Dynoed: what's with my A/F grapth

[spederman]

Dynoed: what's with my A/F graph

My car is pretty much stock. Its an 02 GT 5 spd with borla catback, underdrive's, and gears for performance mods. What's with the A/F graph, Why is it so lean in the beginning? Is there something wrong or is it just the way they dynoed my car that it starts out lean and then drops.

 

[csledd]

wow, for your mods that seems kinda weird. I don't know what stock GT's A/F usually looks right, but I'd imagine it's not suppose to look like that lol. Hmm, hopefully someone else can post some insight into this. Your HP/TQ lines doesn't look like it's starving for fuel like mine did when I was running lean.

 

[DBMSTNG]

if that a/f ratio is correct, you need that fixed asap. but i'm guessing it has something to do with the stock h pipe and 4 cats.

 

[Venom_Nitrous]

My guess, and only that, is that the dyno operator didn't get on the throttle 100% until the afr started to go down around 3700. It looks like it is in open loop before that and it is trying to make it stoich (sp?). The cats may be throwing off the actual afr if he used a sniffer in the tail pipe. That is how mine was done and when he was spinning up the rollers at partial throlle I notice the afr jumped alot and was around 16:1 until he really got on it then it was right on. If he was at WOT then the culprit may be a bad TPS not telling the computer that it is at WOT or the gas pedal hits the floor preventing WOT. It could also be a bad filter in the wideband. These are just guesses though,

 

[spederman]

Oh, i forgot, I also have a catted bassani x pipe.

But Venom, That's exactly how my car was dynoed. The operator would spin up the dyno at partial throttle. They also used the tail pipe sniffers to measuer the A/F. Once he got it spinning he would go through the gears at partial/light throttle, then he would go WOT. So that's what is probably doing it huh? That would make sense.

 

[blackink00]

wow thats awsome!! i think its just how the dyno was driven