Home » Public Forums » GMCnet » Mech Fuel Pump
| Mech Fuel Pump [message #173440] |
Fri, 15 June 2012 20:51  |
LNelson
Messages: 335
Registered: December 2008
Location: Springfield, MO
Karma: 0
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I want to pick up a new mech fuel pump. I notice in the cross reference guide, some mention of pumps with return lines. I got under my coach today, and saw that there seemed to be one port with siamese connections, but one of those hoses went forward about 3" and had a plug in it. The other went aft to the tank, and the hard line went to the carb. So, do I have a standard setup or one with a return line? Thanks in advance.
Larry Nelson Springfield, MO
Ex GMC'er, then GM Busnut
now '77 Eleganza ARS WB0JOT
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| Re: [GMCnet] Mech Fuel Pump [message #173441 is a reply to message #173440] |
Fri, 15 June 2012 21:00  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Larry,
You have the pump intended for a car with air conditioning -- thus the
plugged return line.
Ken H.
On Fri, Jun 15, 2012 at 9:51 PM, Larry Nelson wrote:
>
>
> I want to pick up a new mech fuel pump. I notice in the cross reference
> guide, some mention of pumps with return lines. I got under my coach today,
> and saw that there seemed to be one port with siamese connections, but one
> of those hoses went forward about 3" and had a plug in it. The other went
> aft to the tank, and the hard line went to the carb. So, do I have a
> standard setup or one with a return line? Thanks in advance.
> --
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Ken Henderson
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www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Mech Fuel Pump [message #173443 is a reply to message #173441] |
Fri, 15 June 2012 21:14 |
LNelson
Messages: 335
Registered: December 2008
Location: Springfield, MO
Karma: 0
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Thanks,Ken,but which of the pump options in the interchange book is the one(s) for me?
Larry Nelson Springfield, MO
Ex GMC'er, then GM Busnut
now '77 Eleganza ARS WB0JOT
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| Re: [GMCnet] Mech Fuel Pump [message #173444 is a reply to message #173440] |
Fri, 15 June 2012 21:11 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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you have one with return line blocked off. A big word of caution! If it is blocked off with a rubber cap that can crack and spray fuel back onto the engine.. It can be used but I would crimp and braze the line to block it.
Emery Stora
On Jun 15, 2012, at 7:51 PM, Larry Nelson wrote:
>
>
> I want to pick up a new mech fuel pump. I notice in the cross reference guide, some mention of pumps with return lines. I got under my coach today, and saw that there seemed to be one port with siamese connections, but one of those hoses went forward about 3" and had a plug in it. The other went aft to the tank, and the hard line went to the carb. So, do I have a standard setup or one with a return line? Thanks in advance.
> --
> Springfield, MO
> Ex GMC'er, then GM Busnut
> now '77 Eleganza ARS WB0JOT
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| Re: [GMCnet] Mech Fuel Pump [message #173446 is a reply to message #173444] |
Fri, 15 June 2012 21:21 |
k2gkk
Messages: 4452
Registered: November 2009
Karma: -8
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Senior Member |
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One part number for the "correct" pump is M-6108.
The one with the extra port is M-6109. I bought
mine at Advanced. 10% discount for military
(active or retired). I think that 10% discount is
also offered at NAPA.
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
~~ ~ 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 ~
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
______________
*[ ]~~~[][ ][|\
*--OO--[]---O-*
> From: emerystora@mac.com
> Date: Fri, 15 Jun 2012 20:11:58 -0600
> To: gmclist@temp.gmcnet.org
> Subject: Re: [GMCnet] Mech Fuel Pump
>
> you have one with return line blocked off. A big word of caution! If it is blocked off with a rubber cap that can crack and spray fuel back onto the engine.. It can be used but I would crimp and braze the line to block it.
>
> Emery Stora
>
>
> On Jun 15, 2012, at 7:51 PM, Larry Nelson wrote:
>
> >
> >
> > I want to pick up a new mech fuel pump. I notice in the cross reference guide, some mention of pumps with return lines. I got under my coach today, and saw that there seemed to be one port with siamese connections, but one of those hoses went forward about 3" and had a plug in it. The other went aft to the tank, and the hard line went to the carb. So, do I have a standard setup or one with a return line? Thanks in advance.
