Gas gauge issue

[Spikedog08]

So I replaced my standard dash with a rallye setup and when all done the gas gauge doesn't work?  It worked fine with the standard setup so I assume all is good at the tank and it is something I'm missing at the dash?  So other then hooking up the wire at the gauge, is there something else that needs done?  I know I had to change the oil sending unit to work with the Rallye package . . Is the gas gauge sending unit compatible with the Rallye package.  All help is always greatly appreciated . . Probably just me forgetting something . .

[BIGSHCLUNK]

Ground?   

[cuda hunter]

Ground is what I would start with. 

[MoparLeo]

https://www.e-bodies.org/videos/

Click on the above link to our inhouse videos. Check out the one for testing gauges.

[Jay Bee]

Sending unit is the same for standard and rallye. Simplest initial test is ground the blue wire the turn ignition switch to ON or ACC, gauge should move.

[Chryco Psycho]

You should have 5v / pulsing power in & out of the guage & 5v at the tank wire , , if the guage is faulty there will not be power out on the blue wire

[Spikedog08]

Thanks guys!  Will check it out soon . .

[Jay Bee]

Make sure the meter's leads have good connections, a solid valid ground and I usually put a bolt inside the blue wire's connector. Just a reminder, key ON or ACC to see the pulsating voltage. I take it the Temp & Oil gauges are working. 

[chaps70rt]

I am unfortunately in the same boat!!  Here are the items I have checked (eliminated so far)

a) 12V at the IVR  (Multi-Meter)
b)  5V out of the IVR 
c)  all gauges tested for function with three AA batteries
d)  Check that the threaded posts on the back of the gauges are not touching the chassis of the cluster (grounding)
    Each gauge should have a non-metal gasket between the nut and chassis of gauges.  I even added some heat shrink to
    each post
 e)  Check the 4-post jumper from the IVR to each gauge for internal shorts.

My next test will be to see how many ohms I have coming off the blue harness from the tank at the kick panel, then again at
the back of dash (blue wire).

Failing that ..... I am out of options.    Will need to check all the other entries on this forum for other ideas.

[captcolour]

My fuel gauge stopped working abruptly.  Bought a new sending until but haven't installed it yet.  Also bought the interface module from Tanks, Inc to calibrate and improve accuracy of the gauge once it starts working.  Again not installed yet.

[Spikedog08]

Make sure the meter's leads have good connections, a solid valid ground and I usually put a bolt inside the blue wire's connector. Just a reminder, key ON or ACC to see the pulsating voltage. I take it the Temp & Oil gauges are working. 

Yes other gauges did appear to be working . . 

[chaps70rt]

At least you have Oil and Temp .......  Hope you can resolve the Fuel signal soon.   Let us know.   I just started my own post.

[chargerdon]

Here is a writeup (from 66 Charger The Source guide on the gas gauge,   There is one major difference in that the gas gauge itself was also the 12v to 5v limiter where as our challengers have a separate 5V supply mounted on the back of the cluster.

The fuel gauge reacts to the sending unit in the gas tank. The sending unit is a variable resistor (reostat) that goes from 30 ohms when the tank is full to around 80 ohms when empty. The amount of resistance offered to the fuel guage controls the amount of current the fuel guage is subjected to. More current, the needle in the gauge moves more and that movement is toward the full mark. More resistance by the sending unit and less current and the needle moves less of course.

Since I have mentioned the gauge reacting to current, then there must be something on the gauge to cause the current to occur, and that is on one lug of the fuel gauge is a terminal where +12 volts is applied and that is a black wire. There are two other terminals on the fuel gauge and one is where +5 volts is picked off that goes to the oil gauge and the temperature gauge, and that wire is a brown wire. The other terminal is where the tank sending unit is attatched and that is a dark blue wire. If you place a jumper wire to the dark blue wire then you will be telling the fuel gauge no resistance and the gauge should then read FULL. Just don't touch the black wire with the ground jumper as that will cause sparks.

If the gauge doesn't read full then you might have a bad ground on the fuel gauge and that comes from being mounted in the gauges housing. If the tank reads full with the ground jumper, then that leads to a broken wire or connection coming from the sending unit. Sometimes people fail to connect the ground strap from the sending unit to the gas line back there at the gas tank. The ground strap must be connected to connect the sending unit gas line past the rubber hose that connects to the gas line coming from the fuel pump. Possibly the sending unit is bad and that happens over time as the reostat goes bad and will not offer any reading to the fuel gauge.

Posted by Daniel Daigneault on 07/29/03
With the tank filled, the reading measured between the terminal on the sending unit and its grounding clip should be 10 ohms. With no fuel remaining in the tank, the reading should be 73 ohms. +- 1ohm

These readings are @ the sending unit itself in the thank. I personally took off the ground strap and cleaned it properly then put it back on before checking the ohms. If the ground isn't perfect, the gauge will not work properly

[Spikedog08]

Ok so I finally had a chance to tear the dash apart and hook a ground to the blue side of the gas gauge and the gauge went from completely empty to way over full.  Nothing changed at the tank and the standard gauge cluster gas gauge worked just fine.  Thoughts?  What should my next step be?  Really would like a gas gauge . . .

[Jay Bee]

Simplest initial test is ground the blue wire the turn ignition switch to ON or ACC, gauge should move.

When I wrote this it was meant to say to ground the blue wire....at the sending unit. Pull it off the sending unit then ground it there. If the gauge pegs that will tell you that everything from the sending unit to the gauge is fine and that there's a problem with the sending unit.

Could be a sunk float, bad internal ground, rheostat arm inside the unit fell off (all of which actually happened to various units of mine). Also, may have bad rivet connections on the unit etc, etc, etc.