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RV Onan Generator Wont Stay Running without Start Depressed

Provience

Provience

Kill!
Joined
Jul 8, 2009
Member Number
15
Messages
9,376
Loc
Gatesville, TX
Need some help with my generator. It DID work a couple years ago, then the start switch inside quit working, then it quit staying running altogether :homer: yes, it has sat for a while without running and that likely caused it to fail initially. I have found several threads on various forums about this and 100% of them either are resolved with "replaced carb with new" or "replaced oil level switch".

It's got oil, so I unplugged the oil level switch, when grounded it won't attempt to run at all, when open it runs fine until I release START and just slows down until it dies, just like hitting the STOP button back when it used to run right.

I took apart and cleaned the old carb somewhat, no change and nothing appeared plugged up or altogether dirty. Went ahead and ordered a new carb and it is still doing the same thing. Circuit breaker on or off, no change.

any idea what would be next?

ONAN 4kw Gasoline (over 1/4 fuel in the tank) Model # 4KYFA26100A which is among the earliest of the 4KY series. You can see in this picture, in the lower right corner, where the oil level sensor lead is disconnected.

20220827_162426.jpg


2 bolts through the front, 10mm socket on short extension to remove the old carb, fuel line disconnected.

20220827_162936.jpg


picture of the hole and the links.

20220827_163024.jpg


https://smile.amazon.com/dp/B085G6LJXH?psc=1&ref=ppx_yo2ov_dt_b_product_details used this amazon carb, claims it is for all the 4ky generators. came with the banjo bolt which my A model uses instead of the electric stuff.

20220827_163235.jpg


plugged in the new one, takes a while to get the air horn, gaskets, carb, insulator and more gaskets all lined up.

20220827_165805.jpg




and cranked it until fuel came up, and cranked it some more to fill up the bowl. It seems to pump out plenty of fuel through the line without issue.

just won't stay running if i'm not holding start :homer:

halp.
 
Is it putting out voltage? Seems like there are some that need to see the AC output to keep running. Had one with a broken winding in the alternator not allowing it to keep running.
 
When you hold the start button does the starter continue to run?

Sounds like the switch or a latching relay (probably the wrong term) but something to keep the running circuit energized.

Sounds like an electrical issue
 
Tizken said:
Is it putting out voltage? Seems like there are some that need to see the AC output to keep running. Had one with a broken winding in the alternator not allowing it to keep running.
Click to expand...
should it be putting out voltage when holding start?

i'll have to go digging through the paperwork records and see if i can find where to pick up the output on the generator. it's got several wires, but none that look obvious :homer:
 
Stingray said:
When you hold the start button does the starter continue to run?

Sounds like the switch or a latching relay (probably the wrong term) but something to keep the running circuit energized.

Sounds like an electrical issue
Click to expand...
yes, it sounds like the starter stays engaged. the engine comes up to what sounds like normal rpm and sounds smooth, then I let off the switch and it just shuts down. Manually holding the throttle/choke blades in various positions doesn't change anything other than the sounds.
 
www.cummins.com

RV Generator Manuals | Cummins Inc.

You can find copies of some of our most popular RV generator manuals below, free and downloadable. Looking for the EC-AGS+ manual or manuals for Cummins Commercial Mobile generators? You can find them here. If what you need is not listed below, please see the complete inventory of all our...
www.cummins.com www.cummins.com

list of manuals from cummins, who apparently owns onan now :confused:



operators and install manuals...let's see what they hold
 
downloaded those manuals, they have troubleshooting AND wiring diagrams, so i'm going to upload them from my computer to the forum as attachments. I came across many old threads on various forums and blog posts which had dead links, at least this way the links will hopefully stay here for a while.

hopefully tomorrow i'll be able to do more digging and figure out WTF is going on

edit: parts manual added

edit2: You searched for onan service manual - Yakima Generator

yakima generator, for all your service manual and parts needs :smokin:
 

Attachments

  • install manual gensest.pdf
    3.3 MB · Views: 12
  • operators manual genset.pdf
    1.4 MB · Views: 5
  • parts manual genset.pdf
    2.6 MB · Views: 5
  • generator service manual.pdf
    3.1 MB · Views: 18
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kenney180 said:
There is a double pole latching relay thing in the control box, my 10k onan standby did the same thing.
Click to expand...
inside the box? alright, welp sounds like i'm going digging more tomorrow into it. Need to flip the whole thing around, i've been working ~18" away from the fence currently on that side and it is slowing things down.

it doesn't actually want to tell me very much about what happens inside "control, assembly" and there isn't a corresponding part number to order for it, so i'm looking forward to seeing what is under the cover.

