Onan issues

Got it going and as long as I keep the switch pushed and the carb pulled open, it will run. As soon as I let go of the carb wire it shuts and the
engine chokes out. IF I keep hold of the choke so it's open and let go of the start button it goes out. I think I can, I think I can...
--
-James Palmer, Traverse City, MI
1976 Eleganza
 
> Got it going and as long as I keep the switch pushed and the carb pulled open, it will run. As soon as I let go of the carb wire it shuts and the
> engine chokes out. IF I keep hold of the choke so it's open and let go of the start button it goes out. I think I can, I think I can...
Is the starter still spinning it when it is trying to run or has it disengaged and the Onan running under its own power and the start button just
seems to be keeping the ignition energized?

If the starter is still spinning it, it might be not getting enough gas to run. If the starter is not keeping it spinning (it is getting enough gas to
run), it might be that the board is not getting voltage on pin 8 so it turns off the spark, and you are overriding that with the start switch.

What happens when you jumper pin 5 to 9? That should force spark and fuel pump no matter what pin 8 sees. If it won't run then, it just about has to
be a fuel problem.

Also make sure you have enough oil in it. AND make sure all the circuit breakers inside are OFF. I don't think it will start under load.

Since it gets fire at crank, the ignition system is sound. Gotta be something turning off the spark, or a fuel delivery problem. Both curable.
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality."
 
When 5 to 9 is jumped it keeps running and I was able to run it for about 10 minutes until it started to rain and I packed it all away for the day.
I've been looking at Mr. Simmons sheets and it appears that I'm getting down to it being the control board. I tried taping up the voltage regulator
wires. Tried removing 1-3 and also removing the LOP #12. I didn't necessarily try all three of these at once but I don't think that is what he is
advocating. None of these kept it running without the jumper. Sounds like my last question is where is the best place to buy a new control board?!?

Suspect low AC voltage (terminal 8 to 11) must be 26 to 30 VAC running
! Disable / disconnect Onan voltage regulator wiring
! Remove single wire and tape up without touching ground or other wires
! Remove double wire with adapter (keep connected) and tape up without touching ground or other wires

Suspect remote control panel or wiring faulty
! Remove wires from upper terminals 1, 2 and 3 and try running again.

Suspect faulty low oil pressure (LOP) switch or wiring failure
! Remove wire from board terminal 12 and try running again

Suspect control board faulty
! Test and / or repair board as required
--
-James Palmer, Traverse City, MI
1976 Eleganza
 
> ...if I leave it jumped from 5 to 9 it continues to run. ...
The two things that will make it shut itself off are: Doesn't know it is running because it doesn't see enough voltage at pin 8 (voltage from the
flywheel alternator). Or thinks the oil pressure is low (the low oil pressure switch, or something else is grounding pin 12).

When it is running, make sure you have 26 - 30 VDC on pin 8. If it does, lift pin 12 and then unjumper 5 and 9 to see if it keeps running. If it keeps
running, your oil pressure switch is telling the board there isn't enough oil pressure. It might be right, OR it might need to be replaced.

If a PO has incorrectly disconnected the voltage regulator, and didn't leave the connection from the flywheel alternator to pin 8 (or corrosion on the
connections), that will shut down the generator. And a bad oil pressure switch will too. And it also might actually have low oil pressure.

If you got enough voltage at pin 8 and the oil pressure switch is not stuck in short circuit mode, I suspect the board.

If you are pretty sure you do not have low oil pressure, run it with the jumper from 5 - 9. Check an inside outlet for 120V. Then try running the roof
AC. If it runs the roof AC, you got a good genset and it would be worthwhile to service or replace the board.
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality."
 
I guess I honestly hadn't thought about the possibility of it not powering into the GMC once I got it running! What goes wrong with them where they
wouldn't make power?
--
-James Palmer, Traverse City, MI
1976 Eleganza
 
> I guess I honestly hadn't thought about the possibility of it not powering into the GMC once I got it running! What goes wrong with them where they wouldn't make power?

