O.K. I've had an issue pop up recently on my N/A. At idle afr's are around 13.3 on my wideband, at WOT they average 12.8, but at part throttle cruise the wideband goed out of range lean, or +18:1. Fuel is good, no vac leaks, timing seems to be spot on. What could be causing this?

 

I don't have the Answer but only an idea or two.

Make sure the 02 sensor is connected up. If it was not, then reconnect it and compare the results with what you were seeing before.

And or put the stock airfilter back on and compare the results with what your seeing. That only applies if you running with a non stock filter now.

I've a hunch you running with the 02 disconnected.

 

Do you have all you emissions equipment connected? Both the closed loop operation and the air injected by the air pump will effect readings.

 

A WORKING ACV would not allow the 13AFR at idle if it was working right.

If the 02 sensor is installed, you won't/can't get a true AFR of over 16afr. When turning disconnect the 02 sensor. Once finished tuning, reconnect the 02 sensor. Most people tune for WOT, not cruise. Most. If tuning to get mpg........buy another car. What you will gain is insignificant.

 

All emissions stuff(ACV, EGR ect.) has been removed and blocked off properly, and the O2 sensor is connected, changing back to the stock airbox did nothing.

Its strange, for the first couple min after startup it drives perfectly, goes into closed loop just like it should, then out of nowhere it goes lean. Burned out O2 sensor?

Checked the TPS while i was at it, seems to be good as well as the coolant temp sender for the ECU.

I'm gonna go check the O2 wiring, mabey sonething broke.

 

Just an opinion, but if it went into closed loop the 02 sensor would not allow the afr to get as high as you describe.. With the 02 not working the afr will go higher than 15-16 afr.

Narrow band 02 are pretty sturdy things as long as their center conductor isn't shorted to gnd.