Located in this section is a description of the Engine Fuel and Emission Control System (ECCS) for the 1992-1994 Nissan VE30DE engine found in the 92-94 Maxima SE models. This information is graciously borrowed from the Nissan Factory Service Manual and is intended for reference purposes only. Using this section will allow you to better understand the systems controlled by the ECCS and what they accomplish.

Multiport Fuel Injection (MFI) System

This system takes information from the crankshaft position sensor, mass airflow sensor, engine coolant temp sensor, heated oxygen sensor, throttle position sensor, closed throttle position switch, neutral position/inhibitor switch, vehicle speed sensor, ignition switch, air conditioner switch and the battery. The ECM takes this information and controls the fuel injector pulses (amount of time fuel injectors are open, and thus how much fuel in injected into the engine). The program value is preset by engine operating conditions determined by input signals (for engine speed and air intake) from both the crankshaft position sensor and the mass airflow sensor.

The amount of fuel injection is compensated for to improve engine performance under various operating conditions. The fuel is increased during warm-up, when starting the engine, during acceleration and hot-engine operation. The fuel is decreased during deceleration.

This system incorporates a mixture ratio feedback control designed to precisely control the mixture ratio to the stoichiometric (ideal) point. This system uses the heated oxygen sensor in the exhaust flow to check the air-fuel ratio. The ECM adjusts the injection pulse width according to the oxygen sensor voltage so that the mixture ratio will be within the range of the stoichiometric air-fuel ratio. This stage refers to the closed loop control. The engine will operate open loop mode which is when the ECM feedback control stops in order to maintain stabilized fuel combustion. These open loop mode conditions are as follows: deceleration, high-load operation, engine idling, oxygen sensor circuit malfunction, insufficient activation of heated oxygen sensor at low engine coolant temperature, and engine starting.

A mixture ratio feedback control system monitors the mixture ratio signal transmitted from the heated oxygen sensor. This signal is then sent back to the ECM to control the amount of fuel injection to provide basic mixture control as close to the theoretical mixture ratio as possible. However, due to certain manufacturing tolerances (mass air flow wire) or changes in operation (partially clogged fuel injector), the ECM can detect this operation and automatically compensates between this and the ideal ratios for a compromised fuel flow.

Two types of fuel injection timing is used – simultaneous and sequential. The simultaneous system sends fuel to all injectors at the same time and is used for engine starting and failsafe mode. The sequential system is used for normal engine operation.

Electronic Ignition (EI) System

This system uses all the same sensors as the MFI system except that is substitutes the knock sensor in place of the heated oxygen sensor. The ignition timing is controlled by the ECM in order to maintain the best air-fuel ratio in response to every running condition of the engine. The ignition timing is stored in the ECM in the form of a map. The ECM detects information such as injection pulse width and crankshaft position sensor signal which varies every moment the engine is running. Then responding to this information, ignition signals are transmitted to the power transistor which leads to the ignition coils firing. In addition to this, the ignition timing is revised by the ECM according to other data stored in the ECM at the following times: at starting, during warm-up, idle, acceleration, and during fuel shut-off.

The knock sensor retard system is designed only for emergencies. The basic ignition timing is pre-programmed within the anti-knocking zone, even under dry air conditions. Consequently, the knocking system doesn’t operate during normal driving conditions. However, if knocking occurs, the ECM retards the ignition timing to avoid knocking.

Idle Air Control (IACV) System

This system uses inputs from the crankshaft position sensor, engine coolant temp sensor, ignition switch, throttle position sensor, closed throttle position switch, neutral position/inhibitor switch, air conditioner switch, power steering oil pressure switch, battery and the vehicle speed sensor in its operation. The system automatically controls engine idle speed to a specified level. Idle speed is controlled through fine adjustments of the air by-pass in the IACV-AAC valve.

The crankshaft position sensor calculates actual engine speed and sends that signal to the ECM, which then controls the on/off time of the IACV-AAC valve so that engine speed coincides with the target value memorized in the ECM. The optimum speed is the lowest speed at which the engine can operate steadily during various engine conditions such as warm-up, during deceleration and engine loading.

Fuel Pump Control

The ECM activates he fuel pump for 5 seconds after the ignition switch is turned on to improve engine start-up. If the ECM receives a 120 degree signal from the crankshaft position sensor, it knows that the engine is rotating and causes the pump to activate. If the 120 degree signal is not received, the engine is assumed to be stalled and the fuel pump will cease operation. The ECM controls the fuel pump through the fuel pump relay.