I tried cranking it with a multi-meter shoved into the 120v outlets and didn't get anything. but that may not mean much as I wouldn't expect it to try and supply to the load while on the starter. Turning off all the circuit breakers inside and out doesn't help anything, so it is unlikely that it is pulling too much load too early
 
Try asking here

Onan Generators

Restoring, operating, and maintaining vintage Onan generators. When asking questions about your generator, give your model number AND serial number. Smokstak Subscriptions, Support and Information
www.smokstak.com

Mine is a 1971 CCKB and when I had that problem it was because the brushes were worn out. They werent cheap, but if they last another 50 years... btw, the brushes are ¼th x1w 2"long
 
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Working through the diag manual, I am getting 11.5vdc from the flash voltage at plug 4, so that should be good.

I am getting 0.5vdc instead of either 7-13 vdc or 40-100vdc from the gen. Field voltage. Either bad regulator or bad brushes/stator/etc.

Voltage regulator diode test comes back good, however the manual says "it may test good and still be bad, replace with known good and try again" :homer: known good is about $300, so I'm going to assume good and see what it takes to get the gen out to inspect the brushes and such.

With the voltage regulator unplugged and jumper wires in its place, I'm still only getting 27 vac instead of "approximately 40 vac" so not sure if that is close enough, but it is something
 
20220828_121715.jpg


Tapped off the flywheel/cooling fins.

With a piece of welding wire holding the brushes up, there is no connection between the slip rings and rotor snout, as it should be.

Slip rings look good. Brushes make good smooth contact, max wear is 1" and I am closer to half or 3/4 wear. So good there.

Measuring the stator, none of the terminals are short to ground, so that's good. None of the windings test short to each other either, all appropriate resistance.


So....damn, that leaves either the regulator or the control board.
 
Provience said:
1661656241972.png


1661656191423.png



alright, taking notes, going to check brushes on the front while taking everything apart tomorrow
Click to expand...
Provience said:
Tapped off the flywheel/cooling fins.

With a piece of welding wire holding the brushes up, there is no connection between the slip rings and rotor snout, as it should be.

Slip rings look good. Brushes make good smooth contact, max wear is 1" and I am closer to half or 3/4 wear. So good there.

Measuring the stator, none of the terminals are short to ground, so that's good. None of the windings test short to each other either, all appropriate resistance.


So....damn, that leaves either the regulator or the control board.
Click to expand...
Good connection at the terminals for P5 and P6 (ie: the wire isn't broken between the brushes and the box)?

Aaron Z
 
aczlan said:
Good connection at the terminals for P5 and P6 (ie: the wire isn't broken between the brushes and the box)?

Aaron Z
Click to expand...
correct, wires are making good connection all the way through.

i'm starting to thing that the 27VAC that I was getting with the regulator removed is close enough to the 40vac I was looking for. All of the stator winding test that I got was a little bit higher than what the chart says. Failure is anything below what the chart says, and the chart says "at 77*F +/- 10%" and it is ~100*F here right now, so maybe that is all related back to it.

which points me to a bad regulator
 
Provience said:
correct, wires are making good connection all the way through.

i'm starting to thing that the 27VAC that I was getting with the regulator removed is close enough to the 40vac I was looking for. All of the stator winding test that I got was a little bit higher than what the chart says. Failure is anything below what the chart says, and the chart says "at 77*F +/- 10%" and it is ~100*F here right now, so maybe that is all related back to it.

which points me to a bad regulator
Click to expand...
Cha-ching...

Aaron Z
 
yakimagenerator.com

Onan 56-305 Voltage Regulator - Yakima Generator

The 305 replaces Cummins Onan Regulator Voltage, 305-0851, 305-0809-01, 305-0782-01, 305-0830-01, 305-0826, Microlite & Emerald Generators, KY
yakimagenerator.com yakimagenerator.com

cummins/onan wants $590 for the 305-0851 exact replacement regulator. Ebay wants $200 for a used probably works one.

Yakima generator, where I was able to get the service manual, wants $300 for a 56-305 regulator which is "new, upgraded, direct replacement" for several others, so that gets my vote.

edit: and yes, I did price out just replacing this with a whole bunch of batteries...plus the panels and such, i'd be about $3-4k to replace the generator, and about $4k to replace the whole unit with another 4k gas gen.
 
God damn piece of shit.

