Gas gauge / sending unit testing

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gsoco

gsoco

gsoco
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Help if you can. I cannot get my 62 Valiant gas gauge to work. It is a new Bosch. I replaced the original gauge (which didn't work either...) The shop that redid my fuel tank says the sending unit is new...is there more to testing it then looking for voltage on the blue wire that runs directly from the sending unit to the gage and a ground? I REALLY don' want to drop the tank...thanks.
 
You look for ohms never put voltage to it.
gauge ohms.jpg
 
Get a multi meter and measure resistance from the sender at the tank to the sender tube.

You shoud read between 10 and 70 ohms give or take.

Next measure same but between sender at tank to body ground should read same or there abouts.

Next do same at sender wire at back of guages to body ground.

Next you can VERY temporarily ground the sender wire at the tank and have someone else look for guages movement

then report back
 
BTW there are about 1/2 a million posts about fuel senders.
 
Dana67Dart said:
Get a multi meter and measure resistance from the sender at the tank to the sender tube.

You shoud read between 10 and 70 ohms give or take.

Next measure same but between sender at tank to body ground should read same or there abouts.

Next do same at sender wire at back of guages to body ground.

Next you can VERY temporarily ground the sender wire at the tank and have someone else look for guages movement

then report back
Click to expand...
Ok. Thanks.
 
You have your OLD sender and a good multimeter? Or is the new sender out of the tank? Use the multimeter on low ohms, to adjust to the "yellow" settings in the photo. These are lo (empty), mid (1/2) and high (full) readings on either oil, temp, or fuel. So you can cross check by setting the resistance to those three readings, and hooking it in turn to each gauge sender wire. Gauges should read as indicated after a few seconds.
 
Dana67Dart said:
Get a multi meter and measure resistance from the sender at the tank to the sender tube.

You shoud read between 10 and 70 ohms give or take.

Next measure same but between sender at tank to body ground should read same or there abouts.

Next do same at sender wire at back of gauges to body ground.

Next you can VERY temporarily ground the sender wire at the tank and have someone else look for gauges movement

then report back
Click to expand...
Thanks. I will...all other gauges are working...
 
67Dart273 said:
You have your OLD sender and a good multimeter? Or is the new sender out of the tank? Use the multimeter on low ohms, to adjust to the "yellow" settings in the photo. These are lo (empty), mid (1/2) and high (full) readings on either oil, temp, or fuel. So you can cross check by setting the resistance to those three readings, and hooking it in turn to each gauge sender wire. Gauges should read as indicated after a few seconds.
Click to expand...
My old sending unit is long gone and I really do not want o remove the tank -
 
67Dart273 said:
You have your OLD sender and a good multimeter? Or is the new sender out of the tank? Use the multimeter on low ohms, to adjust to the "yellow" settings in the photo. These are lo (empty), mid (1/2) and high (full) readings on either oil, temp, or fuel. So you can cross check by setting the resistance to those three readings, and hooking it in turn to each gauge sender wire. Gauges should read as indicated after a few seconds.
Click to expand...
:thumbsup:
 
gsoco said:
My old sending unit is long gone and I really do not want o remove the tank -
Click to expand...

Well you need a known resistance to apply to the gauge instead of the sender. Since "we" don't have radio shack anymore, you likely have no local supplier to get some test resistors.

One way to "quick and dirty" is some small 12V lamps. rummage around do you have any cluster lighting bulbs, etc. As a random example, you can Good "no. 57 lamp specifications" I just picked that lamp out of the air. google says it is 14V, .24A If you plug that into ohms law (R = E/I or Resistance = volts dlvided by Amps) it comes out 58 ohms. THIS WILL NOT BE terribly accurate because resistance changes as the bulb heats and cools. But 2x no 57 lamps in parallel should give you "somewhere" in the 1/2 scale reading range. Even one bulb---you can put on the temp gauge and see where it reads, then hook to the fuel gauge sender wire and see if the fuel reads the same.
 
gsoco said:
I cannot get my 62 Valiant gas gauge to work. It is a new Bosch. I replaced the original gauge (which didn't work either...) The shop that redid my fuel tank says the sending unit is new.
Click to expand...
I missed this....

It is not an OEM gas gauge.

Now you have another variable. What sender does your Bosch guages recommend?
 
Oh well pzsasdafdsadsfewfoqwel.s............................................................ That's first thing you gotta do......................

Also some (like SW) aftermarket gauges are what are called a "bridge." This means that the gauge either has a ground terminal or the case MUST be grounded. "Bridge" type meters actually have 3 terminals.........hot coming in (usually right off battery NOT through a factory IVR, the sender terminal and the ground to the bridge

Jus' sayin...........find out what you have and heed.

Example of a bridge type circuit...........quite different from factory Mopar

aircraft_11-3.jpg
 
67Dart273 said:
Oh well pzsasdafdsadsfewfoqwel.s............................................................ That's first thing you gotta do......................

Also some (like SW) aftermarket gauges are what are called a "bridge." This means that the gauge either has a ground terminal or the case MUST be grounded. "Bridge" type meters actually have 3 terminals.........hot coming in (usually right off battery NOT through a factory IVR, the sender terminal and the ground to the bridge

Jus' sayin...........find out what you have and heed.

Example of a bridge type circuit...........quite different from factory Mopar

View attachment 1715719345
Click to expand...
OK. Thanks.
 
I seem to recall a ground strap at the tank sending unit, make sure that is hooked up properly. The gasket keeps the sending unit from grounding. Now, keep in mind I haven't played around with mine in 20 years ,this is what I remember and it may be foggy. I remember hooking that ground up and it worked just fine. another thing I remember is my brass float had a hole in it and I brazed it to get it "floating again" it always read "empty" LOL! That was fun waiting for the gas to flash off then lighting a torch to "braze" it on the bench vise...:)
 
Not faliure with early As really have to drop tank to change sender?

Also maybe be cheaper / easier to fix /replace oem guages?
 
Yes there is a ground strap bridging the small rubber hose that connects the tank to the hard line.
Are you getting continuity through the dash gauge?
Even if the sender is the wrong one I would think it'd still work. It would just read 1/2 as full, etc.
 
I just measured an Ebay sender and it read 10 ohm full and 80 empty, linear measurements.
 
Dana67Dart said:
Not faliure with early As really have to drop tank to change sender?

Also maybe be cheaper / easier to fix /replace oem guages?
Click to expand...
I was able to replace the sender on my '70 Duster while the tank was installed. No big deal, plenty of room to twist it around and install it.
 
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