> > --
> > Springfield, MO
> > Ex GMC'er, then GM Busnut
> > now '77 Eleganza ARS WB0JOT
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| Re: Mech Fuel Pump [message #173459 is a reply to message #173440] |
Sat, 16 June 2012 00:52 |
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John Heslinga
Messages: 632
Registered: February 2011
Location: Edmonton, Alberta, Canada
Karma: 4
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Senior Member |
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Hi There:
Buy the Pump without the return line option. It's the one you need. However, you may be interested in reading the following thread that was discussed a few months ago. It's the same as your question but there was a discussion why you might use the return line pump.
mechanical fuel poump question for a 78 403. [message #149296]
Your have to search the forum for this
(I don't know how to refer and link to the thread)Maybe someone can help me
Best regards
John H
John and Cathie Heslinga
1974 Canyonlands 260
455, Manny tranny and 1 ton, 3:70 LS,
Red Seal Journeyman, DTE, BEd. MEd.
Edmonton, Alberta
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| Re: Mech Fuel Pump [message #173462 is a reply to message #173440] |
Sat, 16 June 2012 01:23 |
glacierfl
Messages: 444
Registered: June 2011
Karma: 0
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Senior Member |
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Hello,
Jumped in here cos the topic is mechanical fuel pump. What i am trying to work out is the risk factor, of a mechanical fuel pump allowing fuel into the engine. I have an old one here that i partialy took apart. The membrane in it is fairly thick. How many fires are attributed to this type of fuel pump. What if the pump you have is a cheapo, made in a basement in China 'i know that a simplification'. Is the material in the mech pump resistant to crapanol, personally i doubt that. I have an electric fuel pump on the buy list, and wondering if to get a new mech fuel pump or take it out. Can we have a vote on this. Leave it in, or take it out. An engine costs 1000's to buy and labour costs etc etc. No way i want to find out later on, that the mech pump caused engine to fail. Sorry if this seems to be going over old ground.
cheers and beers
Steve & Debbie
Monticello, FL
77 Palm Beach :- Aurora
EX G4WDT
[Updated on: Sat, 16 June 2012 01:36] Report message to a moderator |
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| Re: [GMCnet] Mech Fuel Pump [message #173464 is a reply to message #173462] |
Sat, 16 June 2012 01:41 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Steve,
JimB installed a little Facet fuel pump that comes on and sends 1 - 4 psi to
the inlet of the mechanical fuel pump when I switch from Main to Aux in
Double Trouble.
It stops vapor lock problems instantly
It has been installed for over two years and has not caused any problems.
I do remember that someone reported that a defective fuel pump diaphragm
took out two engines before it was discovered.
Regards,
Rob M.
-----Original Message-----
From: steve & debbie
Hello,
Jumped in here cos the topic is mechanical fuel pump. What i am trying to
work out is the risk factor, of a mechanical fuel pump allowing fuel into
the engine. I have an old one here that i partialy took apart. The membrane
in it is fairly thick. How many fires are attributed to this type of fuel
pump. What if the pump you have is a cheapo, made in a basement in China 'i
know that a simplification'. Is the material in the mech pump resistant to
ethanol, personally i doubt that. I have an electric fuel pump on the buy
list, and wonderirng if to get a new mech fuel pump or take it out. Can we
have a vote on this. Leave it in, or take it out. An engine costs 1000's to
buy and labour costs etc etc. No way i want to find out later on, that the
mech pump caused engine to fail. Sorry if this seems to be going over old
ground.
cheers and beers
Steve & Debbie
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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: Mech Fuel Pump [message #173466 is a reply to message #173440] |
Sat, 16 June 2012 02:11 |
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John Heslinga
Messages: 632
Registered: February 2011
Location: Edmonton, Alberta, Canada
Karma: 4
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Senior Member |
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Hi Steve:
I'll have to say that there are a fair amount of benifits of an electric fuel pump, (Many here have one and for good reason will probably swear by them.) My experience, however, is that there are a lot more failures of electric pumps than mechanical. Almost all cars today have electric pumps. (For differnt reasons however)
A large percentage of people have never had a problem, ( Other than fuel pump failure itself)with a mechanical pump that they would need to change pump styles. Make sure you have a good reason (other than the "Cool factor") why you want to change over. Many issues are not the fault of a "Mechanical Pump" per seh.
