I THINK I AM THROWING IN THE TOWEL

[Keith V]

Probably not the problem, but my brother had a car that would run fine, then randomly die. if you wait 30 min, it would run fine again.
Turns out there was a small piece of paper in the tank, it would get stuck to the pickup sock, starve the engine, then float away!
________________________________
From: Gmclist on behalf of slc via Gmclist
Sent: Thursday, July 30, 2020 11:47 AM
To: gmclist
Cc: slc
Subject: Re: [GMCnet] I THINK I AM THROWING IN THE TOWEL

======== Install a vacuum/pressure gauge on the inlet side of fuel pump.

Go take it for a test drive and when you get into it and it starts to
act up you should see the gauge go into a vacuum. If this is the case
you now know that you have a restriction from there back to the tanks somewhere.

We know the problem is in the tanks/hoses up to the Fuel Sol Valve. The Fuel Sol valve was replace a year ago.
I ran a test run with a external tank, eliminating the tanks and hoses, she ran good. that proved the tanks/hoses in trouble.

I would bet the fuel socks are plugged, selector solenoid is stuck in between or the hoses
got crushed when they put the tanks back up.

The tank filter socks were blown off a couple years ago and I added a filter on the hose after the tanks and before the Mech Fuel pump. We have
changed the filters as method of trying to eliminate a problem, they never had anything in them

At the end of the day the fuel system is simple. When we go about diagnosing it
we just need to follow a systematic approach.

One other thing to check for if it is not fuel related. If the distributor is a
factory HEI setup and could be the wires to the pickup coil in the distributor.

I have seen one wire break at the coil itself. When enough vacuum is applied to the
vacuum advance the connection will come apart and you have no spark. When vacuum drops
off connection is made again and it will keep on running. Easy way to check for this is
with a handheld vacuum pump. With the coach parked hook up the vacuum pump to the vacuum
advance. Start the engine and let it idle. Now pump up the vacuum pump to about
20 in of vacuum. Engine should speed up but run smooth. If it dies check the two wires
going to the ignition pickup coil on the distributor advance plate.

The problem is not acting electrical at all. However, I will have it checked
.
I think the overall plan will be to put the OEM fuel tanks and hoses to the fuel solenoid out of service
and use an external fuel tank and electric fuel pump to supply the fuel to the carborator.
I know the tanks and hoses are in trouble and there is nothing I can do about it until they can be
dropped and hoses changed.

THANK YOU
=============

--
GatsbysCruise. \
74GMC260 Former Glacier Model style. \
Waukegan, Illinois \ Keep those MiniDiscs Spinning \ MY GREYHOUND IS FASTER THAN YOUR HONOR ROLL STUDENT \ WindowsXP-Win7-Win8.1-UBUNTU STUDIO -
UBUNTU VOYAGER - Berzin Auto Center

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[dave stragand1]

Also, rust in the tank can accumulate on the sock as you drive, building up even to the point of a stall. Once the suction stops, the rust flakes fall
off and all seems just fine again for a while. I usually put a couple of strong magnets on the bottom of our old cars’ tanks, but out of the path
of the float arm. It helps keep the rust away from the pickup sock.

Way back in my days a mechanic, the culprit in a similar situation was a superball someone put in the tank getting sucked up to the pickup tube.

-Dave
1978 Transmode near Pittsburgh
--
1978 Transmode (403)
Pittsburgh, PA

 

[Ken Shaffer]

as others have said, I would definitely get fuel pressure gauge added to
your set up. Without knowing that you have the right pressure, how would
you ever know where to begin???
I monitor my pressure constantly. Even when the main tank is running out
and the engine stumbles, I look at pressure to confirm.... yup, out of
fuel, then switch to the aux tank and watch the pressure go back up. Just
last weekend, I was on a 1100 mile trip and stopped at a rest area for a
bit. When returning, I turned my coach over for 8-10 seconds before it
started up. (With fuel injection, its usually running the instant I hit the
key. ) I checked the fuel pressure and sure enough, I only had 4 psi. I
just happened to be out of fuel on the main tank when I stopped. After
switching tanks, pressure went back up and she ran perfectly.
Just an example of how and why I use a fuel pressure gauge. Good luck on
your adventure and we all hope it works out for you one way or another.

