Home » Public Forums » GMCnet » [GMCnet] Fuel Starvation When Onan Runs
| [GMCnet] Fuel Starvation When Onan Runs [message #312882] |
Tue, 07 February 2017 10:29  |
bdub
Messages: 1578
Registered: February 2004
Location: Central Texas
Karma: 5
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Senior Member |
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This came up on Facebook this morning. One suggested possible cause intrigues
me. I'd like some of your opinions on its merit as my eletrical/electonics
knowledge is limited to keeping the smoke contained.
1977 Eleganza II (455) with new OEM fuel pump as well as an electric backup.
Concern:
When I drive the coach it runs fine, when I drive it with the generator on for
the roof air, the coach engine is starving for fuel. Almost seems like the vent
isn't letting enough air in.
---------------
Explanation:
The problem may be coming from the Onan generator itself. Although not common it
is possible that one(1) diode of the bridge rectifier has opened. If this has
happened you may be inducing enough alternating current in to the ground and
wiring to interfere with the electronic module in the distributor. The same
thing happens when the engines alternator has only one diode fail open. Not very
common, but it does happen. If you still have regular light bulbs in the coach
you might notice a slight flickering of the light - like what you see in a
fluorescent light.
Does this explanation have merit?
Thanks
bdub
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bdub
'76 Palm Beach/Central Texas
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| Re: [GMCnet] Fuel Starvation When Onan Runs [message #312883 is a reply to message #312882] |
Tue, 07 February 2017 11:05  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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It's possible - anything's possible - but it ain't likely. A poorly grounded distributor would exacerbate the condition if it exists.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Fuel Starvation When Onan Runs [message #312887 is a reply to message #312882] |
Tue, 07 February 2017 13:22 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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bdub wrote on Tue, 07 February 2017 11:29This came up on Facebook this morning. One suggested possible cause intrigues me. I'd like some of your opinions on its merit as my eletrical/electonics knowledge is limited to keeping the smoke contained.
1977 Eleganza II (455) with new OEM fuel pump as well as an electric backup.
Concern:
When I drive the coach it runs fine, when I drive it with the generator on for the roof air, the coach engine is starving for fuel. Almost seems like the vent
isn't letting enough air in.
---------------
Explanation:
The problem may be coming from the Onan generator itself. Although not common it is possible that one(1) diode of the bridge rectifier has opened. If this has
happened you may be inducing enough alternating current in to the ground and wiring to interfere with the electronic module in the distributor. The same
thing happens when the engines alternator has only one diode fail open. Not very common, but it does happen. If you still have regular light bulbs in the coach
you might notice a slight flickering of the light - like what you see in a fluorescent light.
Does this explanation have merit?
Thanks
bdub
Billy,
I read that explanation, but did not then have time to respond.
The explanation is an Extremely Remote possibility.
The only bridge in the Onan is the one that powers the field. Its connection to the outside world is at best very isolated as it is only connected to the AC side of the machine. It could not (IMEO) put enough hash on any part of the engine electrics to amount to an issue. Even if he has a combiner instead of an isolator, it still has the main engine battery (read wet capacitor) to hammer things flat.
Even if he still has the Prestolite voltage regulator on the Onan and one of the the components in it was to go solid (the usually burn - go open), that can still only effect the house 12V and then the above applies again.
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: [GMCnet] Fuel Starvation When Onan Runs [message #312889 is a reply to message #312882] |
Tue, 07 February 2017 13:24 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Sounds to me like the problem's on a Birchaven or Royale. Remember that
Coachment did not connect the Onan to the dedicated 75% pickup in the Main
tank. Instead, they tee'd into the engine fuel line from the main tank so
that the Onan and the engine have to share the line from the tank to the
tee. Especially if the hose is old and internally deteriorated, it may not
be able to pass enough fuel for both of them. OR, there could be an air
leak, probably on the Onan side of its solenoid valve, which allows the
engine to suck air when that solenoid's open.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc., etc.
www.gmcwipersetc.com
On Tue, Feb 7, 2017 at 11:29 AM, Billy Massey wrote:
> This came up on Facebook this morning. One suggested possible cause
> intrigues
> me. I'd like some of your opinions on its merit as my eletrical/electonics
> knowledge is limited to keeping the smoke contained.
>
> 1977 Eleganza II (455) with new OEM fuel pump as well as an electric
> backup.
>
> Concern:
> When I drive the coach it runs fine, when I drive it with the generator on
> for
> the roof air, the coach engine is starving for fuel. Almost seems like the
> vent
> isn't letting enough air in.
>
> ---------------
>
> Explanation:
> The problem may be coming from the Onan generator itself. Although not
> common it
> is possible that one(1) diode of the bridge rectifier has opened. If this
> has
> happened you may be inducing enough alternating current in to the ground
> and
> wiring to interfere with the electronic module in the distributor. The same
> thing happens when the engines alternator has only one diode fail open.
