Engine Fuel & Emissions Control

This article discusses the myriad of sensors and controls utilized by the Z32's electronic fuel injection system. While every internal combustion engine follows the same basic principles (suck, squeeze, bang, blow!), cars with EFI are a bit more complicated and use various sensors and an electronic concentrated control unit (ECCS, or colloquially called the ECU or Engine Control Unit).

This section is primarily based on the Parts Description section from EF&EC of the Z32's FSM.

ECCS or ECU

The ECU (Engine Control Unit) or ECCS (Electronic Concentrated Control System) is the primary computer used in the Z32 to control the engine and various other components in the car necessary to it running properly. Practically every component in the car related to driving communicates on some level with the ECU.

Crank Angle Sensor

The CAS is a device that reads the rotational speed and position of the engine in real-time. It is mounted in front of the driver's side exhaust cam, which uses a splined drive pin to rotate the CAS. The CAS uses a metal disc with 360 slots cut out to indicate 1 degree of motion, and an additional 6 slots (of varying widths) that are used to determine the position of the engine in its rotational cycle. As the disc rotates (by motion of the exhaust cam to which it is affixed), an LED light passes through the slots on the disc and is read by a photocell on the opposite side of the disc. An on-board circuit transforms the reading into two wave circuits (one for the 360 degree reading and one for the 120 degree signals) and sends the signals to the ECU. The ECU relies on both of these to determine when to fire injectors, spark plugs, how to adjust the fuel/timing maps, and the gauge cluster uses it for the tachometer reading.

Air Flow Meter (MAF)

The MAF (Mass Air Flow [sensor]) is a device used to measure the amount of air being ingested by the engine. An accurate reading of the amount of incoming air is necessary so the ECU can determine how much fuel to use in order to achieve the desired air/fuel ratio.
The MAF contains a small, thin, wire that heats itself up. The temperature of the wire directly affects the resistance of the wire. As air passes through the MAF, it carries away heat from the wire, and the change in temperature is measured and transformed into a voltage reading (between 1 and 5 volts) and sent to the ECU.
The MAF is an effective device for measuring air flow because it is extremely accurate and very versatile.
There is often a perception that different altitudes, temperatures, densities, etc of air could give the MAF an inaccurate reading. In reality, all these factors affect the mass of the air being meter, and that's exactly what's metered--the mass of the air. It's true that these factors can effect how an engine performs, but that's because of the air itself--the MAF still takes an accurate reading of the mass of the incoming air, regardless of the situation.

In the 90's, it was understood (primarily by JWT) that the MAF hits a ceiling at 5 volts. At 5 volts, it's reading about enough air to produce 500hp. To counter-act this, JWT developed a dual-intake system that utilized two intake filters, but only one MAF sensor. They also employed a modified EPROM that would utilized fuel for basically twice the air content metered by the MAF sensor, effectively doubling the MAF's reading at the ECU side. This allowed the "500hp" ceiling to be surpassed; as "500hp" of air would be metered as about 2.5 volts, rather than 5 volts, and then doubled by the ECU.
This created a common mode of thought that a dual-intake system wasn't necessary until one desired more than 500hp. While this was true electronically, recent events have shown that even a completely stock NA can benefit greatly from a dual-intake system. This was partially brought to light by Jim Selin, with the advent of his Dual MAF Translator, which allows one to connect two MAF sensors and run them together on a completely stock ECU.

Engine Temperature Sensor

The Engine Temperature Sensor is a small device that uses a thermistor to determine the temperature of the engine's coolant. Thermistors are resistors which change their resistance level depending on their temperature. This resistance level is then read by the ECU, and the ECU uses this information to determine which fuel/timing maps to use.
Note that there are technically two temp sensors used on the Z's coolant system. While the single-wire "Coolant Temp Sensor" is used only by the gauge cluster, the two-wire Engine Temp Sensor is used only by the ECU. They are functionally very similar, and despite how vague the temp gauge is on the Z32, the engine temp sensor is very accurate.
If the Engine Temp Sensor reports a temperature over ~220F (without the AC on, the threshold his lower with the AC on), the ECU switches to a "limp-home mode." It switches to "safer" fuel and ignition timing maps, raises the idle to 1000 RPM, and enables the auxiliary fan. This limp-home mode is also activated if the ECU cannot get any reading from the Engine Temp Sensor, which will also cause it to throw Code 13 on the ECU's self-diagnostics.

Throttle Position Sensor

The throttle position sensor measures the open-close position of the throttle valves. It also determines if the valves are completely closed to tell the ECU to idle the engine.
Main article: Throttle Position Sensor.

Fuel Injector

The Fuel Injector is a small solenoid valve used to inject fuel into each combustion chamber. It is precisely controlled by the ECU to inject a specific amount of fuel at just the right time.
Main article: Fuel Injector.

Fuel Pressure Regulator

The fuel pressure regulator is a vacuum-actuated diaphragm device used to ensure that fuel pressure remains at 43.4psi, relative to the intake manifold pressure. Because fuel is injected into the lower intake manifold, the amount of fuel injected is affected by the pressure in the intake manifold. A higher amount of pressure would result in less fuel, so the fuel pressure regulator "follows" the intake manifold pressure to ensure that the fuel pressure will always equal 43.4psi relative to the intake manifold pressure.
For example, at idle the Z's intake manifold is at about -22inHg. For illustrative purposes, this would be equivalent to about -10psi. Therefore, the fuel pressure is reduced to about 33psi. At wide open throttle, an NA engine approaches 0psi intake manifold pressure, and the fuel pressure rises to 43.4psi. In a boosted application, the fuel pressure continues to rise with the boost pressure. A TT Z32 running 10psi of boost will see fuel pressure peak at about 53psi, and so on.
Note: Z32s were shipped with their fuel pressure regulator and fuel dampener painted black originally. Replacements were zinc-coated and are light-gold colored. This is an easy way to determine if the FPR and Fuel dampener have been replaced in a Z32.

Exhaust Gas Sensor (or Oxygen Sensor, O2 Sensor)

O2 sensors are used to measure the oxygen content in the exhaust gas produced by an engine. As the Z32 features true dual exhausts, it uses two parallel oxygen sensors, one for each bank of 3 cylinders. The O2 sensor uses a zirconia tube that generates electricity depending on the oxygen content in the exhaust gas.
Main article: Oxygen Sensor.