This is a tough one. I'll list all the knowns and troubleshooting I've done. History: Several months ago my gas gauge started acting up. It would move all over... full, empty, drift, etc. I ended up tracking my gas usage by the trip meter. Finally it just started displaying full with an intermittent dip to empty, then back to full. I did some on-line research for troubleshooting and finally decided to change the fuel pump (although my original pump was working; just the gauge has an issue) rather than just the sensor. The job took about 1 hour 10 minutes. My tank was full at the time, so, I could not readily tell if the gauge was working properly or not... it did show "full." Well, yesterday evening I had put 108 miles on the car and the gauge had not moved. I re-checked that I had properly installed the new in-line four pin connector. All was good. I disconnected the plug and inserted a 100 ohm resistor across the black and purple pins and my gauge read 1/4 to 1/3 full. I removed the "new" pump and checked all the wires for continuity - all good. I put my meter on the pins and moved the float up and down - resistance changed. I plugged in the fuel pump outside of the tank and moved the float - gas gauge level moved with the float movement. I checked inside the tank for any obstruction that could prevent the float from properly operating - saw none. I removed the float, manually set the wiper arm about center position, inserted the fuel pump into the tank and the gas gauge read appropriately. Removed the pump and reinstalled the float. I put the pump back into the tank (without locking ring), attached the connectors, raised and lowered the fuel pump, gas gauge needle moved with my movement. I reinstalled the locking ring and the gauge went to "full" again. I removed the fuel pump again, removed the float, set the wiper at mid point, attached the connectors, compressed the fuel pump to see if there may be an issue when the pump is "pushed" into the tank, and the gauge did not go to "full" as I hoped. So to somewhat summarize, continuity is good on all connections; splices are good for the new connector; gauge reads using 100 ohm test; gauge reads when float is removed, wiper is set, and placed in tank; gauge reads when fuel pump is not installed and float is manually moved, gauge reads when everything is properly attached and the fuel pump is manually raised and lowered in the tank (indicating the float is moving the wiper arm and resistance is changing with the movement)... everything seems to work properly until the fuel pump is completely installed. There are no indications of pinched or stressed wires. According to my specifications, the car has a 17 gallon tank. I have put 115 miles on it since last fill-up ( I also added a gallon from a gas can). My car averages 20-21 mpg around town, so if I added a gallon (making 18 gallons for calculating mileage) and drove 115 miles, I should've used about 5.5 gallons. When the previous sensor was working I would see the gauge read about 3/4 full at the 90-100 mile point from fill up. I have tried every possible combination and test I can think of. Everything works as it should until I fully install the fuel pump... then my gauge reads "full." The fuel pump is a PFS Gasoline Fuel Pump C5331031, purchased at Auto Zone, and is supposed to be an OEM replacement. It has a limited lifetime warranty. Has anyone else seen this issue before? Any ideas???

 

Could it be the stepper motor that moves the actual gauge? Its very common in (I think) '95 and up for them to go bad..

 

I don't think it's the stepper motor because it works as it should until I put it all back together. If it were the stepper motor, I'd think I wouldn't get a reading at all, one way or the other, i.e., the 100 ohm resistor test, the gauge reading with the fuel pump removed and the float being moved up and down, or when I put the fuel pump into the tank and move it up and down manually without pushing it all the way down. I could be wrong but it seems to work properly until I put it complete in and lock it down.

I talked with a friend of mine and he suggested comparing the float arm of the original to the float arm of the replacement and see if there is any difference in position. The positions are as close to identical as they could possibly be.

 

I also suggest it is likely the stepper. My 2001 gas gauge has been doing the same thing since last year - it will go from all the way full to empty instantly or empty to full slowly or instantly and I will hear a noise from the instrument cluster . However, I have the DIC panel on my headliner and it displays fairly accurate gallons used regardless of the type of driving I do. I don't know if it reads from the fuel pump sending unit but it will read within about 10% of the number of gallons to fill up every time. When I get time, I'm going to swap out the used cluster I got yesterday and have mine gone through with new steppers. For now I'll just continue filling up and resetting the trip meter and the DIC.

 

I don't think I have a stepper motor problem because of all the tests that showed a good indication would have to use the stepper motor to work. I have been using my trip meter as a quasi gauge and been in the ball park on every refill. I did not think about looking at the DIC cluster. I just checked, and based on my trip meter, I should be at about 1/2 tank. The DIC is showing 7.7 gallons used, which would be close, as I have a 17 gallon tank. The new gauge/fuel pump finally moved some. It is showing about 7/8 full but should be near 1/2. Still troubleshooting.