Installing an electric fuel pump needs to be done properly, so have that discussion with experienced people if you choose to do so. I suggest that you choose electric or Mechanical, not both. Having both has a higher risk of failure.
In My humble opinion !!!!
Best Regards
John and Cathie Heslinga
1974 Canyonlands 260
455, Manny tranny and 1 ton, 3:70 LS,
Red Seal Journeyman, DTE, BEd. MEd.
Edmonton, Alberta
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| Re: [GMCnet] Mech Fuel Pump [message #173469 is a reply to message #173462] |
Sat, 16 June 2012 02:48 |
emerystora
Messages: 4442
Registered: January 2004
Karma: 13
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Senior Member |
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I had a diaphram fail in a Jeep Wagoneer once and it wiped out all of the bearings. That was back in about 1980. With the millions of cars using mechanical fuel pumps it is probably a very rare occurrence though.
I am not going to vote -- you have to make up your own mind.
Emery Stora
On Jun 16, 2012, at 12:23 AM, steve & debbie <zzdebz@yahoo.com> wrote:
>
>
> Hello,
> Jumped in here cos the topic is mechanical fuel pump. What i am trying to work out is the risk factor, of a mechanical fuel pump allowing fuel into the engine. I have an old one here that i partialy took apart. The membrane in it is fairly thick. How many fires are attributed to this type of fuel pump. What if the pump you have is a cheapo, made in a basement in China 'i know that a simplification'. Is the material in the mech pump resistant to ethanol, personally i doubt that. I have an electric fuel pump on the buy list, and wonderirng if to get a new mech fuel pump or take it out. Can we have a vote on this. Leave it in, or take it out. An engine costs 1000's to buy and labour costs etc etc. No way i want to find out later on, that the mech pump caused engine to fail. Sorry if this seems to be going over old ground.
>
> cheers and beers
>
> cheers and beers
>
> --
> Steve & Debbie
> Monticello, FL
> 77 Palm Beach :- Aurora
> EX G4WDT
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: Mech Fuel Pump [message #173474 is a reply to message #173466] |
Sat, 16 June 2012 06:53 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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In 50 years I have never had a mechanical fuel pump fail. I have had 7 electric fuel pumps fail in various vehicles.
I will admit to helping 2 friends change mechanical pumps. One was a 1954 Ford in about 1962 and the other was in a 1978 GMC.
I actually carry a spare electric pump for my Blazer and another one in my wife's Jimmy. I probably should buy one for my Colorado. My daughter has the replacement procedure down to about 2 hours to change one in a Blazer / Jimmy by dropping the tank on a garage floor.
I just remembered one more electric one I changed in a Ranger.
I have a mechanical pump on my airplane with a boost electric one in series with it. That is the way it is certified and the only arrangement that is allowed by the FAA.
This worry about breaking a diaphragm and filling the crankcase with gas is way over blown. While it could happen, it is very rare.
I like the idea of electric pumps (plural) on a GMC but I sure would make sure I have a Plan B for when the single electric pump failed.
Back on the mechanical pump. Get the one WITHOUT the extra return line. That is the one that should be on your GMC.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Mech Fuel Pump [message #173476 is a reply to message #173472] |
Sat, 16 June 2012 06:58 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Steve,
I've had my say about fuel pumps, repeatedly, so no vote. However,
regarding "back flow": My first electric pump on the GMC was tee'd into
the hard line between the mechanical pump and the carburetor. My thinking
was that the outlet valve in the mechanical pump would eliminate the need
for a check valve.
That assumption worked fine from GA to Yellowstone NP. There, after
filling up at the gas station in the far eastern edge of the park, I saw
gas pouring out of the right front of the engine. It turned out that the
mechanical pump had developed a leak ABOVE its output valve. Fortunately,
I had a cap and a plug to seal off the mechanical branch until I could get
a new mechanical pump.