Ken Shaffer
Marion, Iowa
73 GMC Canyonlands (455)
73 GMC Glacier (455)

On Thu, Jul 30, 2020 at 1:45 PM Dave Stragand via Gmclist <

> Also, rust in the tank can accumulate on the sock as you drive, building
> up even to the point of a stall. Once the suction stops, the rust flakes
> fall
> off and all seems just fine again for a while. I usually put a couple of
> strong magnets on the bottom of our old cars’ tanks, but out of the path
> of the float arm. It helps keep the rust away from the pickup sock.
>
> Way back in my days a mechanic, the culprit in a similar situation was a
> superball someone put in the tank getting sucked up to the pickup tube.
>
> -Dave
> 1978 Transmode near Pittsburgh
> --
> 1978 Transmode (403)
> Pittsburgh, PA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[john r. lebetski]

The great Smokey Yunick said something like “9 out of 10 carburetor problems are ignition”.
Worth a look. I was helping a Buick guy with his Powermaster brakes and he was telling me his lawn tractor had a bad PTO because at full throttle he
couldn’t engage the blades without killing engine. This was over phone and I couldn’t witness. He replaced PTO still same issue. Turns out there
was some crud across the plug gap. Started fine. Ran full throttle fine but could not support load. Could be bad coil wire or coil if non HEI
--
John Lebetski
Woodstock, IL
77 Eleganza II

 

[SteveW]

Bobobob13-

“ Install a vacuum/pressure gauge on the inlet side of fuel pump.

Go take it for a test drive and when you get into it and it starts to
act up you should see the gauge go into a vacuum. If this is the case
you now know that you have a restriction from there back to the tanks somewhere. ”

Are you sure you mean to say the inlet side of the pump ??

Wouldn’t there always be a vacuum there when the pump is running ??

I’m in the midst of replumbing my system and plan to incorporate a fuel pressure gauge. Low pressure as I’m carbureated...

Thanks !!

Steve W
1973
Southern California.

--
Steve W
1973 : 23'
Southern California

 

[Keith V]

Man that sucks!
it really sounds like a bad gas line, I assume youve tried switching tanks? Run with the gas cap loose?

Brake lines have a weird problem where the liner tears and makes a check valve, brake fluid gets under the liner and puffs up the liner closing the hose off. The hose looks good from the outside!

I'd run the heck out of it with your external tank, if that works drop the tanks and replace the lines with the best you can get. I use nylon these days whenever possible
________________________________
From: Gmclist on behalf of Steve Weinstock via Gmclist
Sent: Saturday, August 1, 2020 10:19 PM
To: gmclist
Cc: Steve Weinstock
Subject: Re: [GMCnet] I THINK I AM THROWING IN THE TOWEL

Bobobob13-

“ Install a vacuum/pressure gauge on the inlet side of fuel pump.

Go take it for a test drive and when you get into it and it starts to
act up you should see the gauge go into a vacuum. If this is the case
you now know that you have a restriction from there back to the tanks somewhere. ”

Are you sure you mean to say the inlet side of the pump ??

Wouldn’t there always be a vacuum there when the pump is running ??

I’m in the midst of replumbing my system and plan to incorporate a fuel pressure gauge. Low pressure as I’m carbureated...

Thanks !!

Steve W
1973
Southern California.

--
Steve W
1973 : 23'
Southern California

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[BoboBob]

Yes install the vac gauge on the inlet side of the pump. There should
be no restriction there so you will not pull a vacuum. If it does then
you do have a restriction.

If you want to check pressure you would put the pressure gauge on the
outlet side of the pump. Also you can check volume on the outlet
side of the pump. I forget how much volume we used to look for
but I would think if you had 1 pint in about 30 seconds of running
the should be more than enough.

Bob
--
Bob Broadwell
75 Eleganza II-Rebuilt performance engine, Manny trans, Manny 1-ton front end, 73 23ft with a side bath getting some updates-both living in Las Vegas

 

[SteveW]

Got it - thank you Bobobob13.

