Fuel Gauge Fix
05-12-2012, 04:25 PM
#1
Fuel Gauge Fix
Some years ago the fuel gauge in my '87 F-150 began pegging past full when the rear tank was between 3/4ths and 1/2 full. It then got progressively worse and the front tank followed suit, until the gauge would only work correctly when either tank was less than 1/8th full.
I removed the front tank and pulled the fuel pump/sending unit out for a look, hoping a good cleaning would resolve the problem. Instead, what I found was that the contact that rubs against the circuit board had worn through most of the circuits.
The auto parts shop had difficulty determining which was the correct replacement sending unit. The one they thought was correct looked a little different. The wire arm holding the float was bent in the opposite direction, but the float still moved through the same arc.
The first problem I ran into is that my mounting plate is welded to one of the fuel tubes. It is not clear how the engineers who designed this stuff intended the new unit to be installed. Are you supposed to chisel off the old plate and weld on the new one? Since the way the plastic housing mounts to the plate is identical, I simply removed the plate from the new housing and mounted the new housing on the old plate.
The second problem was that the float pivot is slightly different. The old one has a bushing that fits in a hole, whereas the new one had no bushing. The new plate has a much smaller hole into which the bare rod (really more of a wire) fits. When moved to the old plate there is lot of slop because the hole is bigger.
The third problem was that the float arm would not fit through the tank opening because it was bent in the opposite direction. Problems 2 and 3 were solved by using the old housing and replacing only the circuit board, which was the only thing that needed to be replaced anyway.
However, this brings us to problem 4, the circuit board was wired backwards from the original. I noticed that the electrical wire was soldered to the top of the circuit board instead of the bottom as on the original. So I checked it with a meter and sure enough, the gauge would have read full when the tank was empty and empty when the tank was full. Why would some sending units be wired backwards from others. This is most puzzling.
So I went back to the parts place and since all I wanted was the correct circuit board, they let me go in the back and look through boxes until I found one with the correct orientation. I pulled the circuit board out and installed it in my old housing and it works great.
The one with the correct circuit board was Motorcraft PS26 F3CZ9275A and cost $109. The first one with the backwards circuit board was Motorcraft PS19 FOTZ9A299AA and cost $125.
It would sure be nice if someone on the forum could figure how to obtain the circuit board from the manufacturer, or figure out the cheapest sending unit replacement that has the correct circuit board.
I removed the front tank and pulled the fuel pump/sending unit out for a look, hoping a good cleaning would resolve the problem. Instead, what I found was that the contact that rubs against the circuit board had worn through most of the circuits.
The auto parts shop had difficulty determining which was the correct replacement sending unit. The one they thought was correct looked a little different. The wire arm holding the float was bent in the opposite direction, but the float still moved through the same arc.
The first problem I ran into is that my mounting plate is welded to one of the fuel tubes. It is not clear how the engineers who designed this stuff intended the new unit to be installed. Are you supposed to chisel off the old plate and weld on the new one? Since the way the plastic housing mounts to the plate is identical, I simply removed the plate from the new housing and mounted the new housing on the old plate.
The second problem was that the float pivot is slightly different. The old one has a bushing that fits in a hole, whereas the new one had no bushing. The new plate has a much smaller hole into which the bare rod (really more of a wire) fits. When moved to the old plate there is lot of slop because the hole is bigger.
The third problem was that the float arm would not fit through the tank opening because it was bent in the opposite direction. Problems 2 and 3 were solved by using the old housing and replacing only the circuit board, which was the only thing that needed to be replaced anyway.
However, this brings us to problem 4, the circuit board was wired backwards from the original. I noticed that the electrical wire was soldered to the top of the circuit board instead of the bottom as on the original. So I checked it with a meter and sure enough, the gauge would have read full when the tank was empty and empty when the tank was full. Why would some sending units be wired backwards from others. This is most puzzling.
So I went back to the parts place and since all I wanted was the correct circuit board, they let me go in the back and look through boxes until I found one with the correct orientation. I pulled the circuit board out and installed it in my old housing and it works great.
The one with the correct circuit board was Motorcraft PS26 F3CZ9275A and cost $109. The first one with the backwards circuit board was Motorcraft PS19 FOTZ9A299AA and cost $125.
It would sure be nice if someone on the forum could figure how to obtain the circuit board from the manufacturer, or figure out the cheapest sending unit replacement that has the correct circuit board.
Last edited by JKLedbetter; 05-12-2012 at 04:30 PM. Reason: typo's
