Tach problem can't figure out

[texas7816]

Hi new member here, with a problem I cannot figure out for anything. I have a 90 f250 7.3 with an e4od. I losing my tach when I hit bumps on the freeway or anytime I drive over a washboard road. My tach drops for just a few seconds and my transmission goes crazy. It always comes right back and the truck is happy again until I hit another bump. So far I have done the following:
-New tach sensor
-New EEC and TECA relay
-New FIPL and connector
-New vehicle speed sensor and connector
-New ABS sensor and connector
-New solenoid pack connector
-New(used) TECA from a 93 7.3 idi
Truck runs and shifts perfect, until I hit a pothole. I'm completely out of ideas here. I'm planning on taking it to the shop this weekend if all else fails, but I'm open to any ideas anyone might have. I'm about ready to pull my hair out here. Thanks in advance.
P.S. If anyone has a good transmission shop in the Dallas or east of Dallas area I'd love to know. Thanks again

 

[FORDF250HDXLT]

your throwing parts like darts.no bulls eye yet? im afraid you've spent hundreds due to probably just a dollar repair.
well it sounds like a bad/burnt fuseable link.Gary just ran into this issue too.though he had a bad repair i guess it was down below his battery.
anywho,take a look at the fuseable links on the fender mounted solenoid.

 

[79jasper]

Well, or a chafed/bad wire.
With someone watching the tach, start wiggling wires until you find the one that makes it go off.
Just be careful around the fan.

Sent from my SAMSUNG-SM-G890A using Tapatalk

 

[icanfixall]

This is correct. My issue was a repaired fuseable link that had 2 blue crimp on connectors in a run of about 3 inches.. They are behind the passenger side battery. All the fuseable links get power from the battery off the fender mount solenoid so be careful cause they are always hot. That TECA has a hot all the time power line running from the fender solenoid across the front of the rad support to the solenoid. I found my problem by running a jumper from the drivers side battery positive directly to the hot wire to the TECA. For you to find this intermittent short will be tuff but watching the running tach and having someone wiggle wires might show the bad area.