Microlite 4000 Gen

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So I have a Onan generator that wont stay running after you release the start button. Doesnt matter if you use the button outside or in the home. If you leave your finger on the button it will happily run all day. At first it was an intermittent thing but now it persist, Thought maybe the start solenoid but not so. I checked both switches they are good. Any ideas?
 

DonTom

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Any ideas?
Yes. Your control board is shutting down the genny because of a fault, such as it is running too fast, too slow, voltage wrong, etc.

Use the start button on the genny itself. Try to start and notice 3 blinks on the red light.

Now hit prime fast, one time. Now count the blinks. They will repeat a two digit code. Such as one blink and then four blinks of red. That will be code 14, running too fast and off frequency.

That is the first step. Get that code. And then see here.

-Don- Everglades Nat'l Park, FL
 

Isaac-1

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You don't say the age of your generator, only ones built after about 1998 have the computerized blink codes
 

DonTom

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Sorry didnt know this is a 1996, no computer board.
I think it still has the computer board, just doesn't display the codes. When the button is pressed in, the control board cannot shut it down until you let go. But you still have a fault shutting down the genny.

How to determine what is wrong will be more difficult in a genny that old.

Hopefully Isaac-1 or somebody else here can help you out, I am not familiar with those older gennies.

-Don- Everglades Nat'l Park, FL
 

Gary RV_Wizard

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The generator has detected a fault and is shutting itself down. The start switch overrides the internal auto shutdown, so as soon as you release the switch, it shuts off. Old, less smart, generators still check for things proper voltage & frequency and (most important) adequate oil pressure.
 

Isaac-1

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The older units do still shut down on faults when the start button is released, though they don't sense as many faults as later models, and don't display fault codes, which makes finding the problem a bit harder, can you post the full model number of your generator including the Spec code. (found on the data tag mounted to the generator)

I am going to be a bit busy today, so here is a link to the service manual for your era generator, which has a trouble shooting guide, to follow through it you will need to know the spec code for you unit, https://www.rvwithtito.com/wp-content/uploads/2017/08/Onan4000MaintenanceManual.pdf
 
Joined
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LAKESIDE, CA
Yeah there is no codes (or at least a way to check them) old tech. But the link for the manual is definitely a great help. Now I can trouble shoot. It has oil so maybe a bad level sensor switch. Cause it was intermittent at first. I will trouble shoot and post results. Thanks for the support.
 

DonTom

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It has oil so maybe a bad level sensor switch.
Try not to do too much guessing or you will probably waste a lot of time.

Too many possibilities. Running too fast was my issue, caused by a broken pin in the Onan carb. I replaced it with a cheap $40.00 carb from Amazon and now it runs perfectly. That is in my Y2K RV, last year around this time of year.

-Don- in the rainy Everglades!
 
Last edited:

Isaac-1

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Just have a second, there is no oil level sensor after I think Spec B on the Onan KY 4000 it was too problematic, so they removed it in later versions, being 1996 I am guessing yours is at least spec C
 

Alontheway

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check the oil for the first step.
Yes, I found it easier to buy a $40 ebay carb rather than clean or rebuild the onan carb. Keep the onan carb as it is superior, but the cheapo ebay carb will run just fine. Because your gen runs it might not be the carb at all though. Nobody knows.
 
Joined
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Yeah oil is full. But here are some things I have had happen. I think my chassis battery is marginal but never so low that it wont start the engine. But I have been monitoring it and my house battery (just for MOI) I "think" it seems like when its low 11.54 or lower, there seems to be "some coincidence" that it wont stay running after releasing the start switch. I have charged up the chassis battery to 12.85 and then tried it and after what seemed like 30 seconds with the starter button depressed it ran after releasing it. But I dont have full confidence it would do that every time. So after getting home from a 4 day, (did not use the gen) I tried to run it (chassis batt at 12.45) It did not want to stay running. AHH but I noticed the micro wave was not on indicating that it was not charging or producing 110. THEN the microwave came on and when I released the button it stayed running. Again this is and older unit no codes. I did notice in the manual it said something about no field flash voltage. What is involved with repairing that? Doable without removing it from the motorhome?
 

Alontheway

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some definitions so everyone is on the same page:
chassis battery should only run the vehicle engine.
coach battery should run the camper stuff and the generator.
There should be a solenoid or something that connects all the batteries when the vehicle is running so that the alternator will charge everything, but when the vehicle is off the coach and the chassis batteries should not be connected together; your generator only should have the coach battery available.

When you say, chassis battery, are you talking about the battery dedicated for the camper (you have the terms backwards)? The battery for the vehicle should not be a factor at all for the generator unless you are pressing the "jump start" button to try to get more amps. Many RVs do not have this feature though.

12.45 is not a healthy battery, but is still fine to start most vehicles. Charged up should be around 12.6 when it was new. Below 12 is pretty low. 11.6 is considered dead.
12.4 should be plenty to make the generator happy for starting, but have you measured how low it drops when starting? Sounds like it starts ,so the battery should not be an issue. The generator will make 12 volts DC (or 13 or even 14) so that will be what the generator sees despite a lower battery.
I suspect it is not a battery issue.
 

Kirk

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I did notice in the manual it said something about no field flash voltage.
The Onan is designed to stop running when you release the start switch if there is no output from the generator. The field is flashed from the battery voltage initially and when you release the switch it then shifts to the generator's output. I'm not sure how to measure that.
12.45 is not a healthy battery, but is still fine to start most vehicles.
That is not true. This is a battery charge level chart from Exide battery.
Temperature: 77 degrees Fahrenheit

Percent ~ Hydrometer ~ Unloaded
charge ~ reading ~ voltage
100 ~ ~ 1.265 ~ ~ 12.63
75 ~ ~ 1.210 ~ ~ 12.30
50 ~ ~ 1.160 ~ ~ 12.00
25 ~ ~ 1.120 ~ ~ 11.76
0 ~ ~ 1.100 ~ ~ 11.64
 
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