Fuel Starvation When Onan Runs

[bdub1]

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

 

[johnny]

It's possible - anything's possible - but it ain't likely. A poorly grounded distributor would exacerbate the condition if it exists.

--johnny
--
'76 23' transmode Norris upfit, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"The road goes on forever, and the party never ends" --Robert Earl Keen

 

[Matt Colie]

> 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

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 - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Still Loving OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

 

[Ken H.]

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

> 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
>

 

[Jim Hupy]

What Ken said.
Jim Hupy
Salem, Or.

> 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
>

>
> > 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
>

 

[Matt Colie]

> What Ken said.
> Jim Hupy
> Salem, Or.
>

>
> > 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
> >

> >
> >> 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 - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Still Loving OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

 

[emerystora]

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

>
> 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
>

>>
>> 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

 

[Ken H.]

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

> 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.
>

 

[jim miller]

> 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

 

[steve southworth]

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

 

[tyler]

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

 

[terry1]

"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.

 

[Ken B]

> 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

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

 

[bdub1]

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