NTPOG 5th Gen Air/Fuel Controller - Programming the V-AFC

Author: Todd Marcucci
 


Programming the AFC
Tuning your AFC is not something you should do by the seat of your pants. Running then engine too lean can be damaging, and too rich may not make as much power (and extremely rich can foul plugs, the O2 sensor, or damage the catalytic converter). To find that "perfect" spot and the ideal settings for your car you need to locate a dyno that has a wideband O2 sensor and can give you an accurate a/f ratio reading across the RPM spectrum. You should not rely on a dash-mount wideband, either, unless you have the ability to datalog. Even then you will need the ability to datalog RPM and be able to match air/fuel ratio to recorded RPM, then make your adjustments. This will allow you to accurately tune you AFC and then verify proper air/fuel ratio.

In general, with a stock or mildly modified car (bolt-ons), you will find that the factory mapping is good at lower RPMs, or below VTEC in VTEC Hondas, and then the mapping becomes progressively more rich on the top end. Depending on your modifications this may vary greatly, for instance most turbo/SC vehicles will need a much richer air/ fuel mixture than a naturally aspirated (NA) vehicle. Also, the factory mapping is rich for a reason- this provides for a much greater range of operation, such as operation in very cold temperatures at sea level (more fuel injected) and also in very hot weather at higher altitudes (less fuel injected). Honda has to make sure the car will run well independent of whether it is in Phoenix in summer or Minneapolis in the winter.

Consult a local, experienced tuner for the most appropriate air/fuel ratio based on your vehicle and your driving, and tune the VAFC appropriately. As a point of reference the factory mapping will oscillate around 14.7 (stoich) when closed loop (may vary from 14.5 to 15.0) depending on the situation and run as rich as 11:1 when starting or in WOT/VTEC at or near the rev limiter. I would not recommend NA vehicles going any leaner than 13.5:1 for reliability's sake (can lead to detonation or burning valves) or FI vehicles going any richer than 11:1 (it will likely be too hard to ignite the air/ fuel mixture and cause stumbling).

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This page last updated 5/15/07.