I was thinking about my (new) electric pump(s) located back by the tanks...

Steve W
1973 23
Southern California

--
Steve W
1973 : 23'
Southern California

 

[slc]

******************

Alright, I am about to begin the attack.

Testing of the various devices is going on. I intend to put the OEM tanks and hoses out of service since it is a known problem for fuel starvation,
and I will use a external 18 gal fuel tank with an electric fuel pump.
I will not be able to use the mech fuel pump because it sends fuel back to the OEM tanks, it has 3 ports, not the normal 2. That shop sold it to my
mechanic when we were trying to find the fuel starvation problem.

So I have a question????

My goal seems to be to replace the Mechanical fuel pump with electric fuel pumps and check valves in the long term.
So I need to make a circuit so if the oil pressure drops to zero, the fuel pumps will cut off in emergency.

So did you take the Ign power from the DASH SWITCH for the Main and Res tank solenoid switch???

I am assuming the IGN side of the switch is used for the relay coil that connects to the oil low pressure sensor

and the switched side of that switch (used for the res tank solenoid) would be used to power the electric pump at the tank. (at this point
I am talking about the Temporary 18 gal fuel tank electric fuel pump.)

After the OEM fuel tanks, Main and Res, have been dropped and the fuel lines replaced, the circuit can be revised so it switches, via relay to
run the main or Res fuel tank electric fuel pumps.

I know the lines from the OEM main and Res will need check valves and that is in the plan to prevent the fuel circulating from the pump back to the
other tank.

Have I missed anything???

Thank you all, trying to move ahead..........

slc

--
GatsbysCruise. \
74GMC260 Former Glacier Model style. \
Waukegan, Illinois \ Keep those MiniDiscs Spinning \ MY GREYHOUND IS FASTER THAN YOUR HONOR ROLL STUDENT \ WindowsXP-Win7-Win8.1-UBUNTU STUDIO -
UBUNTU VOYAGER - Berzin Auto Center

 

[Jim Hupy]

Yes. That mechanical fuel pump is the wrong pump for your coach. The
correct pump only has an inlet and one outlet. The one with 3 spouts is
specifically for an Oldsmobile Toronado. If you have any fuel hoses hooked
to that third spout, it does not belong there. I am not saying that this is
the source of your problem, but, it will not improve it at all. You are
wise to discontinue use of that 3rd port.
Jim Hupy
Salem, Oregon

On Wed, Aug 5, 2020, 8:00 AM slc via Gmclist
wrote:

> ******************
>
> Alright, I am about to begin the attack.
>
> Testing of the various devices is going on. I intend to put the OEM
> tanks and hoses out of service since it is a known problem for fuel
> starvation,
> and I will use a external 18 gal fuel tank with an electric fuel pump.
> I will not be able to use the mech fuel pump because it sends fuel back to
> the OEM tanks, it has 3 ports, not the normal 2. That shop sold it to my
> mechanic when we were trying to find the fuel starvation problem.
>
>
> So I have a question????
>
> My goal seems to be to replace the Mechanical fuel pump with electric fuel
> pumps and check valves in the long term.
> So I need to make a circuit so if the oil pressure drops to zero, the fuel
> pumps will cut off in emergency.
>
> So did you take the Ign power from the DASH SWITCH for the Main and Res
> tank solenoid switch???
>
> I am assuming the IGN side of the switch is used for the relay coil that
> connects to the oil low pressure sensor
>
> and the switched side of that switch (used for the res tank solenoid)
> would be used to power the electric pump at the tank. (at this point
> I am talking about the Temporary 18 gal fuel tank electric fuel pump.)
>
> After the OEM fuel tanks, Main and Res, have been dropped and the fuel
> lines replaced, the circuit can be revised so it switches, via relay to
> run the main or Res fuel tank electric fuel pumps.
>
> I know the lines from the OEM main and Res will need check valves and that
> is in the plan to prevent the fuel circulating from the pump back to the
> other tank.
>
>
> Have I missed anything???
>
> Thank you all, trying to move ahead..........
>
> slc
>
> --
> GatsbysCruise. \
> 74GMC260 Former Glacier Model style. \
> Waukegan, Illinois \ Keep those MiniDiscs Spinning \ MY GREYHOUND IS
> FASTER THAN YOUR HONOR ROLL STUDENT \ WindowsXP-Win7-Win8.1-UBUNTU STUDIO -
> UBUNTU VOYAGER - Berzin Auto Center
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[roy keen]

