I have a 91 prelude si and i need to know spec of my engine. i did a vin on numerous sites and they come back different. mine is an automatic and it is fuel injected. vins come back as 2.0 L and 2.1L and how do i find out which engine I have? The car needs work but I have no idea how to find out my specs. Please help :-? btw I have also had vin decoders tell me my car is a manual...so really i need to identify what I have.

 

Those years have both the B20a5 2.0ltr, and the B21a1 2.1ltr motors. So technically your documentation is correct.

But for a more specific answer, just look at the engine stamp and you will see what motor you have.

And to know if you have an OBD1 wiring vs the OBD0 wiring, just pull the passenger carpet back and unbolt the ecu case from the floor and see if you have the two plug OBD0 harness plugged into the ecu or the 3 plug OBD1 harness.

 

91 prelude Si is b21a1 (2.1L, aka 2.05L) and is obd1.
91 prelude 2.0Si is b20a5 (2.0L) and is obd0.
^from the factory^. the b21's tend to die early, so people usually swap b20a5's or b20a's into them to bring em back to life. so to know what you have, do what sean above me said and just look at the engine stamp. it's to the left of the exhaust manifold on the block, right next to the flywheel view window.

 

thanks for your help. it is a 21a.