Technical Information

The RX-8 Power Control Module is a powerful computer that has been programmed with strategy carefully optimized for the Renesis engine. The module is supplied with 3 maps for each main variable - leading timing, trailing timing and fuel. These maps are for hysteresis (deceleration), first through fourth gear, and fifth and sixth gear. Some of these maps are the same.

This PCM is a "learning" computer (like most OEM units) and uses heated oxygen sensors to build (3) long term fuel trim levels - idle, low speed and cruise. The computer undertakes this by first calculating the fuel injector "ON" dwell time based on the Mass Air Flow (MAF) meter output, then adjusting that amount with numbers from an "Enrichment Table" (which is what Racing Beat modifies). Once this "ON" time is output to the injectors, the #1 (front) oxygen (O2) sensor measures the resulting exhaust for oxygen concentration, converts that reading to a "Lambda" value (the ratio of the actual fuel mixture to an ideal "14.7" mixture), compares that to a "look-up table" of target Lambda values, then adjusts the mixture to exactly match the target Lambda value. This is necessary because no engine system (the engine and all of its components) is actually identical to any other - and even if it was, age and wear would soon change that. This system "corrects" the mixture, but it also keeps track of the changes it has to make with a "statistical algorithm" that looks for a pattern of average changes it finds necessary. When it identifies such a pattern, it makes this "trim" value part of its basic calculation to allow it to get closer to the target mixture more quickly. Most importantly, when the PCM switches to "open loop" (no oxygen feedback control) at throttle settings above freeway cruise RPM and load, the system continues to use the highest trim level to correct the mixture. In other words, the PCM generates a "correction factor" at freeway cruise, and then continues to use that factor at high power. These trim quantities can be built in as little as a few minutes, depending on the operation of the engine.

As mentioned earlier, there are 3 levels of trim, all independent of each other. This is why "piggyback" controllers can cause such problems - when the controller changes some output, often the long-term learning corrects for this change. This complexity also had a lot to do with the time it took for us to understand this information.

In developing this flash, we disconnected the Front Oxygen Sensor so that we had a stable, unchanging platform. Otherwise, the system would continually develop new trims that we would have to chase. Of course, it is not appropriate for you to do this (except in racing) because the system NEEDS the oxygen feedback information to correct the engine’s operation at light to moderate throttle settings. The fact is, in our experience, the PCM will usually build a 2% to 3.5% top level trim, which means the engine is running that much richer than best power mixture. In general, this is a small amount, and will only cause a fraction of 1% loss of power. On the other hand, if you don't want to run with this factor (i.e. racing applications), you have two choices:

1. Disconnect the Front Oxygen Sensor (at the top of the bell housing), pull and reinstall the "ROOM" fuse (in the left kick panel) to eliminate the 3 trim levels, and the PCM will NEVER build a fuel trim (it will turn on the "Check Engine" light, but that's all).

2. As an alternative, you can simply warm the engine prior to a competition run, shut off the engine, pull and reinstall the "ROOM" fuse, and begin your competition shortly after starting the engine. In this way, the engine never sees the "cruise" operation it needs to build the trim level.

The system has huge amounts of self-diagnosis capability. It detects most malfunctions immediately, although it may delay turning on the "check engine" light for a number of start cycles, depending on the malfunction. In many cases it can clear a malfunction (i.e., turn off the "check engine" light) by itself if the problem is corrected or stops occurring.

2. As an alternative, you can simply warm the engine prior to a competition run, shut off the engine, pull and reinstall the "ROOM" fuse, and begin your competition shortly after starting the engine. In this way, the engine never sees the "cruise" operation it needs to build the trim level.