Don’t think you missed anything that is the way I have done it with success
--
Roy Keen
Minden,NV
76 X Glenbrook

 

[hal stclair]

> Yes. That mechanical fuel pump is the wrong pump for your coach. The
> correct pump only has an inlet and one outlet. The one with 3 spouts is
> specifically for an Oldsmobile Toronado. If you have any fuel hoses hooked
> to that third spout, it does not belong there. I am not saying that this is
> the source of your problem, but, it will not improve it at all. You are
> wise to discontinue use of that 3rd port.
> Jim Hupy
> Salem, Oregon
>
>
>
> Actually Jim we used to install those pumps on cars with vapor lock issues and they did indeed work. GM used them on AC equipped cars for that
> purpose. Living in the Las Vegas area for 45 years, especially the early 70's& 80's tested the best of the mechanics trying to keep engines cool.
> The summers aren't fit for man nor beast in that area.
> Hal
>
> On Wed, Aug 5, 2020, 8:00 AM slc via Gmclist

>
> > ******************
> >
> > Alright, I am about to begin the attack.
> >
> > Testing of the various devices is going on. I intend to put the OEM
> > tanks and hoses out of service since it is a known problem for fuel
> > starvation,
> > and I will use a external 18 gal fuel tank with an electric fuel pump.
> > I will not be able to use the mech fuel pump because it sends fuel back to
> > the OEM tanks, it has 3 ports, not the normal 2. That shop sold it to my
> > mechanic when we were trying to find the fuel starvation problem.
> >
> >
> > So I have a question????
> >
> > My goal seems to be to replace the Mechanical fuel pump with electric fuel
> > pumps and check valves in the long term.
> > So I need to make a circuit so if the oil pressure drops to zero, the fuel
> > pumps will cut off in emergency.
> >
> > So did you take the Ign power from the DASH SWITCH for the Main and Res
> > tank solenoid switch???
> >
> > I am assuming the IGN side of the switch is used for the relay coil that
> > connects to the oil low pressure sensor
> >
> > and the switched side of that switch (used for the res tank solenoid)
> > would be used to power the electric pump at the tank. (at this point
> > I am talking about the Temporary 18 gal fuel tank electric fuel pump.)
> >
> > After the OEM fuel tanks, Main and Res, have been dropped and the fuel
> > lines replaced, the circuit can be revised so it switches, via relay to
> > run the main or Res fuel tank electric fuel pumps.
> >
> > I know the lines from the OEM main and Res will need check valves and that
> > is in the plan to prevent the fuel circulating from the pump back to the
> > other tank.
> >
> >
> > Have I missed anything???
> >
> > Thank you all, trying to move ahead..........
> >
> > slc
> >
> > --
> > GatsbysCruise. \
> > 74GMC260 Former Glacier Model style. \
> > Waukegan, Illinois \ Keep those MiniDiscs Spinning \ MY GREYHOUND IS
> > FASTER THAN YOUR HONOR ROLL STUDENT \ WindowsXP-Win7-Win8.1-UBUNTU STUDIO -
> > UBUNTU VOYAGER - Berzin Auto Center
> >
> > _______________________________________________
> > 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

--
"I enjoy talking to you. Your mind appeals to me. It resembles my own mind, except you happen to be insane."

