AlleyKat

I think Mechohaulic is on the right path here. I believe it is a "Variable Resistance Ground" system. The better the Ground, the higher the gauge reads. I am assuming the truck has a separate gauge that is not part of a instrument panel with a circuit board. I am not familiar with Superliners. Would love to have one someday though. I had similar problems on my "93 CH613. This is what I did to troubleshoot the system. It sounds like you did a continuity test on the wiring from the gauge to the sending unit. If you have "0" Ohms resistance, the wiring is good. The gauge likely has three pins on it. Power, Ground, and Signal. The Signal pin would be the wire returning from the sending unit. To test the gauge, remove the gauge from the dash and connect 12v to the Power pin and ground to the Ground pin. Then momentarily jumper the Signal pin to the Ground pin and the gauge should read Full. If not, you likely have a bad gauge. To test the gauge and wiring, reconnect the gauge and disconnect the plug from the sending unit and momentarily connect a jumper across the two pins, the gauge should read full. This means the wiring and gauge is good. To test the sending unit, reconnect the plug and physically move the float up and down, the gauge should respond accordingly. I removed the sending unit from the tank, it was easier for me to work on it. If all of those check out and it doesn't read correctly, I suspect there may be a mismatch between the sending unit and the gauge. My fuel gauge only reads to 5/8 full on a full tank. Sending unit from Mack and Fuel Gauge from PAI. I suspect there is a mismatch or calibration issue going on. I was lucky enough to get a complete wiring diagram from my local Mack dealer, it was very useful in tracking all of this down in the truck. Hope this helps and Good Luck. The truck looks awesome!!

PMS once a month you can deal with. PMS every day for the rest of their life is a little tougher. I find keeping my mouth shut helps a lot.🤐

Here is what NAPA Online comes back with.

No. I was working on my truck today and snapped a picture so I would remember to pick one up next time at NAPA. It my mobile parts list.

Here is the number on the filter itself. I don't have the Napa #.

Hi BMT Fans! I have been lurking on here for about a year now and found a thread I can actually contribute to. It's a little late for the OP, but good reference for someone in the future. I just replaced the air line from the air compressor to the bulkhead fitting on transmission on my '93 CH613 this week. The air line is 1/2" Teflon lined SS braided. The 90 deg. fitting on the compressor is a 3/4" NPT x JIC-10 and the bulkhead fitting is a JIC-10 x JIC-10. The bracket that mounts to the transmission is a 2"x2.5" L bracket that is 1.75" wide. The 2" leg mounts on the transmission. The clearance hole for the bulkhead fitting is 15/16" diameter. From the top corner it is located 3/4" to the right and down 3/4" from the top. The mounting hole is 3/8" clearance. From the bottom right corner it is located 3/4" to the left and up 3/4" from the bottom. I will post a dimensioned drawing when I get my CAD program working again. Thanks for all of the knowledge everyone shares on here. I have certainly gained from it. -Al Pics to follow.