M38 fuel pump differences

pickle · Post by **pickle** » Sun Mar 24, 2013 3:27 pm

Hello;

I was looking through the M38 reference book and I am trying to understand the differences between the early and late fuel pumps, or was there any?. i can see from the ordinance manual that later ones started after engine MC 74419 (ordinance G7408330132). I know on my unit it was replaced, and it is "AC" on it, but I haven't seen a number. Thanks guys.

Mk

Post by **wesk** » Sun Mar 24, 2013 7:31 pm

The first two pump listings on page 72 are the factory original part numbers installed. Before eng MC74420 is non-fording vented pump and after MC74419 is fording vent system pump also the rocker arm pin changed. The two pumps are the field service replacements for the applicable serial groups. This essentially means the first two pumps were only installed at the factory in new jeeps and new spare engines. They were not stocked on the military shelf.

pickle · Post by **pickle** » Sun Mar 24, 2013 10:45 pm

Thanks Wes. so if I understand correctly, the non fording vented one has only 2 ports (on the top half only), while the fording ones would have in essence 3 (two fuel ports on either side of the top half, and a small one at the front? I am looking at the reference book (pages 70-72) and I only see the two lines. I saw an earlier posting for an M38A1 discussion about fuel pumps....

where was the hand primer on the pump for the M38A1s? were they pretty similar units?

Post by **wesk** » Mon Mar 25, 2013 1:11 am

The small fitting in the middle at the front is a vent fitting which vents the crankcase. An early unit would have a plain pipe plug in that hole and the late is as you show in your photo. Has nothing to do with fuel or vacuum pump activity.

pickle · Post by **pickle** » Mon Mar 25, 2013 9:44 pm

thank you again Wes for the info.

I see my pump actually has the plug in it...it has "AC" on it (AC15399197 or AC5592659?)....I could have sworn it was outfitted to a replacement pump, according to my father. There is no vent line to the crankcase. My engine serial is MC99254. question...could a later pump be outfitted with the plug if the vent line was not present? Does this mean this jeep likely had the early venting system too?

I tried to capture a photo, but I did not have my good camera. It is missing one of the bolts, and has me concerned as I see the pump was not straight on the motor. As soon as it warms up here, I want to see the condition of that pump arm.

Post by **wesk** » Mon Mar 25, 2013 9:51 pm

Yes the later pump could simply have that plug installed or vice versa. Those pumps saw many service changes and improvements over the years and at least 6 different part numbers are listed in the various manuals and all interchange.

AC normally stamped only the last four digits of the pump Part Numbers on the pumps' mounting flange edge.