Onan diesel 8kw start by itself on off after a minute and start again 5 minutes later. is it a defective control box 2911442

possible a faulty voltage regulator or wiring problem from corrosion
most generators need a current in the field windings before the power can be produced so look for a voltage regulator problem

Drain the fuel out and flush the fuel lines and the filter. Failure to purge the unleaded fuel from the system can destroy the engine due to severe pre ignition.

Spark Plug # RS17YX for Onan 167-0272 on RV Gensets ...

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Generator Parts Spark Plug # RS17YX for Onan 167-0272 on RV Gensets ... for this plug require the spark gap to be set at .025" (25 thousandths of an inch).

Onan Gen HGJAB What is the best spark plug and gap? - Heartland ...

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Jun 8, 2013 - 3 posts - ‎3 authors Also what is the the correct gap on the plugs? ... brands · Generators; Onan Gen HGJAB What is the best spark plug and gap? ... Gap: 0.025

Some engines have a low oil cutoff switch. If the oil level drops to a certain point it kills the engine. Your oil level may be close enough that after starting and running for a little bit the level drops enough to kill the motor. After sitting for awhile the level rises enough to allow the engine to run again check the level and add oil if necessary.
Hope this helps.
Bob

If this unit dies under load conditions, decrease your load and try it again.
If this happens under no-load conditions, check your fuel supply. Start with the filters, then check pressure and flow.

Check rotor slip rings for cleanliness, brushes, stator resistance, rotor resistance. Then replace control board if they check out.

You say Guardian that is Generac???? Then you indicate Onan 4.0KY. If it is a Onan and it stops after you release the button there are a couple of things. 1 st check the brushes, and polish the rotor slip rings, check the resisitance of the rotor, the electrical harness plugs are tight. The control requires a voltage feedback while cranking to engage the PCB run circuits, if all those check out you have a bad control board.

What is the Spec number?
Also can you read a fault code on the start switch?
Do you know how to read the codes and post? if not let me know

Possible solution: if it's been sitting idle for some time, you might need to flash the windings. see this link:
http://www.endtimesreport.com/dead_gen.html
If you're uncomfortable doing it yourself, your Onan dealer can do it in 10 minutes.
Don't forget to check the circuit breaker on the generator itself!

a 10 year old genset with only 45hrs on it...sound like the carb may need replace. working with these rv units for 6+ years has taught me that you cannot clean one well enough to fix it. you will need a new carb. your local onan dealer can help. when new the warrenty makes known that 1hr per month under load will keep the carb clean and problem free. evaporating gas leaves deposits and eventualy plug fuel jets. no replacement parts are recommended. i've personaly worked on rv's with 200+ hous and no issues at all. hope this helps, good luck...