90-91 Distributor TD-23U / 24U difference??

I searched for TD-23U & Td-24U before posting…only found a WTB thread.

Does anyone know the difference between these? I’ve rebuilt a B18A composed of 2 junkyard motors, niether of which came with a distributor. It’s getting to be time for a dist. and I ran into this snag.

What’s the difference?
I’m using a PR4-2 head (# cast above the #1 ex port) and a PR4-A10 ECU if it makes a difference.
The head is definately a 90/91 head; A 90 if you can go by the other numbers on the EX side.

Thanks for any help.

The only wiring difference between 90 and 91 is the PA sensor.

PA sensor…What’s different? Wire color/position?

I did a little search for you and I think they are interchangeable.


Yeah, that’s where I was going to get one & where I learned about the 2 different units…
I didn’t bother reading this part until now though:
* This distributor is compatible with the following OEM housing #'s: TD-23U & TD-24U

Still curious what the difference is though.