Fuel injection System Function
The fuel is injected via electromagnetically controlled injectors. Each cylinder is assigned an injector, which sprays a precisely metered quantity of fuel onto the intake valve. The injectors are connected directly to positive and are actuated by ground impulses from the engine control module (N3/4).
The injectors are actuated in ignition firing order sequence. Depending on engine load and rpm, the injector spray timing is advanced accordingly and upon opening of the intake valve, the fuel is mixed with intake air and drawn into the combustion chamber. The engine control module calculates injection time (duration) according to engine operating conditions. The injected fuel quantity is determined by the opening time of the injectors.
Minimum Injected Fuel Quantity
The engine control module (N3/4) determines the minimum injected fuel quantity according to operating conditions and the following:
- Engine speed,
- Throttle valve position (via CAN).
- Air mass.
Start Control
To improve cold starting of the engine, additional fuel is injected during cranking according to the engine coolant temperature. The increased fuel quantity is achieved by an increase in injection time.
Fuel Injection Synchronization
To properly coordinate the fuel injection timing for each cylinder, the injection sequence must be synchronized. Synchronization occurs during cranking. The camshaft position sensor (L5/1) signal is used to determine ignition TDC of cylinder 1.
The following information is processed in the engine control module (N3/4) for fuel injection synchronization:
- Engine speed/crankshaft position,
- Cylinder 1 TDC camshaft position.
After-start Enrichment
After starting a cold engine, enrichment of the fuel mixture is required for a short period.
Warm-up Enrichment
The engine receives the exact amount of fuel depending on engine coolant temperature. The injector duration is increased accordingly.
Acceleration Enrichment
In order to maintain a good transition during acceleration, the injectors are actuated with additional impulses.
Wide Open Throttle (WOT) Enrichment
The WOT enrichment is determined by the engine control module (N3/4) at a throttle valve angle greater than 80°.
Deceleration Shut-off
Engine speeds at shut-off and turn-on of injectors
Injectors shut-off > 1600 rpm
Injectors turned-on < 1200rpm
Deceleration shut-off is dependent on:
- Engine speed,
- Closed throttle position (CTP) recognition (via CAN),
- Throttle valve position (via CAN),
- Engine coolant temperature,
- Vehicle speed signal (via CAN).
Engine Speed Limitation
In order to protect the engine and the powertrain, the fuel/air mixture is leaned out or the fuel injection is interrupted, and the ignition timing is retarded at specific engine speeds and operating conditions. The rpm limitation originates from the engine control module (HFM-SFI). The following information is processed in the control module:
- Engine speed
- Transmission range (TR)
- Vehicle speed signal (VSS)
a) Torque converter protection: When the selector lever is in PNP, the torque converter is subject to increased internal static pressure. Therefore, in PNP, at vehicle speeds less than 3 mph (5 km/h), the engine speed is limited to 4000 rpm.
b) Powertrain protection: To reduce the consequences of extreme acceleration (take-off), the engine speed is limited to 3500 rpm for one second when engaging a transmission range at vehicle speeds less than 18 mph (29 km/h).
c) Maximum engine speed limitation:
Intake camshaft adjuster (transmission range selected and medium load):
Acronym
PNP = Park/Neutral Position
Maximum Vehicle Speed Control
The maximum vehicle speed is limited to 155 mph (250 km/h). If this speed is exceeded, the fuel/air mixture is leaned out and the camshaft timing is adjusted in direction "advanced".
Secondary Air Injection
Secondary Air Injection:
The secondary air injection function is controlled by the engine control module (N3/4). The secondary air injection pump switchover valve (Y32) and secondary air injection pump clutch (Y33) are actuated by the control module depending on engine coolant temperature. Secondary air injection occurs after starting the engine with the engine coolant temperature between +10 and +40 °C (50 and 104°F). At wide open throttle (WOT) or at engine speeds exceeding 3600 rpm, secondary air injection is turned off. The secondary air injection pump is activated for a maximum of 120 seconds after starting the engine (as long as the Lambda control is inactive). The following information is processed by the engine control module (N3/4):
- Engine coolant temperature,
- Engine speed,
- Lambda control inactive.
