What do you do to accommodate the smaller threading, do you have to get another downpipe or is there some kind of fitting you can put in there?

 

Look up "O2 Bung" on ebay. A lot of performance exhaust shops sell them too.

 

Basically, you'll have to cut or grind out the original O2 bung and weld in the new one.

 

Welp, I put my car up on a dyno this weekend. It's confirmed I'm running lean for some reason. I was getting detonation at full boost at around 4100rpms. I guess that means it's time to get my butt in gear on the Z31 ECU conversion. Since I got an '88 Z31T ECU, I have to use high impedance injectors (or else use resistors). So I guess I may as well look into some new injectors with a higher flow rate. Hopefully that'll solve my problem. Still, I'm puzzled why it's going lean..

 

If anything it sounds to me like a vacuum related issue, because like I said I was having the same problem, but it wasn't until hard throttle/higher RPMs, which first turned out to be a vacuum leak, but then I hooked up the wrong line which had a regulator or something on the line that would cut off the flow of that line at a certain RPM/Throttle position that it was the same as the leak.

Also you could be having a problem related to your Ignition timing. Which could mainly be your Ignition Module or coil.

 

on a turbo any leak turns to a boost leak at high rpms. That would cause things to go rich. Mine does stumble at 4200 rpm as well but my gauge shows rich still. I'm only running stock boost.

 

Has the thread author tried wiggling the wiring harness right where it meets the ecu?