Fuel gauge issue

[JEB]

I'm back with a problem I can't seem to fix on my M38A1.
Fuel gauge still reads 1/2 a tank when full.
So far...
-New sending unit from Midwest Military.
-Re-grounded gauge.
-Correct fuel gauge per Army manual.

Everyone says It's a ohms issue.

How to fix?
Buy every freaking' gauge on the internet until you find correct one?

 

[DeetFreek]

Are you on FB? More specifically, there's a group titled M38/M38A1. I did a quick search and came up with a thread that Wes Knettle commented on, and since he's the closest thing to the Bible, I saved the pics of his replies. If you're not, shoot me a message and I'll send you the TM pages.

Secondly, a lot of guys responded with they bent the float arm until it read correctly.

 

[JEB]

Sorry, I don't do Facebook...
But I do have a TM.

I haven't looked at it thinking the ohms mismatch issue between the gauge and sender would not have happened when everything was new and units were made by OEM suppliers.

Does anyone have any experience with bending the sending unit float arm?

 

[m38inmaine]

You can test it two ways, with or without a multimeter, best to have a meter but let's try a simple test first. Remove the sending unit from the tank, attach a temporary ground wire from the sending unit body to a known good ground on the body, with the sending unit wire plugged in and a temporary ground attached turn on the ignition, with the float hanging down it should show empty, as you slowly raise the float you should see the meter read and all the way raised should show full. If this test works then it is a float level issue and the arm will have to be bent to correct it.

If you have a meter, set it to ohms and with the sending unit removed, no wires attached place one meter lead to where the wire plugs in and one to the sending unit body, as you move the float up you should see a steady increase or decrease in ohms, if I remember I think it goes from 0-60 ohms, the manual will have that info. If this checks out the sending unit is good and you probably have a bad tank to ground issue. It is a very simple system and will be easy to fix once you understand how it works.

 

[lpcoating]

Here is another possible option:

https://www.amazon.com/gp/aw/d/B0BQ3R4VN4?psc=1&ref=ppx_pop_mob_b_asin_title

There is a guy on the Humvee threads that has one of these units and is very happy with it. I've not bought one yet but I'm tired of NOS ones only lasting for a year. My experience with the 151 units is they seem to swell up and bind. Good luck!

Guy

 

[JEB]

Finally resolved.
It took three tries, but it was firmly re-grounded....
So, it reads fairly accurately (with fuel up to the base of the huge filler neck, it reads a tick below the "full" hash mark)....which I'm told is about as good as a 70 year old Jeep is going to get.

 

[Mud Diver]

You say regrounded. Did you have to find a good ground for the gauge? I have the seeding unit grounded to the tub with an extra wire and gauge to dash.

 

[JEB]

I didn't Ser what the repair was, I believe he used an extra wire to a good surface.
The gauge works better but still shows about 3/4 of a tank when full.
So whay next adjust the float?

 

[Mud Diver]

Well at least yours reads something. Mike barely moves past “E”.

 

[JEB]

That's just it, I don't know how accurate ANY would be 70 years on...


Maybe it is as good as its going to get without All new aftermarket gauges...which I don't want.

Why doesn't someone make new gauges that look correct?

 

[Mud Diver]

We may be talking pineapples and oranges. I’m working with 12 volt aftermarket gauges that like correct, but don’t have the windows for the panel lights. Dumb a**s me tossed the 65’ish instruments when I got the new stuff and shit still doesn’t work.

 

[JEB]

My issue (or trouble) is mine is still 24 volt and I want the correct OEM units. So the issue is a combination of getting correct grounds and trusting ancient gauges work.