Tach is totally dead.

Here's what I know so far:

Brand new 90 coil pack and tach adapter from extremepsi.

Car runs great.

The 4-pin plug that the coil pack connects to on the engine harness has tight connections. (Tested by sticking a single male pin in each one)

The resistance of the tach wire from the 4-pin coil pack plug on the engine harness to the noise filter plug is 0.2 ohms.

I had an MSD box on the car a month ago and ran a wire off the "Tach Output" port on the side of the MSD box directly into where the noise filter normally plugs into and the tach worked perfect except above 5500 rpm (needed an MSD tach adapter to work at all rpm ranges). This means the wire from the noise filter plug to the tach is good and that the tach is good and working.

The car has a 90 tach (5 mph increments)

The car has a 90 Power Transistor.

The car has an AEM EMS V2 with 1990-1994 Eclipse coil pack selected in the setup wizard.

I've looped the noise filter plug and tried the noise filter which ohms out correctly (2.2 kohms)

I'M STUMPED!