Got it all back together, cleaned and sanded all connections as I went. Wife goes "and poof. Magically it works"

What the hell, primed it and fired it off. Fucker is still running.

Little bit of light smoke and a little lope for now, let's see if it smoothes out

Not a video, just a picture of what it looks like while it works :rasta:

20220828_155344.jpg
 
Just thinking out loud, does the start switch send power or ground somewhere to bypass the low oil shutoff? Messing with it at the switch might not be where the problem is. You might have bumped a connection when you were playing with it and got it all working again.
 
D Nelly said:
Just thinking out loud, does the start switch send power or ground somewhere to bypass the low oil shutoff? Messing with it at the switch might not be where the problem is. You might have bumped a connection when you were playing with it and got it all working again.
Click to expand...
Maybe, but if the low oil circuit was forced open (unplugged) it didn't help. I'm leaving the low oil switch unhooked for what it's worth, just in case.

I had taken the entire wiring harness out while I had it apart, so if it was a loose connection, I cleaned and touched all of them going back together.

Saving the old carb for a spare in the rv anyways. All of this was so i could use the air conditioning, and after warming everything up, it didn't want to kick on :lmao: oh well, got a couple issues sorted at least


edit: Digital Thermostat - Jayco RV Owners Forum link with pictures about swapping RV style thermostat to home style thermostat.

edit: Coleman Mach RV Air Conditioner Parts this looks like the link for parts if/when i get to check out the ac unit

edit: http://old.rvcomfort.com/pdf_documents/1976342.pdf once i get my model numbers, there will be a spinoff for the A/C. Looks like there are a bunch of places that sell a bunch of the parts and doo-dads. biggest issue will then be getting the unit charged/recharged depending on the issue
 
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Messing with the brushes probably freed them up. Doesn't take much to make a brush hang up in its holder, lifting and letting it snap back down probably cleared it up. Just a little shmoo in the holder will hang them up and cranking the engine is enough to bounce them off the slip ring enough to have bad contact.
 
My Onan diesel generator has done that a couple of times even after new brushes. Cleaning the slip rings with Scotchbrite taped to a paint stick fixes it.
 
Went to go mess with the air con today, it's so old all the labeling stickers and information is obliterated.

Went to fire up the gen set to run it some more....fucker won't run without holding down start switch again :lmao:

Very seriously back to considering using that space for batteries instead with a decent inverter
 
20220902_145214.jpg


Problem solved, problem staying solved.

$450 and it will be more easily mobile, just need to cajigger a mount for it, going to go above the rear bumper.

Lose out on the electric start and auto tie in to the coach fuel tank, but I can leave the electric fuel pump and just transfer as needed.
 
little thing at the bottom is to adjust for elevation, turn it all the way in.

mine does what you describe, and i start it with the elevation all the wall in, and back it out after a couple minutes




maybe someon already said that??
 
tracyb said:
little thing at the bottom is to adjust for elevation, turn it all the way in.

mine does what you describe, and i start it with the elevation all the wall in, and back it out after a couple minutes




maybe someon already said that??
Click to expand...
Yeah leans or fattens the main jetting, doesn't matter where in the swing it ends up :laughing:
 
Derailing my own thread. Obvious concern about buying any other gen set than onan permanently mounted is space. So here is my progress on where I'll be mounting the mobile one.

20220903_173848.jpg


With a spacer I can still get 2 spare tires back here as well. High enough up so that I can mess with the hitch while mounted, low enough that I can put it there by myself

20220903_173857.jpg


This the the existing 3" c channel with spare tire mounting studs

20220903_153607.jpg


Mostly using 2x3 box tube because that is what I have, drilled holes to get to existing studs.
20220903_161512.jpg


Flux core is life, used 1 90 wall and 1 120 wall so as to stick with scraps, 13.5" wide and about 16" long.
20220903_171654.jpg


Adding in a third leg brace, need to pick up some 1/2" I.d. tube and a 5" or so long bolt, going yo just drill at an angle rather than cut and bend the brace to be flush mounted
20220903_185413.jpg
 
I went through all that with an older Onan gen set on an RV. The ecm or whatever they call it didn't test out. Power/ground going in, nothing coming out. I could jumper around it and get the motor to run just fine. Finally replaced the ecm. Still no start/run. New ecm didn't test out either. Place I bought it from said it was good and wouldn't send me another. I sold the gen set to a guy for parts and happy to see it gone.

I'm convinced the ecm went bad and the new one was bad as well. I wish I would have had a known good ecm to try out.

Good luck!
 
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