okay so i have a wideband in car and going to T1 wed. to get a tune but i have drove the car a little bit and afrs were lik3 12.5 at partial throttle and all of a sudden the jumped up to 14.5 ? so i havent driven the car since... looked over everything and everything looks fine? kinda confused on what is going on... i can richen it up in s300 but i dont understand why it changed... any ideas

 

I just had a walbro 255 fail on me. Still pumped fuel but didn't maintain pressure, even when pinching off the return line. For me, AFR went from stoich to 16-17.

 

A failed injector, a vacuum leak or wide band sensor failed causing bad readings.

 

Something as simple as an exhaust leak can do that too, outside air gets sucked into the hole at low loads, tricking the o2 sensor it's lean.