Geez,it's been 4 or 5 years since those installs,old brain is kinda foggy,but I do remember trying everything with the mfg's of the unit's and it would not work. I have since installed the same unit on the 24V's and we just tapped into the cam sesor wires at the PCM. No problems. I think either the tach sensor output was too low,or not within a specific range to work for that type of unit. We ended up installing a unit with adjustable crank times.
On my 97,I have a unit made by design tech,and it lets you program individual crank times (so many seconds). It also has the tach input wire,but it just won't pick up off the tach sensor. I have it dialed in and it starts perfectly everytime. It is also the type that monitors the wait to start lamp before cranking.