Exhaust Gas Recirculation (EGR) System

This system precisely cuts and controls the port vacuum applied to the EGR valve to suit engine operating conditions. The ECM controls the EGR through the EGRC solenoid valve and will close the EGR valve under these conditions: low engine coolant temperature, engine starting, high-speed engine operation, engine idling, excessively high coolant temperature, mass airflow sensor malfunction.

Power Valve Control (Manual Transmission Only)

This system uses inputs from the mass airflow sensor, throttle position sensor, closed throttle position switch, ignition switch, crankshaft position sensor and the engine coolant temperature sensor. When the engine is running at low or medium speed under a heavy load, the power valve is energized by a signal from the ECM. This signal introduces the intake manifold vacuum into the power valve actuator to close the power valve. Under this condition, the effective suction port length is equivalent to the total length of the intake manifold collector. This long suction port provides increased air intake which results in improved suction efficiency and higher torque generation.

The surge tank and one-way valve are provided so that the power valve can be maintained in the fully closed position under heavy loads when the manifold vacuum is insufficient. In other conditions, the power valve control solenoid is de-energized, and the power valve actuator is vented into the atmosphere. This opens the power valve to two suction passages together in the collector. Under this condition, the effective port length is equivalent to the port provided independently for each cylinder. This shortened port length results in enhanced engine output with reduced suction resistance under high speeds.

Acceleration Cut Control

When the accelerator is fully depressed, the air conditioner is turned off for a few seconds if it is on in the first place. This system improves acceleration when the air conditioner is being used.

Valve Timing Control (VTC) System

This system uses inputs from the mass airflow sensor, crankshaft position sensor, engine coolant temp sensor, throttle position sensor, closed throttle position switch, vehicle speed sensor, and neutral position switch/A/T control unit. This system is utilized to increase engine performance. Intake valve opening and closing time is controlled, according to the engine operating conditions, by the ECM. The intake camshaft pulley position is regulated by oil pressure, which is controlled by the VTC solenoid valves.

This system is often thought to increase power at high engine speeds, sort of like Honda’s VTEC system. Actually, the opposite is true. Nissan designed the VE30DE as a high-strung powerplant which made all its power up high, then added the VTC and power valve systems to enhance low-end power. The VTCs energize to bump the low-end torque and horsepower up a bit, then return to normal at 4600rpm to return to increased high-end power.

The VTCs are only on to increase the low-end torque when these conditions are met: except at idle, engine coolant temp is below 110 degrees C or 230 degrees F, engine speed is below 4600rpm, engine load is high, selector level other than “N” or “P” positon for automatics. At any other engine condition, the VTCs are off for high-end horsepower.

Radiator Fan Control

The ECM controls the radiator fan corresponding to the vehicle speed, engine coolant temp, and air conditioner ON signal. The control system has a 3-step control (High/Low/Off).

Fail-safe System

The fail-safe system makes engine starting possible if there is something malfunctioning in the ECM’s CPU circuit. When the fail-safe system activates, the Malfunction Indicator Lamp (check engine light) lights up to warn the driver. When the fail-safe system is operating, many system operations are controlled under certain limitations.

Fuel injection: simultaneous multiport fuel injection system timing

Ignition Timing: Ignition timing preset value is fixed at the factory

Fuel pump: Fuel pump relay is on when engine running and off when engine stalls

IACV-AAC valve: Full open

Radiator Fans: Radiator fan relays on

Activation of the fail-safe system is canceled each time the ignition switch is turned off. The system is reactivated if all of the activating conditions are satisfied after turning the ignition switch back to on.

Mass Airflow Sensor malfunction: If the MAF voltage is below the specified value, the ECM senses a mass airflow sensor malfunction. In this case, the throttle position sensor substitutes for the mass airflow sensor. Although the MAF is malfunctioning, it is possible to start the engine and drive. However, engine speed will not rise more than 2400rpm.

Engine Coolant Temp Sensor malfunction: When engine coolant temp sensor output voltage is blow or above specified value, water temp is fixed at the preset value as follows:

Ignition switch is turned to On or Start: 40 degrees C or 104 degrees F

More than 6 minutes after ignition On or Start: 80 degrees C or 176 degrees F

Except as shown above: 40-80 degrees C or 104-176 degrees F (depends on time)

Knock Sensor malfunction: When the output signal of the knock sensor is abnormal, the ECM determines it to be malfunctioning and will retard the ignition timing according to operating conditions.

Throttle Position Sensor malfunction: When the output signal of the TPS is abnormal the ECM judges it to be malfunctioning and starts using the closed throttle position switch. Hence, the ECU only knows when the throttle plate is closed, and when it is open, but it doesn’t know the degree of which the throttle plate is opened. The result of this is a normal idle but poor acceleration.