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Onan Generators

onan microlite 4000 won't start


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  #1  
Old 10-05-2015, 06:54:18 PM
Skydivemark Skydivemark is offline
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Default onan microlite 4000 won't start

Model 4.0 KY-FA/26100H (spec H?) S/n H980787544 with about 1014 hours on it.
in a 99 class C jayco.
it's not getting spark, verified with spark tester. It is getting fuel, spark plug is wet when I pull it out and I smell gas while cranking it.
I read in an old thread here (from 2009) to check wire #12 on the connector with 15 holes, supposedly it's the wire to the low oil sensor, well that connector doesn't even have a wire on the engine side of the connector (coming from behind start switch area and never did, it's all dusty) but does on the other side (the bundle coming from behind/under the solenoid area).
When it quit running it had only been running a minute or so and ran several hours the day before with no issues.
It cranks & turns over fine (glad the battery is recently new).
Once in awhile it will spark once, usually when I haven't messed with it in at least an hour or more.
I understand the low oil sensor is impossible to reach while installed in the RV so I'm trying to figure out which wire actually goes to / comes from it so I can disconnect it &/or ground it for troubleshooting. I also read somewhere in this forum that onan/cummings has recommended disconnecting the low oil sensor due to high fail rate.
next will ohm out the coil (the little blue block).
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  #2  
Old 10-05-2015, 07:27:11 PM
Doug Reed Doug Reed is offline
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Default Re: onan microlite 4000 won't start

According to the manual, the KY-series only holds one quart of oil. A common complaint seems to be they get a little low and damage the engine. I don't have one of these so I don't know if it can have problems from being over full too. But if the engine is on a slant it may tip the oil toward the dip stick or maybe away from the oil sensor. Just something to check....
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  #3  
Old 10-06-2015, 06:41:30 AM
Kevin K Kevin K is offline
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Default Re: onan microlite 4000 won't start

A good place to begin is to download the manuals for your generator:

http://www.twinslan.net/~n0nas/manuals/onan/

981-0154 Operator Spec D to H
981-0503 Service Spec A to H
981-0607 Install Spec B to H
981-0246 Parts

I don't think your spec H generator has an oil level switch. At some point Onan stopped using them due to the constant problems.

Changing the spark plug would be the first thing to do.

The 4.0KY uses a two piece ignition system: A pickup coil/magneto mounted under the flywheel, and a coil. A good explanation of how the system works can be found on page 8-6 of the service manual. The control board shuts down the generator by grounding a terminal on the magneto. In addition to a defective magneto or coil, a defective control board that keeps the "Ignition Enable Output" grounded can also cause a no spark problem.
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  #4  
Old 10-06-2015, 07:09:24 AM
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Default Re: onan microlite 4000 won't start

You may as well pull it from the unit and install a new coil and check the brushes while you have apart.
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Old 10-06-2015, 09:59:09 AM
Skydivemark Skydivemark is offline
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Default Re: onan microlite 4000 won't start

My owners/operators manual says 1.6 Qt. I have verified it's full and actually have parked it to lean to the right when I fill it (I try to do it this way whenever I fill &/or change the oil).

---------- Post added at 09:59 AM ---------- Previous post was at 09:28 AM ----------

I thought it does have a low oil sensor only because one time (a few years ago) we were on a long trip and at one point it started sputtering so I shut it down and found the oil a little low. Topped it off and no further problems. But yes, according to the manual the sensor is only effective to A-F spec.
I've read several places here of others having problems with control boards, seems to be a common weakness/failure.
Kevin K; Thanks for the info for the manuals. Previously the only ones I found were not free. Also I'm not getting spark to the plug as the tester plugs into the plug wire & ground point.
I think next I'll ohm the coil - easy access next to the oil fill port.
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  #6  
Old 10-06-2015, 11:31:05 AM
len k len k is offline
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Default Re: onan microlite 4000 won't start

I recall a few people having failures in one of the 2 coil modules (G2-magneto, and ignition coil).
See page 30 of part manual for pics of these parts (# 3, 5)

To test if failure is in control board or spark modules I'ld try to disconnect wire that goes from control board to G2 and try to start engine. I believe control board grounds that wire when it wants to stop engine. I would rig up an extension wire to G2 so you can stop engine when you want to, or a string to pull spark wire off spark plug.

Looks like your wiring schematic is # 611-1265 on page 12-20 of service manual.

Last edited by len k; 10-06-2015 at 12:02:30 PM. Reason: page 30 of parts manual not, service manual
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  #7  
Old 10-06-2015, 11:50:56 AM
Skydivemark Skydivemark is offline
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Default Re: onan microlite 4000 won't start

Thx Len K, Yes, 611-1265. Just printed it so I'll have it when I get home. also have resistance #'s for both sides of the ignition coil.
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Old 10-06-2015, 12:05:26 PM
len k len k is offline
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Default Re: onan microlite 4000 won't start

I corrected post #6 , it's page 30 of parts manual, not service manual.

To disconnect wire might have to remove pin from connector. If it's a round pin connector sometimes a plastic straw slipped over it will depress the tab that holds pin sleeve into plastic connector.

Last edited by len k; 10-06-2015 at 02:01:38 PM. Reason: spelling
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Old 10-06-2015, 01:47:20 PM
okcnewbie okcnewbie is offline
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Default Re: onan microlite 4000 won't start

I accidentally bumped the spade terminal off the Ignition coil one time and it will remove the spark.
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  #10  
Old 10-06-2015, 05:59:22 PM
Skydivemark Skydivemark is offline
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Default Re: onan microlite 4000 won't start

Well this is totally weird. I disconnected both terminals from the ignition coil, leaving ground connected. Resistance was right what the manual called for. Hooked everything back and for grins tried to crank it up. It fired up and has been running for 1/2 hour now. I'll leave it run for an hour or 2 (with air conditioner running to insure partial load), I'm sure the battery needs charged anyway after all the attempted starts I did.
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  #11  
Old 10-06-2015, 06:27:51 PM
Kpack
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Default Re: onan microlite 4000 won't start

Well that's good news that wouldn't happen to me on a 4 ky.
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  #12  
Old 10-06-2015, 06:43:54 PM
len k len k is offline
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Default Re: onan microlite 4000 won't start

Check for corroded connection, bad wire crimp to spade connector.

Also possible to have broken wire inside insulation, try wiggling wire while running to see if it dies.
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  #13  
Old 10-07-2015, 09:32:47 AM
Skydivemark Skydivemark is offline
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Default Re: onan microlite 4000 won't start

Ran it for over 2 hours under load, no problems. All I can figure is the primary coil wire had enough corrosion to interrupt the circut and taking it off & back on removed enough to get it working again (it happens A LOT on the planes I work on = common practice to "re-rack" a component or connector). it took what I consider a normal amount of effort when I removed it to check resistance and same when I re-connected it. I didn't notice any obvious corrosion either but that doesn't mean it wasn't there.
I appreciate everyone's help. I learned a lot about this Onan during the last few days including where to find & download manuals at "the right price" !
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