In decreasing order of likelihood:

1. Loss of magnetism in the field if it has been sitting unused for a significant time (needs flashing procedure)
2. Defective bridge rectifier.
3. Damaged coil(s) in the field assembly.
4. Damaged armature (coils, slip rings, or brushes)
5. Defective excitation circuit (bad compounding reactor = no power, bad thyristor = too much voltage).

—Jim
Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
 
Two choices I know of. Dinosaur Electronics makes a replacement control board, I think Jimmy The K has them. I fix the originals but I'm not quick.
4 - 6 week turnaround isn't uncommon.... but the price is right :)

--johnny
--
'76 23' transmode Norris upfit, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.

"Sometimes I wonder what tomorrow's gonna bring when I think about my dirty life and times" --Warren Zevon
 
How does one test the bridge rectifier? Seems that these are cheap to replace if that's the issue. And as far as sitting for a long time, I would
say that describes this gen pretty well. What is the "flashing procedure"?
--
-James Palmer, Traverse City, MI
1976 Eleganza
 
> How does one test the bridge rectifier? Seems that these are cheap to replace if that's the issue. And as far as sitting for a long time, I
> would say that describes this gen pretty well. What is the "flashing procedure"?
You didn't say if it was producing 120VAC. Is it?

Don't worry about the "flashing procedure" and the Bridge Rectifier until you are sure it is not producing power. It probably will when it is running.
Check it.

They almost never need to be "flashed". To test the Bridge Rectifier, the resistance between the + and each of the ACs will be off the scale, and
between the - and each of the ACs will be low. It is just 4 diodes arranged as shown below:
http://www.gmcmhphotos.com/photos/data/10/medium/Onan_6kW_End_Bell_Wiring.jpg
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality."
 
> They almost never need to be "flashed".

I’d beg to differ - of the dozens of units that have been through the Miller compound at our work rallies - and many more that I’ve helped people repair from afar - there were many that needed flashed. This includes some that had sat idle for only a year or two. In fact, I’ve seen more that needed flashed than needed bridge rectifiers.

In any case the original poster was asking about what *can* go wrong and thus the flashing procedure was listed for completeness.

Of course he should test it for AC output before doing anything else!

—Jim

Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
 
Looks to me to be time to replace that old board to save a lot of agrivation.
Dino boards are only about $135.00 and well worth it.

--
1977 Kingsley 455 as stock as it gets except lots of Ragusa parts
 
> Looks to me to be time to replace that old board to save a lot of agrivation. Dino boards are only about $135.00 and well worth it.
Doesn't know yet if the flywheel alternator voltage is getting to pin 8, OR if the oil pressure switch is bad. A new board won't let the genset run if
it is one of those issues. Gotta sort those two out before buying a board. I am not convinced he needs a board.

Waiting for the report on the voltage on pin 8 while running and if pin 12 is a short circuit to ground while the genset is running.

And if pin 12 is being shorted to ground, we don't know if that is a bad oil pressure switch, or an actual low oil pressure condition.
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality."
 
This will solve the alternator problem (3 pix down
http://gmc49ers.blogspot.com/2015/09/onan-gmc-propane-conversion.html

> > Looks to me to be time to replace that old board to save a lot of
> agrivation. Dino boards are only about $135.00 and well worth it.
> Doesn't know yet if the flywheel alternator voltage is getting to pin 8,
> OR if the oil pressure switch is bad. A new board won't let the genset run
> if
> it is one of those issues. Gotta sort those two out before buying a board.
> I am not convinced he needs a board.
>
> Waiting for the report on the voltage on pin 8 while running and if pin 12
> is a short circuit to ground while the genset is running.
>
> And if pin 12 is being shorted to ground, we don't know if that is a bad
> oil pressure switch, or an actual low oil pressure condition.
> --
> 73 23' Sequoia 4 Sale
> 73 23' CanyonLands Parts Unit 4 Sale
> Upper Alabama
> "Highest price does not guarantee highest quality."
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://bdub.net/gmcmotorhome.info/
Alternator Protection Cable
http://bdub.net/gmcmotorhome.info/APC.html
 
