[Diy_efi] Post 4-Wire O2 Sensor Swap Observations...

[Mike Frels]

About a month ago as part of preparation for my header install I swapped out my single wire O2 sensor for a four wire AFS97 from a fourth gen F-body. I wired the heater in via a relay to hot at all times in the back of the fuse block and grounded via the A.I.R. Port Solenoid ground line. The sensor I gounded to the back of the diver's side head. Since the the swap I noticed two what I consider contradictory results. My BLMs went up between 5 and 10 to what were already lean ranges. My idle was around 145 before and now it's up to 150. Same approximate changes in all my easy driving ranges. The second nice but puzzling change has been my gas mileage. Previously with my not yet properly tuned Vortec headed 350 I was getting 15-17 mpg for all driving types. Now I get 17-18 mpg stop and go short distance driving and low 20s highway. Why does this not make sense to me?

FWI one of the main reasons for wanting to get the headers on before getting the tuning right is tuning ability. In the passenger side collector I have added a bung which will allow me to use a wide band O2 sensor so I can see whats really going on.

Mike
'86 MAP TPI Z28