Onan 4K won't run unless the start button is kept on.

[Kahoona]

Originally Posted by cimplexsound

If the genset runs then there is no need to replace the rotor. You should check the transfer switch. (The transfer switch is installed on the genset just behind the start/stop button) When you release the start button the transfer switch on the genset is suppose to stay on unless you hit the stop button or plug your RV into shore power. In this case the transfer switch would automatically shut the genset down. So this an electrical issue and the transfer switch is the first place I would check for shorts or loose connections. These gensets usually weigh in ay a whopping 300 pounds so if you don't have to mess with the motor, don't. Cummins builds an awesome genset, I've seen these things sit around for year with no use and they start up on the first turn. Also you can clean it with compressed air without taking it apart or taking it out of the RV. Just remove the motor cover, and air filter and give it a good blow. The dirt will be expelled from the shaft when you fire up the genset.

Ahhh I only wish... This one is the dreaded KY J series. No transfer switch. Uses a chip in the board which cannot be tested or troubleshot. Process of elimination only. Motor is great and starts easily but the control board won't let it run. Windings have to be tested to rule them out. Needed to be cleaned to rule out shorts. Can't get to them in their position inside the RV ect. ect. I know about that weight! In the end provess of elimination points at the board so I am replacing it. One of the old timers on the Smokestack board said "can't troubleshoot them just get a junk parts unit and throw parts at it till it starts."
Onans reputation is"just keep it in gas and oil and it will run forever" but they forgot that when they made the KY and KYD line. That having been said my biggest problem now is how to get the parts I need from Cummins Onan's primitive dealer based telephone only system in time to re-assemble it and get it back in. I will then have a like new unit with improved electronics and added sound deadening. I hope.

[okcnewbie]

With the rotor and stator checking good I think the board is going to get you up and running again. Good luck and thanks for the updates.

[Kahoona]

Just a status report while I wait (abd wait) for parts. Got the new altered brain in its clear semi silid plastic coating yesterday. Still waiting for the wiring harness, brushes and springs, isolator feet ect. Taking time to wire brush and repaint/undercoat the tray and base parts as well as getting the goo off of the metal bits and giving them a shot of Rustoleum. It just looks better and it is so much easier to work on if it is not a rusty oily mess.

One important thing I saw and fixed. I had noticed that there was a slight throttle delay when a load was added. Lights might dim just a tiny bit. Thile I was checking out the carb linkages I say that there was a groove worn in one of the moving parts which open the throttle when the governor opens. The groove caused binding. Five minutes with a couple of grades of emery stick fixed it. That metal is soft. Should have been harder. This is why I like to clean stuff up and pay attention to it. If you want to check yours just unhook the linkages and work it by hand. You will feel it.

Spent over a half hour on the phone with South Miami Cummins. Since I had once spoken to Mike nobody else would talk to me so I had to wait. Once you are put on hold you can be shunted to a fax machine. Then you hang up and start over. Probably get the parts Monday.

[Kahoona]

Mt wire harness came in the mail yesterday so I am ready to reassemble. I am also getting some info from the good folks at Smokestack. I have run into a problem already. Both wires going to the brush block are the same color. I would like to assume that they are interchangeable. I am nervous doing that because of the effort needed to get back inside if it does not run. One side of the brush block seels like it has a - sign but it could be something else. There is no + on the other side.

In the attached diagram from the manual the wires are labeled F+ and F-.Do I need to dismantle the harness and go back to the plug to trace the + side or are they for sure interchangeable? Has anyone done this?

[okcnewbie]

Originally Posted by Kahoona

In the attached diagram from the manual the wires are labeled F+ and F-.Do I need to dismantle the harness and go back to the plug to trace the + side or are they for sure interchangeable? Has anyone done this?

Most likely the original was working fine. Can't you just compare it? There aren't that many pins. Just ohm it out or use the schematic to find the other end. (Unless I'm missing something)

[Kahoona]

Originally Posted by okcnewbie

Most likely the original was working fine. Can't you just compare it? There aren't that many pins. Just ohm it out or use the schematic to find the other end. (Unless I'm missing something)

I have a photo but the original 2 wires going to the brush block were both black so my photo does not help. The new ones are both white. I am working on understanding the diagram and schematics. Here is the schematic.

