Home » Public Forums » GMCnet » [GMCnet] Onan - Vapor Lock?
| Re: [GMCnet] Onan - Vapor Lock? [message #178608 is a reply to message #178606] |
Tue, 31 July 2012 22:55   |
k2gkk
Messages: 4452
Registered: November 2009
Karma: -8
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Senior Member |
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The only way I can see that the fuel pump could
"overcome" the float and needle valve would be
if crud in the fuel kept the needle from seating
correctly. High pressure SHOULD simply push the
needle onto the seat with more force.
I believe that the small Mr Gasket pump by Facet
is the one that somebody directed me to. If I
recall, the pressure available is 1.5 to 4.0 psi
and that is not really all that much.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~~ ~ D C "Mac" Macdonald ~ ~~
~ ~ Amateur Radio - K2GKK ~ ~
~ ~ USAF and FAA, Retired ~ ~
~ ~ ~ Oklahoma City, OK ~ ~ ~
~~ ~ ~ "The Money Pit" ~ ~ ~~
~ ~ ~ '76 ex-Palm Beach ~ ~ ~
~ www.gmcmhphotos.com/okclb ~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
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> From: robmueller@iinet.net.au
> To: gmclist@temp.gmcnet.org
> Date: Tue, 31 Jul 2012 21:42:04 -0600
> Subject: Re: [GMCnet] Onan - Vapor Lock?
>
> Steve,
>
> See my last message under Onan replacement pump. It is supposed to have an anti-siphon function (positive shut off).
>
> Having said that I do agree that at some point if there was enough pressure in the fuel tanks on a hot day it could drive fuel
> through the pump and into the carb inlet and overcome the float valve.
>
> Regards,
> Rob M.
>
>
> -----Original Message-----
> From: gmclist-bounces@temp.gmcnet.org [mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Steve Southworth
> Sent: Tuesday, July 31, 2012 9:19 PM
> To: gmclist@temp.gmcnet.org
> Subject: Re: [GMCnet] Onan - Vapor Lock?
>
>
>
> Robert Mueller wrote on Tue, 31 July 2012 19:30
> > Steve,
> >
> > The solenoid has two wires going to it (+/-) they come over from the control board. It appeared to me that it is either on/open or
> > off/closed. I don't know of any device on the Onan that would cause it to regulate pressure or flow from the tank to the pump /
> > carb.
> >
> > I vaguely remember reading that the solenoid was added because of some Canadian rule.
> >
> > Rob M.
>
>
> Correct - the solenoid valve has no pressure regulating function other than: Onan off = zero fuel flow. The example was that the
> GMC was parked with the Onan off. Fuel was spilling from the carb.
> --
> Steve Southworth
> 1974 Glacier TZE064V100150 (for workin on)
> 1975 Transmode TZE365V100394 (parts & spares)
> Palmyra WI
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| Re: [GMCnet] Onan - Vapor Lock? [message #178612 is a reply to message #178609] |
Wed, 01 August 2012 00:43 |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
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Rob,
That's an interesting comment about your gas cap. What would happen if you remove the cap while the Onan is sputtering? Do you think she'd even out?
Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, CA
On Jul 31, 2012, at 9:26 PM, "Rob Mueller" <robmueller@iinet.net.au> wrote:
> Mac,
>
> Go to page 38 in the 6KW Onan Manual below:
>
> http://www.bdub.net/manuals/Onan/Onan6kwNH_Major-Service.pdf
>
> There you will find the parts list for the carb. The fuel comes in the pointy end of the needle valve so it would be possible for
> pressure to "blow" it open.
>
> HOWEVER, when one considers how much surface area is exposed to the pressure I believe you are correct as it would take one hell of
> a lot more than the gas expanding on a hot day. Also I reckon the vent lines to the carbon canister should keep the pressures down
> in the tanks.
>
> I have noted on hot days when I remove the gas tank fill valve I do get a burst of pressure.
>
> I like the Facet Gold Series as it appears it is a direct replacement for the existing pump which I will verify when I check the
> output pressure of the existing pump.
>
> Regards,
> Rob M.
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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| Re: [GMCnet] Onan - Vapor Lock? [message #178616 is a reply to message #178612] |
Wed, 01 August 2012 01:28 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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When I was stuck in Montana the second time, I rolled backwards into a gas station / restaurant. While I was parked waiting for it to cool down, two different locals came by and suggested to me that I remove the gas cap. They said that is what they do when they have a problem around there. I do not quite understand that since the tank(s) is/are already vented through the charcoal canister.
All I can come up with in this solution is the ethanol component of the gasoline is already vaporized and removing the cap allows the ethanol vapor to escape before it cools down and turns back into a liquid again.
My other thought for the Onan is to install a separate tank (5 gallons or so) up high either inside or on top of the coach and gravity feed the Onan.
