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Silpe · 17-07-2019, 09:23

Hi,

I have an Onan MDKBN 13.5kw generator that does not start consistently. When it starts it runs fine. When it does not start the scenario is - push the start button, blower comes on, raw water gurgles in strainer, there's a click noise, and emergency switch throws. It may do this a couple times and then it just starts right up and runs. Because this is prior to an actual start there are no flashing lights for a diagnostic code.

The issue is intermittent and when it first happened I thought it was the fuel pump (which looked like the previous owner had not maintained) so I tapped on it and it started. I replaced fuel pump but still have the same issue. I have also checked that all connections are clean, the switch looks ok visually, and I have replaced the oil pressure sensor and the temp sensor on the cooling system thinking one of those may have been failing. Still no luck. Sometimes she starts right away, other times it takes 3-4 tries and then she turns over runs fine for hours.

Does anyone have any other ideas for troubleshooting?

Thanks in advance.

Pitchondesign · 17-07-2019, 12:40

The starting sequence of most generators includes an overide of the oil pressure switch until the engine gets up to speed and builds pressure. If this overide does not engage, the low oil pressure switch will prevent the engine from starting. Different manufactures use various methods to achieve this. You need to find out how the overide works and test it.

Good luck

Zanshin · 17-07-2019, 12:56

I've got the same generator, just one size down. The manual and the shop manual are available on my website and I'm wondering what you mean by

Quote:

...and emergency switch throws...

Is this a physical breaker that you need to reset? Normally, when you press the start button the engine primes for several seconds and then the starter kicks in.

Silpe · 17-07-2019, 13:21

Thank you both for your replies.

Zanshin - On my unit there is a red "emergency shutoff" switch that is like a breaker you can throw or that is thrown by the unit when certain errors are found. Unit does start to prime but then throws the physical "emergency shutoff" switch. I have the manuals but troubleshooting is rough going with the intermittent nature of the problem. Ruled out voltage issues, temp sensor, fuel pump, oil pressure sensor,

Pitchondesign - Thank you. I tried replacing the oil pressure sensor but it did not help.

Pitchondesign · 17-07-2019, 13:53

Its not the oil pressure switch, its the override switch or relay you need to look at. When the oil pressure is at zero, (when starting) the circuitry senses this and performs an emergency shutdown. The oil pressure override prevents this from happening during start up, allowing the engine to start and build up oil pressure for normal operation. Without the override, the engine could never start because the oil pressure switch would show zero pressure (at startup) and emergency shut down before it could start. If the override relay/switch or wiring is intermittent, it would czuse the symptons you report.

Zanshin · 17-07-2019, 16:14

Do you have the Service Manual? There are some possibilities discussed there regarding the emergency switch. If not, download the PDF file from here.

Locquatious · 18-07-2019, 08:26

Our Northern Light was difficult to start. A fuel lift pump helped. But replacing and tightening all the fuel connections, especially the highest ones above tank level significantly improved start performance. Basically between usage, air bled into the fuel lines allowing the fuel to flow back into the tank. Air can be sucked in more easily than liquid fuel can bleed out. You can't always see or feel wetness at the faulty connection.
We also had problems with the generator stalling when loaded. This stalling occurred at the same time we had the fuel line leaks leading us to conflate the two problems. But in our case the contacts on a relay contactor were burning out. The contactor was "3 phase" and we only used two of the "phases" for switching. Jumpering the bad contact to the third unused phase temporarily solved the problem till we could get a new contactor at a refrigeration supply.

Scrimshaw4 · 18-07-2019, 08:46

Possibly a problem with the starter (solenoid or dead spot), start relay or stop / emergency switch.

JDanielBryant · 18-07-2019, 11:31

Is there a starter relay on it? Sounds like a relay going bad. If you can jump start it by shunting the battery directly to the solinoid, that’s your issue.

waterman46 · 19-07-2019, 07:32

Quote:

Originally Posted by Scrimshaw4

Possibly a problem with the starter (solenoid or dead spot), start relay or stop / emergency switch.

Yes I think you left out one vital piece of info. You mentionef a click but nothing about starter motor turning. Problem sounds like it could be just a bad starter solenoid, if the emergency cutoffs only shut off the injection pump and do not act on the starter motor circuit. A description of this will be in the manual.
Why not apply a temporary external 12V source to the injector pump shutoff solenoid to bypass those emergency circuits?