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?

 

No insight from the super gurus?

 

Your logic seems good if you have the cause and effect correctly figured. What if the cause is weak spark so the PCM leans out the bank in order to get ignition. I guess I am saying this to get you to go after the lean condition, since the trouble code says that's the problem. Once fixed, if you are correct in your thinking, the weak spark will than be adjusted and not be a problem. Go for the likely causes: air infiltration or lack of fuel to that bank. Good luck.

 

replace the o2 and you will be fine 90% sure of it that a commin code