Low Throttle Maps on AFC?

4G63dsmpwr · 11-04-2002, 03:01 PM

I was wondering how everyone goes about tuning their low throttle settings on their AFC w/a datalogger? For example at 20% throttle, how do you guys figure out a good fuel map on the AFC? I'm getting crappy gas mileage and thought that maybe this might be my problem? I looked at the logger and 02s while just keeping the throttle under 35% and the 02s just jump around, so I can't tell how rich/lean I'm running and don't know how to adjust fuel. I have 510 inj., my MAF has no lower section (the whole things is removed), and I have a Walbro 255. Anyone have a similiar setup? I know every car differs but just as a starting point for the low throttle fuel map? My fuel trims are all usually around 80-83% (low, mid, and high) and I've heard that its good to have them at 100%? I dunno, any help/ideas/opinions on this topic would be APPRECIATED a lot - Erick

jw · 11-04-2002, 08:26 PM

Low setting on the AFC are use for tuning part throttle/cruising. The conditions for changing fuel trims are pretty simple. Van posted these values a while back:
Low trim - 0-175hz
Mid trim - 175-225hz
High trim - 225 up (before open loop)

The fuel trims will only change in close loop, once you go open, fuel trims dont mean #@%#@%#@%#@% to the ECU anymore. With that in mind, your trims tuning go from idle to 4krpm before it start to go open loop.

Low trim normal adjust itself even at idle. So your affecting rpm range should be 1k-2k range. Mid trim should be around 2k-3k and high 3k-4k before open loop begins. For the obvious reason, the rpm will range depending on which gear you are in so what I stated is just a guide. If you want to adjust high trims, you should hit the highway and maintain throttle position with airflow stated above.