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Ask Hank F. Your Own Question
Hank F.
Hank F., Technician
Category: Small Engine
Satisfied Customers: 14537
Experience:  Certified on Onan and Generac generators
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Just bought a used rv with Onan 4KY-Fa generator. It worked

Customer Question

hi, just bought a used rv with Onan 4KY-Fa generator. It worked fine for 3 days and the other day just would not start, but in a strange way
JA: Do you have fuel in the tank? If so, is the shut-off valve open and the fuel clean?
Customer: fuel is there...if I start and keep pressing START, it will run...but as soon as I let go of a STSRT button, it shuts off like someone just pushed STOP
JA: Do you plan on doing the work yourself?
Customer: well, at least try to find out what the problem is...I thought, it may be a faulty switch of some sort...
JA: Anything else we should know to help you best?
Customer: Im not familiar with ONAN gens, so, thought it might be a common failure
Submitted: 5 months ago.
Category: Small Engine
Customer: replied 5 months ago.
I was driving when it shut off. I do not know the reason why it shut off....possibly vibration induced some failure...i know, it gets fuel, because it starts when I I push start ( on either panel inside the RV and outside on the gen itself)...it behaves the same way. It starts, but as soon as I let go of START, it stops...it seems to be an electrical disconnect of some sort. (but both switches acting the same way is unlikely)....is there a relay somewhere that switches from a battery to alternator?...maybe alternator is bad and does not generate voltage to spark the plug...(there has to be some coil to generate voltage for a plug....right? :O)
Customer: replied 4 months ago.
Customer: replied 4 months ago.
disconnected remote switch... - same thing, so, it is not a remote switch sticking!
Expert:  Hank F. replied 4 months ago.

What is the full model number of the genset?

Customer: replied 4 months ago.
4.0 KY-FA/26100H
Customer: replied 4 months ago.
I wasn't sure if this website is working...thanks for replying.
I have read about visible damage on a control board on some blog, but have not pulled mine out to look at it yet.
Is there a way to test a board through a connector to find out if it's faulty?
The engine starts and sounds like a good working engine as long as I keep my finger on a start button...
Customer: replied 4 months ago.
Hank, are you on central or pacific time?
Expert:  Hank F. replied 4 months ago.

Sorry, I work 2 jobs, and help on Just Answer in the evenings. I am not ignoring youi, I just can't be online 24/7.

I am on Eastern time.

The most common cause of your issue is that the genset is no longer producing power.

Connect an AC voltmeter to the output leads of the genset.

Press and hold the stat button to keep the genset running for 5 or 6 seconds.

What voltage reading do you get?

Customer: replied 4 months ago.
where do I measure that?..I don't know which connector is output...or do you mean 110 AC converted from 12 V
Customer: replied 4 months ago.
I did not think, you are ignoring me, I just wanted to figure out a good time to chat
Expert:  Hank F. replied 4 months ago.

The output leads are the 120V lines coming out the left side of the genset. They are in a gray conduit.

Customer: replied 4 months ago.
I don't have any schematics of my RV(unfortunately) It seems like the engine is supposed to run regardless of the "generator" component..the engine is the driver for generating power, but power generated is not used to run the engine (I think) am I right?
Customer: replied 4 months ago.
I am hooked up to the house AC now...do you suggest I disconnect and stick a volt meter into the RV AV outlet and see what it reads while I run the engine?
Expert:  Hank F. replied 4 months ago.

No, the engine will not run if the genend is not producing power. This is a safety feature to prevent further damage.

If your coach has a transfer switch, you will not be able to use a receptacle to check for power. You need to check ti directly at the genset.

Customer: replied 4 months ago.
I see a 30 amp circuit breaker..., but I can't get to its' connectors...
The conduit that you said, is a plastic tube...it looks like it has 3 wires...maybe 12 gauge or so, they seem to be leading to or near the control board...I don't see the lugs. I would have to take apart a few things before I get to it...unless you know a better place to put a voltmeter to...
Expert:  Hank F. replied 4 months ago.

