Fuel gauge(s) issue

[trijjicon]

Hello to all: Been awhile so I hope all is well with you guys. I've run outa gas twice now. The shop I use has installed 3 new gauges & all of them failed. Two from KaiserWillys and one was an aftermarket. The head mechanic told me I'll never get a true reading anyway unless I was stopped & on relatively level ground cuz my gas tank has no baffling. Probably is truth to that or is there?.  Now i'm curious, cuz when Full it reads way over the F mark. It showed about half-full when I ran out. I wonder if the needle or perhaps the gauge itself could be tweaked (needle moved back or gauge re-calibrated in some way or the float?). Or r 3A's notorious for this? Could it b a wiring problem. I know some of u have been there too, so I would definitely like to hear what u guys think I should do next. Ty  Ty

[aboyandhisdog]

To get my gauge to read correctly (years ago), as I recall all of my efforts centered around getting a sender that worked correctly and then adjusting it to make sure the float would read "full" at the top position, and "empty" when, well, empty.  It is important that the gauge and the sender are of the same ohms rating for them to work right.  If you buy a gauge and sender as a set, I would think they would be paired correctly.  (but don't hold me to it!)  :-?

[squidtone]

I agree that a sender in a '3A tank will never be terribly accurate, and it also might be a little jumpy since fuel will slosh around, (I think there is at least one baffle in there) but I think there is no reason that you can't get a reasonably decent working sender/gauge combo.

The original CJ3A fuel gauges were, I believe, a balanced coil design which I think are quite sensitive to source voltage. I'm thinking that new gauges are also of the balanced coil design. Does your replacement gauge voltage needs match what you're running in your Jeep now? (6V or 12V?) I wonder if that's the root of the problem; mismatched voltage needs for the gauge and sender.

Here's what I would do: take out your sender and gauge, and set it all up on a bench with a power supply, or lacking that, use a bunch of double A batteries in series to mimic what your Jeep runs now. Connect the power to your gauge and wire the sender output to the gauge, and be sure to also ground the "case" of the sender to the negative of the battery pack as well. When the sender is hanging down, the gauge should read "E" within reason, and when you push the sender arm up, the gauge should go up to "F".

(If the gauge doesn't move at all, suspect something is not connected right.)

If you get 1/2 full when the sender is hanging all the way down, either the voltage rating of the gauge is not appropriate, or the resistance of the sender is wrong. Change the voltage to see if you can get it to go to "E" with the sender hanging down. (this is where having a bench top adjustable power supply would be helpful). Let us know what voltage your Jeep and gauge are....

[trijjicon]

Ok, thnx guys. This info is very useful & I'll show this post to my mechanic. This Jeep has been converted to 12V. i can't b sure if the units I ordered from Kaiser/Willys or even the aftermarket one were gauge/sender paired. I'll mention this to my mechanic also. Again, much appreciation for the help.

[trijjicon]

No tweaking of the gauge,float, or sending unit has worked. It still won't read correctly. It's all 12V. The shop is now talking about just getting a new tank (poly, they suggest) with matching gauge,sending unit alrdy installed. I only c Omix having that but I've heard negative comments on Omix products. Any other suggestions?

[aboyandhisdog]

I don't know much about the poly tanks.  The steel would of course be a bit more "period correct" if that is worth anything to you.  Makes sense if you can buy all together as a kit.  There are some who can't stand anything Omix.  I am not one of them.  I have had very good luck with a number of their products, and others are marginal.  Maybe some of their selection isn't the best, but IMHO we're lucky to have them.  If for no other reason to keep some of their competition's pricing in check.

[Tumbleweed]

My gauge I purchased from KW had an issue and when I called them I was told to run a second ground. Not sure what you have but does your in dash gauge have 3 poles or just 2? The one I purchased form KW had 3 and until I added the second ground it was a bit squirrelly.

[trijjicon]

My gauge does have a 3 post. The shop has run 3 wire grounds the way u guys said in the posts. I even had them read athawk's post about fuel gauge acting like ammeter. The shop said they had alrdy done it that way. It still won't read correctly. What should we try next?

[mtnman37879]

A stick never fails...

[Gunslinger]

Seems to me that replacing the tank with a poly tank/ kit is a short cut to figuring this out.  If your tank is in good shape you shouldn't have to replace it.

I've got the same problem in my M38A1 right now and I struggled a bit with my 3a as well.  If your gauges are from Omix you  may have to try a couple different ones to get one that works well with your sender.  It just seems thats the way of it.

My 38a1 only reads to 1/4 tank, so I pulled the sender out to test it, making sure I had a ground from the housing to the tank.  Moving the arm up and down did  not give me full range on the gauge, so I pulled the ground off, at that point the gauge went to full.  So that told me that the gauge has full range of motion, and is working electrically.  I replaced the sender with a new one and repeated that process, looks like I have it responding now so we'll see when I fill it up.

Good luck, Gun