Fuel Sending unit to fuel gauge

[Mopar-Charger]

I recently bought a Sun Pro fuel gauge and a new fuel sending unit. When I have the gauge hooked up and the car on, the gauge acts like a volt-meter. With the car off and ignition on it works fine.

Won't go below 1/4 even if it's empty.

Wont go above 3/4 even if it's full.

My wiring is fine? Is there anyway to change the throw on the sending unit, or sensitivity on the gauge?

Thanks,

Jake

I'll post pictures if you need them.

 

[Dennis H]

Good luck. Lots of traffic on this here, search around. No one I know with a B Body has a gauge that works. Mine won't read over 3/4 when full. Everything new.

 

[HawkRod]

Most of the issues with fuel gauges are the senders.

The first thing is to verify your wiring and operation of the gauge. With the power on, unplug the sender wire and touch it to a GOOD CLEAN ground. If the gauge goes to full, then your issue is the sender. If it does not go full, your issue is your wiring and/or gauge.

With the assumption that it is your sender, you should check it where you can manipulate the float manually. When the float is manually set to full, the resistance should read close to zero, maybe an Ohm or two. You can double check the needle operation by hooking up the wire to the sender and then having a good ground wire from the sender to the body. Many senders are not made to be adjustable, but there will be a metal "arm" that rides up and down on a coil of wire. If the arm does not go off the coil of wire when in the full position, this is likely why the gauge does not read full. See if you can adjust the arm or coil.

On the other end of the scale (empty), this is where there should be higher resistance. I forget the values, if my poor memory is correct it is like 70 Ohms. Regardless, to get it to properly read empty you need to get the gauge to have more resistance when empty.

Take a quick look and let us know what you find. The second issue with it operating "like a voltmeter" sounds odd, but makes me wonder about wiring issues...

 

[Mopar-Charger]

Most of the issues with fuel gauges are the senders.

The first thing is to verify your wiring and operation of the gauge. With the power on, unplug the sender wire and touch it to a GOOD CLEAN ground. If the gauge goes to full, then your issue is the sender. If it does not go full, your issue is your wiring and/or gauge.

With the assumption that it is your sender, you should check it where you can manipulate the float manually. When the float is manually set to full, the resistance should read close to zero, maybe an Ohm or two. You can double check the needle operation by hooking up the wire to the sender and then having a good ground wire from the sender to the body. Many senders are not made to be adjustable, but there will be a metal "arm" that rides up and down on a coil of wire. If the arm does not go off the coil of wire when in the full position, this is likely why the gauge does not read full. See if you can adjust the arm or coil.

On the other end of the scale (empty), this is where there should be higher resistance. I forget the values, if my poor memory is correct it is like 70 Ohms. Regardless, to get it to properly read empty you need to get the gauge to have more resistance when empty.

Take a quick look and let us know what you find. The second issue with it operating "like a voltmeter" sounds odd, but makes me wonder about wiring issues...

I took the sending unit out, and have it in the drive seat, testing it right now.

FOr the wiring i have it going directly from the ignition from the fuse box to the + on the gauge. Found out my negative to the unit was off, going to see if that's the problem.

The sending unit is no older than a week, and the gauge is brand new.

http://www.sunpro.com/publish/2007/09/27/pdf_english_16430.pdf

gauge specs

 

[HawkRod]

So first check your wiring. Clean grounds are really important. make sure you have hooked it up per the instructions. Since you have it out, connect the sender to ground and the ground of the gauge to the same spot. You still want to be sure that is a good ground for the car as well.

Then check and let us know what you find. You sender looks like it is adjustable, and you can set the float depth as well as the arm length - but worry about that after you verify that it works out of the car. Those adjusters should be changed to ensure the float can travel all the way from the full to empty levels that the sender needs, correlated with the fuel level in the tank.

Good luck

 

[Mopar-Charger]

I was doing a little research, and it says that the Sun Pro gauges are specific to the Sun Pro sender. I bought just the generic sender for my 73 charger. It doesn't look like the float is adjustable. When doing the tests, full was 3/4 and empty was 1/4, so I guess those will become my new full and emtpy.

Thank you for your help. Especially the quick response, I really appreciate it.

jake

 

[moparmarks]

Yep Sun as with most aftermarket fuel gauges don't use the same ohm scale as our factory Mopar gauges do. Might see if Sun make a convertor.

Just a note I try to use original sending units when possible. My 72B is quite accurate empty to full..

 

[Mopar-Charger]

The sender I replaced with was a OEM replacement, looked exactly the same as the old one. My dash doesn't recieve an electricity (I use triple gauges for temp/oil) so I had to use a level gauge.

 

[HawkRod]

If you are willing to mess around, the sender can be taken apart. Once you pry up the tabs that hold the cover on, you will see that the sender is really very simple. If you play around a bit you may be able to adjust it better, at least for the full mark. Empty may be a bit harder though.

It would make me nuts if I only had half a gauge to display my fuel level...

 

[AMX364]

At least on the early Jeeps you could just stick your arm in and feel how much gas you had. It did smell afterward. LOL

 

[Mopar-Charger]

At least on the early Jeeps you could just stick your arm in and feel how much gas you had. It did smell afterward. LOL

Haha, though about that. For the longest time I would push the trunk up and down to hear how much was left on the bottom.

 

[nm9stheham]

Maybe you can sell the OEM sender and then buy the right SunPro sender.