Don't take it apart at the genset - it is impossible to get it back together without taking the genset out of the coach.

It is normally easier to open the conduit from the other end, as the conduit leads to a junction box.

If you have one of the oddball j-boxes that is just too hard to get to, you will need to remove the control panel from the genset to access the back of the circuti breaker.

Customer: replied 4 months ago.
I found a conduit junction box closer to the middle of the chassis bolted to the bottom.
had the leads hooked up, but forgot to turn on the circuit breaker...cranked the engine - it started - no AC voltage (obviously-breaker is off)
Well, now, the starter won't turn - seems like house battery discharged from me cranking ( i suspect that battery is old and half dead)
But if I start my main motor, it should charge it up and start...right?....I assume, the generator starts frm a house battery, not from the main car battery...right?>
Expert:  Hank F. replied 4 months ago.

The chassis engine may or may not charge the house battery. It depends on how the coach is wired.

Most gensets are connected to house battery, but sometimes I see them on the chassis battery. I can't say how yours is without seeing it.

Customer: replied 4 months ago.
ok, I managed to crank and start the gen...while I was holding it running - it measured 10 v AC in the conduit box....
Expert:  Hank F. replied 4 months ago.

Remove the access cover from the genset.
Inside, you will see a ‘divider’ about 2/3 the way to the left.
Attached to, and going through, this divider, are 2 white plugs.
The plug on the bottom is a 15-pin plug and is for the controller. The plug on top is a 12-pin plug, and is for the voltage regulator.

Disconnect the 12-pin voltage regulator plug. On the right side of the plug (the side leading back to the generator), locate the wires marked J4-9 and J4-10.
Set your meter to ohms and connect one lead to each of these wires. It should read about 18 ohms.
Now reconnect the plug and set your meter to VDC.
Connect the negative lead to a good ground, and back probe the positive lead into the plug at wire J4-7.
Press and hold ‘Start’ for about 5 seconds. It should read at least 10V.
Now back probe the positive lead into the plug at wire J4-9 and press ‘Start’ for about 5 seconds. It should read a minimum of 12V, and preferably between 20-30 volts.
Now back probe the positive lead into the plug at wire J4-10, and press and hold ‘Start’ for about 5 seconds. It can read anywhere from 1-30 volts, as long as there is a reading.

What do you get with these tests?
.

Customer: replied 4 months ago.
ok
I got 27 Ohms on 9-10 pins (btw on my gen they are labeled P4-9, P4-10
p7 to ground was 17 V
P9 to ground was 0 while cranking/running
P10 to ground was also 0 while cranking/running
Customer: replied 4 months ago.
I did not re-connect the 12-pin plug when I did this....ooops....maybe that's why the last 2 readings were 0...
Will try tomorrow - i don't want to upset the neighbors by cranking that gen all night...:)
Expert:  Hank F. replied 4 months ago.

Ok.

Customer: replied 4 months ago.
ok, measured 9 to ground = 8.3 v dc
10 to ground = 2.1V dc
it was hard to get a good contact thru a connector shell, I used a thin copper wire to reach in.
so, what's the verdict? - bad voltage regulator?
Customer: replied 4 months ago.
Hank, you here?
Expert:  Hank F. replied 4 months ago.

Yes, a bad voltage regulator.

Customer: replied 4 months ago.
thanks....do you happen to know a price range and a part number for that?
thanks,my rv came without a service cover for the genset....do you recommend getting one?
thanks,
Expert:  Hank F. replied 4 months ago.

Part number of VR is(###) ###-#### Don't know the cost.

Do NOT run the genset without the maintenance door. It will over heat and burn up.

Part number of door is(###) ###-####

Customer: replied 4 months ago.
thanks for your help!
once I get the part - will let you know the results :O)
cheers,
a
Expert:  Hank F. replied 4 months ago.

OK.

Thank you for using Just Answer, and please remember to take a moment and rate my performance.

