any ideas on this? i have HPtuners and recently upgraded injectors, fuel pump and headers. did some IFR scaling for the injectors and PE tuning for the headers to set the AFR around 13.3 or so. i have a wideband kit as well which agrees with the stock o2's. During WOT, sometimes it reads around 13.3 where I want it and sometimes it goes down to 11.5. If i plot out the WOT O2 data I will see two different distinct levels.. sometimes high and sometimes low. it is not RPM dependent. i have the LTFT set below zero.

why cant it make up its mind what AFR to be at? ideas appreciated.

 

Sounds like COT to me. (catalyst overtemp protection = adds extra fuel to cool the cats when the PCM thinks they are getting too hot)

 

COT sounds possible, 13.3 AFR is kind of lean for WOT IMO.

 

i'm just playing with the AFR now, so i'll probably adjust down to 12.5' sor something (w/ nitrous)
i havent done my reading up on COT yet. do many of you disable this? how does the car decide they are getting too hot? is it the difference between the two O2 sensor readings? i'm just wondering if they really are getting too hot, or the car just thinks they are.

 

just nuke the cats, then nuke cot.

 

I haven't disabled mine, not sure about others. The PCM figures out COT from the rear O2 sensor, which is right after the cat. 12.8 AFR is good for WOT N/A, 11.5 or so is good AFR with N2O.

 

[QUOTE=samz28]just nuke the cats, then nuke cot.[/QU

thats not an option. at least the cat nuking part. i just shelled out for the hi-flow cat y instead of the offroad to keep emissions good.

 

Can you elaborate? How does COT work if the rear O2's are not installed or the codes are disabled?

 

I guess it wouldn't, not sure. Are you having this problem too?

 

I'm not having the problem. Just trying to clarify the typical response of 'if your AFR is misbehaving, try disabling COT'. If the rear O2's and/or codes are already disabled, and if COT doesn't work in those instances, then we need to find an alternative reason.

I disabled COT after my last dyno session to try to resolve a big 'checkmark' style dip between 5600 and 6100. I hope to find out today if that fixes it - but my rear O2's are filled with plugs and the codes are disabled.

Also - for endurance racing, I'd set the realworld AFR a little closer to 12.5-12.6 if you're naturally aspirated. For daily driving & drag racing 12.8 is fine.

 

The COT overtemp table is layed out in different temp thresholds so it must be using some elaborate temp calculation as I'm not aware of the O2s reading/sending Temp??

1)830.0 ēC
2)840.0 ēC
3)850.0 ēC
4)920.0 ēC

 

fwiw, disabling COT did not fix my sine wave AFR above 5600. Back to the drawing board.

 

whats your duty cycle during the afr instability? Perhaps you are forcing the injectors static with too much duty cycle? iirc most bosch injectors go static around 85% duty cycle, you have not much control over them once they go static

 

my duty cycle was low. this could happen even at low (2-3k) rpms.

i think it was the COT. i tuned the AFR a little richer and disabled COT. i havent seen the problem yet.. at least after 20 minutes of driving. thanks for the advice.