Home » Public Forums » GMCnet » More Onan gremlins.....
| More Onan gremlins..... [message #77403] |
Sat, 20 March 2010 22:16  |
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Well my onan is still behaving strangely and im stumped as to why.
the unit wanders and stumbles under no load and load conditions. I have trouble shooted the fuel system, and replaced the fuel pump. the carb o ring had rotted so I replaced that put it back on, and it seemed to run fine for about 45 minutes then the problems resumed.
it stumbles almost to the point of dying then it takes off again. I tried adjusting the governor, still no dice.
So I then tried to trouble shoot the control board with my DMM, when I got close to the gen, my multimeter goes haywire, with the digital readout literally having a granmaul fit, without the leads even touching anything! thinking my DVM took a dump I tested it on other items and it worked fine, when I got back within a foot of the gen it starts going nuts again, as if the gen is emitting some kind of EM field which is now screwing with my DMM which has never happened before since I have used the DMM to troubleshoot the green turd before.
I can only assume there is something within the genset going bananas which is causing this issue, but what could it be? is it generating some kind of EMP which is freaking out the electronics and ignition causing the stubmeling and the strange behavior of my DMM?
whats going on here! this is very strange behavior to say the least....
73 Canyon Lands, (a.k.a. The Yellow Submarine) West Los Angeles CA
[Updated on: Sat, 20 March 2010 22:18] Report message to a moderator |
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| Re: More Onan gremlins..... [message #77404 is a reply to message #77403] |
Sat, 20 March 2010 22:25  |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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The engine and generator are really 2 separate systems other than the engine turns the generator. Unless there is some sort of short that is loading it way down and causing the stumble ( not likely as this would sound more like a high load situation) It's got to be fuel or ignition.
Try another meter as it is probably intermittant and giving a false reading from induction near the unit.
What method are you using to adjust the carb mixture screws?
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: More Onan gremlins..... [message #77405 is a reply to message #77404] |
Sat, 20 March 2010 22:29 |
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Gonna have to go get another meter I guess. As for mixing the mixture screwes just a screw driver, turn them all the way in, back them out a turn and a half to get it to start then dial it in in under medium load till it humms just right. thats always worked for me before, pretty much the same way you set the A/F on any carbed engine.
its definately got fuel, ive cleaned the carb out compleatly. the only thing left would be something haywire in the ignition. perhaps th coil taking a dump? it has new points...
| JohnL455 wrote on Sat, 20 March 2010 22:25 |
The engine and generator are really 2 separate systems other than the engine turns the generator. Unless there is some sort of short that is loading it way down and causing the stumble ( not likely as this would sound more like a high load situation) It's got to be fuel or ignition.
Try another meter as it is probably intermittant and giving a false reading from induction near the unit.
What method are you using to adjust the carb mixture screws?
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73 Canyon Lands, (a.k.a. The Yellow Submarine) West Los Angeles CA
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| Re: [GMCnet] More Onan gremlins..... [message #77413 is a reply to message #77405] |
Sat, 20 March 2010 23:06 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Shan,
I had a defective coil on the Onan in Double Trouble. Tom Hampton replaced
it and it ran fine after that.
The problem is the coil that Onan sells as a replacement is over $100!
You may have a cheaper option. Harley-Davidsons are a two cylinder engine
with a waste spark just like the Onan. There is one 12vdc power supply to a
dual coil. Both coils fire at the same time. Only cylinder is on the
compression stroke so the other is a waste spark. One of the options that HD
owners install is a single fire ignition system that allows you to set the
timing of the front and rear cylinders separately. I installed lots of them
when I was building hot rod Harleys in my spare time in Hong Kong. Go visit
your local HD shop and ask the mechanics if they have any second hand coils
they want to sell. DON'T ask the parts counter as they will try to sell you
a new one and they're probably just as expensive as the Onan coil (if not
MORE!).
Alternatively if you have any buddies with Harleys ask them if they have a
spare coil or if you can borrow the one off their bike to troubleshoot your
Onan. As long as you're only getting 12vdc to the coil it won't hurt it.
Regards,
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Shan Rose
Sent: Sunday, 21 March 2010 2:30 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] More Onan gremlins.....
Gonna have to go get another meter I guess. As for mixing the mixture
screwes just a screw driver, turn them all the way in, back them out a turn
and a half to get it to start then dial it in in under medium load till it
humms just right. thats always worked for me before, pretty much the same
way you set the A/F on any carbed engine.
its definately got fuel, ive cleaned the carb out compleatly. the only thing
left would be something haywire in the ignition. perhaps th coil taking a
dump? it has new points...
