The GMC CCKW

Hi

Took the CCKW out for a run yesterday; about 70 plus miles. Even with a rebuilt fuel pump (my third fuel pump) in 10 years, the truck seems to run out of fuel on hard mountain pulls.

Has anyone installed an electric pusher fuel pump around the fuel tank (would place a fuel filter inline before the pump) and left the original fuel pump in place? I was thinking of having a switch in the dash for turning it on when pulling steep hills.

Your thoughts? Lee

Hi Lee
On the C15TA that I just got (Canadian Chev) I have an electric fuel pump. There is a switch under the dash that I turn on before starting the truck. This fills the lines and the carb and the old 270 just fires right up. I then shut it off and run on the manual pump. I haven't had to use it on the road yet but I wouldn't hesitate to if the need arose.
Barry

Lee
Which mechanical fuel pump are you using, the early 2 valve or the late 6 valve?
I have a 6 valve on my CCKW and have never had a fuel issue

You may want to check your filter, and the fuel pick-up tube in the tank
sounds like an obstruction or a weak fuel pump is your problem.

Hope this helps
John

Hi

I run the six valve fuel pump which has been rebuilt professionally. Prior to this fuel pump, I had (2) different 2 valve fuel pumps on. With a clear fuel filter right before the carburetor, the gasoline never fills up the filter more that 50% and on hard throttle, it drops considerably. Have cleaned the original fuel filter a number of times and in fact, have a easy drain valve at its base.

Though it is a great running engine, I think the lobe of the cam is warn where the fuel pump bolts on.

Lee

Following up on installation of electric 6 volt fuel pump. While installing the electric fuel pump with a dash switch and a 10 amp inline fuse, I also installed in the fuel line just before the carburetor a fuel pressure guage. Remember, I left in place and operational the 6 valve engine fuel pump.

Results of the manually fuel pressure was about 2-4 psi. With the additional electric running, the pressure jumped up another 1 to 2 psi. This now fills the plastic fuel filter which was installed just before the guage up from almost a dribble at the bottom to more than half full.

Hoping this solves my fuel delivery problem.

Make sure you have a filter before the electric pump or it will not work for long....

Hi Steve

Thanks for the tip on the fuel filter before the pump. Yes, I do have a filter before the electric fuel pump. Actually, I have a total of three filters inline.
Lee

Never too many

just a link for Motto for comment regarding these old posts .... thoughts?

Call me a traditionalist or whatever but I subscribe to the old saying that if it aint broke, don't fix it. I've owned and operated a reasonable range of WW2 vehicles over the last 40+ years and have not had to deviate from the original fuel system installation and components which, if in good shape still perform as they were designed to do. The people that designed and built these vehicles to operate in adverse or even extreme conditions had a good idea of what they were about and in most instances got it right.
I've told the story elsewhere of the Weapons Carrier I owned at one time that had an electric fuel pump fitted when I bought it. That pump could easily have cost me the vehicle and my home if luck had gone against me. The pump was wired so as it ran whenever the ignition was on and I had a short in a battery cable that could very easily have arced a hole in the fuel line which the pump would have then quite efficiently squirted fuel through. There were flash marks on the fuel line and the truck was parked right against the side of the house.
For many years now I understand that any modern vehicle that has an electric fuel pump installed must have the pump powered in such a way as to cease functioning if the engine stops. Other wise the pump will quite likely continue to operate after a collision. I don't know the legal implications of an add-on electric fuel pump particularly if it contributes to a disaster.
Yes, an electric pump is handy for priming the system prior to start but that can be done with the original hand primer. You should be lifting the bonnet to check for oil, water, rat nests or the family cat anyway if the vehicle has been parked up long enough to need priming.
In regards to fuel filters, maybe I'm blessed but the original set up has always proved to be perfectly adequate. They are made to be easily serviced whereas the inline filter has to be discarded when clogged and how do you know when that's about to happen with a metal one. As to the value of using more than one, unless they became progressively finer then the second or third will not stop anything that will pass through the first so are completely useless except as water traps, a function carried out quite well by the original.
Unless you are adding contaminated fuel or the interior of the tank is producing debris the filter should have nothing to do anyway, it is there as a precaution and should not be a necessity.
I've taken my vehicles enormous distances from home and refuelled from gerry cans countless times (a very good source of contamination)and have had very few fuel problems. The later WW2 vehicles with the large filler necks often had an extension which incorporated a wire gauze. I would never add fuel to a tank from a jerry can without that gauze or equivalent. On two occasions I had blockages at the tank pick up on recently commissioned vehicles. The filter played no part and once the debris was removed no further problems.
From the posts that I read it would seem that effort and expense is expended unnecessarily in an attempt to fix problems that either don't or shouldn't exist. Band-aid solutions or belts and braces instead of a holistic approach.
These are my thoughts anyway and I can only advise on what works for me.