I don't think the failure was related to the electrical pump, but the
incident did make me adamant about the need for check valves to isolate
pump outputs. I get mine from McMaster-Carr.
Ken H.
On Sat, Jun 16, 2012 at 7:35 AM, steve & debbie wrote:
>
> ...
> That led me to think about back flow?.
>
> If you have an electric pump and a mechanical pump on the same line, could
> the pressure from the electric pump feed back into the mechanical pump, and
> perhaps damage it ???. Assuming that the pumps, were not equal in pressure.
>
> I guess valves to stop that would be used. Or perhaps i am barking up the
> wrong tree here.....
>
>
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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: Mech Fuel Pump [message #173486 is a reply to message #173472] |
Sat, 16 June 2012 08:06 |
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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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| glacierfl wrote on Sat, 16 June 2012 07:35 |
Hello,
It was a bit stupid of me to ask for a vote, or general consensus on mechanical fuel pump leave in or take out. 
That has to be a choice based on personal preferences.
I did read on some other rv net site, cannot remember which site it was. That stated that that the mechanical ones can vary a bit in the pressure they put out. Not sure why/if that would happen, perhaps down to manufacturer tolerances. I wonder if there is any point in reading the pressure from the mechanical gauge ??
Might be interesting to see the actual pressure it's working at.
That led me to think about back flow?.
If you have an electric pump and a mechanical pump on the same line, could the pressure from the electric pump feed back into the mechanical pump, and perhaps damage it ???. Assuming that the pumps, were not equal in pressure.
I guess valves to stop that would be used. Or perhaps i am barking up the wrong tree here.....
cheers and beers
Steve
|
Steve,
You seem to be very concerned about nothing.
First, most mechanical pumps have safeties in place to prevent damage to engine in the case of a diaphragm failure. This does not mean that they won't leak fuel, but it won't easily get to where it can mix with the engine lube oil. (Yes, they used to do this.)
Second, if you put an electric pump in the system ahead of the mechanical pump, as long as it does not force fuel past the float needle in the carburetor, it can do nothing wrong.
Or, if you T it in after the engine's pump (al'a KenH) the mechanical pump just won't care.
Caution: long winded description of a mechanical fuel pump follows.
Regular old time (like ours) mechanical fuel pumps only work with float bowl controlled carburetors for a reason. Their discharge pressure varies widely, but is very limited to a pre-determined maximum. They do not use engine power to pump the fuel, only to draw it into the pump space. A spring pushes the fuel out.
The process is like this:
- The pump's lever pulls the pump diaphragm so as to cause a low pressure area that draws fuel into the pump cavity through an inlet check valve. That bar that pulls the diaphragm is pulled by the lever with an open hook (or the like).
- As the pumps lever returns, the diaphragm is now free. There is a spring under the diaphragm. This spring got set - "cocked" by the fuel pump lever as it pulled the diaphragm. Now, with the lever not pulling the diaphragm, that spring is now what is pushing the diaphragm to discharge the fuel. So, the discharge pressure is limited to what that spring can push.
- The fuel it prevented from going back the way it came by the previously mentioned inlet check valve. There is another check valve in the discharge line to prevent the fuel from being drawn back into the pump.
So, the maximum discharge pressure that the pump can make only a function of that spring. The pump discharge pressure will be Zero but only during the pump's intake cycle. The pump will only discharge as much fuel as the carburetor will accept.
Those of us that have been around these things too long also know that fuel pumps can get noisy at idle. This happens with some pumps because the pump lever gets loose for most of the time as so little fuel is being pumped. (It can sound like a bad cam follower.)
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] Mech Fuel Pump [message #173496 is a reply to message #173486] |
Sat, 16 June 2012 08:47 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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strange how folks forget that
-- RIGHT HERE--
one mechanical GMC pump destroyed 3 - 455 engines
just saying it does happen, and right here
gene
On Sat, Jun 16, 2012 at 6:06 AM, Matt Colie <matt7323tze@gmail.com> wrote:
>
>
> glacierfl wrote on Sat, 16 June 2012 07:35
> > Hello,
> > It was a bit stupid of me to ask for a vote, or general consensus on
> mechanical fuel pump leave in or take out. :?
