Fuel Gauge

[Hal Edmondson]

My fuel gauge would bounce around at the 1/2 full mark, I changed the sending unit. Now it sits steady at the 1/4 mark,I ran a wire to the battery and thegauge body but it made no difference. Does anyone have an idea as to whats going on?....Hal

[LarrBeard]

My fuel gauge would bounce around at the 1/2 full mark, I changed the sending unit. Now it sits steady at the 1/4 mark,I ran a wire to the battery and thegauge body but it made no difference. Does anyone have an idea as to whats going on?....Hal

The basic circuit is a variable resistor in series with the gauge. Less fuel, higher resistance, lower reading on the gauge. More fuel, less resistance, higher gauge reading.

But, before we can make any better guesses - what Jeep are we talking about? There are significant differences between various models. My '48 truck is a lot different than a CJ 3A.

[LarrBeard]

My fuel gauge would bounce around at the 1/2 full mark, I changed the sending unit. Now it sits steady at the 1/4 mark,I ran a wire to the battery and thegauge body but it made no difference. Does anyone have an idea as to whats going on?....Hal

These may give you some ideas to check out:

https://www.thecj2apage.com/forums/why-doesnt-my-gas-gauge-work_topic17875.html

http://www.cj3apage.com/cgi-bin/3Ayabb26/YaBB.pl?num=1429482195

https://cj3b.info/Tech/FuelGauge.html

I would check out the ground on the gauge case very closely.

[gmwillys]

I concur with LarrBeard on the ground check. The links are great as well!

[bmorgil]

[QUOTE=LarrBeard;7831]These may give you some ideas to check out:

https://www.thecj2apage.com/forums/why-doesnt-my-gas-gauge-work_topic17875.html

http://www.cj3apage.com/cgi-bin/3Ayabb26/YaBB.pl?num=1429482195

https://cj3b.info/Tech/FuelGauge.html


Definitely bookmarking those links! Everything you want to know about the fuel gauge.

[minnesotawillys]

New guy to this forum, but also have a fuel gauge question. Have a '61 CJ5; original fuel gauge stopped working about 6 weeks ago. Put two replacements in, can't get any to work. Also replaced the sending unit. The gauges simply go right to "full", even though the tank is only half full. Don't mean to butt in on Hal's issue, but any ideas? Had a CJ2A owner tell me there's a set screw on the back of the gauge I need to worry about, but I don't even see one and am clueless at the moment.

[LarrBeard]

Have a '61 CJ5; original fuel gauge stopped working about 6 weeks ago. Put two replacements in, can't get any to work. Also replaced the sending unit. The gauges simply go right to "full", even though the tank is only half full. Had a CJ2A owner tell me there's a set screw on the back of the gauge I need to worry about, but I don't even see one and am clueless at the moment.

I'd suggest you read the three links in the email in this link, there is good info about fuel gauges in general there - even though it applies to CJ 2A's..

The set screw is not there on all CJ 2A repro gauges and I haven't seen any reference to it on CJ 5 gauges at all.

I'd check and make sure all of the wires are on the right terminals, and that you have a good ground. Here is a good article:

https://www.morris4x4center.com/jeep-knowledge-center/CJ-Gauge-Troubleshooting/

Let us know what you find, we like to know if our advice is any good!

[minnesotawillys]

Many thanks for the advice; I'll give it all a look. I'm not sure a CJ5 has a set screw -- I sure don't see one. I'm thinking, like you, it's likely a wiring problem. Thanks, again.

[gmwillys]

Welcome Minnesotawillys!

I concur with LarrBeard. I am certain that there is not an adjustment screw on the original gauge. Most of the time, if there is a screw, it is stamped +/- around it for adjustment.

What part of Minnesota do you call home?

[Hal Edmondson]

I added a ground to the sender unit, replaced the gauge after cleaning the back of the dash around the gauge hole. It turned out to be the float rod was to wide and was rubbing the side of the sender unit hole. Replaced the old sender unit now gauge works fine, thanks to all for your great advice. I couldn't get the panel lights to work properly, turns out they have 12volt bulbs in them. I'm just waiting for the 6v bulbs.....Hal

[gmwillys]

Advanced Auto had 6 volt bulbs, at least for the tail lights. I was surprised.

[drypolcher]

Hello, I have a 1949 4x4 Willy's truck, but with an F series engine. The tank is new, plastic, and the sender is new. The gauge is original. I went from 6 volt to 12 volt but got a volt reducer so I could keep all my original gauges. My fuel gauge reads full all the time but with a long stick with some markings I know what is full and what is half full, relatively. Right now the tank is half full but my gauge is still reading full or very very close to full. There has been a little movement in the needle but not much. I checked the sender and it does not seem to me that the float is stuck up against the top of the tank. There seems to be some movement but it is not recording actual fuel level in the tank or at least close to it. I do not mind the stick approach but would like to upgrade from that if possible. I have the rectangular cluster and the "upside down" temp gauge. As always, thank you in advance for your help on my behalf. Tony

[LarrBeard]

The 1948 and 1949 trucks use the same fuel gauges and sending units. I have a similar issue with the ’48, but I suspect mine is because the float is improperly adjusted in the tank. That is going to be one of my cooler weather projects. I went to a plastic tank as well since the truck sits so much; I didn’t want to worry about condensed water, rust and crud.

You have converted to a 12-volt system and have a voltage converter for your gauges. I assume that you have one of the mechanical voltage converters, not an electronic one. The mechanical converters act like an averaging switch. They have a thermostat on-off type element in them and when the switch is closed the output is 12-volts and when open, 0-volts. If the switch operates on a 50% duty cycle (on half the time, off half the time) the average voltage is 6-volts. Since the fuel, oil pressure and temperature gauges are slow responding thermal gauges, they operate OK on this converted voltage.

I’d start by checking the output of the converter. An old analog meter does the best job. See if you are getting a reading of about 6-volts; it may be up around 7.5 or 8-volts. The needle may quiver a bit as the points open and close.

Next, take a look at the actual resistance of the fuel sender. Disconnect the tank lead from the gauge and measure resistance back to a good ground on the frame. My gauge wants to see a fairly low resistance (2 or 3 ohms) to put it up around full. To settle around empty, it wants to see about 25 or 30 ohms. If you see a low resistance, check for a pinched wire back to the sender on the way to the tank.

How did you handle the upside-down temperature gauge with the F-134 and 12-volt conversion?

[drypolcher]

Here is how I handle the upside-down temp gauge.

My meter is fine, it was the King Seeley temperature sender. I found a Ford sender, part number 01A-10990. It's for a 1930 to 1950 Ford six volt. I am pleased with it. My thermostat is for 180 degrees. Once it opens and my meter stays around 180. That close enough for me. With the bad sender the meter would just peg pass 212, that was not good. With my Ford sender it does not peg. Some say Ford used King Seeley senders back then, some say Ford made and used their own, no matter my new sender works with my King Seeley temp meter. Life is good. Now I am off to address my fuel gauge "issue."

Also, I bought a volt reducer, 12 to 6 volt, from Ron Francis Wiring. I was not the cheapest but it seems to be working just fine.

[LarrBeard]

" ...Ford Sensor 01A-10990 ..."

I looked at one of these too, but in my F-134 the thread was the wrong size and the bulb was too big for the hole in the cylinder head. It looked like it would have been OK for the flathead L-134 though.