Fuel Gauge Question

thanks Guys - I'll get on it tonight!

 

Did you put a ground wire from one of the screws holding the sender in the tank to ground? That way you know the the sender is grounded for sure. Just something to consider, Good luck

 

Update: I was finally able to get to work on the jeep today and got the fuel gage/fuel sender situation sorted out. Pulled the sender, grounded it outside of the tank, moved the float manually and the gage responded accordingly. Put the sender back in the tank and re-grounded from one of the sender screws, making sure that I had really good contact at the sender screw and things seemed to work. Drove to a nearby hill and put the jeep at various angles to make the float move and the gage responded as it should. Now, I'm not sure how accurate it really is so I'll start checking with a flashlight and/or "the gas stick" once I start to get under 1/2 tank just in case Thanks for the ideas and assistance. Now, on to the temp gage and sender...

 

So if I understand you correctly, both gauges operate off the 5 volt regulator. In other words, the factory regulator in the fuel gauge is the supply voltage for both the fuel and temp gauges?

 

Yes.

 

ahh, so to bypass the VR in the fuel gauge we just need to attach the output of the 5V Reg (once established in the vehicle) to the strap between the fuel and temp gauge and insure a good ground to the cluster housing...correct? I am assuming the sender/ground at the sender and associated wiring are working correctly which in my case they are. Actually we dont even care about a good ground to the cluster at this point, we just need to know the ground on the new 5 volt source is the same ground at the sending unit to complete the circuit, correct?

 

The ground on the cluster is important to the VR. With a 7805 or 7806, lose the ground and the VR goes open, and you have no reading. Lose the ground with the original vibrator (PWM VR), and the output goes to constant full voltage, destroying the gauges.

I'm not sure about the specifics of the CJ cluster - I've only done the 7805 on the J-truck. However, it is correct that you disconnect the regulator in the gauge and substitute the IC regulated voltage. Pretty sure it's the strap that sends 5V to the other gauge. You need to remove the 12V input connection to the gauge, and let that gauge get its 5V connection through what would normally be the 5V outlet from the regulator. If that's not clear, I'll look at it again in the morning.

 

It is clear. I was planning to mount the 7806 (I have a few of these) external to the fuel gauge and provide an external-solid ground for the 7806 thereby eliminating the need for the cluster ground, then simply provide that 6V input to the strap between the gauges and let the fuel wiring/tank sensor/and sensor ground complete the circuit which is why it is important to have the 7806 ground and the sensor ground back at the tank, common. eh, several ways to complete the circuit for fuel.
thanx for the input and good input as well on the dangers of electric fuel pumps
willie

 

Been following this thread, as I have similar issues. My solution was not to wire in the 7806. But to use a sealed DC to DC converter, [Amazon for 6.99, the following is the part description to search: "5V 1A 5W DC Converter Regulator DC 12V 24V (8V-40V) Step-Down to DC 5V 1A 5W Waterproof Car Power Supply Module Voltage Converter Regulator Transformer"]. Even though the 7806 is a great solution, it does have heat issues and I wanted to use this converter for other 5v supply later on, ie. USB power. Pardon the mess on the bench-always gets like that during a project.

I also purposely used the SW Fuel gauge and the aftermarket Temp as I wanted them to swing down from the top. I also used the vinyl gauge faces from whitegauges.net , bear in mind that they have white or the original style black. Their templates are for the original SW gauges which swing opposite of the Omix style. They also have the later CJ style gauge faces, plus 100's more. I have used them for many restorations.

The early gauges also do not have provisions for turn signals, looking closely you will see the pigtails on the back and the very small LED's on the front face. For new color gels for the brights, amps and oil, I have a lifetime supply-I bought a package of 'theatre stage light color gels,' they come in 10 x 10 sheets. The last picture you can see the bright illuminated with a #57 12v bulb. The amp and oil are equally nice. The paint on the housing is glossy black acrylic urethane and the back is silver cadmium from eastwood.

 

Hey, SW refers to the Stewart Warner original gauge. That is what I am using for fuel, the temp. Is one of the aftermarket ones from crown.

 

oh, okay but a little confused; if you used the original SW fuel gauge I thought it had a 5 or 6 volt regulator within and needs to be sourced by 12 volts. Did you bypass the internal stepper regulator and use your DC to DC converter?
thanx

 

As far as I know, the fuel gauge is a 12 volt unit, fed from a keyed ignition source (I) .the sender feed (S) uses variable resistance from the fuel tank sender to drive the needle. The (A) is the internal voltage regulator 6v output that is hooked to the temp sender (A) with that bar thingy. While my Stewart Warner fuel gauge VR output worked, I wanted a cleaner 5 volts that I could use for some other needs. Hope that helps.

 

oh, okay. I was under the impression both gauges were 5-6 volt and could be damaged when/if the ground was compromised to the cluster. If the fuel gauge is indeed 12 volt I may have mis-diagnosed it to be damaged. I will recheck resistances of my original fuel gauge.

thanx,
willie

 

okay, thank you, thought this was the case. One possibility in diagnosing the gauges is what was mentioned above...either the needle is being restricted by physical interference or as in my case, since the gauge has not worked for such a long time the damping grease may be restricting its movement.
great input all,

cheers,
willie

 

Measure continuity through the gauge. Huge resistance say 20M to infinite, indicates a broken moving coil. Unlikely you can salvage such a gauge.

 

Okay, curiosity got the best of me, I opened my fuel gauge as the resistance measurements were not correct AND I wanted to know about the regulator. From the above image I can see indeed the regulator affects both the fuel and the temp gauge as the 12 volt post (upper left in this view) goes immediately to the "stepper" regulator on the left prior to the fuel gauge and then on to the temp gauge via the strap between the two gauges. As well I can see where the tiny wire has broken from the bottom "adhesive" blob. From the resistance measurements that are specified for both fuel and temp gauges (19-21 ohms), I can see they are the same gauges. Since I have two clusters with two failed fuel gauges and apparently good temp gauges that measure correctly (19-21 ohms), I am thinking I will use one good temp gauge as my fuel gauge, just change the cover plate from temp to fuel from the spare cluster...should work. And of course source them both (independently) with 7806 regulators.

 

both gauges work beautifully with the 7806 regulators...10 ohms for full, 25 ohms (I have a 0-25 ohm potentiometer) about 5/8 full...wonderful,

 

I replaced the fuel gage sending unit which I got from Kaiser Willys. My fuel gage started working with the new sending unit, but the calibration/accuracy seemed to be way off. When I fill up the tank, the fuel gage needle goes past the full mark and disappears behind the gage window. The needle drops down between Full and Empty when the tank is around half full. I have lived with it like this for a couple of years, and I have finally gotten around to trouble shooting the issue.

I removed the sending unit from the tank and measured the resistance at full and empty positions and it measured 1.1 ohms and 83 ohms, respectively. Per the Kaiser Willys website, they claim that the sending unit should be 8 to 10 ohms at Full, and 70 to 80 ohms at the Empty position.

I also hooked the sending unit up the fuel gage and found that the gage read "full" at around 9 to 10 ohms, it read "half full" at 14.5 ohms, and it read empty at around 74 ohms. I think that my gage is good and that the new sending unit was bad when I received it. I am going to order a new sending unit and hope that the next one is calibrated correctly.

By the way, I did check that the ground form the sending unit/to the tank/to the chassis was good, but I added a jumper wire from one of the sending unit mounting screws over to a good clean ground on the chassis.