> Not very
> common, but it does happen. If you still have regular light bulbs in the
> coach
> you might notice a slight flickering of the light - like what you see in a
> fluorescent light.
>
> Does this explanation have merit?
>
> Thanks
> bdub
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Fuel Starvation When Onan Runs [message #312890 is a reply to message #312889] |
Tue, 07 February 2017 14:04 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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What Ken said.
Jim Hupy
Salem, Or.
On Feb 7, 2017 11:25 AM, "Ken Henderson" wrote:
> Sounds to me like the problem's on a Birchaven or Royale. Remember that
> Coachment did not connect the Onan to the dedicated 75% pickup in the Main
> tank. Instead, they tee'd into the engine fuel line from the main tank so
> that the Onan and the engine have to share the line from the tank to the
> tee. Especially if the hose is old and internally deteriorated, it may not
> be able to pass enough fuel for both of them. OR, there could be an air
> leak, probably on the Onan side of its solenoid valve, which allows the
> engine to suck air when that solenoid's open.
>
> Ken H.
> Americus, GA
> '76 X-Birchaven w/Cad500/Howell EFI & EBL,
> Manny Brakes & 1-Ton, etc., etc., etc.
> www.gmcwipersetc.com
>
> On Tue, Feb 7, 2017 at 11:29 AM, Billy Massey wrote:
>
>> This came up on Facebook this morning. One suggested possible cause
>> intrigues
>> me. I'd like some of your opinions on its merit as my
> eletrical/electonics
>> knowledge is limited to keeping the smoke contained.
>>
>> 1977 Eleganza II (455) with new OEM fuel pump as well as an electric
>> backup.
>>
>> Concern:
>> When I drive the coach it runs fine, when I drive it with the generator
> on
>> for
>> the roof air, the coach engine is starving for fuel. Almost seems like
> the
>> vent
>> isn't letting enough air in.
>>
>> ---------------
>>
>> Explanation:
>> The problem may be coming from the Onan generator itself. Although not
>> common it
>> is possible that one(1) diode of the bridge rectifier has opened. If this
>> has
>> happened you may be inducing enough alternating current in to the ground
>> and
>> wiring to interfere with the electronic module in the distributor. The
> same
>> thing happens when the engines alternator has only one diode fail open.
>> Not very
>> common, but it does happen. If you still have regular light bulbs in the
>> coach
>> you might notice a slight flickering of the light - like what you see in
> a
>> fluorescent light.
>>
>> Does this explanation have merit?
>>
>> Thanks
>> bdub
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
> _______________________________________________
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> Unsubscribe or Change List Options:
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| Re: [GMCnet] Fuel Starvation When Onan Runs [message #312892 is a reply to message #312890] |
Tue, 07 February 2017 15:38 |
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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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James Hupy wrote on Tue, 07 February 2017 15:04What Ken said.
Jim Hupy
Salem, Or.
On Feb 7, 2017 11:25 AM, "Ken Henderson" wrote:
> Sounds to me like the problem's on a Birchaven or Royale. Remember that
> Coachment did not connect the Onan to the dedicated 75% pickup in the Main
> tank. Instead, they tee'd into the engine fuel line from the main tank so
> that the Onan and the engine have to share the line from the tank to the
> tee. Especially if the hose is old and internally deteriorated, it may not
> be able to pass enough fuel for both of them. OR, there could be an air
> leak, probably on the Onan side of its solenoid valve, which allows the
> engine to suck air when that solenoid's open.
>
> Ken H.
> Americus, GA
> '76 X-Birchaven w/Cad500/Howell EFI & EBL,
> Manny Brakes & 1-Ton, etc., etc., etc.
> www.gmcwipersetc.com
>
> On Tue, Feb 7, 2017 at 11:29 AM, Billy Massey wrote:
>
>> This came up on Facebook this morning. One suggested possible cause
>> intrigues
>> me. I'd like some of your opinions on its merit as my
> eletrical/electonics
>> knowledge is limited to keeping the smoke contained.
>>
>> 1977 Eleganza II (455) with new OEM fuel pump as well as an electric
>> backup.
>>
>> Concern:
>> When I drive the coach it runs fine, when I drive it with the generator
> on
>> for
>> the roof air, the coach engine is starving for fuel. Almost seems like
> the
>> vent
>> isn't letting enough air in.
>>
>> ---------------
>>
>> Explanation:
>> The problem may be coming from the Onan generator itself. Although not
>> common it
>> is possible that one(1) diode of the bridge rectifier has opened. If this
>> has
>> happened you may be inducing enough alternating current in to the ground
>> and
>> wiring to interfere with the electronic module in the distributor. The
> same
>> thing happens when the engines alternator has only one diode fail open.
