2003 Ranger 4.0, 203k. CEL on, checked with code reader and got a P0171 code, lean condition in bank 1. I know what the possible causes are, but I checked spark on bank 1 and it is very weak. To me a weak spark would cause a rich condition not a lean one, all 3 plugs on bank 1 were weak. Is the PCM trying to compensate for the lean condition by dropping spark to try to fatten it back out on that side? Or is there some magical way that weak spark is causing the lean condition? Maybe the weak spark is only igniting partially and the part that is left over is lean, causing the O2 sensors to read it as lean? I'm stumped, any ideas?