Target AFR

[inj gtr202]

Hi all,

I have a question regarding the target AFR table.

If VE learn is disabled and there is no closed loop. Does this table do anything to your tune? or is it simply as it states... a target.

cheers,
Adam

[Jayme]

yes still affects your tune. your VE table is just that, volumetric efficiency. the ecu uses the VE number to help it know how much air is going into the cylinder. once it knows how much air is going into the cylinder, it needs to know how much fuel to put in. so it looks up the target AFR table and sees what ratio you want. applies that to the current air flow then injects the correct amount of fuel. richen your target AFR then it will inject more.
so it is just a target, but in open loop it is just dividing the currently estimated airflow by the target, it may not land at your target AFR if the VE table is incorrect, which as you know is the purpose of closed loop and VE learn.

so it is actually used all the time whether or not in open or closed loop.

[Holden202T]

the idea is once the VE table is right you should be able to change your AFR table numbers and the wideband should reflect the change.

another thing to keep in mind, i know your tune was using alot of 14.4's i think in light throttle areas, and i have found with big cammed motors you often need to change the say 20-70kpa areas upt to 2000-2400 rpm to something like 14.4 just to slightly richen it up to stop it going into closed loop and being too lean, this causes surging too i've found.

[inj gtr202]

the idea is once the VE table is right you should be able to change your AFR table numbers and the wideband should reflect the change.

another thing to keep in mind, i know your tune was using alot of 14.4's i think in light throttle areas, and i have found with big cammed motors you often need to change the say 20-70kpa areas upt to 2000-2400 rpm to something like 14.4 just to slightly richen it up to stop it going into closed loop and being too lean, this causes surging too i've found.

Bingo... I have only been playing with the VE table.. looks like I will adjust the AFR table to what I think should be right before I go too much further. I'm getting alot of surging in the 2,000 to 2,200 RPM region.

Jayme that makes much more sense now...
cheers guys,
I'll trow up my latest log with an unchanged Bin when I get home

[Holden202T]

yeah but is the VE table right in that area ?

ie. is the wideband showing figures the same as whats in the AFR table being commanded ? if they are then yeah change the AFR table to say 14.4 or 14.2 .... if the VE table is wrong you need to get it accurate too.

[inj gtr202]

yeah but is the VE table right in that area ?

ie. is the wideband showing figures the same as whats in the AFR table being commanded ? if they are then yeah change the AFR table to say 14.4 or 14.2 .... if the VE table is wrong you need to get it accurate too.

no... the wideband is spiking from 12-16... I'll post the log in the other thread.