89xjgrey
NAXJA Forum User
- Location
- Columbus, Ohio
Well, after noticing a dractic decrease in fuel milage, I started doing some investigating. My first obervation was that the o2 sensor was constantly reading 4.98-4.99 volts, I thought it was shorted out causing the engine to run incredibly lean. I replaced the o2 sensor, and still have the same readings. PCM in open loop mode, STFT and LTFT maintain 128 (due to open loop). I have a good ground at the o2 sensor harness, also have good +12 off the o2 heater relay to the sensor. I have good continuity on signal wire between o2 sensor harness and pcm. Signal wire maintains 4.98-4.99 volts in all conditions, cold, warm, load on engine, no load, even 2500 rpms. Now when I add ground to the signal wire (tricking ecm to run rich), I read 0 volts on my MODIS (snap-on scanner), and I notice an engine change so that tells me the wiring is good and pcm is interpereting correct. When I remove ground, momentarily it switches to closed loop, and i watch my short and long term fuel trims climb rapidly, up to 255 (lean limit). Then it defaults back to open loop. I'm at a loss here...and suggestions would be great. Thanks!