Outer Limits 4x4 Board

I'm having trouble with my 80 series auto box with the torque converter
locking/unlocking rapidly.
What i think is causing it is the tacho or its pickup/sender, because the tacho needle dances around 200-300 rpm when u hold the revs steady and the other day i was cruising along the highway at about 100kph but the tacho was saying the motor was pulling 4000rpm.

Anyway I think the auto is getting the wrong signals from the tacho or its pickup.

Just wondering if anyone knows of this problem and what is the cause?

If it is the pickup/sender where is it located on a 1hdt?
The cruiser is a 11/92 model.

Cheers.

the tacho sensor is in the side of the injector pump if you loot your pump its on the inside between the pump and block you need to remove the pump to get to it also your auto should work of the kick down cable and the torque converter will only lock at above 80kmph.
correct me if im wrong

The problem started after i got the pump rebuilt so me thinks its probably
the sensor

thanks for the info mud80d

sender on the pump.... are you sure its not reving that high? Torque converter not locking up?

Is it not getting the high gears? Or its definitely in gear and not revving at 4K??

hows the fuel economy