Electric Fuel Pump Modification

[bigcol]

I know some of you won't like it!!! But am thinking of installing new electric 24 volt fuel pump to my 02/51 M38 due to incline problems in area which is affecting driving. Usual problem with power reduction, motor running rough & stalling when inclining... including front driveway to house!

Looking at Ebay 24 volt fuel pumps & in particular pump with a 6psi to 9psi rating. Could someone advise if this pressure is sufficient for M38 motor?

Regards, Col

[wesk]

A lack of power on incline is not a "usual problem" with the Willys. I could run my M38A1 bone stock up a 60 degree hill for all day if need be.

The electric fuel pump is a band aid for a real issue that needs to be fixed.

In just about every short cut electric fuel pump install the owner will spend more on the parts and the modification then it would have cost to troubleshoot and fix the original problem.

A few of these original problems are:
1-Sediment issues in the fuel tank.
2-The addition of more filters for item 1 which cause more resistance for mechanical fuel pump.
3-Bad mechanical fuel pump. (Have you checked output pressure?)
4-Air leak on suction side of fuel pump. (anywhere from the pump's inlet fitting all the way to the in tank pick-up tube)
5-Incorrect fuel pump, fuel pump mounting or spacer.
6-Incorrect carb settings. (Have you checked float setting, and metering rod and metering rod diaphragm)
7-Corrode pin holes in in tank plumbing.
8-Clogged tank vent system
9-Gas cap vent valve left closed.
10-Fording valves in wrong position.

You should at least check these ten items before modifying with a band aid.

The correct fuel pressure for the M38 is 4.0 to 5.5 at 18" above outlet at 1800 RPM.

Electric fuel pumps will usually require a pressure regulator in line to carb. For safety reasons the electric pump's power supply must use a oil pressure switch to prevent the pump from operating if the engine is not running.

Also note that you will loose the very much needed vacuum boost for your windshield wipers by removing the mechanical pump.

[bigcol]

I knew you where going to say that Wes!!

(9-Gas cap vent valve left closed.)

Regarding the above where would I locate the cap vent valve. I noticed mine is very new and this may be the issue?

Having a non-mechanical back ground I must admit I am having difficulty with the "balance" of enjoying driving my M38 compared to the time it spends in the garage with repairs. I know this goes "hand-in-hand" with owing an older vehicle, but I don't remember having the same on-going problems with old my 45 MB!

Thanks, Col

[wesk]

Your 45 MB did not have vacuum operated accelerator pump and metering rod diaphragms that facilitate waterproofing the carb. They also did not have a dual vacuum/fuel pump not did they have a remote fuel tank vent system with a cap that has a small rotating valve inside with a mark showing closed and open or vent and fording.

Waterproofing the fuel, engine venting, ignition, brake tranny.transfer and electrical systems makes the M38 a much more complicated jeep.

Since you already have a 45 MB with a Carter WO may I suggest if the waterproof carb system is not agreeable to you then just sub the WO off your MB and see if the power on an incline issue resolves itself. If it does then do a proper rebuild on your YS650S Carter using a modern kit from Ron F or John at Midwest. If it doesn't then you know you will need to review my troubleshooting list. And you would not have thrown $120 at a carb from India.

[jeeptj1]

wes. so on normal driving should the cap vent be closed or open. thanks john jr

[wesk]

It should be in the NORMAL Position as show and stated on the top side of the cap.

[jeeptj1]

wes, thanks, pretty sad when i cant even read the dam cap aint it. is the cap shown for an m38 or m38a1. i have the cap shown on my m38 but i thought the m38 book shows that cap as on 1955. thanks

[wesk]

The odds of any M series truck having it's original fuel cap a half century plus is about 1000 to 1.

There were at least 6 or more different M series caps stocked by the military from 1950 thru the 80's and they may have had several suppliers each.

On page 63 of the M38 book the 1st and third caps would most likely have been original on M38's and which would depend on serial number group.

The caps are all interchangeable. Usually whenever a tanks vent line to the air cleaner or vent valve got plugged or stuck the first field repair was to leave the cap loose so the engine could draw fuel from the tank then draw a late selectable cap from supply until you got the jeep in the shop to correct the plugged vent system.