing black smoke.
 
Does the genset produce power? A short in the stator could cause the output power to be very low or non-existent while also overloading the generator engine causing black smoke.
yes it seems to produce power while it's on. it's not on for very long.

on the checking the sensors?

once check engine breaker is activated and the engine shuts off would the status of the sensor remain as it was causing the fault or do i have to check the status while its running?

black smoke is accompanied by what looks like diesel fuel.

could a faulty injector with extra fuel cause the exhaust temp sensor to be activated to excess heat?
 
let’s figure out the shutdown first. Smoke that's from cold running temps or poor burning fuel like dirty injectors.

Here’s what you can try. First verify with a temp gun nothing is really overheating. Unplug one of the high temp sensors one by one and run it. Oil pressure switch rarely fails but possible. The high temp switches they would fail more often. You can also right when the breaker trips, unplug both sensors and ohm them out see if they are closed see which one is it before it cools off.
 
You can also if you found that plug I circled put your meter in ohm setting put one lead there and other to the negative anywhere since it’s all bussed together. See it close when it fails.
 
When it runs for the first 5 min, is there visible, normal water flow out the exhaust? If water flow is diminished, then exhaust will heat up and the safety switch will shut down, exactly as it is doing. An easy check to to carefully feel the exhaust elbow and/or exhaust hose when the engine is running in that first 5 minutes. None of it should be hot. It should be cool, or at most a bit warm. I would do this before bypassing any of the safety switches, just in case there really is an exhaust overheat.

If the exhaust consistently runs cool with ample water flow over the first 5 minutes, then I'd check for faulty safety switched. You can meter them as described previously, or you can just disconnect the wire at the switch, one at a time, and see if the generator now continues to run.

What still puzzles me is the black smoke. Is that only when the gen first starts and is coming up to speed, or is it continuous for the first 5 minutes before it shuts down? I haven't deciphered the schematics completely, but I think I saw a reference to an overload shutdown. This makes me wonder if perhaps there is some sort of generator output short. That would explain the black smoke and subsequent shutdown. So if the smoke continues for the whole 5 minutes before shutdown, I would look into this. If there is an AC output breaker, open it to see if that helps. Also related to this, check the output frequency when the gen is running. It should be within a few hz of 60 (or 50 if so intended). That might also provide a clue about overload or some other issues. For example, there is an overspeed shutdown that might be coming into play.
 
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let’s figure out the shutdown first. Smoke that's from cold running temps or poor burning fuel like dirty injectors.

Here’s what you can try. First verify with a temp gun nothing is really overheating. Unplug one of the high temp sensors one by one and run it. Oil pressure switch rarely fails but possible. The high temp switches they would fail more often. You can also right when the breaker trips, unplug both sensors and ohm them out see if they are closed see which one is it before it cools off.
yes, a fellow boater tried to do that and dropped my temp gun in the water. ordered a new one should arrive today i will try to do that.
 
When it runs for the first 5 min, is there visible, normal water flow out the exhaust?

What still puzzles me is the black smoke. Is that only when the gen first starts and is coming up to speed, or is it continuous for the first 5 minutes before it shuts down?
water flow looks normal for the entire time. ill double check later today.

black some is same level for the duration the generator is running.

Thanks to all for the help
 
Although I agree with TowLou's suggestion to focus on the shutdown problem first, it seems the two may be directly related so I think we need to keep it in mind.

For clarity, I see two fault breakers on the generator. The one on the left is a Generator fault, and the one on the right is an Engine fault. You said it was the Engine fault breaker, but I want to confirm? My theory about a possible short in the AC output would probably only hold if it's the Generator fault breaker that's tripping.

Also, has the generator worked fine in the past and recently started exhibiting this problem? Or is the generator/boat new to you, with unknown history?
 
Although I agree with TowLou's suggestion to focus on the shutdown problem first, it seems the two may be directly related so I think we need to keep it in mind.

For clarity, I see two fault breakers on the generator. The one on the left is a Generator fault, and the one on the right is an Engine fault. You said it was the Engine fault breaker, but I want to confirm? My theory about a possible short in the AC output would probably only hold if it's the Generator fault breaker that's tripping.

Also, has the generator worked fine in the past and recently started exhibiting this problem? Or is the generator/boat new to you, with unknown history?
it's the engine fault breaker.

The generator has worked fine in the past. it always had a small diesel leak in the injection pump at the point where the lines are going to the injectors. i have replaced the O rings at the location and leak stayed same. I don't think this is where the problem started since its been two years of issues. i will do some diagnostics today and report back.
 
it's the engine fault breaker.

The generator has worked fine in the past. it always had a small diesel leak in the injection pump at the point where the lines are going to the injectors. i have replaced the O rings at the location and leak stayed same. I don't think this is where the problem started since its been two years of issues. i will do some diagnostics today and report back.
Ok, thanks. Back to just focusing on the three shutdown switches. I think disconnecting them one at a time and seeing if the generator then continues to run is the easiest way to test and identify which one is at fault.
 
The oil pressure switch needs to be closed to run. The other high temp switches run open and close on fault. So be ready it should shut down anyway if you disconnect the oil pressure switch. Focus on the two high temp switches.


And the fuel leak could be why it’s smoking while running. Poor fuel pressure not popping the injectors right and getting a bad spray.
 
I have bypassed the three switches I think...

Oil pressure, disconnect wire and connect to ground
coolant, disconnect the wire from the sensor.
exhaust, disconnect one side of the wire set. Should i disconnect both sides?

after all that no change with the issue at hand.
 
The oil pressure switch needs to be closed to run. The other high temp switches run open and close on fault. So be ready it should shut down anyway if you disconnect the oil pressure switch. Focus on the two high temp switches.


And the fuel leak could be why it’s smoking while running. Poor fuel pressure not popping the injectors right and getting a bad spray.
Are you sure about the oil pressure switch? It looks to me like it's open to run, i.e. oil pressure opens the switch, loss of pressure closes it.
 
Can unplug one side of the switches. Do one at a time. Oil pressure switch leave ungrounded. Grounding the oil pressure switch out tripped the fault.

@twistedtree you are right it should be open over 14 psi. It’s easier having my own hands on this stuff.

Page 50 in that manual. I was looking at schematic but that’s in a dormant not running state.
 
Can unplug one side of the switches. Do one at a time. Oil pressure switch leave ungrounded. Grounding the oil pressure switch out tripped the fault.

@twistedtree you are right it should be open over 14 psi. It’s easier having my own hands on this stuff.

Page 50 in that manual. I was looking at schematic but that’s in a dormant not running state.
OK, thanks for the second set of eyes.

So I think the OP still has the oil pressure switch to test, with wire disconnected. Maybe that will be the problem. Otherwise I think it's into the various relays.
 
all three engine sensors are disconnected see pics same results.

Engine runs for about 4 minutes first time in the day. check engine breaker pops. after that it only runs for about 30 seconds and pops the check engine breaker.

That is the weirdest part to me...why would it run for 5 minutes when cold? nothing ever feels hot around the engine at anytime.

 

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It shut down right now for the oil pressure switch was disconnected.

Need a meter and need to know how to ohm out circuits. It’s very tough to explain
 
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