Onan 4000 ky no start

tonym · 10-06-2017, 11:20 AM

Don't know where to look next. This unit is about 10 yrs old total hours unknown. It has good fuel and flow ,spark and compression. Carb was gone through completely . New spark plug also. Does the control module tell the engine to start? It does appear to be a timing issues since it makes a "puffin" sound while cranking and cycling. If so can the problem be with the module? Thank you.

Hacksaw · 10-06-2017, 02:23 PM

I once had similar trouble with my 4000. When I was away from my trailer it ran out of fuel. After that it would start and run only while on cranking mode. Put in a new board to fix it. I'm guessing it didn't like the high and low rpm surging as it starved for fuel and fryed something.

tonym · 10-06-2017, 02:31 PM

Thanks, Hacksaw
Is there any way to check module?

Hacksaw · 10-06-2017, 02:52 PM

I'm sure there is but looks tricky to me. I'd bet most trouble shooters swap out the board with a good one rather than go through it. Those Onan gens have several "fail safe" circuits that run through that board.

Hacksaw · 10-06-2017, 03:05 PM

Hey Tonym: Remembered switching boards on mine and no difference. Just dug out copy of receipt for the repair and turns out I was mistaken. My fix was the voltage regulator, not the board. $149.00 in 2008. Sorry to aide in your confusion.

tonym · 10-07-2017, 10:54 AM

Thanks, Hacksaw Ill check it .

Rich Biebel · 10-07-2017, 02:58 PM

Your problem sounds like one I have seen a couple times.

The timing is off and here is why....

The engines crankshaft is keyed to the generators rotor. The rotor is keyed to the blower wheel and the timing is triggered by that blower wheel.

Either the blower wheel moved or more likely the rotor moved on the crank.

All tapered shaft connections and the crank to rotor has a little pin to locate it. The blower wheel has a key slot and a very small key. Once it's all bolted together the taper holds it. A backfire probably happened and sheared the pin at the rotor to crank connection and it moved.

If you have good spark, fuel and good compression this is likely your problem.......It should at least try to fire with carb cleaner sprayed into carb throat cranking. If it pops back or does nothing and you confirmed the spark is good......the timing is off and one of the above 2 items moved....

Like I said I have seen it at least twice and I fix these machines for years and years.....

If it cranks and has spark, it should at least start and would shut right down if it had no AC output or a bad control board. Bad boards sometimes burn up and won't even crank.....

tonym · 10-08-2017, 01:22 PM

Many thanks,Rich I think you are correct. It sounds like it is trying to fire on exhaust stroke.

Can you guide me to how to approach the repair? How much disassembling is required to inspect the components etc and what do I look for?

Do you still run at Island? Think I remember you when me and my son raced there.! I live over in Brodheadsville near Stroudsburg.

Thanks Again.

Rich Biebel · 10-08-2017, 06:08 PM

It's pretty difficult to describe and is a lot to disassemble. The entire generator end has to come apart. A service manual might help but you'd be better off taking it to a professional, like me that is familiar with them. It's not a simple deal to take it all apart and know what you are looking for. I work for a generator service company in Dover, NJ. I do all the RV work so I know those machines very well. I don't race at Island and have not for years. What racing I do is usually in S/C at various races and tracks. Maybe there is an Onan repair place somewhere in your area. You could buy a service manual online but it's not real helpful for a repair like this. There really is no other way to check this other than disassembling it to verify the timing indexing is either good or bad. A new rotor may be needed if the pin broke as it is not repairable. Parts availability is a possible issue but should be available.

tonym · 10-09-2017, 11:34 AM

Thanks again, Rich
The unit is out of trailer and in my pickup. If you do any work on the side I can drive it to your place and leave it. I suspect I am only an hour or so away.
Assuming that's the problem can you give me a rough estimate to fix it . I don't want to put a lot of money in it if its not worth it.
Thanks so much

Tony

10-06-2017, 11:20 AM	#1
tonym Junior Member Join Date: Oct 2017 Posts: 5 Likes: 0 Liked 0 Times in 0 Posts	Onan 4000 ky no start Don't know where to look next. This unit is about 10 yrs old total hours unknown. It has good fuel and flow ,spark and compression. Carb was gone through completely . New spark plug also. Does the control module tell the engine to start? It does appear to be a timing issues since it makes a "puffin" sound while cranking and cycling. If so can the problem be with the module? Thank you.

10-06-2017, 02:23 PM	#2
Hacksaw Senior Member Join Date: Sep 2016 Posts: 862 Likes: 168 Liked 293 Times in 162 Posts	Re: Onan 4000 ky no start I once had similar trouble with my 4000. When I was away from my trailer it ran out of fuel. After that it would start and run only while on cranking mode. Put in a new board to fix it. I'm guessing it didn't like the high and low rpm surging as it starved for fuel and fryed something.

