Fuel Gauge on '01 Santa reading wrong

[DSHornet]

My Friday evening project was to find the problem with my fuel gauge on my '01 Santa Fe reading wrong (falling too quickly). Here's what I found.

The right hand sending unit is under the rear seat and is mounted with six Phillips head screws and was easy to remove after pulling the seat out. I measured the resistance of the strip in it and found it to be about 40 ohms. When reading the variable resistance between the connector pins, which shows the signal coming from the sender that is used to control the fuel gauge, I saw that the resistance change was not smooth as the float was moved. It had a couple of "dead" spots where the movable contact wipes the length of the strip. I VERY carefully cleaned the resistance strip with some very fine sandpaper, about 600 grit, and that solved the problem. I also found a fuel pickup tube and filter sock that is piped to the fuel pump on the left side so the pump can draw fuel from both sides of the tank. I reinstalled the sender and turned to the left hand unit.

The left hand sending unit and the sensor for the low fuel light are a part of the fuel pump assembly. I saw that the head of one of the eight Phillips head screws that mount it was almost stripped out. I also saw that a screwdriver had been on the remaining seven screws, so it looks like the fuel pump had been changed some time in the past. I removed it (spilling some gasoline in spite of my effort to relieve fuel pressure by running the engine to stall with the connector off) and checked the resistance strip on its fuel level assembly. Surprise: The resistance strip measured 80 ohms, not 40 as the right one did. It also had some dead spots on it, so I carefully used the fine sandpaper on it, too. I reinstalled it and went back to the right hand sensor. I jumpered the pins on the connector from the wiring harness to short them together. The next paragraph will explain why.

The level sensors are wired in series with the fuel gauge, so they add their varying resistance readings to show fuel level in both sides of the tank. My problem with my gauge dropping too fast was consistent with TOO MUCH resistance in the gauge circuit (minimum resistance = full, open circuit = empty). I hypothesize that the original fuel pump was replaced with one that was designed for single point fuel level sensing, not dual point. That is why it has an 80 ohm resistance strip in it. The total resistance of the circuit should probably be 80 ohms divided between two 40 ohm devices, but I had a 120 ohm sensing circuit. That explained what I was seeing. I jumpered the pins on the connector for the right sensor to make the gauge work properly. The only downside is the fact that I now have single point (left side) fuel level sensing, but the gauge now seems to work right.

So that's what I found. Any questions? I'll be glad to help if I can.