> > That has to be a choice based on personal preferences.
> >
> > I did read on some other rv net site, cannot remember which site it was.
> That stated that that the mechanical ones can vary a bit in the pressure
> they put out. Not sure why/if that would happen, perhaps down to
> manufacturer tolerances. I wonder if there is any point in reading the
> pressure from the mechanical gauge ??
> > Might be interesting to see the actual pressure it's working at.
> >
> > That led me to think about back flow?.
> >
> > If you have an electric pump and a mechanical pump on the same line,
> could the pressure from the electric pump feed back into the mechanical
> pump, and perhaps damage it ???. Assuming that the pumps, were not equal in
> pressure.
> >
> > I guess valves to stop that would be used. Or perhaps i am barking up
> the wrong tree here.....
> >
> > cheers and beers
> >
> > Steve
>
> Steve,
>
> You seem to be very concerned about nothing.
>
> First, most mechanical pumps have safeties in place to prevent damage to
> engine in the case of a diaphragm failure. This does not mean that they
> won't leak fuel, but it won't easily get to where it can mix with the
> engine lube oil. (Yes, they used to do this.)
>
> Second, if you put an electric pump in the system ahead of the mechanical
> pump, as long as it does not force fuel past the float needle in the
> carburetor, it can do nothing wrong.
> Or, if you T it in after the engine's pump (al'a KenH) the mechanical pump
> just won't care.
>
> Caution: long winded description of a mechanical fuel pump follows.
> Regular old time (like ours) mechanical fuel pumps only work with float
> bowl controlled carburetors for a reason. Their discharge pressure varies
> widely, but is very limited to a pre-determined maximum. They do not use
> engine power to pump the fuel, only to draw it into the pump space. A
> spring pushes the fuel out.
>
> The process is like this:
> - The pump's lever pulls the pump diaphragm so as to cause a low pressure
> area that draws fuel into the pump cavity through an inlet check valve.
> That bar that pulls the diaphragm is pulled by the lever with an open hook
> (or the like).
> - As the pumps lever returns, the diaphragm is now free. There is a
> spring under the diaphragm. This spring got set - "cocked" by the fuel
> pump lever as it pulled the diaphragm. Now, with the lever not pulling the
> diaphragm, that spring is now what is pushing the diaphragm to discharge
> the fuel. So, the discharge pressure is limited to what that spring can
> push.
> - The fuel it prevented from going back the way it came by the previously
> mentioned inlet check valve. There is another check valve in the discharge
> line to prevent the fuel from being drawn back into the pump.
>
> So, the maximum discharge pressure that the pump can make only a function
> of that spring. The pump discharge pressure will be Zero but only during
> the pump's intake cycle. The pump will only discharge as much fuel as the
> carburetor will accept.
>
> Those of us that have been around these things too long also know that
> fuel pumps can get noisy at idle. This happens with some pumps because
> the pump lever gets loose for most of the time as so little fuel is being
> pumped. (It can sound like a bad cam follower.)
>
> Matt
> --
> Matt & Mary Colie
> '73 Glacier 23 Chaumière (say show-me-air) Just about as stock as you will
> find
> SE Michigan - Twixt A2 and Detroit
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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| Re: Mech Fuel Pump [message #173497 is a reply to message #173459] |
Sat, 16 June 2012 08:52 |
Dennis S
Messages: 3046
Registered: November 2005
Karma: 2
|
Senior Member |
|
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| John Heslinga wrote on Sat, 16 June 2012 00:52 |
Hi There:
Buy the Pump without the return line option. It's the one you need. However, you may be interested in reading the following thread that was discussed a few months ago. It's the same as your question but there was a discussion why you might use the return line pump.
mechanical fuel poump question for a 78 403. [message #149296]
Your have to search the forum for this
(I don't know how to refer and link to the thread)Maybe someone can help me
Best regards
John H
|
Link to old thread per John H.
http://goo.gl/sOjRm
Dennis
Dennis S
73 Painted Desert 230
Memphis TN Metro
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