1977 Royale 101348,

1977 Royale 101586, Diesel powered,

1974 Eagle Bus 45',w/slideout,

Rio Rancho, NM

 

[slc]

********************
Yes. That mechanical fuel pump is the wrong pump for your coach. The
correct pump only has an inlet and one outlet. The one with 3 spouts is
specifically for an Oldsmobile Toronado. If you have any fuel hoses hooked
to that third spout, it does not belong there. I am not saying that this is
the source of your problem, but, it will not improve it at all. You are
wise to discontinue use of that 3rd port.
Jim Hupy
Salem, Oregon
*******************

That shop that did the tank drop and hose changes was the shop that recommended that 3 port mechanical fuel pump.

We were having issues with the mechanical fuel pump (now resolved I think but still checking) so we were adding an electric fuel pump to PURGE the
carborator after sitting over winter.
It turned out, when running, the GMC regained its top speeds again.
The 3 port Mech fuel pump was suggested because the electric fuel pump could possibly send too much fuel and the 3rd port would send the fuel
back to the tanks.

thats what they told my mechanic.

So with the speeds back up we thought this trouble was all well behind us but it only lasted about an hour on the road and the problem was back.

The problem is definately in the tanks and or hoses.

I will be installing a external fuel tank and use the electric fuel pump to get fuel to the carb.

Someone just told me I can pinch off that 3rd port and use like a 2 port Mech fuel pump, which I am considering.

I have several senarios in play and setting up the system for test runs and permanent set up do not seem to work together without some kind of
modification after the tanks and hoses are restored again.

I keep thinking how can all this trouble happen, it is basically a big fat car, and yet, its like the bottom dropped out from under it.

Moving on
Thanks for the comments.

slc
--
GatsbysCruise. \
74GMC260 Former Glacier Model style. \
Waukegan, Illinois \ Keep those MiniDiscs Spinning \ MY GREYHOUND IS FASTER THAN YOUR HONOR ROLL STUDENT \ WindowsXP-Win7-Win8.1-UBUNTU STUDIO -
UBUNTU VOYAGER - Berzin Auto Center

 

[wally anderson]

> ******************
>
> Alright, I am about to begin the attack.
>
> Testing of the various devices is going on. I intend to put the OEM tanks and hoses out of service since it is a known problem for fuel
> starvation, and I will use a external 18 gal fuel tank with an electric fuel pump.
> I will not be able to use the mech fuel pump because it sends fuel back to the OEM tanks, it has 3 ports, not the normal 2. That shop sold it to
> my mechanic when we were trying to find the fuel starvation problem.
>
>
> So I have a question????
>
> My goal seems to be to replace the Mechanical fuel pump with electric fuel pumps and check valves in the long term.
> So I need to make a circuit so if the oil pressure drops to zero, the fuel pumps will cut off in emergency.
>
> So did you take the Ign power from the DASH SWITCH for the Main and Res tank solenoid switch???
>
> I am assuming the IGN side of the switch is used for the relay coil that connects to the oil low pressure sensor
>
> and the switched side of that switch (used for the res tank solenoid) would be used to power the electric pump at the tank. (at this point
> I am talking about the Temporary 18 gal fuel tank electric fuel pump.)
>
> After the OEM fuel tanks, Main and Res, have been dropped and the fuel lines replaced, the circuit can be revised so it switches, via relay to
> run the main or Res fuel tank electric fuel pumps.
>
> I know the lines from the OEM main and Res will need check valves and that is in the plan to prevent the fuel circulating from the pump back to
> the other tank.
>
>
> Have I missed anything???
>
> Thank you all, trying to move ahead..........
>
> slc

John Heslinga posted this on the photosite about an oil pressure switch for electric fuel pump safety shut off. Part numbers in the text
http://www.gmcmhphotos.com/photos/electric-choke-conversion/p54560-electric-fuel-pump-and-electric-choke.html
http://www.gmcmhphotos.com/photos/electric-choke-conversion/p54560-electric-fuel-pump-and-electric-choke.html
--
Wally Anderson
Omaha NE
75 Glenbrook
Megasquirt III injection
Bob Stone hydroBOOOOST
Manny reaction arm system
Branscombe Kelsey Hayes park brake
http://wallyandsue.blogspot.com/

 

[6cuda61]

Problem is that it's a big fat car with 2 tanks plumbed together that everyone has played with ( PO, PPO, PPzPO) from stock with little to no
knowledge of what they are doing and no fault of your own you get to fix it.

