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Old 03-09-2022, 07:51 PM   #1
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Onan 4000 K Not Firing

Hello all,

I recently purchased my first motorhome and haven't been able to get my Onan 4000 gasoline generator to turn over at all.

Some back story: the RV was REPO'd from a state out east and brought to the southwest to auction, sat for about a year without putting more than a few hundred miles on the odometer. When I bought the motorhome, the generator fired up after a couple attempts at priming but was only kept on for a few seconds. I didn't check its performance under load or run it for a longer period of time as the RV was an insanely good price and I was going to buy whether or not the generator was healthy. Fast forward to now:

Spent a few days troubleshooting after I got it, new spark plug, oil looks and smells fine, and the engine cranked very strongly without any hint of weakness. Yanked the carb out and it was actually shockingly clean (air filter full of gas and soot) but decided to soak it in berryman12 for 72h (probably overkill) to allow maximum penetration throughout the upper chamber. Cleaned the bowl and plastic components by hand with carb cleaner - everything that was visible was immaculate when I reassembled it today.

Reinstalled the carb and the first attempt at starting it actually turned over one revolution and died (first time it has ever even gotten that far). Every attempt since just ended up with the unit starting strong for 3-4 seconds and descending into sounding like it's dying (very slow crank speed, down to just an intervalled click every 2 seconds or so with zero throttle movement whatsoever - like a slow cough). It seems to be getting fuel as the bowl fills up after a regular period of priming.

I'm sure the oil could use a change, but the latest symptoms have me thinking I blew the starter cranking it the last couple weeks, or there's some kind of short in the AC wiring somewhere. Perhaps the carb will need to be fully replaced, but like I said, it was surprisingly clean when I took it apart.

The MH gas tank is 3/4 full. House batteries read 3/4 charge on the in-house panel but only get charged through the alternator and the rig is in the process of being registered out of state so I have to be careful where/when I drive it and I don't take it but for perhaps 3-4 miles in a loop before parking it again, every 3 days or so.

Thanks!
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Old 03-09-2022, 11:18 PM   #2
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I would try BOOST switch before cranking, or cranking while engine running, or booster cables directly to GEN before condemning STARTER, but YES, OVERCRANK will blow starter. 3/4-battery is very borderline. BUT, might have blown SOLENOID? COMMON GEN start/die issue is DEFECTIVE/ intermittent FUEL PUMP, a $25 DIY fix for most. Amazon by part #, or LOW Pressure generic for CARBuretor engines, as high pressure will cause flooding issues. GEN Model ## and/or Name will help. BEST Test for PUMP is 50%+/- loaded for 2-hours, as many FP issues show up after 60-90-minutes. i SUSPECT you have a KY Model, so download parts and service manuals if so, and READ the CODES, if any? Hopefully, just low battery right now? Good Luck,
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Old 03-10-2022, 08:05 AM   #3
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I agree with checking fuel pump and will add: if you replace the carb, keep the old factory carb.

Onan carbs are hard to get and the cheap aftermarkets are hit and miss in terms of quality.


Are you getting any codes flashing?
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Old 03-10-2022, 08:07 AM   #4
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While you are messing around with the fuel system, add a shut off valve to the fuel line.

It makes future winterizing/storage much easier.
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Old 03-11-2022, 03:14 PM   #5
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BTW, if concern of whether fuel or ignition issue, spray some STARTER FLUID and see if it will kick (after you get starter to crank)? If it will= fuel, if not maybe IGN or Circuit Board?
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Old 03-11-2022, 03:37 PM   #6
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It is unfortunate that you do not know the actual model of the genset. There have been six different 4kW Onans and three of those are still in common use.

The symptoms you are describing point to three very different issues all related to lack of proper maintenance.

Cleaning the carburetor was a good idea, but did you actually blow out all the ports or "wire clear" them?? Did you check the operation of the float/needle&seat?

You did check to see if the spark is healthy, RIGHT?

If it did once, but is not now cranking, it could be that you have damages the starter motor, but it is also very likely (and easier to repair) that you have some (nobody said it has to be just one) connections in the starter power circuit. Disassemble all that you can find, clean them and reassemble them.

It can still be the fuel pump. You can disconnect and test that. While at that, you do not give an age for the coach. If it is more than 10 years old, inspect the fuel lines. The new "motor fuels" can be very hard on rubber parts that barely last 15years in the best of times.

Do you have the owner's and maintenance manuals for the beast. Those may be able to be downloaded on from web sources. Go find them.

As a last thing, most all gensets are designed to be removed and they are all self contained units. Figure out how to get it out, then get a battery and a gas can and work on it out in the daylight.

Frank
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Old 03-11-2022, 03:50 PM   #7
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Quote:
Originally Posted by Onan4000 View Post
Hello all,

I recently purchased my first motorhome and haven't been able to get my Onan 4000 gasoline generator to turn over at all.

