1993 Ford F-350 E40d Tack Fixed!

[mavrick347]

This is just one of those lucky things you run into from time to time.My tach as been acting up for a few months start the truck up and let her run for 10-15 minutes before it begins reading.I went through all the normal steps fuses,grounds,tach sensor, and even a donor tach and nothing worked.Well my fuel housing started leaking around the fuel heater plug, so I had a extra upper fuel filter head (complete with vac. sensor and heater) in the shop that I installed, and my son noticed when he turned the engine over while I bled the air the tach worked perfect! I don't know why but it has not worked cold for months!If someone can explain this I would love to know how one of the two sensors could affect the tach which allows the tranny to shift. Dumb luck or is there a explanation for this?

 

[FORDF250HDXLT]

interesting.so what was happening is your fuel was acting as a short to ground but not enough to blow the fuse.
you see,ford tapped into the power supply to the trans to feed the (unnecessary) fuel filter heating element.so if that shorts out it will cause the trans to act up.in your case,it frigged things up just enough to allow power to the trans but enough of a short to frig with your tach.
for a system upgrade (with keeping the filter heater,since you just replaced it) go ahead and snip off the wire feeding the heating element.a good clean place,is to follow it back over across to just before the under hood fuse panel.you'll see it enters a wire clip resting on the inner fender.unclip and remove the wire going to the heater here and clip the harness back together without this wire now.now that wire is safely dead ended.

now simply run yourself a devoted fused line from the battery.hook it to a relay and find a wire (such as the FSS) to trigger the relay open when you turn the key.
or simply run a toggled switch from inside the cab to toggle the relay instead.use a line to feed your toggle that only gets 12v with the key on,so if you forget and leave it on,it wont drain the battery.if you opt for option one,go ahead and pull the fuse in the spring,and install it in the winter,so as to extend your heating elements longevity.

 

[icanfixall]

Its very true Ford tagged way too many items to a single fuse. Then when a fuse blows you have a devil of a time determining what caused it. The trans relays and switches should never have been tied into other items. You can drive a long ways with no fuel heater but try driving with no tach and have an E4OD trans. Or even worse no tach. Its a trans ruiner for sure..