Reading SparkPlugs:

[Keitha]

At what Air Fuel Ratio do sparkplugs begin to look sooty and black? At a AFR of around 12.5:1 would they still look OK?
I am working on tuning my 383 and an getting consistant WBO2 readings in the 12.5:1 range but my plugs look OK and my NBO2 is switching fine and my BLM's are not excessive (135 range and steady). I am questioning if the WBO2 is off or if there is something else going on w/ my motor.

 

[Fabrimacator21]

135 is lean... which would be a higher A/F ratio then 12.5:1.

Are you datalogging your wb readings? Got any sheets?


No help on the plugs.... but black and sooty means rich IIRC. Might have a bad NB o2.

 

[Keitha]

Yah, I have a thread going at 3rd gen about my WB readings contradicting my BLM's. There are times when my BLM's shoot up and the WB drops to 10:1 range. It has got me puzzled. My heated 3-wire NB is switching and active. Maybe I should try a new NB.

 

[Blue85]

You want to be rich on the tip-ins and at WOT, but that doesn't make your average AFR rich. The plugs will stay clean from the other parts of your fuel map that are leaner. Unless you're at a track/dyno and shut down right away, it's hard to get this info from the plugs alone.

That being said, the way the engine runs is always more important than WB readings. While WBO2 is a great tool, it is wrong sometimes.