>> Not very
>> common, but it does happen. If you still have regular light bulbs in the
>> coach
>> you might notice a slight flickering of the light - like what you see in
> a
>> fluorescent light.
>>
>> Does this explanation have merit?
>>
>> Thanks
>> bdub
Sorry Guys,
This was from FB with no sigfiles and about 3 lines down he said it is a 77 Eleganza II
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: [GMCnet] Fuel Starvation When Onan Runs [message #312896 is a reply to message #312889] |
Tue, 07 February 2017 18:11 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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However the original email said it was a 1977 Eleganza II so the pickup for the Onan should be the stock tube down the top of the tank.
Emery Stora
> On Feb 7, 2017, at 12:24 PM, Ken Henderson wrote:
>
> Sounds to me like the problem's on a Birchaven or Royale. Remember that
> Coachment did not connect the Onan to the dedicated 75% pickup in the Main
> tank. Instead, they tee'd into the engine fuel line from the main tank so
> that the Onan and the engine have to share the line from the tank to the
> tee. Especially if the hose is old and internally deteriorated, it may not
> be able to pass enough fuel for both of them. OR, there could be an air
> leak, probably on the Onan side of its solenoid valve, which allows the
> engine to suck air when that solenoid's open.
>
> Ken H.
> Americus, GA
> '76 X-Birchaven w/Cad500/Howell EFI & EBL,
> Manny Brakes & 1-Ton, etc., etc., etc.
> www.gmcwipersetc.com
>
>> On Tue, Feb 7, 2017 at 11:29 AM, Billy Massey wrote:
>>
>> This came up on Facebook this morning. One suggested possible cause
>> intrigues
>> me. I'd like some of your opinions on its merit as my eletrical/electonics
>> knowledge is limited to keeping the smoke contained.
>>
>> 1977 Eleganza II (455) with new OEM fuel pump as well as an electric
>> backup.
>>
>> Concern:
>> When I drive the coach it runs fine, when I drive it with the generator on
>> for
>> the roof air, the coach engine is starving for fuel. Almost seems like the
>> vent
>> isn't letting enough air in.
>>
>> ---------------
>>
>> Explanation:
>> The problem may be coming from the Onan generator itself. Although not
>> common it
>> is possible that one(1) diode of the bridge rectifier has opened. If this
>> has
>> happened you may be inducing enough alternating current in to the ground
>> and
>> wiring to interfere with the electronic module in the distributor. The same
>> thing happens when the engines alternator has only one diode fail open.
>> Not very
>> common, but it does happen. If you still have regular light bulbs in the
>> coach
>> you might notice a slight flickering of the light - like what you see in a
>> fluorescent light.
>>
>> Does this explanation have merit?
>>
>> Thanks
>> bdub
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
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| Re: [GMCnet] Fuel Starvation When Onan Runs [message #312897 is a reply to message #312896] |
Tue, 07 February 2017 18:22 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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I didn't see that it was an Eleganza II. But I'm still not gonna give up
on my hypothesis 'cause the Canyonlands we recently rescued has the shared
main tank hose. The OEM generator-only hose is still there; but, for some
reason, a PO used the Coachmen technique. It would be worth the trouble to
check the Eleganza II for the same dumb change.
Ken H
On Tue, Feb 7, 2017 at 7:11 PM, Emery Stora wrote:
> However the original email said it was a 1977 Eleganza II so the pickup
> for the Onan should be the stock tube down the top of the tank.
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Fuel Starvation When Onan Runs [message #312898 is a reply to message #312882] |
Tue, 07 February 2017 19:12 |
Jim Miller
Messages: 501
Registered: March 2008
Karma: 10
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Senior Member |
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On Feb 7, 2017, at 11:29 AM, Billy Massey wrote:
> Concern: When I drive the coach it runs fine, when I drive it with the generator on for the roof air, the coach engine is starving for fuel. Almost seems like the vent isn't letting enough air in.
Is there any information available with regard to the condition of the fuel hoses on the vehicle? I can envision a scenario where ethanol-rotted 30R7 hose has become semi-permeable and could allow air incursion under certain operational circumstances. With only one fuel pump (the engine) drawing suction pressure on the hose the permeability may not be bad enough (yet) to interfere with fuel delivery; but with two pumps pulling on the lines the suction becomes great enough that enough air can diffuse into the hose to create a starvation situation.
—Jim
Jim Miller
1977 Eleganza
1977 Royale
Hamilton, OH
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Jim Miller
1977 Eleganza II
1977 Royale
Hamilton, OH
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| Re: [GMCnet] Fuel Starvation When Onan Runs [message #312899 is a reply to message #312882] |
Tue, 07 February 2017 19:47 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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Senior Member |
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It could be a venting problem. Loosen the gas cap and see if the problem disappears.