I have often thought of installing some kind of outside air scoop and blowing fresh air on the rear tank to accelerate cooling.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Onan - Vapor Lock? [message #178624 is a reply to message #178444] |
Wed, 01 August 2012 06:33 |
Steven Ferguson
Messages: 3447
Registered: May 2006
Karma: 0
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Senior Member |
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This is a reach Rob, but I was having exactly the same problem when we
attended the GMCWS Rally at Hart Ranch in SD. Duane Simmons worked on it
for 3 hours and finally tossed in the towel. (I had the only Onal that
kicked Mr. Onan's butt). When we got back home, I checked the timing
(Pertronix unit installed) and when it warmed up, the timing would shift
just enough to keep it from running. Moved the timing one red on and it
never quit again.
On Mon, Jul 30, 2012 at 6:04 PM, Rob Mueller <robmueller@iinet.net.au>wrote:
> G’day,
>
> It seems that whenever the OAT gets to the mid nineties the Onan plays up.
> When the gas is "cold" it runs just fine. As the day
> heats up or if we drive with it on it starts to hunt and then finally
> shuts down. If I try to restart it immediately no joy but if I
> let it sit for about 5 minutes I will start and run for a few minutes then
> it dies again.
>
> When I was here in February I disassembled the carb and cleaned it
> thoroughly which must be true as when it's cool it runs PERFECTLY
> with a voltage output of 120.
>
> Last week before we left I removed the fuel pump and disassembled it. The
> "piston" moved up and down in the "bore" nicely, both
> plastic check valve balls were in fine shape and moved easily.
>
> I removed the solenoid at the inlet to the pump as I reckoned it was one
> thing less to fail.
>
> I installed a Pertronics mod a couple of years ago and a new Onan coil.
>
> I really think this is a vapor lock problem - it was 97° in Carlsberg, NM
> today,
>
> Oh yeah, I did check the fuel level in both tanks and both above 1/2.
>
> As they say in this neck of the woods - any idears?
>
> Regards,
> Rob M.
> USAussie - Downunder
>
> PS - SURE GLAD I INSTALLED A SECOND ROOF AIR LAST YEAR!
>
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--
Fathom the hypocrisy of a nation where every citizen must prove they have
health insurance......but not everyone has to prove they're a citizen.
Steve Ferguson
Sierra Vista, AZ
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| Re: [GMCnet] Onan - Vapor Lock? [message #179089 is a reply to message #178642] |
Sun, 05 August 2012 15:15 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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G'day,
Yesterday Marc and I checked the Onan fuel pump outlet pressure and it was 3 psi when the Onan was cold.
Today we fired it up, turned on both A/C's, water heater, PD converter / battery charger, and all the lights.
The Onan ran for awhile quite nicely but then stumbled once or twice then shut down completely.
We quickly disconnected the fuel line to the carb and cranked it over - 0 psi. We disconnected the fuel line to the tank, nothing came out and I couldn't see any fuel in the line. When I tried to suck some through I could feel resistance which told me that there was fuel in the line to the tank.
I'm going to order a new pump and install it.
It is interesting that this occured as the OAT is currently 81°. I was able to keep my fingers on the fuel pump so it isn't at the 180° spec.
Oh yeah, BOTH tanks are FULL!
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] Onan - Vapor Lock? [message #179096 is a reply to message #179089] |
Sun, 05 August 2012 16:03 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| Robert Mueller wrote on Sun, 05 August 2012 15:15 |
G'day,
Yesterday Marc and I checked the Onan fuel pump outlet pressure and it was 3 psi when the Onan was cold.
Today we fired it up, turned on both A/C's, water heater, PD converter / battery charger, and all the lights.
The Onan ran for awhile quite nicely but then stumbled once or twice then shut down completely.
We quickly disconnected the fuel line to the carb and cranked it over - 0 psi. We disconnected the fuel line to the tank, nothing came out and I couldn't see any fuel in the line. When I tried to suck some through I could feel resistance which told me that there was fuel in the line to the tank.
I'm going to order a new pump and install it.
It is interesting that this occured as the OAT is currently 81°. I was able to keep my fingers on the fuel pump so it isn't at the 180° spec.
Oh yeah, BOTH tanks are FULL!
|
Do not throw away the old pump
Ken B.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Onan - Vapor Lock? [message #179128 is a reply to message #179100] |
Sun, 05 August 2012 20:37 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Senior Member |
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Rob,
My Onan has been acting EXACTLY the same way. I did not check pressure on the pump, but had symptoms that pointed to the same results that you have experienced. I have a new pump and will be replacing it in the near future. I will save my old pump as well and try to figure out why it won't pump fuel when hot. I would be most interested in your 'failure analysis'.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: [GMCnet] Onan - Vapor Lock? [message #179146 is a reply to message #179128] |
Sun, 05 August 2012 22:39 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I do not plan on doing much of a failure analysis. My plan is to clean it up and reuse it. We fix those Facet pumps all the time on aircraft rather than buy new ones. When they say aircraft that triples the new price on those Facet / Bendix pumps. We'll see what Rob has planned.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Onan - Vapor Lock? [message #179617 is a reply to message #179089] |
Wed, 08 August 2012 23:13 |
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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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G'day,
Well it's Wednesday and I decided to play with the Onan some more. After I sent the message below Marc and I discovered something
else. The Onan wouldn't fire when cranked but the INSTANT the start switch was released it would fire. We pulled the plugs and sure
enough with the start switch depressed no spark, the INSTANT the switch was released you'd see a spark.