JohnL455 wrote on Sat, 20 March 2010 22:25
> The engine and generator are really 2 separate systems other than the
engine turns the generator. Unless there is some sort of short that is
loading it way down and causing the stumble ( not likely as this would sound
more like a high load situation) It's got to be fuel or ignition.
> Try another meter as it is probably intermittant and giving a false
reading from induction near the unit.
> What method are you using to adjust the carb mixture screws?
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GMCnet mailing list
List Information and Subscription Options:
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] More Onan gremlins..... [message #77468 is a reply to message #77413] |
Sun, 21 March 2010 12:33 |
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Rob,
Was your onan running like mine? Wondering and stumbling? Itested it and it seemed within spec. I know the replacement coil is about 80 bux here. Was thinking pf even snatching a couple of COP from the mens mall and seeing if I could wire up a cop setup. But I don't wanna get into all that unless I can be reasonably sure its the coil... Maybe the coil is also making the em field causing my dmm to act all daffy?
| Robert Mueller wrote on Sat, 20 March 2010 23:06 |
Shan,
I had a defective coil on the Onan in Double Trouble. Tom Hampton replaced
it and it ran fine after that.
The problem is the coil that Onan sells as a replacement is over $100!
You may have a cheaper option. Harley-Davidsons are a two cylinder engine
with a waste spark just like the Onan. There is one 12vdc power supply to a
dual coil. Both coils fire at the same time. Only cylinder is on the
compression stroke so the other is a waste spark. One of the options that HD
owners install is a single fire ignition system that allows you to set the
timing of the front and rear cylinders separately. I installed lots of them
when I was building hot rod Harleys in my spare time in Hong Kong. Go visit
your local HD shop and ask the mechanics if they have any second hand coils
they want to sell. DON'T ask the parts counter as they will try to sell you
a new one and they're probably just as expensive as the Onan coil (if not
MORE!).
Alternatively if you have any buddies with Harleys ask them if they have a
spare coil or if you can borrow the one off their bike to troubleshoot your
Onan. As long as you're only getting 12vdc to the coil it won't hurt it.
Regards,
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Shan Rose
Sent: Sunday, 21 March 2010 2:30 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] More Onan gremlins.....
Gonna have to go get another meter I guess. As for mixing the mixture
screwes just a screw driver, turn them all the way in, back them out a turn
and a half to get it to start then dial it in in under medium load till it
humms just right. thats always worked for me before, pretty much the same
way you set the A/F on any carbed engine.
its definately got fuel, ive cleaned the carb out compleatly. the only thing
left would be something haywire in the ignition. perhaps th coil taking a
dump? it has new points...
JohnL455 wrote on Sat, 20 March 2010 22:25
> The engine and generator are really 2 separate systems other than the
engine turns the generator. Unless there is some sort of short that is
loading it way down and causing the stumble ( not likely as this would sound
more like a high load situation) It's got to be fuel or ignition.
> Try another meter as it is probably intermittant and giving a false
reading from induction near the unit.
> What method are you using to adjust the carb mixture screws?
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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73 Canyon Lands, (a.k.a. The Yellow Submarine) West Los Angeles CA
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| Re: More Onan gremlins..... [message #77472 is a reply to message #77403] |
Sun, 21 March 2010 12:55 |
idrob
Messages: 645
Registered: January 2005
Location: Central Idaho
Karma: 0
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Senior Member |
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| Duce Apocalypse wrote on Sat, 20 March 2010 20:16 |
Well my onan is still behaving strangely and im stumped as to why.
the unit wanders and stumbles under no load and load conditions. I have trouble shooted the fuel system, and replaced the fuel pump. the carb o ring had rotted so I replaced that put it back on, and it seemed to run fine for about 45 minutes then the problems resumed.
it stumbles almost to the point of dying then it takes off again. I tried adjusting the governor, still no dice.
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When I first got my GMC my Onan ran just like that. Stumbling and almost quitting and then take off again. I finally found that the mounting (and thus ground) screw on the very hard to get at points condenser in the ignition system was loose. Apparently some PO had replaced it (very shiny and new looking) and due to the location, had a hard time getting it installed right. Once I got it tightened up, it ran like a champ. Just a thought, it sure sounded familiar as the way mine ran.
