Onan MDKAF dies when start button is released

Dear Forum,

I am new here. My name is Alex, and I am from Austria. My family owns a Horizon 70 from 2002 with an Onan MDKAF installed. It has only about 2.500 hours on it. It has been running fine without any troubles for 20 years. It has been serviced every year.

Since this year, we have had the problem of the generator stopping after around 1 hour (fuel solenoid turns off fuel). Sometimes, it happens after 5 minutes, so there is no pattern. When restarting, it runs fine as long as the start button is pressed; when it is released, it dies (the fuel solenoid turns off fuel). When the start button is pressed, the generator produces AC. So we had several mechanics on board, and they did the following things:

• New fuel pump
• New fuel solenoid valve
• New oil pressure sensor
• New coolant temp sensor
• New exhaust temp sensor
• New alternator
• New belt, new oil, new filter
• Checked coolant level
• Cleaned intercooler
• Bypassed K4 relay

All parts were original Onan.

Now, we have already spent a tremendous amount of money and still the problem has not been solved.

Do you have any ideas?

Thanks,
Alexander

Welcome aboard. Most gensets will overide faults when the start button is pressed and when it is released any serious fault will shut the genset down. Check the service manual to see how ro read the fault codes and go from there. I am not familiar with that genset but they are all pretty similar. Good luck.

There are two fault circuit breakers, Check Generator, and Check Engine. Which of the two is tripping, if either?

Has anyone actually checked the oil pressure and coolant temp on the unit when it's misbehaving? It's entirely possible the sensors are fine but there's an actual problem occurring.

As rslifkin says 1st verify you don't have a real problem. If you don't it is likely as Comodave and Twistedtree point out a problem in the control circuitry. You'll need to spend some time with the manual to understand how it works. I had similar problems with a MDJE which was even older. I found a lot of help on Smokstak There are some very knowledgeable Onan people over there.

Do you have enough cooling water running through the engine ? It will shut itself down when there is not enough water supply and that can be caused by barnacles in the through hull. Have you checked the water flow via the thru hull ?

Mambo42 said:

Do you have enough cooling water running through the engine ? It will shut itself down when there is not enough water supply and that can be caused by barnacles in the through hull. Have you checked the water flow via the thru hull ?

Click to expand...

Good point. Some Onans have a high exhaust temp shutdown that will trip if there's low water flow.

Going back to OP's statement

When restarting, it runs fine as long as the start button is pressed; when it is released, it dies (the fuel solenoid turns off fuel)

Click to expand...

I don't think it's a cooling problem. There hasn't been enough time for high exhaust temp or high cooling system temp. I would verify that I have good oil pressure before releasing the start button. If so then I would suspect control system problems.

OP states the oil pressure sensor has been replaced. I'm not familiar with the MDKAF. Does it have two oil pressure sensors? One for gauge and alarm. One for overriding control shut down until oil pressure builds up? If two which one was replaced?

OP states the K4 relay has been bypassed. Is this the start - stop disconnect relay?

Keeping in mind my experience with ONAN is the MDJE I'd put the K4 back in service and verify that it works correctly. I had a lot of issues with this. It would work fine on the test bench, not on the gen set. Turned out to be a voltage problem. It was over voltage cooking the relay coil. A new relay would run fine for about 50 hrs, the it would begin to fail. Eventually failing as OP states, as soon as the start button is released.

After being sure OP has oil pressure, cooling and proper RPM consider hot wiring the fuel solenoid to force the gen to run. Put a switch in the hot wire circuit for an easy way to kill it. A short run time to verify proper oil pressure and cooling will not harm the gen set. Keep an eye on the starter. If the start process is like the MDJE where the operator presses the start button until the gen is running properly the starter must be disconnected to prevent damage to the starter while the start button is pressed.

Watch everything closely while temps build to normal operating temp. Oil pressure, electric output, start batt charging voltage, voltage to the control circuit. If all is OK with the fuel solenoid hot wired there is a problem in the control circuitry. And OP is off on a wild chase to find the issue. Start with the easy stuff, lose or corroded connection. Fuses. Etc.

As I said above get on over to Smokstak and ask for help.

Portage_Bay said:

Going back to OP's statement

I don't think it's a cooling problem. There hasn't been enough time for high exhaust temp or high cooling system temp. I would verify that I have good oil pressure before releasing the start button. If so then I would suspect control system problems.

Click to expand...

I have a 6.5 Kva Onan and an Onan will shut itself down when it senses no water flow. Had that happen to me recently. I don't use my generator anymore, only run it once or twice a month to keep it in good condition. So I keep the seacock closed at all times. Had forgotten to open it and the generator immediately shut itself down after start up.

