I run a FJO wideband in my truck all the time. I observed some odd readings after installing the headers and high flow cats last week on the truck. The only change I made was the headers and cats, no other changes where made not even to the tune. The truck before the headers would hold very tight control on the 14.7 cruise and idle A/F ratio but now it seems to be struggling to get to the 14.7 (stoich) and usually idles 15.0 - 15.3 but light loads and cruising its stays near 14.8?

The other weird thing is that its going dead lean on decelaration, it was going to 17.0 on decel where before it never did that before. The WOT and high load A/F seems to right on the money with a 11.0 - 11.3 A/F. It was tad richer before but I would expect the headers to lean it out a tad.

My tuner has suggested that its just the ECU re learning but I have driven at least 10 drive cycles with no change in the values I posted above. It not bothering me much and the truck runs like a beast. Im just curious to what you guys might think? The sensor itself is fairly new and is in near the same location it was with the stock exhaust on the truck?

My Silver 01 Lightning made 407/530 and this one feels a good bit stronger then that. I am going to get it dynoed in a few weeks to see what she we will put down.

Thanks,
Bob

 

Mine does the same thing when decelaration, and I have stock exhaust, I think it is pretty normal so I wouldnt worry about it. As far as when you are cursing, sometimes I can curse and it will bounce from low 14's to high 15's, and then sometimes it will stay around 14.7's, so I think you are fine, hopefully somebody can chime in with more info. Good luck.

later
brian

 

Bob,

with the old GT it took about a week, or about 10 key-on cycles to learn the Longtubes. My A/F was straight up goofy, till about 1 week. Stay safe.

joe