A few months ago, I decided on purchasing an Apex'i S-AFC for my '91 GT. I figured that once I turned up the boost, I would want to upgrade the injectors. Although a small upgrade in injector size wouldn't require major modifications, I wanted a large enough increase to be able to run 17-18psi of boost safely (after the forged pistons go in, of course). Running this high would require monitoring and modification of the air/fuel mixture. Although the S-AFC didn't list the Probe as a supported vehicle, I read through all the information on the Probe's fuel system and ECU wiring diagrams and I figured I could make it work.

On September 1st, I figured it was time and I ordered the unit from MVP Motorsports. I had it shipped for Fedex Saturday delivery and it was in my hands by 10am Saturday morning. After I hooked up the unit to the ECU (everything but the airflow signal wire), I ran though all the sensor tests and started the engine. Throttle position was working, oxygen sensor was fine, engine RPM, etc. Everything looked perfect. I turned the engine off, hooked up the air flow wire connection, and checked the unit's Sensor voltage. That's where the problem arose. Out of 16 presets for flapper-type air flow sensors, the Apex'i unit didn't have any settings that were in the correct order for my unit. All the settings saw anything from 3 to 4 volts as the air sensor being closed, and 0v as the sensor 100% open. The second generation Probes work this way, which is why the unit can be installed on them. First generation Probes, however, signal 0v as being closed and 8v as being 100% open. I did find that by setting the sensor type as 'pressure', the readings were in the correct order, but this is where I ran into the second problem... the sensor signals the ECU with 8v when the unit is 100% open, but the S-AFC can't see more then 5v. This leaves the unit thinking that the sensor is at 100% open, when it's actually only about 25% open. There's no way around this obstacle.

This was a big disappointment. I was relying on the unit to get my car to the next level of performance. It's also a shame because I really liked the unit. You can monitor values, such as the throttle position on anolog-style gauges, or the engine rpm on a graph.