Foxbody Tachometer "Jumpy"

[KaLiKo Street]

My 92 that im currently in the middle of doing the 5.0 swap with, has always had a problem with the tachometer either not working or being jumpy. Anyone know why? My old 85mph gauges did it and now a whole newer set of 140mph gauges do the same thing...It must be a wiring problem somewhere. Heres two vids of what I mean...

This one is where it just stopped working...
View attachment 154061

And this one is where its kinda jumpy and wants to work...
View attachment 154062

 

[jrichker]

Look closely at the wiring coming off the TFI module. One of the wires is dark green/yellow and is labeled IDM. It has a 22k K ohm resistor and the wire connects to pin 4 on the computer. The same wire feeds signal to the tach. If the wire is loose, damaged or the resistor is damaged, you could have tach problems.

Diagram courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

 

[KaLiKo Street]

I believe everything you just posted was for a 5.0 and that top diagram says for 88-91...mines a 92 with the dual coil pack 8 spark plug 2.3 for now...