If it makes more sense to you or your mechanic work it like it is one system.....one tank, one pump, one carb...forget about the rest till the one
system works properly.

When i get a basket case problem the first thing i do is put it all back to OEM then start troubleshooting and upgrading. IE: put the correct pump in
it and plug that bypass line (who knows what its hooked up too, heck for all anyone knows it might be presurizing the tanks) etc....

Your on the correct path but perhaps you might explore the original one first....jmho.
--
Rich Mondor,

Brockville, ON

77 Hughes 2600

 

[Richard RV]

> We know the problem is in the tanks/hoses up to the Fuel Sol Valve. The Fuel Sol valve was replace a year ago. I ran a test run with a external
> tank, eliminating the tanks and hoses, she ran good. that proved the tanks/hoses in trouble.

You may have more than one fuel line issue.

I had my fuel lines replaced shortly after buying my Birchaven. The PO installed the electric fuel pump outside the frame rail (yes, I know I'm going
to die!) just ahead of the front tank. I was experiencing a number of fuel delivery issues. The rubber fuel lines were being sucked flat before the
pump, the selector valve was sucking from both tanks, and there were hose clamps before the pump that were never tightened. Different issues causing
different problems under different conditions.

Selector valves fail and you already have serious concerns about the mechanic's knowledge and skills. As onerous and unwelcome as it may be, your
tanks will be coming down again. At least this time you'll be benefiting from the knowledge and advice from the really experienced guys on this forum
- I'm not one of them.

Knowing what I do now, I wouldn't replace the lines with all rubber again. I'd go with Nicopp on top of the tanks to eliminate the PIA factor of
replacing them. Costs more, drop in the bucket, peace of mind.

I hope your external tank experiment proves fruitful.

Richard
--
'77 Birchaven TZE...777;
'76 Palm Beach with 18,477 verified miles;
‘76 Edgemonte

 

[Matt Colie]

>
> When i get a basket case problem the first thing i do is put it all back to OEM then start troubleshooting and upgrading. IE: put the correct pump
> in it and plug that bypass line (who knows what its hooked up too, heck for all anyone knows it might be presurizing the tanks) etc....
> Your on the correct path but perhaps you might explore the original one first....jmho.

Rich,

While I agree with your basic premise (going back to OE), I would just like to add that I have worked with both pumps. There is no way that the
second discharge from the pump could cause pressure in the fuel system. It is just an orificed bleed out of the pressure side of the system so there
is no new volume added. unless all the fuel got really hot, whatever should just re-condense in the tanks.

That pump exists because the Toros with A/C did have vapor lock problems. I have one of those pumps and was considering plumbing it back to the fill
vent for the auxiliary tank. My problem is someone beat me to it and wrote all about what a failure the plan was. That saved me that effort.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

 

[6cuda61]

Matt if they plumbed it back to the tank vents instead of the filler neck etc it might cause a problem...my point i guess was more to do with who
knows how they set it up so just best to get rid of it.

> >
> > When i get a basket case problem the first thing i do is put it all back to OEM then start troubleshooting and upgrading. IE: put the correct
> > pump in it and plug that bypass line (who knows what its hooked up too, heck for all anyone knows it might be presurizing the tanks) etc....
> > Your on the correct path but perhaps you might explore the original one first....jmho.
>
> Rich,
>
> While I agree with your basic premise (going back to OE), I would just like to add that I have worked with both pumps. There is no way that the
> second discharge from the pump could cause pressure in the fuel system. It is just an orificed bleed out of the pressure side of the system so
> there is no new volume added. unless all the fuel got really hot, whatever should just re-condense in the tanks.
>
> That pump exists because the Toros with A/C did have vapor lock problems. I have one of those pumps and was considering plumbing it back to the
> fill vent for the auxiliary tank. My problem is someone beat me to it and wrote all about what a failure the plan was. That saved me that effort.
>
>
> Matt

--
Rich Mondor,

Brockville, ON

77 Hughes 2600

 

[slc]

U P D A T E -------------------------

here is where I am at present on the GMC power loss problem. Sort of where I was 10 years ago only with lots of new part.

