reason: have a 90 si motor in my 89 hf.
using hf ecu result: slow and sputters but no check engine for o2 sensor
using Si ecu results: sputters when not warm. warmed up = quick but throws a code for o2sensor.

the question. Is Si and HF ecu pinouts different?
i have bought a brand new O2sensor already.

 

I might be wrong but i think the O2 on the HF is different, so you may need to rewire that.

 

HF and Si ECU pinouts are the same

 

they cant be the exact same because the HF has an EGR valve and the SI has a fast idle control valve. I'm doing the exact same swap and mine runs like shiznit (fast idles not wired throwing codes out the a$$)

 

they are the same:

the HF has yellow wire at ECU pin C8 for EGR - the Si has no wire at C8

the Si has blue wire at ECU pin B2 for FICV - the HF has no wire at B2

FICV missing or not working will not cause a check engine light or codes - neither the 88 Si nor the JDM DOHC ZC have a FICV and either will run just fine using any 88-91 Si PM6 ECU

you probably should look somewhere other than the FICV to cure your codes

 

they are exactly the same when i bought my car as a 90 hf first thing i did was pull the hf engine and put a d16z6 with a crx si ecu and it ran fine with no check engine codes for 3 years and chipped the ecu all i did was leave the egr unhooked