Got busy today and didn't have much time to work on it. I did check the electrical inside while the generator was running and I don't have any. I
had it hooked up to power at a campground 2 weeks ago and everything ran so I know the problem is generator related. I'll get the voltage numbers for
pin 8 tomorrow. I made an amazon order today so I included the bridge rectifier. (They're pretty cheap.) If that's not the problem at least I'll
have a spare. Does anyone have "idiot proof" instructions on how to do the flashing procedure? Any Youtube videos out there?!? I assume it doesn't
hurt the unit to do this if it turns out that it wasn't necessary?
--
-James Palmer, Traverse City, MI
1976 Eleganza
 
You have not answered these questions as far as I can see
1) is the oil level correct
2) do you have at least 1/2 tank of fuel? GM upfit coaches shut off gen at about 1/4 tank
I would get it running right and then meter on both sides of the main breaker Using a meter correctly for ACV,DCV and ohms saves throwing parts at
it and lots of time.

--
John Lebetski
Woodstock, IL
77 Eleganza II
Source America First
 
> Got busy today and didn't have much time to work on it. I did check the electrical inside while the generator was running and I don't have any.
> I had it hooked up to power at a campground 2 weeks ago and everything ran so I know the problem is generator related. I'll get the voltage numbers
> for pin 8 tomorrow. I made an amazon order today so I included the bridge rectifier. (They're pretty cheap.) If that's not the problem at least
> I'll have a spare. Does anyone have "idiot proof" instructions on how to do the flashing procedure? Any Youtube videos out there?!? I assume it
> doesn't hurt the unit to do this if it turns out that it wasn't necessary?
There is a circuit breaker on the Onan. Also, there is a procedure to change from shore power to generator that varies by year/model and upfitter. You
need to make sure that circuit breaker is on and the changeover procedure is complete before you decide the Onan is not putting out.

Jim Miller has seen stuff because of the number of units he works on. I am not aware of a single time that an owner has posted on this forum that it
required a flash, or that it fixed the lack of AC power out. Folks have asked how to do it, but it was never clear if it made a difference. Also am
not aware of a post of a bad compounding reactor problem.

Bridge rectifier, open or short circuited windings are the norm here on the forum. But you need to make sure the circuit breaker on the Onan is on and
that you have correctly implemented the procedure to changeover from shore power to generator before you start chasing that gremlin. And you need to
make clear what you did so people don't tell you to repeat stuff you have already done.
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality."
 
Sorry, yes, I just changed the oil and filter and have triple checked the level before and after getting it running. It is right up to the full line.
And I had just topped off the GMC fuel tanks before starting in on the Onan. Breaker button is pushed in. I should probably check that current is
going through it though as I have heard these can go bad.

Didn't know there was a procedure for changing from shore power to generator. Is there something I'm supposed to change?
--
-James Palmer, Traverse City, MI
1976 Eleganza
 
> Sorry, yes, I just changed the oil and filter and have triple checked the level before and after getting it running. It is right up to the full
> line. And I had just topped off the GMC fuel tanks before starting in on the Onan. Breaker button is pushed in. I should probably check that
> current is going through it though as I have heard these can go bad.
>
> Didn't know there was a procedure for changing from shore power to generator. Is there something I'm supposed to change?
On my 73s, I have to plug the 50A power cord into whatever source I plan to use. For shore power I unplug it from the 50A Onan receptacle in the cord
storage compartment and plug it into the shore power outlet. To switch back I coil the cord back up in the cord storage compartment and plug it back
into the Onan receptacle. I understand some GMCs have a changeover switch in addition to fiddling with the cord. What does your Operating Manual say?

--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality."
 
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