Some back story: the RV was REPO'd from a state out east and brought to the southwest to auction, sat for about a year without putting more than a few hundred miles on the odometer. When I bought the motorhome, the generator fired up after a couple attempts at priming but was only kept on for a few seconds. I didn't check its performance under load or run it for a longer period of time as the RV was an insanely good price and I was going to buy whether or not the generator was healthy. Fast forward to now:

Spent a few days troubleshooting after I got it, new spark plug, oil looks and smells fine, and the engine cranked very strongly without any hint of weakness. Yanked the carb out and it was actually shockingly clean (air filter full of gas and soot) but decided to soak it in berryman12 for 72h (probably overkill) to allow maximum penetration throughout the upper chamber. Cleaned the bowl and plastic components by hand with carb cleaner - everything that was visible was immaculate when I reassembled it today.

Reinstalled the carb and the first attempt at starting it actually turned over one revolution and died (first time it has ever even gotten that far). Every attempt since just ended up with the unit starting strong for 3-4 seconds and descending into sounding like it's dying (very slow crank speed, down to just an intervalled click every 2 seconds or so with zero throttle movement whatsoever - like a slow cough). It seems to be getting fuel as the bowl fills up after a regular period of priming.

I'm sure the oil could use a change, but the latest symptoms have me thinking I blew the starter cranking it the last couple weeks, or there's some kind of short in the AC wiring somewhere. Perhaps the carb will need to be fully replaced, but like I said, it was surprisingly clean when I took it apart.

The MH gas tank is 3/4 full. House batteries read 3/4 charge on the in-house panel but only get charged through the alternator and the rig is in the process of being registered out of state so I have to be careful where/when I drive it and I don't take it but for perhaps 3-4 miles in a loop before parking it again, every 3 days or so.

Thanks!
Hello sir and welcome, the first thing to do is check to make sure your house batteries are at full charge. After you make sure the house batteries are good you should be able to find the positive lead into the generator and make sure you have 12 volts minimum. I know it's been suggested to check your starter but I cannot in my 5500 yours's may be different. After making sure your house batteries are good make sure you are using the start switch at the generator and again I'm not sure if you have a remote start or not so again I apologize if you don't. It really sounds like your house batteries are low on charge, if I'm wrong there will be several more well versed people to claim different here shortly. LOL Good luck
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Old 03-13-2022, 04:59 PM   #8
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pull spark plug.. put a new plug in the wire,, touch plug to motor . try to crank... without plug in it may spin... this will show spark..

but you may have fried starter.. it she clicks and no spin,, no click check solenoid or battery
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Old 03-17-2022, 06:19 AM   #9
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Here is the link for the owner's manuals.

https://www.cummins.com/rv-generator-manuals
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Old 03-26-2022, 08:42 PM   #10
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Late reply

Wow! I never realized how many of you responded to this -- thank you. I figured out the problem and simply moved on. Will post a very detailed run through of the symptoms and fixes in the near future to serve as a reference for someone else.
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Old 03-26-2022, 08:55 PM   #11
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OK all, here it goes. This is the run-through of generator tribulations over a period of about a month that finally led to my generator firing and purring like a kitten under full load.

Couldn't get the generator to turn over at all after buying the RV. Pulled the carb out and soaked it for 72hours (and no I didn't blow or wire clean it - novice engine repairman here, first engine I've worked on). Reinstalled the carb and got the engine to turn over once before it went back to cranking hard but never starting. Also changed the spark plug and air filter.

Then, a new symptom occurred: I would crank it like before, but after 3-4 seconds the crank slowed down to the cadence of a human cough - quite literally 1-2 seconds between cranks.

Out of the blue, I decided to take the valve cover off and lo and behold, one valve spring was snapped and at the bottom of the vertical basin with the retainer and clip, and the other spring was snapped in the same spot but still pressing against the rocker.

Picked up new valve springs from Cummins, got a feeler gauge set, installed the springs and set the lash. Boom, fired right up.

Next issue: the genny would run under no load for about 30 minutes and die, and under load (AC) for about 5 minutes and suffer the same death. Waited until it died and loosened the screw on the bottom of the fuel bowl and only about 10 drops of fuel came out. Ordered a fuel pump and filter from Cummins. Installed them the next day and the genny runs perfectly with a full load.

Also changed the oil somewhere in the interim there, and screwed around with oil levels (as per the famous youtube video) for about two hours before I finally checked the damn fuel bowl like I should have from the get go.

Model number is 4KYFA26100K

Thanks again for all the replies.
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Old 03-27-2022, 08:41 AM   #12
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Thanks for following up.

Glad you got it all fixed up.
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