Power Transistor pullup

[tmbg]

On my '88 300zx, I'm taking tach signal from the 120 degree line of the Crank Angle Sensor, which required a 12V pullup (pulled my hair out trying to figure that one out!)

I'm looking at the Nissan diagram on the MSnSE page:
http://megasquirt.sourceforge.net/extra/setup-msns.html

This diagram shows the 12V pullup for the input signal, but then it also shows a 5V pullup on the HEI module. Why exactly would that pullup be there, and is there any possible way I might need some kind of pullup on my stock power transistor?

My timing seems to jump around quite a bit, hold the engine speed steady and the timing light shows the mark bouncing around as much as 15 degrees either side of where MS says advance should be.

[tmbg]

for what it's worth, a 12V 1K pullup on pin 36 made the car not start, no spark I think. Taking the pullup away let it start right up.

I didn't try a 5V pullup like the nissan HEI diagram shows