Rob Allen
former owner of '76 x-PB
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| Re: More Onan gremlins..... [message #77482 is a reply to message #77472] |
Sun, 21 March 2010 14:10 |
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Well I guess I could recheck the points, they have less then 15 hours on them. maybe something rattled loose, but I doubt it...
that still doesnt explain the strange behavior of the digital multimeter.
as for the heads, I have not decarbonized them. the blugs are very clean, indicating a good burn, and the gen ran just fine up till about 2 weeks ago. so im leaning to this being some kind of electrical/ignition issue...
| idrob wrote on Sun, 21 March 2010 12:55 |
| Duce Apocalypse wrote on Sat, 20 March 2010 20:16 |
Well my onan is still behaving strangely and im stumped as to why.
the unit wanders and stumbles under no load and load conditions. I have trouble shooted the fuel system, and replaced the fuel pump. the carb o ring had rotted so I replaced that put it back on, and it seemed to run fine for about 45 minutes then the problems resumed.
it stumbles almost to the point of dying then it takes off again. I tried adjusting the governor, still no dice.
.
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When I first got my GMC my Onan ran just like that. Stumbling and almost quitting and then take off again. I finally found that the mounting (and thus ground) screw on the very hard to get at points condenser in the ignition system was loose. Apparently some PO had replaced it (very shiny and new looking) and due to the location, had a hard time getting it installed right. Once I got it tightened up, it ran like a champ. Just a thought, it sure sounded familiar as the way mine ran.
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73 Canyon Lands, (a.k.a. The Yellow Submarine) West Los Angeles CA
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| Re: [GMCnet] More Onan gremlins..... [message #77526 is a reply to message #77468] |
Sun, 21 March 2010 17:50 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Shan,
My Onan would run PERFECTLY for about 15-20 minutes and then start wandering
and stumbling.
I suspect it was breaking down when it got hot.
The coil was replaced at Tom Hampton's shop in Marysville, OH.
I have no idea if the coil could cause the EMI that is interfering with your
DMM.
What's COP?
Regards,
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Shan Rose
Sent: Monday, 22 March 2010 4:34 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] More Onan gremlins.....
Rob,
Was your onan running like mine? Wondering and stumbling? Itested it and it
seemed within spec. I know the replacement coil is about 80 bux here. Was
thinking pf even snatching a couple of COP from the mens mall and seeing if
I could wire up a cop setup. But I don't wanna get into all that unless I
can be reasonably sure its the coil... Maybe the coil is also making the em
field causing my dmm to act all daffy?
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] More Onan gremlins..... [message #77537 is a reply to message #77526] |
Sun, 21 March 2010 19:02 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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| Robert Mueller wrote on Sun, 21 March 2010 18:50 |
Shan,
My Onan would run PERFECTLY for about 15-20 minutes and then start wandering and stumbling.
I suspect it was breaking down when it got hot.
The coil was replaced at Tom Hampton's shop in Marysville, OH.
I have no idea if the coil could cause the EMI that is interfering with your DMM.
What's COP?
Regards,
Rob Mueller
Sydney, Australia
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Oh, man - those thermal breakdowns are only a little bit easier to diagnose than intermittents. Coils and condensers are famous for thermal breakdowns that clear by the time you get the meter there.
Could the EM noise a failing coil might make interfere with a DVM - and a dear friend used to say "Sh*t Miss Agnes - You bet is could. A Marconi radio transmitter was just about an ignition coil and antenna and a telegraph key. He just doesn't have a very tall antenna. I wonder if the burzerk DMM doesn't make a good case for a bad coil.
COP is Coil-On-Plug. Very common on modern automotive engines. No spark plug wires! Just a module that get stuck on top of the plug directly. I'm not at all sure there is room for it in a NF box, but it is a good thought. You just have to be careful which one type you collect. Some are pulse transformer (you shoot a low voltage pulse at the plug to fire it and others are Kettering (like a traditional coil) and fire when you break the power. I bet a Pertronic would not mind firing a pair if the later type.
Good Luck there Duce
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: More Onan gremlins..... [message #77541 is a reply to message #77482] |
Sun, 21 March 2010 19:10 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Decarbonize the heads. You can do both of them in less than an hour. You will be surprised at the difference in how it runs and also when trying to adjust the carb. Onan says to de-carbonize the heads every 200 hours.
The DMM is picking up RF from the generator. Short the two leads together when not connected and see what happens. Also if the DMM is auto-ranging you will see the effect even more. If the DMM is auto ranging, turn off the auto ranging and set it manually to the appropriate scale. The effect should be greatly reduced.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: More Onan gremlins..... [message #77649 is a reply to message #77403] |
Mon, 22 March 2010 11:09 |
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thas why I love this place, its a brain trust! i'll try some of the stuff here and post the result!
much thanx 
73 Canyon Lands, (a.k.a. The Yellow Submarine) West Los Angeles CA
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