Not saying that this is what is happening to OP, but it is worth checking it.

Mambo42 said:

I have a 6.5 Kva Onan and an Onan will shut itself down when it senses no water flow. Had that happen to me recently. I don't use my generator anymore, only run it once or twice a month to keep it in good condition. So I keep the seacock closed at all times. Had forgotten to open it and the generator immediately shut itself down after start up.

Not saying that this is what is happening to OP, but it is worth checking it.

Click to expand...

Yes, newer gen sets will sense flow. The newish Kohler I have on the present boat does that. I made the same mistake you did. But it takes a few seconds to shut down. Guessing a time delay to let the water pressure develop. OP is saying as soon as the start button is released it quits. And his gen is 20 yrs old. Not sure the water pressure shutdown is on gens that old.

So many things to consider. A thorough undersanding of the control circuitry and perhaps some experienced advice is in order. It does sound like his mechanic is a parts replacer not a troubleshooter.

I wouldn’t be surprised if there is a push button circuit breaker that has popped and gone unnoticed. I suffered from one of those for a whole day with a similar situation. I only discovered it when I started following the electrons with a meter.

While you press the start button, the safeties are bypassed. When you release the button, the safeties control the engine. Common safeties are oil pressure, coolant temp, and exhaust temp. Some have coolant flow and raw water flow sensors. The problem is usually the sensor but can be relays in the box or on the control board.

I run 20MDKAE from1995 which likely has the same engine (Kubota V2203) as your AF. The control could be also the same or entirely different, I don’t know. I would try these things if you are confident that your sensors, being new, are good.

There was an option available for my Genset for a Coolant Level Sensor. I don’ t have it.
Do you? If so, is it operating correctly?

The ground bus on my engine is mounted on the block right below the raw water pump.
What could possibly go wrong there? Take all the connections off of the bus, then take the bus off the engine. Clean everything to bright metal. Remount everything and once this issue is resolved paint the assembled bus. Twice.

The fuel start/stop solenoid (it’s new, right?) has inside it 2 coils. A pull-in coil which is feed by a 16 Ga. wire on the Aux. terminal and a Hold coil powered by a 10 Ga. wire on the Pos. terminal.
Have a really good look at these 2 wires (and the ground wire) along their entire length, feeling for a parting of the copper conductor inside the insulation.
I would consider temporarily running new wires just to see if the fault continues.

After this you will need the schematic (check the underside of the control box lid) and the fault to be present so you can look for where there is power and there should not be or the opposite.

I 2nd Smokestack, there is a great body of knowledge on there.

You need the wiring diagram for your model. Then you can properly troubleshoot the issue. We’re all just guessing.

Portage_Bay said:

OP is saying as soon as the start button is released it quits.

Click to expand...

I got the sense that was immediately after a shutdown. That would be consistent with an overheat.

Good discussion.

Hi everyone,

thanks for all your replies!! Here is a short summary of your questions:

- the generator is so old that it does not show fault codes
- no fault circuit breakers pop
- even when generator is stopping after 1 hour, the water pump housing feels cold, coolant level is full, so it is not getting too hot
- oil pressure is fine according to the gauge, the alarm sensor (not the gauge sensor) was replaced
- water temp, voltage and oil temperature gauge is fine even when the generator is running 1 hour
- I will check the water flow through the hull
- yes, K4 is the start - stop disconnect relay
- the seacock is open
- we have the coolant level sensor, it is replaced, coolant is full

The problem occurs without any pattern. Sometimes, it does not run for even a second when the start button is released. Sometimes, it is running fine for about 1 1/2 hours with a 50 amp load and then suddenly dies. Am I assuming it must be something simple like a sensor or faulty cable?

I have the wiring diagram for the generator here, shall I post it?

Should we try to bypass the sensors through a wire attached to the grounding to see if one is faulty?

I will as well ask for help on Smokstak.

Thanks everyone for helping.

Best,
Alexander

I'd start by bypassing the safety switches, one at a time to see if you can identify which one is tripping, or eliminate them as possible causes.

It sounds more like a short in the wire to the stop solenoid or positive and negative connections need to be cleaned. When you activate the starter a lot of amps flow and will often push thru corrosion, but small loads like the stop solenoid don't draw enough. So the engine runs, vibrates and loses the electrical connection.
I'd clean cable connections and run a temporary jumper wire to the stop solenoid. Just a wire with clips to the solenoid and + terminal on the starter solenoid.

Lepke said:

It sounds more like a short in the wire to the stop solenoid or positive and negative connections need to be cleaned. When you activate the starter a lot of amps flow and will often push thru corrosion, but small loads like the stop solenoid don't draw enough. So the engine runs, vibrates and loses the electrical connection.
I'd clean cable connections and run a temporary jumper wire to the stop solenoid. Just a wire with clips to the solenoid and + terminal on the starter solenoid.

