The downwind tattles as a primary function, but they also provide fine tuning to the a/f.. true story.. from what I can intercept and translate, it has about as much function as the iat while in closed loop, meaning it plays a small role..

If I dangle the downwind out of the pipe but hidden from direct wind, I'll see a richer burn, by as much as a full point, but rarely see it trip a code.. if it hits the airstream, it will trip a code and fatten like a pet pig, and right before it opens loop.. if its in the pipe, lambda bounces a lote more frequently, but in small movements- it comes closest to stoich in that condition..

Conclusion: it absolutely plays a role... I then found several tech articles supporting this, where the japs were the primary culprits, but guess who else was confirmed doing it? Good ol' mother mopar, and as far back as the obdii swap.. I had those articles linked in that thread I think, and I know I linked them in another forum..

The curious part to me is that the japs obviously have it nailed down and find it useful.. mother mopar? Not so much.. dodge suffers from bad fuel economy across the board, they are one of the toughest scripting codes to hack, and at least on these engines the holy grail of 14.7:1 is a fleeting thing.. without program tuning, that is.. and even then, folks like Sean aka hemifever, play hell to get it.. they can't address it head on because mopar does the trim game differently than others.. they have to cause and effect it until they nail it, and then its up to you to keep your rig tuned as best you can to maintain it..

So... In a basically stock rig, you're best off to leave the downwind alone.. or non foul it.. or plug the exterior vents on it.. but when you do even that, you're eliminating one of the measures that trim.. if you don't mind running slightly rich- then no worries.. a slightly rich engine produces slightly more power, at the risk of running slightly cool and at the risk of particulate build up in your exhaust and on your valves, maybe plugs.. its up to you how you want to run.. best fuel economy is 15.8:1 a/f, best power is 13.5:1 a/f.. lean wears an engine terribly, rich gums it up..

 

my o2s never moved. and the downstream is already defouled.

 

OK. I am old...and did not notice that you revived a 2 year old thread (or 2 years after last post). I confuse easliy at my age.

You can get by with a canned tune form www.hemifevertuning.com as Zman stated - or at least I think you can. Contact Sean at Hemifever to be sure. Custom tune not required unless you have some serious mods.

 

+1..........