Exhaust Gas Recirculation (EGR)
Secondary Air Injection:
The EGR system is regulated by the engine control module (N3/4) according to engine speed and load signals. With the closed throttle position (CTP) contact open and a coolant temperature above 48°C (118°F), the EGR switchover valve receives an activation signal from the control module.
The following information is processed by the engine control module (N3/4):
- Engine speed,
- Air mass,
- Engine coolant temperature.
Idle Speeds
Gear engaged In neutral
600 ±50 rpm 700 ±50
Charcoal Canister Purging
In order to reduce fuel vapor discharge into the atmosphere, a evaporative emission (EVAP) system is installed. Fuel vapors stored in the charcoal canister are purged at engine coolant temperatures above 80 °C (176°F) via the purge switchover valve (Y58/1) and combusted in the engine (except during deceleration). The engine control module processes the following information for this purpose:
- Engine speed,
- Air mass,
- Engine coolant temperature,
- Intake air temperature.
Purge quantity is regulated by the purge switchover valve (Y58/1) which is controlled (cycled) by the engine control module with rpm dependent frequencies of 5,10 or 20 Hz. Each cylinder is thereby supplied with equal amounts of fuel vapor. The purge quantity is determined by the constant opening and closing of the purge switchover valve at various on/off durations.
Transmission Upshift Delay
In order for the catalytic converter to reach its operating temperature faster, the closed throttle and partial load upshifts are delayed for a maximum of 150 seconds after engine start at engine coolant temperatures between -40 to + 100 °C . Therefore, the upshift takes place at a higher engine rpm. The closed throttle 3 to 4 upshift is delayed up to 34 mph (55 km/h).
The delayed upshift is controlled by the engine control module (N3/4) via the upshift delay switchover valve (Y3/3) and the upshift delay vacuum element (98) (see group 14). The engine control module processes the following information for this purpose:
- Engine coolant temperature (ECT),
- Vehicle speed signal (VSS),
- Transmission range (TR),
- Elapsed time after start.
Camshaft Adjustment
Condition: transmission range in a drive gear and partial throttle.
In transmission range "P" or "N" the camshaft advancement occurs at 3000 rpm.
Fuel Shut-off Due To Ignition Failure
To protect the TWC from overheating, the injector of the affected cylinder or those of all cylinders will be switched off in case of ignition failures (50 consecutive ignitions).
If the ignition fault is no longer present, the fuel is switched on again if:
- 255 consecutive ignitions were successful,
- Vehicle was in deceleration mode,
- Engine speed of approximately 2500 rpm has been exceeded.
The following faults are recognized by the engine control module via primary current monitoring:
- Ignition final stage in engine control module defective,
- Ignition coil defective or open circuit,
- Short circuit (also on high voltage side),
- Defective spark plug(s).
The engine control module processes the following information for this purpose:
- Primary voltage (combustion voltage, combustion duration),
- Camshaft position, TDC cylinder no.1,
- Engine speed/ignition circuit recognition.
Fuel Safety Shut-Off
For safety reasons, the engine control module (N3/4) is connected to the switch contacts in the electronic accelerator or cruise control/idle speed control actuator (M16/1 or M16/2) via a separate wire. At idle and while driving, the switch contacts send a positive (+) signal to the control module.
If, due to malfunction, the throttle valve opens further than the position specified by the accelerator pedal and the cruise control is not engaged, a safety contact in the actuator (M16/1 or M16/2) sends a ground signal via the electronic accelerator or cruise control/idle speed control module (N4/1 or N4/3) to the engine control module (N3/4). This will switch the injectors off, which reactivate only after the engine speed drops below 1200 rpm.