Fuel Gauge nightmare

[removalmachine]

Hope someone here has some insight!

93 Sub 5.7 TBI.

Had the fuel pump and sender replaced few months ago. Carter pump, can't remember the name of sending unit.

Immedialty after, gauge would not read properly. Would read from full to about half only. Had the sending unit replaced under warranty - still did same thing.

Third time back they test the replacement sending unit before dropping it in tank. Plugged in, they can move it from one extreme to the other and the gauge reads properly (full to dead empty) - install it - same problem. Order gauge from wrecker - same problem, reads the same as mine.

They can't see anywhere where the float would be hanging up - looks free - and all voltage and resistance at all positions is within spec.

HELP!!!!

Thanks

[chuck's]

Were you able to check the overall length of the original sending unit with the replacement unit?I know you say that nothing is in the way of the float,but is the rod that the float is on adjustable?My last suggestion is with the wiring.Does it get pinched when the tank is put into place?I hope this will be of help.
chuck's

[removalmachine]

Originally Posted by chuck's

Were you able to check the overall length of the original sending unit with the replacement unit?I know you say that nothing is in the way of the float,but is the rod that the float is on adjustable?My last suggestion is with the wiring.Does it get pinched when the tank is put into place?I hope this will be of help.
chuck's

Thanks - it's finally been solved. They were finally able to get it traced to the fuel sending unit quite by accident. With the tank empty (and dropped) and the gauge still reading half full, they put on guy in the cab to keep an eye on the gauge while they removed the sending unit to move it up and down by hand. As they tapped the retainer ring loose, all of a sudden the gauge went to E. They resnugged the retainer - the closer to tight it got, the more the gauge moved back to half.

Dropped a delco unit in ($200 more) and it worked perfectly.

Looks like the plastic housing around the plug connection on the SPI pump is really thin and somewhat flexible - I guess flexible enough the it contorts when the retainer ring is tapped on and pinches wires enough to raise resistance.

Word of caution to anyone replacing a sending unit - these SPI units seem like a bad choice for our application