10-06-2017, 02:31 PM	#3
tonym Junior Member Join Date: Oct 2017 Posts: 5 Likes: 0 Liked 0 Times in 0 Posts	Re: Onan 4000 ky no start Thanks, Hacksaw Is there any way to check module?

10-06-2017, 02:52 PM	#4
Hacksaw Senior Member Join Date: Sep 2016 Posts: 862 Likes: 168 Liked 293 Times in 162 Posts	Re: Onan 4000 ky no start I'm sure there is but looks tricky to me. I'd bet most trouble shooters swap out the board with a good one rather than go through it. Those Onan gens have several "fail safe" circuits that run through that board.

10-06-2017, 03:05 PM	#5
Hacksaw Senior Member Join Date: Sep 2016 Posts: 862 Likes: 168 Liked 293 Times in 162 Posts	Re: Onan 4000 ky no start Hey Tonym: Remembered switching boards on mine and no difference. Just dug out copy of receipt for the repair and turns out I was mistaken. My fix was the voltage regulator, not the board. $149.00 in 2008. Sorry to aide in your confusion.

10-07-2017, 10:54 AM	#6
tonym Junior Member Join Date: Oct 2017 Posts: 5 Likes: 0 Liked 0 Times in 0 Posts	Re: Onan 4000 ky no start Thanks, Hacksaw Ill check it .

10-07-2017, 02:58 PM	#7
Rich Biebel VIP Member Join Date: Jun 2007 Location: Northern New Jersey suburbs Posts: 2,306 Likes: 25 Liked 537 Times in 211 Posts	Re: Onan 4000 ky no start Your problem sounds like one I have seen a couple times. The timing is off and here is why.... The engines crankshaft is keyed to the generators rotor. The rotor is keyed to the blower wheel and the timing is triggered by that blower wheel. Either the blower wheel moved or more likely the rotor moved on the crank. All tapered shaft connections and the crank to rotor has a little pin to locate it. The blower wheel has a key slot and a very small key. Once it's all bolted together the taper holds it. A backfire probably happened and sheared the pin at the rotor to crank connection and it moved. If you have good spark, fuel and good compression this is likely your problem.......It should at least try to fire with carb cleaner sprayed into carb throat cranking. If it pops back or does nothing and you confirmed the spark is good......the timing is off and one of the above 2 items moved.... Like I said I have seen it at least twice and I fix these machines for years and years..... If it cranks and has spark, it should at least start and would shut right down if it had no AC output or a bad control board. Bad boards sometimes burn up and won't even crank..... __________________ Rich Biebel S/C 1479 Stock 147R

10-08-2017, 01:22 PM	#8
tonym Junior Member Join Date: Oct 2017 Posts: 5 Likes: 0 Liked 0 Times in 0 Posts	Re: Onan 4000 ky no start Many thanks,Rich I think you are correct. It sounds like it is trying to fire on exhaust stroke. Can you guide me to how to approach the repair? How much disassembling is required to inspect the components etc and what do I look for? Do you still run at Island? Think I remember you when me and my son raced there.! I live over in Brodheadsville near Stroudsburg. Thanks Again.

10-08-2017, 06:08 PM	#9
Rich Biebel VIP Member Join Date: Jun 2007 Location: Northern New Jersey suburbs Posts: 2,306 Likes: 25 Liked 537 Times in 211 Posts	Re: Onan 4000 ky no start It's pretty difficult to describe and is a lot to disassemble. The entire generator end has to come apart. A service manual might help but you'd be better off taking it to a professional, like me that is familiar with them. It's not a simple deal to take it all apart and know what you are looking for. I work for a generator service company in Dover, NJ. I do all the RV work so I know those machines very well. I don't race at Island and have not for years. What racing I do is usually in S/C at various races and tracks. Maybe there is an Onan repair place somewhere in your area. You could buy a service manual online but it's not real helpful for a repair like this. There really is no other way to check this other than disassembling it to verify the timing indexing is either good or bad. A new rotor may be needed if the pin broke as it is not repairable. Parts availability is a possible issue but should be available. __________________ Rich Biebel S/C 1479 Stock 147R

10-09-2017, 11:34 AM	#10
tonym Junior Member Join Date: Oct 2017 Posts: 5 Likes: 0 Liked 0 Times in 0 Posts	Re: Onan 4000 ky no start Thanks again, Rich The unit is out of trailer and in my pickup. If you do any work on the side I can drive it to your place and leave it. I suspect I am only an hour or so away. Assuming that's the problem can you give me a rough estimate to fix it . I don't want to put a lot of money in it if its not worth it. Thanks so much Tony