[Kahoona]

The answer is ridiculously simple and I should have seen it. Laxer printed on the insulation of one of the wires is the F+. That must go on the other side from the "-" molded into the brush holder. It is hidden beneath the black protective covering. That will make reassembly easier!

[Kahoona]

It started and ran today. It now needs a starter relay but it does run fine. Relay comes on Friday and I hope to put it in the RV Saturday. I'll let you know if it works out.

[cimplexsound]

The only thing the starter relay does is allow the starter motor to turn when you depress the start button. A transfer switch or operating board is usually mounted behind the start/stop switch on the genset itself. The transfer is the electronic device that allows you to start and stop the generator from inside your Motorhome via the start/stop switch on the dashboard at the drivers seat. It is also like a mini computer that makes sure your genset keeps running until you push the stop button or if shore power becomes present. It is a good idea to take to the transfer switch or board apart once a year and clean it with compressed air. dirt or grim could easily shorten the circuit board out. The board is really the brain of the generator that keeps everything working. I also have the Onan 4K. I did quite a bit of work on my genny the other day. Cleaning the air filter, spark plugs, transfer board etc. these Onan gensets have a fuel filter and 12 volt electronic fuel pump that runs off your house battery while their in operation. Some gensets charge the house batteries, others do not. If your house battery is not fully charged, the fuel sometime cuts off when you release the start button or it just won't start. So make sure the circuit board keeps the circuit open after you tap the start button. Even if the genset is running good now, you should test it to make sure the same problem doesn't reoccur later. If the motor dies after you release the start button then there is usually a relay on the circuit board that is going out and needs replacement.




Class A 30 Foot Ford Fleetwood Flair with Ford 460 motor.

[okcnewbie]

Originally Posted by cimplexsound

The only thing the starter relay does is allow the starter motor to turn when you depress the start button. A transfer switch or operating board is usually mounted behind the start/stop switch on the genset itself. The transfer is the electronic device that allows you to start and stop the generator from inside your Motorhome via the start/stop switch on the dashboard at the drivers seat. It is also like a mini computer that makes sure your genset keeps running until you push the stop button or if shore power becomes present. It is a good idea to take to the transfer switch or board apart once a year and clean it with compressed air. dirt or grim could easily shorten the circuit board out. The board is really the brain of the generator that keeps everything working. I also have the Onan 4K. I did quite a bit of work on my genny the other day. Cleaning the air filter, spark plugs, transfer board etc. these Onan gensets have a fuel filter and 12 volt electronic fuel pump that runs off your house battery while their in operation. Some gensets charge the house batteries, others do not. If your house battery is not fully charged, the fuel sometime cuts off when you release the start button or it just won't start. So make sure the circuit board keeps the circuit open after you tap the start button. Even if the genset is running good now, you should test it to make sure the same problem doesn't reoccur later. If the motor dies after you release the start button then there is usually a relay on the circuit board that is going out and needs replacement.




Class A 30 Foot Ford Fleetwood Flair with Ford 460 motor.

Did you actually read this entire thread before trying to help?

The OP has become quite an expert on his particular model 4ky.

[Kahoona]

Originally Posted by okcnewbie

Did you actually read this entire thread before trying to help?

The OP has become quite an expert on his particular model 4ky.

Thanks. New relay coming in today USPS willing. Assuming it runs properly I hope to drag it over to the RV and reconnect it tomorrow. With a few 8x8 wood blocks and a couple of floor jacks I think I can get it op inside and working tomorrow. Alternately I can get my "Suns out Guns Out" neighbor from 'Jersey to bench press it up there while I put in the bolts.

[Kahoona]

It is running fine now. All I have to do is connect it to the RV and lift it up into place. I had a bad couple of days when nothing worked or scary things happened when I tried. The main problem turned out to be a bad connection.
The wire in the harness that caries 12v from the battery to the brain was not making proper contact in the plug/socket. Once the plug was pulled out and put back in it worked fine.
Another confusing thing to know about this is that the 2 terminals on the top of the relay are not both positives as we had thought. One is + and one is - or gnd. Both need to be connected to the brain to work. I was trying to test the relay by touching 12v to either one while grounding the mounting.
Another confusing thing is that, unlike the original Onan brain the Flight Systems modified brain requires that the start switch be held down for a second after ignition occurs otherwise it shuts down. I am hoping that this will last for a while now. Crossing fingers but not holding my breath. This is like a member of the family. A brother in law with bad habits that steals our money and deserts us when we need him but can be nice to have around