M151a1 Fuel Pump Issues

[bobward152]

Hiya fellas.....I am by no means a mechanic, and have very little mechanical aptitude; that's why I'm coming to you guys. I have a 1967 M151a1 , with what appears to be ALL original equipment (ie. M151a1 engine etc.). On veteran's day it just up and died in the middle of the road and I "think" that it was the fuel pump that went out (right in the middle of the veteran's day parade). It died, but still cranked over....when I checked under the hood, I found that the fuel filter was dry (the tank was full); that's why I'm suspecting the pump. I have had some people tell me that the A1 only has a mechanical fuel pump on the side of the block, while others have told me that there are 2 fuel pumps...the mechanical pump on the block, and an electric pump in the tank. I have also had some tell me to take the electric pump out and just run it off the mechanical pump. If there are 2 pumps, what is the reason for two, and if so, can the electric pump be eliminated and the MUTT run entirely off just the mechanical pump? If anyone can help I would really appreciate it...Thanks

[Rickf]

The A1 only has an electric pump unless someone changed it to the mechanical pump from an A2. The engine is the same through all all years, just the fuel pump and alternator change.

[hambone]

Is there still a wire hooked up where the electric pump is in the tank? short wire goes to pump, long wire to sender. If it's original, it will have a vacuum pump, which operates your wipers, mounted to the lower right side of the block. Many people replace the vacuum pump with a mechanical fuel pump when the expensive original(electric) one goes out, they will usually plumb the wipers into the manifold if needed.

IMG_3163.jpg (105.31 KiB) Viewed 464 times

[W. Winget]

When you turn on the power switch, do you hear any ticking or whirring noise from under the drivers seat? (Indicates pump circuit is working)
If you pull the fuel line and place it in a container, then hit the power switch, does fuel come out (are there any in-line filters someone has installed?)
Next step try to remove your in tank pump, start by removing the driver seat, then the rest is under the large plate (lots of bolts to get stripped off if you hurry, so penetrant and take your time).

Two options: Find an original replacement in tank pump $$$ (One site is selling "Electric Fuel Pump M151 Tested reconditioned.) no price mentioned.
Another dealer sells a complete intank kit: M151A1 FUEL PUMP IN TANK KIT 2910-00-921-5618 $699.95 or they also sell the refurbished set for $599:
https://tnjmurray.com/m151a1-pump-assem ... ested.html

I searched for filters (Iten 7 in below photo) and found one dealer for $35:
https://www.armyjeepparts.com/p-3180-m1 ... -7283.aspx

TNJ Murray: M151A1 FILTER FUEL IN TANK 2910-00-678-7283 $32.00

or

Buy a mechanical fuel pump (Get the NAPA one for $60 VS $290 for an original) and install it where the vacuum wiper pump currently resides, replumb fuel hoses as needed for new pump, and buy a fitting to adapt the vacuum hose to the manifold for wipers to remain functional (accept when accelerating they will slow down)

Option three doesn't exist: Find a 24V in tank pump (google is your friend) from a Ford or Chevy, either install it in-line, remove your pump, have someone modify the pump top plate so it holds the NEW model in tank pump and then reassemble. Now a 12V pump may work if a resistor is placed to drop the voltage flow to 12V, but again....lots of minor engineering.

Option 4 get an A2 tank (no in-tank pump) and put a standard fuel pump on engine then plumb in the vacuum hoses.

I am quite certain a 1963-64 Chevrolet GMC Double Action Fuel Vacuum Pump 6603
or
1952-53 FORD 6 CYLINDER CARTER DUAL ACTION FUEL PUMP WITH VACUUM NOS CARTER 624
might be able to be fitted and have the best of both worlds (several on e-bay) but the days of searching old parts manuals are limited mainly to on-line searches as most shops tossed their paper manuals with photo references. It's out there, just don't know which late 60's -70's AMC or ?? had combined mechanical fuel and vacuum wiper pumps. V/R W. Winget
PS: To all concerned, Ron does not sell M151 parts or I would have directed a search toward his parts 1st.

[Rickf]

M151 electric fuel pump operation. The fuel pump will not run just by turning on the switch, if it does then the oil pressure safety switch is bad. There are two operation that cause the fuel pump to run. The first is switch on and starter motor engaged (wire #77B). The other is motor running and oil pressure detected by the safety switch. It does not run with just the switch on because the engine will start and run on the gas in the carburetor bowl initially. Remember, it does run while the starter is cranking. If you need the pump to run with switch on and nothing else you can jump the #77and #77A terminals in the oil pressure switch plug.
People that modify the circuit so it will run on the switch do not realize the danger of a pressurized line all the time. Any small leak will continue under pressure until the tank is empty. And in an accident you could have the same issue.

[bobward152]

You guys are awesome! That's why I came to all of you....It still has me scratching my head a little bit, but I really appreciate all of your input. Thank you everyone. I still don't understand why there would be 2 fuel pumps (one mechanical and one electric). But I'm going to take another look; I'll double check to see if there is actually a wire hooked up to the pump in the tank.

[W. Winget]

There are two types of systems, as the upgraded A2 went to mechanical pump for simplicity, as it had electric wipers so no need for the vacuum pump. They could have kept the in-tank electric but then would have had to place a blanking cover over the former pump hole.

Rick: I have had two A1's so far, and both ran the pump when switched on. The most recent rewire job I did on a friend with everything by the book has the pump pumping when the switch is flipped. I did not modify it, and because of this I pulled the wire off the pump so I could check all the circuits like lights, etc. Without fuel pumping out of the carb.
So I believe you, but this is what I have encountered.
V/R W. Winget

[Rickf]

There is no worry of fuel pumping out of the carb as nce the needle closes the pump will stop. But the circuits are set up as I mentioned. If you do not believe me check the wiring diagram. If it runs on switch on but not engine running then something is wrong. Either the plug on the oil pressure safety switch was jumped or the insulation came off the wires there and the wires have shorted together. if you unplug that switch and verify no jumper and turn the ignition on with it unplugged and the pump runs then someone has monkeyed with the wiring. I used to see this on the Ford 429 SCJ engine which had the same setup and people would hot wire the pump to the ignition.

[W. Winget]

Reason the fuel pumped out of the carb was it had not run in over a year (burned wiring) so when I hooked up the new wiring and followed the wiring number for number (with the chart you provided as well) and following the manual it performed as stated. Three days later when I connected the fuel tank pump again, the float and needle valve sealed (I had a friend start it on while I observed to ensure it wasn't pumping fuel out)
Have to move it inside, it's cold here, and will verify if it does it tomorrow.

By the way, I successfully transcribed the old turn signal "Letters To Numbers" wiring harness upgrade which we the TMs did not elaborate on, I will post them in a separate post when I can.
V/R W. Winget