I have a couple of spare boards so I figger'd I stick on in and see what happened. NOTHING! SAME PROBLEM. Tomorrow I'll stick in the
second spare and see if that works.
I did a few other minor jobs on the GMC which needed doing which pleased Helen and that's important! ;-)
Regards,
Rob M.
-----Original Message-----
From: Robert Mueller
G'day,
Yesterday Marc and I checked the Onan fuel pump outlet pressure and it was 3 psi when the Onan was cold.
Today we fired it up, turned on both A/C's, water heater, PD converter / battery charger, and all the lights.
The Onan ran for awhile quite nicely but then stumbled once or twice then shut down completely.
We quickly disconnected the fuel line to the carb and cranked it over - 0 psi. We disconnected the fuel line to the tank, nothing
came out and I couldn't see any fuel in the line. When I tried to suck some through I could feel resistance which told me that there
was fuel in the line to the tank.
I'm going to order a new pump and install it.
It is interesting that this occured as the OAT is currently 81°. I was able to keep my fingers on the fuel pump so it isn't at the
180° spec.
Oh yeah, BOTH tanks are FULL!
--
Rob M.
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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] Onan - Vapor Lock? [message #179626 is a reply to message #179617] |
Thu, 09 August 2012 01:07 |
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ljdavick
Messages: 3548
Registered: March 2007
Location: Fremont, CA
Karma: -3
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Senior Member |
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Rob,
Thinking about your spark issue - when cranking is it possible that the voltage is low enough that the Pertronix won’t Pertron? (I’m guessing that you have the Pertronix electronic ignition in place.) Maybe it’s a matter of a loose or corroded battery connection.
Does that make any sense?
Also from the Onan manual on page 23 -
B - ENGINE CRANKS BUT DOES NOT START -
1B Is F1 fuse on control board OK?
3B While engine cranks, check K1-I start solenoid voltage. Is 12 vots present between terminals 10 and 1? If no Replace K1 start solenoid.
4B Jumper terminals 9 to 11. Does engine start when start switch is pushed? If yes - K2 contacts are defective. Replace printed circuit board. If no - Fuel solenoid K4 must be open during starting and running...
Then it goes on to diagnose the fuel pump and then the choke. If none of these then it states
13B - The fault is in the ignition system. Check points, plugs, wires and coil. Refer to IGNITION section.
On page 28 it states STARTING;
Push start switch S3. Battery current flows thru K1 solenoid, K2 contacts and start switch S3 to battery negative (GND). K1 solenoid closes contacts, feeding current to starter motor and to choke E1 plus K3 relay. K3 relay contacts close the circuit to the ignition coil T1 and fuel pump E2 plus fuel solenoid K4. The engine cranks and the fuel pump, fuel solenoid, and ignition operate to start the engine.
Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, CA
On Aug 8, 2012, at 9:13 PM, Rob Mueller wrote:
> G'day,
>
> Well it's Wednesday and I decided to play with the Onan some more. After I sent the message below Marc and I discovered something
> else. The Onan wouldn't fire when cranked but the INSTANT the start switch was released it would fire. We pulled the plugs and sure
> enough with the start switch depressed no spark, the INSTANT the switch was released you'd see a spark.
>
> I have a couple of spare boards so I figger'd I stick on in and see what happened. NOTHING! SAME PROBLEM. Tomorrow I'll stick in the
> second spare and see if that works.
>
> I did a few other minor jobs on the GMC which needed doing which pleased Helen and that's important! ;-)
>
> Regards,
> Rob M.
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GMCnet mailing list
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Larry Davick
A Mystery Machine
1976(ish) Palm Beach
Fremont, Ca
Howell EFI + EBL + Electronic Dizzy
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| Re: [GMCnet] Onan - Vapor Lock? [message #179627 is a reply to message #179626] |
Thu, 09 August 2012 02:03 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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Clean the plugs. With a bead blaster if possible. Very carefully check the gaps. Set both of them EXACTLY to what they should be. I believe it is .016". Take an ohm meter and meter between the two (high voltage) plug wires. It should have continuity. (a few thousand ohms)
What I am thinking is there is lower battery voiltage during cranking and the corresponding out put voltage of the coil is also lower. At thsi lower voltave you do nto have enough to go through an ope wire and across both spark plug gaps.
Note: This is a wasted spark ignition. Both plug fire at the same time and fire is series. One open spark plug wire or one wide gap will affect both plugs.
Second thing to check. Put a voltmeter on the +12 volt side of the coil. Check to see if there is +12 volt It will probably read 11+ volts there when cranking. If there is, then forget chasing anything on the board.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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