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| GMC Mechanical pump [message #130809] |
Sun, 19 June 2011 00:57  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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I have often thought about why not use the other AC pump available for our coach that has the fuel return on it. All that would be required on this would be to add a low pressure return line from the pump to the tanks or fuel filler line. You could tee it into the Onan tap on the rear tank so you know where all returned fuel goes. I have not checked, but that tap may also be available on the front tank with nothing attached to it.
What got me thinking about this is a friend called with a problem on his Ranger. Every time he started the truck it dumped lots of gas all over the ground. I ended up going out with my trailer and towing him back to my hanger. We ended up pulling the bed and found that the return line had come loose at the tank. He had just filled up and had driven it less than 10 minutes when someone flagged him down and told him about the leaking gas problem. When we started it to drive it on the trailer it was dumping gas at an unbelievable rate. We had gasoline everywhere. I never realized before how much gas is returned to the tank. With this much flow I can not see how the gas would have a place to vapor lock in.
After we fixed the leak and reassembled the truck we went back and filled it again. It took 10 gallons. That means he lost 10 gallons through that leak in less than 10 minutes. Some of the returned gas went back into the tank as the hose did not come off. It was just loose.
I think this would be a good solution for people out west experiencing vapor lock problems. It would not take much to implement and sure could not hurt anything.
I've never had vapor lock problems here but I almost always buy 100% real gas, have my wheel liners removed for better cooling, run a 180 degree thermostat, have my steel fuel line between the pump and carb insulated, and have the exhaust crossover blocked. I do on occasion buy 10% alcohol diluted fuel (mostly by mistake) and still have not see any vapor lock problems.
My point in the above paragraph is I have no way to test this alternate fuel pump installation.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: GMC Mechanical pump [message #130835 is a reply to message #130809] |
Sun, 19 June 2011 08:00  |
Jim Wagner
Messages: 339
Registered: February 2004
Location: Brook Park, Oh
Karma: 0
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Ken, This is the way I have my Caddy500 setup. The return line goes to a fitting at the gas filler tube.
Works for me
Jim Wagner
Brook Park, oh
I have often thought about why not use the other AC pump available for our coach that has the fuel return on it. All that would be required on this would be to add a low pressure return line from the pump to the tanks or fuel filler line. You could tee it into the Onan tap on the rear tank so you know where all returned fuel goes. I have not checked, but that tap may also be available on the front tank with nothing attached to it.
What got me thinking about this is a friend called with a problem on his Ranger. Every time he started the truck it dumped lots of gas all over the ground. I ended up going out with my trailer and towing him back to my hanger. We ended up pulling the bed and found that the return line had come loose at the tank. He had just filled up and had driven it less than 10 minutes when someone flagged him down and told him about the leaking gas problem. When we started it to drive it on the trailer it was dumping gas at an unbelievable rate. We had gasoline everywhere. I never realized before how much gas is returned to the tank. With this much flow I can not see how the gas would have a place to vapor lock in.
After we fixed the leak and reassembled the truck we went back and filled it again. It took 10 gallons. That means he lost 10 gallons through that leak in less than 10 minutes. Some of the returned gas went back into the tank as the hose did not come off. It was just loose.
I think this would be a good solution for people out west experiencing vapor lock problems. It would not take much to implement and sure could not hurt anything.
I've never had vapor lock problems here but I almost always buy 100% real gas, have my wheel liners removed for better cooling, run a 180 degree thermostat, have my steel fuel line between the pump and carb insulated, and have the exhaust crossover blocked. I do on occasion buy 10% alcohol diluted fuel (mostly by mistake) and still have not see any vapor lock problems.
My point in the above paragraph is I have no way to test this alternate fuel pump installation.
--------------------------------------------------------------------------------
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: GMC Mechanical pump [message #130836 is a reply to message #130809] |
Sun, 19 June 2011 08:01 |
chasingsummer
Messages: 434
Registered: May 2011
Location: asheboro, nc
Karma: 0
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my 1 cents worth on return fule line is old porsche aircolled so mayne t be worth full one cents
fuel injection which used return line also used much higher fuel pressure. it also had what i will call a pressure valve that when needing a lot of pressure, thru vacuum would somewhat choke off this return so that full preasure was there at higher rpms, not a complicated system, but i am not sure how i could adopt this return line, and be able to maintain the pressures we need hwhich i assume is mush smaller, which i aslo assume means more critical to keep constant.
but yet i told you it may not be worth a half a cent
brian
asheboro, nc
75 eleganza, 74 build
119k miles and counting,
DOG HOUSE
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| Re: GMC Mechanical pump [message #130843 is a reply to message #130809] |
Sun, 19 June 2011 08:55 |
GeorgeRud
Messages: 1380
Registered: February 2007
Location: Chicago, IL
Karma: 0
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It seems that the fuel pump is always trying to pump fuel from the tanks when the engine is running, and the float valve in the carb is shutting the flow when the float bowl is full. With the low pressures in this system, it works well. However, I cannot see why a return to the tank would not be a reasonable modification to keep the fuel cooler. The only problem may be if it ISA too easy for the fuel to return to the tank, and not enough getting to the carb since the fuel has to be pumped upwards to the carb instead of back to the tank.
