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Start with VE or AFR table once idling?

Posted: Thu Jun 21, 2012 5:18 am
by kccampro
Another Newbie question… on the hierarchy of tuning, which table is really the best starting point once I’ve gotten my engine to idle?  I started out by messing with the req_fuel and injector open time values but I’m realizing that the proper way to adjust the mixture is to adjust the VE and AFR tables and leave the req_fuel and opening time at set values.  At this point the engine idles but runs way lean at any TPS value above 0% (and that’s not even under load, that’s just revving the engine in the driveway).  So I assume that once I take it out on the road it would be so lean that it’s un-drivable.   So, I was going to start by 1) bringing my req_fuel and injector opening time back to where they should be 2) begin to adjust my VE table to get it back to a good idle 3) continue to adjust the VE table until the AFR reading from my WB O2 sensor remains in an acceptable level over the full RPM range.  But back to my original question – should I be starting with the ARF table first?  Just trying to work out the order…  does the VE table dictate the AFR table, vice versa, both? Thanks!

Re: Start with VE or AFR table once idling?

Posted: Thu Jun 21, 2012 9:49 am
by Bernard Fife
kccampro,

It depends.

If you are using 'Combined VE/AFR' tables (the default), then the AFR is used only for EGO feedback, and you should tune the VE table first. The AFR table is then tuned to adjust the EGO feedback as you want.

If you are using 'Separate VE and AFR' tables (the default), then the AFR is used to also calculate the fuel pulse width (as well as EGO feedback), and you should first calibrate the VE table until the EGO correction is zero at all times (i.e. the EGO reading from the wide band matches the AFR table at all rpms and loads you run). That ensures that the VE table is correct. From then on you would tune for maximum performance/efficiency/whatever using the AFR table only.

See: http://www.megamanual.com/mt29.htm#so

Lance.