IAC-Idle air control valve. This is really an ECU output that controls idle rpm by controlling the amount of air, at idle, that is bled into the engine. Think of it as a second set of throttle plates that the ECU controls, but only at idle. This is sometimes called an Idle Air Control motor.

Crank signal-Crankshaft trigger signal. This is an ignition pulse usually from a reluctive-type input. It can be the typical output from a distributor pickup or a crank trigger itself. This is set up to create an ignition signal at a fixed advance. The ECU then delays from this pulse to control timing and generate the actual trigger pulse.

CAM signal-Camshaft position signal. This is a pulse that signifies the start of an engine cycle (once every two crankshaft revolutions). Since the crankshaft goes through two revolutions per engine cycle, the crank signal cannot be used to determine the engine cycle. This signal is only required for those ECU applications that require engine synchronization-sequential fuel injection and/or a distributorless ignition.

ESC-Knock sensor. This is a sensor similar to a small microphone that bolts to the block and "listens" for spark knock. The ECU can then retard the spark to minimize knock. However, a high-performance engine can generate enough mechanical noise to make this type of sensor ineffective.

Special System Considerations
The CAM Signal (Once Per Engine Cycle)
Many factory EFI engines use bank-to-bank injection schemes, where each injector is not timed to its individual cylinder-four injectors fire at once. This works better than you might think, because the injector is mounted in the manifold runner at the intake valve, the injected fuel hits the back of a hot valve, atomizes, and the atomized charge sits there and waits for the valve to open. Since the charge does not travel back up the manifold runner, distribution problems are minimal. In an aftermarket bank-to-bank EFI conversion system, where a distributor is used, no cam signal is required.

In cases where the engine cycle must be known, a cam signal is required. These cases are sequential EFI and/or an electronic distributor. The normal timing for this cam signal is to have it occur just before TDC on the number-one cylinder. A simple way to create the cam signal is to grind off seven of the reluctor points on a normal distributor. That one remaining reluctor-point is a signal for once every engine cycle. Timing of that signal, how-ever, usually requires that the reluctor be relocated on the distributor shaft. This is because the rotor must still be phased properly to the distributor cap.

The Crank Signal (Once Every 90-Crankshaft Degrees)
A normal distributor generates a pulse every 90-crankshaft degrees. The problem is, the distributor will generate this signal when it wants the plug to fire because there is nothing else in the system that controls the timing. When using an ECU, the signal must occur much earlier, allowing the ECU to determine when to actually fire the plug. In addition, since timing is under control of the ECU, the signal to the ECU must be timing fixed.

A typical EFI crank signal would occur at something like 50 degrees (fixed) BTDC. Then the ECU has enough time to create the ignition pulse between 10 degrees and 40 degrees BTDC.

Since there is only one reluctor in a Mopar distributor, if you have to generate both the cam and crank signals, the normal approach would be to use a crank trigger for the 90 degree crankshaft signal, do the grinding and relocation of the reluctor for the cam signal, and use a simple coil and distributor cap. But this wouldn't work for a distributorless Hemi, because we don't want any distributor at all.

CAM and Crank Signals For The EDIST HEMI
We used a crank trigger for the 90-degree crankshaft signal and fabricated a special mount for the cam sensor. Then we used individual coils for each plug so no mechanical distributor cap was required.