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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| Re: [GMCnet] Fuel Starvation When Onan Runs [message #312902 is a reply to message #312882] |
Tue, 07 February 2017 21:50 |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Senior Member |
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Dang it, this thread is going to make me drop my tanks on my 75...! Last summer I had issues that seemed like vapor lock, but the generator would shut down as well. My next step has been mustering the courage and parts to pull the intake manifold, check for cracks, and block the crossovers (which still may be a good thing). But, it did it worse when i filled with gas. Gas should have been cool and made vapor lock less likely. IF my vent hose is blocked, and the full tank and heating up of the gas closed off the liquid valve thing in the driver wheel well shut off as it is supposed to, and perchance someone replumbed my generator on a T instead of a dedicated pickup, a bad hose in the right place would explain what was happening. Generator would run fine on those hot days, but not when the engine was pulling full load. Opening the gas cap didn't help, and a few times indicated a pressurized tank (15-30 minutes post fill up, hot days). Shoot, could be crossover and bad hoses
Now I wish i hadn't filled back up after the Christmas light tours we did! Seriously, short a trip to the beach, what do i do with the gas? I guess a pump rig to the cars for a month or so will have to do.
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: [GMCnet] Fuel Starvation When Onan Runs [message #312905 is a reply to message #312902] |
Tue, 07 February 2017 23:30 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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Senior Member |
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"what do i do with the gas?"
A) "Stabil" it and save it in your other vehicles, or
B) Drive the coach to work and the grocery store, or
C) Use it up while diagnosing the fuel system problem, or
D) All of the above
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: [GMCnet] Fuel Starvation When Onan Runs [message #312908 is a reply to message #312882] |
Wed, 08 February 2017 00:32 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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bdub wrote on Tue, 07 February 2017 10:29This came up on Facebook this morning. One suggested possible cause intrigues
me. I'd like some of your opinions on its merit as my eletrical/electonics
knowledge is limited to keeping the smoke contained.
1977 Eleganza II (455) with new OEM fuel pump as well as an electric backup.
Concern:
When I drive the coach it runs fine, when I drive it with the generator on for
the roof air, the coach engine is starving for fuel. Almost seems like the vent
isn't letting enough air in.
---------------
Explanation:
The problem may be coming from the Onan generator itself. Although not common it
is possible that one(1) diode of the bridge rectifier has opened. If this has
happened you may be inducing enough alternating current in to the ground and
wiring to interfere with the electronic module in the distributor. The same
thing happens when the engines alternator has only one diode fail open. Not very
common, but it does happen. If you still have regular light bulbs in the coach
you might notice a slight flickering of the light - like what you see in a
fluorescent light.
Does this explanation have merit?
Thanks
bdub
Wow. That is a real stretch considering that the 2 items are on separate ground systems and 20 some feet away from each other.
He is equating a blown diode in the alternator to a field diode in the AC generating system. If a diode were blown in the Onan I would expect low or not AC voltage coming out pf the Onan. I do not see it, but I guess anything is possible.
If he thinks it is a distributor grounding noise issue, the first thing to do is to install a ground wire from the base of the distributor to the engine block.
This really sounds more like a fuel deliver problem. The next time it happens, try switching tanks.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Fuel Starvation When Onan Runs [message #312915 is a reply to message #312882] |
Wed, 08 February 2017 10:18 |
bdub
Messages: 1578
Registered: February 2004
Location: Central Texas
Karma: 5
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Senior Member |
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Thanks for the comments, guys. I'll pass on the suggestions to ground the
distributor and check out the fuel feed location.
bdub
-----Original Message-----
From: Gmclist Behalf Of Billy Massey
Sent: Tuesday, February 7, 2017 10:29 AM
This came up on Facebook this morning. One suggested possible cause intrigues
me. I'd like some of your opinions on its merit as my eletrical/electonics
knowledge is limited to keeping the smoke contained.
1977 Eleganza II (455) with new OEM fuel pump as well as an electric backup.
Concern:
When I drive the coach it runs fine, when I drive it with the generator on for
the roof air, the coach engine is starving for fuel. Almost seems like the vent
isn't letting enough air in.
---------------
Explanation:
The problem may be coming from the Onan generator itself. Although not common it
is possible that one(1) diode of the bridge rectifier has opened. If this has
happened you may be inducing enough alternating current in to the ground and
wiring to interfere with the electronic module in the distributor. The same
thing happens when the engines alternator has only one diode fail open. Not very
common, but it does happen. If you still have regular light bulbs in the coach
you might notice a slight flickering of the light - like what you see in a
fluorescent light.
Does this explanation have merit?
Thanks
bdub
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bdub
'76 Palm Beach/Central Texas
www.bdub.net
www.gmcmhphotos.com
www.gmcmotorhomemarketplace.com
www.gmcmhregistry.com
www.facebook.com/groups/classicgmcmotorhomes
www.facebook.com/groups/gmcmm
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