ok- have a gsr motor 84mm pistons, bottom end all built, head ported/polished, .5mm oversized valves, springs, stock gsr cams, 440cc inj's, jg manifold, intake, header, exhaust, running off tuned p28 hondata obd1. the more i drove the car the leaner it ran, now it only runs rich when it starts up cold for about 30 seconds, then leans out. i have an a/f gauge, i know they're not accurate but i ran a tester on the o2 wire and the gauge is reading right, mixture barely shows up on the gauge, it's SO lean! why does this happen and how could it be fixed? it didn't do this at all for the month i had it running. any input would be great thanks.

 

this same instance happened with me. My rear O2 sensor needed some help even though it checked out ok. It seemed that the wires got a bit fried and were inside the heat shield...my fault when i was messing with my new tanabe exhaust. Anyway, it turned out that after my car warmed up (20 - 30 minutes of driving) the car leaned out hardcore. My car died 3 to 4 times while driving like this. On start-up it seemed to be way too rich and bog down with gas. Anyway, I would look into your rear O2 sensor some more and see if maybe a wire or two could be causing this trouble. What car are you running this setup on anyway?

 

its a 99 gsr, but the computer is a hondata s100 on a p28 obd1 so there's only one o2 sensor

 

oh roger that. The one on the front side of the header? hmm, well never mind then , i think we are having the same problem but with different solutions...sorry i cant help much more...gl