NTPOG 5th Gen Air/Fuel Controller Install

Author: Todd Marcucci

Got a new air/fuel controller for your Prelude? Thinking of getting one? This article is for you. This overview page will cover the "basics" of the A'pexi V-AFC controller and a summary of the steps. This installation is very similar to the Field and the wiring section is essentially the same.

I performed this installation over the course of a weekend. You could probably squeeze it into a long day, especially if you don't paint the AFC, paint it beforehand, or just double-stick the thing to the dash. I wanted it to look nice, though, and spent a lot of time on it. Hopefully this install guide will help you do the same.

I'd like to give a special thanks to Arax and his web page on the A'pexi V-AFC. It's what I used as a guide for my install... good work, check it out!

A Note on OBDII (updated May 15, 2007)
"OBD" was a requirement set forth by the EPA based on EPA and SAE standards. It was intended to standardize and set specific requirements for On Board Diagnostics related to vehicle emissions and performance. Set forth in the late 80's, it was simply a monitoring and diagnostic system with no impact on peformance, other than setting slightly stricter emissions.

In 1996 OBDII was implemented. This new requirement set even stricter emissions limits and added/standardized more monitoring and diagnostic functions. Automakers were forced to add Long Term Fuel Trim (LTFT) correction in addition to existing Short Term Fuel Trim (STFT) correction to better adjust the air/fuel mixture (and thus emissions) based on driving habits, available fuel, and environmental conditions. The net result is that certain modifications that affect the air/fuel ratio will be undone over time. The 4th and 5th gen Preludes made from '96 and up are one of these vehicles. When I first did this writeup back in '99 or so the popular consensus was that you could do the "OBD2 workaround" which caused the ECU to reset every time you turned off the car and dump the STFT and LTFT values. It was generally held that this would prevent the ECU from "learning" your mods and removing power. We now know this to be entirely false. At least, it will certainly lose all stored values, but in general 1) all PGM-FI Hondas will correct for any modification of the a/f mixture when in closed-loop operation through STFT adjustments and 2) the LTFT values are not suspected to be applied when in VTEC.

It is absolutely certain now that the OBD2 workaround/resetting the ECU does nothing positive, at least nothing with regards to tuning and we've taken our workaround instructions off of NTPOG.org.

We'll try to keep this broken up and as easy as possible so you can skip steps you don't need to perform. It's certainly not necessary to paint the V-AFC or dash mount it- it's perfectly useable the way it is, out of the box, using the bracket mount and tape that comes with it. Please use the links below to proceed with your installation:

- Painting the V-AFC
- Dash Mounting the V-AFC
- Wiring the V-AFC to the ECU
- Programming Your Air/Fuel Controller

This page last updated 5/15/07.