200825
GMC TESTING

MECHANICAL FUEL PUMP tested good on pressure
The ELECTRICAL FUEL PUMP, located in the rear, tested with low PSI. Unkown if this low pressure is caused by a blockage in the hoses or actual
fuel pump failure. Testing further................

Installed the TEMP 18 gal fuel tank on the rear rack.
Removed and plugged the hose from the Sol valve.

Connected the hose from rear temp external fuel tank to the fuel hose that goes forward.
This hose is new as of last year.

This leaves the OEM fuel system cut off and plugged, and using an all new fuel supply system feeding the mechanical fuel pump.

TEST DRIVE.

Put 5 gallons of gas in the External fuel tank took a couple minutes to prime the fuel line to the
mechanical fuel pump. Started the engine and let run idle for 15 minutes. Ran well.

TEST got in to drive around the block, put in drive, and moved forward fine. Made the first
turn got about 100 feet then the fuel problem began again.

Engine began to stall, and I struggled to get the GMC back to the shop.
Mech checked the carb. Said he pumped the carb, saw the first two pump spray fuel, then nothing
so fuel supply is again the problem.

WE are going to extensively test the MECHANICAL FUEL PUMP to see if we can force it to fail.
The Mechanical fuel pump is the only thing suspect in this senario.
Testing next week to see what comes up.

Also planning to add electric fuel pump in the fuel line from the external fuel tank.

Hope one of these options will find the fix.

slc


--
GatsbysCruise. \
74GMC260 Former Glacier Model style. \
Waukegan, Illinois \ Keep those MiniDiscs Spinning \ MY GREYHOUND IS FASTER THAN YOUR HONOR ROLL STUDENT \ WindowsXP-Win7-Win8.1-UBUNTU STUDIO -
UBUNTU VOYAGER - Berzin Auto Center

 

[Jim Hupy]

Sounds like you might have a float level in the carb that is too low, or an
inlet needle that might be stlcking, or swelled up from alcohol in the
fuel. Worth a look.
Jim Hupy
Salem, Oregon

On Tue, Aug 25, 2020, 5:10 PM slc via Gmclist
wrote:

>
>
> U P D A T E -------------------------
>
> here is where I am at present on the GMC power loss problem. Sort of
> where I was 10 years ago only with lots of new part.
>
> 200825
> GMC TESTING
>
> MECHANICAL FUEL PUMP tested good on pressure
> The ELECTRICAL FUEL PUMP, located in the rear, tested with low PSI.
> Unkown if this low pressure is caused by a blockage in the hoses or actual
> fuel pump failure. Testing further................
>
> Installed the TEMP 18 gal fuel tank on the rear rack.
> Removed and plugged the hose from the Sol valve.
>
> Connected the hose from rear temp external fuel tank to the fuel hose that
> goes forward.
> This hose is new as of last year.
>
> This leaves the OEM fuel system cut off and plugged, and using an all new
> fuel supply system feeding the mechanical fuel pump.
>
> TEST DRIVE.
>
> Put 5 gallons of gas in the External fuel tank took a couple minutes to
> prime the fuel line to the
> mechanical fuel pump. Started the engine and let run idle for 15
> minutes. Ran well.
>
> TEST got in to drive around the block, put in drive, and moved forward
> fine. Made the first
> turn got about 100 feet then the fuel problem began again.
>
> Engine began to stall, and I struggled to get the GMC back to the shop.
> Mech checked the carb. Said he pumped the carb, saw the first two pump
> spray fuel, then nothing
> so fuel supply is again the problem.
>
> WE are going to extensively test the MECHANICAL FUEL PUMP to see if we can
> force it to fail.
> The Mechanical fuel pump is the only thing suspect in this senario.
> Testing next week to see what comes up.
>
> Also planning to add electric fuel pump in the fuel line from the external
> fuel tank.
>
> Hope one of these options will find the fix.
>
> slc
>
>
> --
> GatsbysCruise. \
> 74GMC260 Former Glacier Model style. \
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