Click to expand...

Excellent advice to the OP. A short in the wire to the speed sensor points was one of my problems. If OP's gen uses the very old style centrifugal switch and point, like old style ignition points, that is an intermittent weak point.

twistedtree said:

I'd start by bypassing the safety switches, one at a time to see if you can identify which one is tripping, or eliminate them as possible causes.

Click to expand...

Thanks, but would the check engine circuit breaker activate if a sensor is faulty? It is so strange that the breaker is not activated, which indicates a wiring/electrical connection issue?

As soon as I am back on the boat, I will start cleaning grounding points and tracing the voltage loss of the fuel solenoid.

the_schick said:

Thanks, but would the check engine circuit breaker activate if a sensor is faulty? It is so strange that the breaker is not activated, which indicates a wiring/electrical connection issue?

As soon as I am back on the boat, I will start cleaning grounding points and tracing the voltage loss of the fuel solenoid.

Click to expand...

Yes, I think you are correct.

Schick, upthread you called a CB a "check engine circuit breaker". Where did you get that name from? Which CB is this check engine one? On my AE, neither of the face mounted CBs are named on the front of the panel or in the parts book.

I don't think either of the face mounted circuit breakers open in the case of a sensor derived fault condition.
These CBs simply protect the wires from an overload.

To me it still looks like something is opening the circuit to the hold-in coil on the Stop Solenoid.
I think the approach to ensure that the wiring and the connections are sound, will bear some fruit.

The shut down scenarios go like this.
Oil pressure fault
High coolant temp
High voltage
Low voltage
Low frequency
High frequency
All work through a several second inhibit
That, to lesson nuisance shut downs
Immediate stoppage on release of start button is no a.c. Output, or, the controller does not recognize that the machine is making a.c. Power.
Seems none of the steps taken reflect on the symptom.
Nothing wrong with the work but need to look at the a.c. Output.
With a serial I will be happy to look up your wire diagram and share it
God bless

Dear Iuna, please find a picture of the main board attached. We have two circuit breaker, "check engine" and "check generator". Neither of them popped, so I assume it is a grounding issue. I will be on boat end of August and will do further checks.

Regards

@mysweetLord: please find attached a picture of the production sticker.

Thanks!

Well your front panel has a lot more writing on it than mine does and despite the fact that I don't have the 3 panel mounted gauges, I only have 2 Circuit Breakers. Otherwise my front panel looks similar with the writing that is there, still in great shape. Perhaps my entire control system is of an earlier vintage than yours.

If you were to loosen (no need to remove them) the 4, 5/16" hex headed machine screws on the sides of the enclosure the top of the enclosure lifts straight up. Flip the lid over and you should see the wiring schematic sticker.

Perhaps Mysweetlord, now with the serial number will opine on further troubleshooting technics.

the_schick said:

Dear Forum,

I am new here. My name is Alex, and I am from Austria. My family owns a Horizon 70 from 2002 with an Onan MDKAF installed. It has only about 2.500 hours on it. It has been running fine without any troubles for 20 years. It has been serviced every year.

Since this year, we have had the problem of the generator stopping after around 1 hour (fuel solenoid turns off fuel). Sometimes, it happens after 5 minutes, so there is no pattern. When restarting, it runs fine as long as the start button is pressed; when it is released, it dies (the fuel solenoid turns off fuel). When the start button is pressed, the generator produces AC. So we had several mechanics on board, and they did the following things:

• New fuel pump
• New fuel solenoid valve
• New oil pressure sensor
• New coolant temp sensor
• New exhaust temp sensor
• New alternator
• New belt, new oil, new filter
• Checked coolant level
• Cleaned intercooler
• Bypassed K4 relay

All parts were original Onan.

Now, we have already spent a tremendous amount of money and still the problem has not been solved.

Do you have any ideas?

Thanks,
Alexander

Click to expand...

Frequently manufacturers used two separate systems when addressing the auto start or safety shut down systems on engines - particularly gen sets. There is quite possibly a separate oil pressure and water temp sender for the shut down system. The fact that it runs when the start button is pressed and held indicates this problem as the start circuit bypasses the safety shut down circuit until the engine oil.pressure switch kicks in and hold that circuit open during the "run" phase.

Is there voltage present when it runs?

Hope these manuals help

I hope you have the unit running by now.
Lots of suggestions but to Lepkes suggestion I suggest that as you check wiring and clean it use either NoALox or a dielectric paste/grease to coat all the cleaned connections as you go. They both will prevent corrosion if that was the cause. All it would take is a goofy connection to prevent current from travelling.