David

Thanks David
makes sense to me

I performed this upgrade a couple of years ago. Thought I would put a few miles on it to make sure it worked before sharing the results.

My truck had an electric fuel pump on it when I bought it - installed by the previous owner. After sitting the first winter, it stopped working. I was thinking about converting back to the original mechanical system, but I was concerned about everything I had read regarding these old fuel pump diaphragms failing. That, coupled with potential hot fuel handling issues associated with today's gas, I decided to stick with the electric option.

As mentioned previously in this thread, the straight wiring to the ignition switch method (i.e. the way mine was wired) is pretty much an invitation to disaster (OK.. well, maybe not one of those fancy formal invitations with an RSVP envelop, but at least an email or phone invite). Using some type of cutout switch to kill the fuel pump when the engine is not running is the only safe option. I chose an oil pressure based switch made by Holley, model 12-810. It is easy to wire, and also has a normally closed contact that is handy for priming. They are available from a number of performance shops.

https://drive.google.com/open?id=0BwZqh ... 2F2aEl4U28

The only drawback with oil pressure switches, is that they need a source of oil pressure. For me, this actually helped with another problem. The flex line at the back of the engine feeding the oil pressure gauge looked like it was about ready to spring a leak at any minute. That and the tubing coming from the front of the engine looked kinked near the clip that holds it in place near the flex line connection. Since it had to be replaced anyway, this seemed like a good junction point to mount a tee for the pressure cutout switch.
I modified a brake tee, and mounted it to a piece of angle, then bolted it to the top of the bell housing, under the starter linkage spacer.

https://drive.google.com/open?id=0BwZqh ... Th1Qml6Y1U

I made a new shorter spacer to compensate for the width of the bracket.
The oil line from the engine now comes in from the bottom, the flex line to the gauge goes out the top, and the cutout switch goes out the side. This is a much more robust method than the original design which had that small piece of tubing kinda hanging there in space.

https://drive.google.com/open?id=0BwZqh ... FlaSUdDOUk

Speaking of lines, one method I found that works well for making connections to either fuel or oil lines, is to silver braze an AN fitting on the end. Sometimes it's hard to find one for 5/16", so you can just take one made for 1/4" tubing, and bore it out to 5/16". This setup allows a lot of flexibility in selecting mating componentry as there are hundreds of different configurations available from the various hose and fitting vendors (Aeroquip, Earls, Russel, etc.)

https://drive.google.com/open?id=0BwZqh ... 2czVHdfaFE

For the new electric fuel pump, I picked one made by Carter, model P4259. Surprisingly, the auto parts store near my house actually had one of these. The P.O. had welded a mounting plate onto the frame near the tank for an electric pump. I would have preferred bolting on an adapter, but since the bracket was already there, I figured that I might as well use it. It actually worked to my advantage, as I needed a place to mount the inlet fuel filter anyway. It ended up packaging nicely behind the bracket, held in place with a couple of plastic coated steel straps. The inlet filter I picked is designed for this application (pump inlets) is also made by Holley. It has a removable stainless steel element that can be cleaned, and at 100 microns, it is fine enough to catch debris that will hurt the pump, but not too fine as to cause an undue restriction.

https://drive.google.com/open?id=0BwZqh ... UlhSFRpLVU

https://drive.google.com/open?id=0BwZqh ... VZwTlVHdTQ

The rest of the existing fuel system was pretty sad. It was essentially a smorgasbord of mismatched fittings, kinked tubing, spliced together hoses, etc. A good part of the line running up the frame to the filter by the engine was just lying there, bouncing around. It wasn't even clamped down.

I replaced all of it with stainless tubing - bending it to what I believe is the original route, using the witness marks on the frame. The only deviation was near the electric pump, where it turns up and out to make the connection to the pump. I could have used rubber hose and clamps, but I had some AN line and fittings left over from a previous project, so this seemed like a good place to use them up.

https://drive.google.com/open?id=0BwZqh ... 2MzdF9qUjg

Next came the engine mounted pump. Totally removing it would require even more fuel line changes, so I decided to keep it, relegating it to a pass through by making some internal mods. I found a cheap replacement on e-pay, gutted it and installed a stainless steel block-out plate. I also added a fake priming lever to the side to make it look like an original.

https://drive.google.com/open?id=0BwZqh ... Vd2SmpEWlE

https://drive.google.com/open?id=0BwZqh ... lFsWW90RTQ

With the plumbing in place it was time to wire up the switch. I was already thinking about putting in a key type switch anyway, so I purchased a heavy duty marine switch with a crank position. Wired up as in the schematic below, this allows the system to be primed in “crank” via the normally closed contacts in the cut out switch.

https://drive.google.com/open?id=0BwZqh ... lFBcndOVlE

So far it has worked out well. The prime feature is actually pretty nice if the truck has been sitting for awhile. The oil pressure cutout gives peace of mind, ensuring that the fuel pump will not keep pumping if the engine stops.

Best Regards...