I Changed my plugs on my '94 Z (obd1) 2 days ago because the car had a slight miss. I also lowered the fuel pressure from 65psi to 50 psi (which I have since raised back up to 60 psi). It ran fine for about 15 minutes then it started to miss badly, The miss seemed to begin about the time I would have expected it to go into closed loop. I should also point out that this morning when the car was first started and still in open loop it was missing badly.
Today I changed Spark plugs and wires (2 of the plugs on the passenger side seemed to be running lean) When I started the engine it sounded great not a trace of a miss, I should point out that I just changed the Opti less than 200 miles ago. On the way home I hooked up my lap top and using Data Master did a scan, almost as soon as the PCM went into closed loop the engine started to miss again.
I suspect that I have at least one faulty injector but there are no injector faults showing and there are no DTC codes either.
Looking at the STERM % I seem to be getting some very lean conditions such as +3.1 as well as an O2mv of 75. I don't know how to interpert this data and am hoping some of you guys that are famaliar with Data Master can help me.
I also got a tune from Brian At PCMFORLESS which I installed about a month ago, did a data run and then reinstalled my original tune, to do a comparison of the performance change, but have not reinstalled Brian's tune yet as I am waiting for him to make some changes.
Here are the files if any of you can look at them and give me your suggestions as to how I should go about diagnosing the problem.

was hoping to post the zip files but I see we cant do attachments, if anyone is interested enough I will email them to you.

 

If it's going into closed loop and the problem lies there then it's your O2's.