A/F Ratio Anomaly (please read)

[jefflee]

This is the first time taking the car out on the thruway/highway with my latest upgrades (S-Trim, 42lb inj, 255 in-tank pump) for a constant period of time…70 miles.
About 10-20 miles into my drive, with the cruise set at 75 (medium load), my LM-1 wideband A/F ratio goes from high 13’s, low 14’s to low 10’s!
With AFR in the 10’s it doesn’t feel like it’s loaded up.
After reaching my destination it had a rolling idle and A/F was in the 11-12 range. When I shut the car off and wait a few minutes then start the car back up A/F slowly returns to its usual mid to high 14 A/F range. Same symptoms on the way back later that day.
Car runs and drives fine on the street in stop and go traffic.
It’s a shot in the dark, but my only theory is that with the 42lb injectors after a certain length of time in a constant load condition the extra fuel is cooling off the O2’s and making the EEC think it’s cold therefore run rich.
Is this even possible? Has anyone experienced the same or similar phenomenon?
I’m stumped.
Any insight would be appreciated.
Thanks!
http://www.cardomain.com/id/jefflee

[root]

I had a similar problem and it turned out my O2 sensor for the LM1 was shot.

Ian

[jefflee]

Both the LM-1 and factory O2 read rich. Granted the factory is a narrow band but the gauge reads pig rich which reflected what the LM-1 reads.
It only does this after driving at a constant speed for a lngth of time. Stop and go, street driving the LM-1 reads "normal" A/F.
Thanks.