Dead Onan 4000 generator

[DouglasC]

Went to fire up my Onan 4000 generator for the 1st time this year. Held the Start/Prime switch down on Prime and the light came on and flashed like usual. After about 5 seconds I released the switch as usual and pushed the Start side of the switch. Nothing happened - - totally dead. Tried the Prime side of switch again - - nothing happened. Last time this happened (generator dead) 7 years ago the cause was a faulty circuit board that needed to be replaced.

Anything else I should be checking before I order a new circuit board?

[DouglasC]

Thanks for all the replies. Waiting for warmer weather again to continue working on the genset as the motorhome is stored outside. Have yet to figure out how to remove the control board so as to replace it with a new one. My connector plug does not look like the one in the manual. That one has 15 contacts (5 rows of 3), mine only has 8 contacts (4 rows of 2). And there are only 6 wires going into and out of my connector.

[craz_z]

Took the plunge with drew e link and went through the password process to get some of the info.

so the wiring diagram you need for spec k is 611-1267
By the looks of it fuses are not there for 12v side.
the breaker on the gen is only for 120v as u probably already know that.


on the diagram it looks like J1-8 on the pinout is bat+ J1-6 is bat-
J1-16 is starter wire that goes to solenoid that allows starting to happen.

looking at the diagram you need 12v on the large lug on solenoid and you also need 12v+ on the small pin on the solenoid while push the start button. this energizes the coil and ignition

With a test light lead connect bat+ and check ground on outside of frame lug. I would also check if possible J1-6 with a pin or paperclip to verify results that you have good ground light should come on if it doesnt BAD ground.

next would be move test light to bat- and check solenoid which i think you did. i would also check the signal wire or J1-16 which is small pin on solenoid WHILE push the start button if light comes on bad solenoid if nothing problably bad board as long as grounds check ok.

Then I would call the board now there also could be pin fitment issues as well as corrosion so i would take a careful look at the J connector on the board and the pinout to rule this out pin fitment can be as simple as unplug replug or spray contact cleaner if you see any green crusties. as your board is 327-1413 and is approaching 500$

your solenoid is 307-2586 theoretically you could add a small 10amp fuse to a jump wire and jump from bat positive to the small wire on the solenoid to verify your starter turns this might even be the quicker way to verify board however pin fit and corrosion can still be the wild card.

[DrewE]

larry cad wrote:

clicky doesn't seem to work!

You're right; I messed it up. Sorry about that. The post has been edited to work now. This is the correct link.

[larry_cad]

DrewE wrote:
Download your Cummins/Onan RV generator manuals here. You'll have to register (free account) to download them, but they're all there for whatever spec level you happen to have.

The "parts manual" also generally has some service information (troubleshooting guidance, valve clearance specifications, that sort of thing).

clicky doesn't seem to work!

[DrewE]

Download your Cummins/Onan RV generator manuals here. You'll have to register (free account) to download them, but they're all there for whatever spec level you happen to have.

The "parts manual" also generally has some service information (troubleshooting guidance, valve clearance specifications, that sort of thing).

[craz_z]

I'm struggling to find the documentation on the spec K it sucks cause this particular spec is on like every motorhome made in the last 20 years.

I tore one of these down but its been a couple of years. There is a possible fuse to the control board maybe F1 is number.

You could try to take out the switch panel where the start stop is on the genny it could be hiding behind it.

early models (not spec K) did have this fuse near the switch in plain view.

Option 2 is to start taking out the stuff around the control box as there could be another fuse hiding near it.
Bat+ comes direct to starter solenoid ground is on the outside of the frame where all the wires enter the genbox. that solenoid also has the signal to fire the starter I would trace any smaller wires to see where they lead hopefully to a fuse.

there is a pinout to the J1 P1 connector you could backprobe to verify voltages to the control box.

After that control box could be a possibility just cover all your basis as those are silly expensive. the fact you have already replaced it once indicates a short could be hiding in the wiring somewhere.

Onans are great until they are not and if it wasn't for the fancy switch in the cab i would rip it out and use the space for a portable gen as for the cost of the control box alone you can buy any cheappy genny on the market.

[DrewE]

craz z wrote:

I had a bad starter that would work half ass then finally nothing the starter needs to wind up to throw out the gear into the flywheel once locked out nothing happens and seems to go when you least expect it.

I had a bad starter for awhile, with what sound like similar symptoms: it had trouble getting the engine over the compression stroke, and would sometimes need a running start to do that. It also cranked over the engine without much vigor. Eventually, it burned out and I had to replace it.

On examining the remains of the bad starter, I found that one of the four brushes was not working properly, which meant the starter had been operating at half power for quite some time. (The starter has four brushes and four poles, unlike many motors that have but two.) It finally died due to some of the coils on the armature burning out, probably due to being stalled or nearly stalled since it lacked torque. At any rate, before that happened, I probably could have repaired it simply by fixing the bum brush.

[DouglasC]

The generator is dead! No prime, no starter - - nothing! I checked the voltage at the starter solenoid when the "Start" switched is pressed - - zero volts. So the signal from the control board to send voltage to the starter isn't happening. That's a control board problem. This happened to this generator once before about 7 years ago. A new circuit board fixed the problem then.

[craz_z]

A few questions
On prime does the fuel pump hum like normal?
Checking 12v input is fine what about output to starter?
Can u take out plug to release compression maybe reach in deep an bang on starter?
I'm thinking starter the bendix on the Onan is plastic trash that locks up an falls apart a current meter on the output should help.

I had a bad starter that would work half ass then finally nothing the starter needs to wind up to throw out the gear into the flywheel once locked out nothing happens and seems to go when you least expect it.

If you don't have a slideout Gen it sucks to get to the starter as it's on the back side.

Another option is to see if you can gain access to the fan an turn the flywheel it may unlock the bendix you may get a few more starts but will indicate its time to change the starter.

[DrewE]

DouglasC wrote:

Never knew that an Onan 4000W generator has a 12VDC fuse. I don't see one. Where is it located?

On mine, it's in plain sight, on the generator itself, right next to the generator-mounted start/stop switch. Looking at some parts manuals, it seems that your spec level (spec K, the last character of the model number) they omitted the fuse. Mine's a spec H generator.

[DouglasC]

DrewE wrote:
Have you checked the 12V fuse on the generator? It's an easy, low-hanging fruit sort of check. Checking that all the connectors in the guts of the generator (through the firewall) are clean and tight is also worth checking/trying.

Double checked my incoming voltage at the generator today and got a reading of 13.55VDC. All connections in the generator look clean and tight.

Never knew that an Onan 4000W generator has a 12VDC fuse. I don't see one. Where is it located?

[DouglasC]

time2roll wrote:
Most Onan experts want the full serial number to avoid playing 20 questions about what you have.

Model #4KYFA26100K

Serial #B060888956

Built in 2005

[time2roll]

Most Onan experts want the full serial number to avoid playing 20 questions about what you have.

[Ranger_Smith]

Mine would prime then nothing. There are 3 separate relays in there. Search the internet for your model of generator and you will find a maintainence and troubleshooting manual.