Customer: replied 4 months ago.
Hi, Hank.
Well...a new regulator came....I installed it and...SAME OLE THING...same symptoms...
I let go of a start - it diesI measure 17 volts on the conduit box on the output of the gen.
j7 to ground = 11 vdc
j10 to ground =1 vdc
...what is next.....BRUSHES????
Customer: replied 4 months ago.
slip ring?
how do i get to them?....do I have to take the unit out?
Expert:  Hank F. replied 4 months ago.

Remove the access cover from the genset.
Inside, you will see a ‘divider’ about 2/3 the way to the left.
Attached to, and going through, this divider, are 2 white plugs.
The plug on the bottom is a 15-pin plug and is for the controller. The plug on top is a 12-pin plug, and is for the voltage regulator.

Disconnect the 12-pin voltage regulator plug. On the right side of the plug (the side leading back to the generator), locate the wires marked J4-9 and J4-10.
Set your meter to ohms and connect one lead to each of these wires. It should read about 18 ohms.
Now reconnect the plug and set your meter to VDC.
Connect the negative lead to a good ground, and back probe the positive lead into the plug at wire J4-7.
Press and hold ‘Start’ for about 5 seconds. It should read at least 10V.
Now back probe the positive lead into the plug at wire J4-9 and press ‘Start’ for about 5 seconds. It should read a minimum of 12V, and preferably between 20-30 volts.
Now back probe the positive lead into the plug at wire J4-10, and press and hold ‘Start’ for about 5 seconds. It can read anywhere from 1-30 volts, as long as there is a reading.

What do you get with these tests?
.

Customer: replied 4 months ago.
Hank, im reading your old message...(cut/paste)...I just gave you the readings with a new regulator....same thing as with the old one...
what else could be bad besides the regulator(it is unlikely that they sent me a bad one...
a
Expert:  Hank F. replied 4 months ago.

You only gave partial results.

If you are still getting 27 ohms across P4-9 and P4-10, your brushes are fine.

Customer: replied 4 months ago.
27 ohms is correct
Customer: replied 4 months ago.
it did not change
Customer: replied 4 months ago.
how do I check if it's oil level sensor (I assume, it checks oil level)...there is plenty of oil in it maybe even too much....should i try draining it?
Expert:  Hank F. replied 4 months ago.

There is no oil shut off on this unit.

You may need to test the stator.

It is somewhat unusual for them to go out, but when they do, they tend to take the voltage regulator and rotor out with them.

The genset needs to come out of the coach and the top cover removed to test a stator.

Customer: replied 4 months ago.
great...
how do you test the rotor and stator?
do you have any wire diagrams?
could it be any other relays shutting it down?
Customer: replied 4 months ago.
how heavy is the unit? you think i can use car jack to get it out? :)
Customer: replied 4 months ago.
would you recommend replacing a fuel filter while im at it?...I have to disconnect fuel line anyway....right?
Expert:  Hank F. replied 4 months ago.

The rotor is good, or you wouldn't have gotten 27 ohms across the brushes.

Click here to download the stator test.

I am not going to be able to continue with this issue much longer. It is already past the point where it just isn't worth my time.

Customer: replied 4 months ago.
would you recommend replacing a fuel filter while im at it?...I have to disconnect fuel line anyway....right?
Customer: replied 4 months ago.
where are these pages from ? a maintenance manual? where can I purchase it?
A new stator costs around 500 and a rotor about the same or a bit more....I already spent 200 + on a regulator that did not do me any good...
I might be better off buying a portable used generator for 5-600 and be done with it...pull the old one out and throw it out...
your thoughts?
Expert:  Hank F. replied 4 months ago.

It never hurts to change a fuel filter, but is usually unnecessary.

You do not have to remove the filter alone, but it is attached to the fuel pump, and you do have to remove the pump.,

Yes, those are the pages from the service manual.

You can order one through any Onan dealer. The part number for the one you need is(###) ###-####

Some people do get a portable, but they are a major hassle. You have to carry the genset, as well as the fuel. Then you have to load an unload the genset wherever you go.

The old saying "you get what you pay for" REALLY counts when buying a genset. If you do decide to go with a portable, stick to a brand name unit. Don't get chincy on a Chinese unit.