George Rudawsky
Chicago, IL
75 Palm Beach
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| Re: GMC Mechanical pump [message #130845 is a reply to message #130836] |
Sun, 19 June 2011 09:00 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| chasingsummer wrote on Sun, 19 June 2011 08:01 |
my 1 cents worth on return fule line is old porsche aircolled so mayne t be worth full one cents
fuel injection which used return line also used much higher fuel pressure. it also had what i will call a pressure valve that when needing a lot of pressure, thru vacuum would somewhat choke off this return so that full preasure was there at higher rpms, not a complicated system, but i am not sure how i could adopt this return line, and be able to maintain the pressures we need hwhich i assume is mush smaller, which i aslo assume means more critical to keep constant.
but yet i told you it may not be worth a half a cent
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My point is GM already used this pump with a return on Olds 455's when they were installed in Toronado. If fact it is difficult find a new one today that does not have this return. Some GMC people have bought these pumps with return and just blocked off the return line. So why not just use this proven pump set up and run a return line back to the tank(s) to help limit vapor lock problems.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] GMC Mechanical pump [message #130848 is a reply to message #130843] |
Sun, 19 June 2011 09:09 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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On a mechanical diaphram type fuel pump that is operated by a push rod or
lever off the camshaft, there is a heavy spring that keeps the lever end in
contact with the camshaft, a pivot point, and a direct connection to the
diaphram. Often times the connection point to the diaphram has a slot in it
with a small spring that is slightly stronger than the pressure required to
push fuel to the float valve. When the float valve is closed, the link can
move back and forth the length of the slot without moving the diaphram,
thereby limiting the output pressure of the pump. The Air Conditioning pumps
with the extra return line have a slightly stronger small spring that
enables the pump to also return fuel. All springs fatigue over time, and
have a definite length of service life. The diaphram may still be
serviceable but the springs are corroded, gummed up from oil vapors from the
crankcase, or fatigued, and the result is the same. The pump no longer
operates at it's designed pressures. A good fuel pressure gage will detect
this problem, and it may/can contribute to vaporlock problems. Just what I
know.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Sun, Jun 19, 2011 at 6:55 AM, George Rudawsky <GeorgeRud@aol.com> wrote:
>
>
> It seems that the fuel pump is always trying to pump fuel from the tanks
> when the engine is running, and the float valve in the carb is shutting the
> flow when the float bowl is full. With the low pressures in this system, it
> works well. However, I cannot see why a return to the tank would not be a
> reasonable modification to keep the fuel cooler. The only problem may be if
> it ISA too easy for the fuel to return to the tank, and not enough getting
> to the carb since the fuel has to be pumped upwards to the carb instead of
> back to the tank.
> --
> George Rudawsky
> Chicago, IL
> 75 Palm Beach
> _______________________________________________
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| Re: [GMCnet] GMC Mechanical pump [message #130857 is a reply to message #130853] |
Sun, 19 June 2011 10:24 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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I agree with Ken (strangely enough) about the likelihood of the
Toronado pump helping some vapor lock victims.
I suspect the objective of the return line is not cooling of the fuel
but elimination of the bubbles.
If I had a vapor lock problem, your fuel/water heat exchanger would be
a viable option since I do capture condenser run-off. With the OEM
HVAC, it would be something of a challenge to capture enough to be
useful.
Ken H.
On Sun, Jun 19, 2011 at 10:48 AM, Rob Mueller <robmueller@iinet.net.au> wrote:
> Ken,
>
> Would circulating the fuel from the tanks up to the fuel pump and back to
> the tanks in rubber lines remove heat or add it?
>
> You could add a small fuel cooler and mount it in the airstream. You could
> plumb condensed water from the A/C system to the fuel cooler and it would
> help cool the fuel.
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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: GMC Mechanical pump [message #130882 is a reply to message #130809] |
Sun, 19 June 2011 13:14 |
idrob
Messages: 645
Registered: January 2005
Location: Central Idaho
Karma: 0
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| Ken Burton wrote on Sat, 18 June 2011 22:57 |
I have often thought about why not use the other AC pump available for our coach that has the fuel return on it. All that would be required on this would be to add a low pressure return line from the pump to the tanks or fuel filler line. You could tee it into the Onan tap on the rear tank so you know where all returned fuel goes. I have not checked, but that tap may also be available on the front tank with nothing attached to it.
(snip)
My point in the above paragraph is I have no way to test this alternate fuel pump installation.
|
Ken: years ago I had a 1978 Jeep Cherokee (the old big full sized one) with a 360 V8. Hot sucker under the hood.
Original factory system for it had a fuel pump on the engine, and rubber lines (gasp) up to the top of the engine where there was an inline fuel filter next to the 2 bbl carb. On the filter was an outlet to the carb, and a smaller outlet to a fuel return line back to the tank. So, original Jeep setup was to use a fuel return from the filter near the carb. That fuel filter is still available today I am sure.
The rubber lines to the top of the engine we know (and you sure would know) are something that is most questionable, but it is how Jeep did it from the factory (I got the rig brand new).
