I can't give you any definite ways of testing your CAS, but I will say there was a time I washed under my hood and my CAS got wet. It did the same thing. Ran one day but not the next. This was on a 2G with a 1G green top CAS, but it at least on 2Gs, also controls the fuel pump and that's how I figured out that it was the CAS.

So just something to check to see if the fuel pump is on during cranking. It won't turn on without an RPM signal which is from the CAS.

Check the MPI relay against a known good one. Check the wires to the CAS and coils.

Ok so my fuel pump does pump fuel. I unhooked the fuel line and cranked to verify, so does that rule out the CAS? I’ll change out the MPI fuse to verify that as well.

Also when I tested the CAS this way I just turned the key on I did not crank, again not sure if this is correct or not.

I assume when you first turn the ignition to on, you see the check engine light come on, then go off? If so the ECU is not totally dead. You have replaced the ignition coil, so that's not it. Did you check the transistor module? It bolts below the ignition coil down behind the timing belt enclosure. The ECU drives the ignition coil through this power transistor unit, and it is a common failure point.
picture:



Here is a basic electrical diagram for the 1G from twicks69:


You will be interested in page 8-74 of the above PDF. Make sure you have 12V at pin 3 of connector B-14 coming from the car. There might be a test procedure in volume 2 of the Factory Service Manual to test the transistor unit. I would look but mine is way out in the shop. Anyway, there is a thread on here about testing these as well:


BTW- Have you had the capacitors replaced in the ECU? If not they need to be. I can't see any obvious corrosion in the photo. I may have some of those transistor modules in my parts stash if you confirm yours is bad.

Warren asked the key question, "When you first turn the ignition to on, you see the check engine light come on, then go off?". While the ECU doesn't look too bad from here (what I can see) it still could be the cause of your no spark. If it's not powering up nothing interesting is going to happen.

Since you have a 90 use this set of diagrams for your MFI wiring.

steve said:

Warren asked the key question, "When you first turn the ignition to on, you see the check engine light come on, then go off?". While the ECU doesn't look too bad from here (what I can see) it still could be the cause of your no spark. If it's not powering up nothing interesting is going to happen.

Since you have a 90 use this set of diagrams for your MFI wiring.

https://www.dsmtuners.com/threads/1990-mpi-circuit-diagrams.540595/

Click to expand...

The check engine light does not come on at all when the key is turned to the on position. I attached a photo for reference. Key turned to the on position

Given that your troubleshooting should be focused on why the ECU isn't powering up and not replacing parts (unless you have a spare good ECU to test with).

I guess the first step would be to see if the MPI relay is getting power (MPI fuse on battery) and if the ECU is getting power when you turn the key on.

Pretty much what was expected.