Are they all compatible? Can I take an ECU from a 1992 EX and plug it right into a 1990 LX?

 

Was there a vtec engine in the 4th gens?

If there was, you shouldn't put a vtec ecu on a non-vtec engine. You'll throw a CEL right off the bat, and I think a/f and timing plots would be off

 

Yes you can, All the P0A Accord ECU's from 1990-95 F22Ax engines are interchangeable. To be safe make sure you match the ECU with your type of transmission Auto/Manual. The only exception would be the 94-95 EX. It is an F22B1 VTEC P0A ECU so it will throw a CEL if used with an F22Ax Accord.

 

I thought they stopped the F22Ax in 93 or 94. My 95 is the B2

 

Adding onto this,
I have a 1992 Accord ex coupe manual. I'm trying to figure out what other ecu's are compatible with it as to save money.