So, I believe that the fuel return you mention from the pump would not be a bad idea, however the longer steel fuel line to the carb on the GMC could still over heat and cause vapor lock issues. Jeep solved that by returning fuel very close to the carb at the engine top.
Rob Allen
former owner of '76 x-PB
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| Re: GMC Mechanical pump [message #130896 is a reply to message #130882] |
Sun, 19 June 2011 15:07 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| idrob wrote on Sun, 19 June 2011 13:14 |
| Ken Burton wrote on Sat, 18 June 2011 22:57 |
I have often thought about why not use the other AC pump available for our coach that has the fuel return on it. All that would be required on this would be to add a low pressure return line from the pump to the tanks or fuel filler line. You could tee it into the Onan tap on the rear tank so you know where all returned fuel goes. I have not checked, but that tap may also be available on the front tank with nothing attached to it.
(snip)
My point in the above paragraph is I have no way to test this alternate fuel pump installation.
|
Ken: years ago I had a 1978 Jeep Cherokee (the old big full sized one) with a 360 V8. Hot sucker under the hood.
Original factory system for it had a fuel pump on the engine, and rubber lines (gasp) up to the top of the engine where there was an inline fuel filter next to the 2 bbl carb. On the filter was an outlet to the carb, and a smaller outlet to a fuel return line back to the tank. So, original Jeep setup was to use a fuel return from the filter near the carb. That fuel filter is still available today I am sure.
The rubber lines to the top of the engine we know (and you sure would know) are something that is most questionable, but it is how Jeep did it from the factory (I got the rig brand new).
So, I believe that the fuel return you mention from the pump would not be a bad idea, however the longer steel fuel line to the carb on the GMC could still over heat and cause vapor lock issues. Jeep solved that by returning fuel very close to the carb at the engine top.
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That is exactly where they put the fuel return line on my 1977 airplane. Right at the carb.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] GMC Mechanical pump [message #130940 is a reply to message #130857] |
Sun, 19 June 2011 19:07 |
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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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Ken,
If I understand you correctly you're saying that the bubbles would head back
to the tank and only liquid would be pumped up to the carb. I don't
understand how the fuel pump would separate them.
I agree there wouldn't be much gained by dripping the HVAC condensate on the
face of an air/fuel heat exchanger; I would only do it if it was easy. The
water removed from cabin air by the water separators in aircraft A/C systems
is sprayed onto the face of the bleed air heat exchangers.
Regards,
Rob M.
USAussie - Downunder
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 Ken Henderson
Sent: Monday, June 20, 2011 1:24 AM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] GMC Mechanical pump
I agree with Ken (strangely enough) about the likelihood of the
Toronado pump helping some vapor lock victims.
I suspect the objective of the return line is not cooling of the fuel
but elimination of the bubbles.
If I had a vapor lock problem, your fuel/water heat exchanger would be
a viable option since I do capture condenser run-off. With the OEM
HVAC, it would be something of a challenge to capture enough to be
useful.
Ken H.
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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] GMC Mechanical pump [message #130949 is a reply to message #130940] |
Sun, 19 June 2011 19:50 |
Arthur Mansfield
Messages: 290
Registered: April 2010
Karma: 0
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Senior Member |
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I had to use the pump with the return line and plugged the extra line. Then one day my wife said she smelled gas. It was the plug leaking. Now the pump I replaced it with did not have the proper angle on the outlet. I had trouble make it work with getting in the way with the fan belts.
By the way I had rubber hose with a filter after the steel line and the pump. The rubber line gets replaced every year along with the filter which includes the small filter in the Carb. The rubber line came about while I used a Holley when the Q Jet gave trouble. I like the power from the Holley but not the gas mileage loss. Yes I could have changed the jets in the Holley but I rebuild the Q Jet. Gave up some get up and go for gas mileage.
I tried to bend a new steel line but my tube bender would not bend sharp enough.
Art & Doris
76 EL
On Jun 19, 2011, at 7:07 PM, Rob Mueller wrote:
> Ken,
>
> If I understand you correctly you're saying that the bubbles would head back
> to the tank and only liquid would be pumped up to the carb. I don't
> understand how the fuel pump would separate them.
>
> I agree there wouldn't be much gained by dripping the HVAC condensate on the
> face of an air/fuel heat exchanger; I would only do it if it was easy. The
> water removed from cabin air by the water separators in aircraft A/C systems
> is sprayed onto the face of the bleed air heat exchangers.
>
> Regards,
> Rob M.
> USAussie - Downunder
> 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 Ken Henderson
> Sent: Monday, June 20, 2011 1:24 AM
> To: gmclist@temp.gmcnet.org
> Subject: Re: [GMCnet] GMC Mechanical pump
>
> I agree with Ken (strangely enough) about the likelihood of the
> Toronado pump helping some vapor lock victims.
>
> I suspect the objective of the return line is not cooling of the fuel
> but elimination of the bubbles.
>
> If I had a vapor lock problem, your fuel/water heat exchanger would be
> a viable option since I do capture condenser run-off. With the OEM
> HVAC, it would be something of a challenge to capture enough to be
> useful.
>
> Ken H.
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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