Command air fuel ratio

[Kevspec]

On a vt ecu what determines the command air fuel ratio? Essentially car ive previously tuned on the dyno with sensor in tail pipe everything was fine now new engine and getting ready for retune etc but randomly decides to go either rich or lean and when it does that from what I can see is the command air fuel is what's causing that. Weird thing is I have all closed loop turned off and my open loop afr table is no where near where it's going. Car does have a wideband but for some reason we could not get ecu to read same as the gauge so wideband not controlling ecu its just set all in open

Also with dfco the ignition lock does not seem to work with all settings correct aswell.

[immortality]

Is the new engine different to the old?

When in open loop there is no correction going on so if the tune is off so will the AFR's be.

[antus]

commanded afr is calculated based on what the computer knows about its environment and includes warm up / temp corrections. Check DTCs and input sensor data all looks sain, you might find some damage in the loom where something got knocked or a bad ground and something is reading off.

[Kevspec]

Yes engine is different but I tuned it na before the turbo went back on and been driving it last few weeks without any issues. Will have to go over everything again as there are no dtc and from what I can see when there are massive swings in the command afr goes anywhere from 9.7-17 and all other temps etc are the same

[Wade]

Not sure if vt is the same as vx-vy but there could be a ramp rate that the dfco spark is applied. Based off load and also each gear and maybe other things.

[Kevspec]

None of that has changed but it does it on idle aswell so it's not load dependent

[VX L67 Getrag]

are you logging it to see what sensors are working & what is being commanded & what fuel & idle modes it is in?

[Wade]

Yeah I don’t think it’s dfco, just pointing out that dfco has a fair few targets to meet. I think it ramps timing down based on each gear ect and a whole bunch of other things. Probably worth while turning dfco off while tuning fuel in.

[Wade]

As for fuel. Have you checked for vacuum leaks, all wiring and sensors ect? Wideband all good? Maybe try replicate that condition when it happens and share a log?

[Kevspec]

Yeah I will log it all and have a look over it all