ME-SFI driving function

P07.61-0376-01

t1 Start enrichment (duration e.g. 2 seconds)

t2 Post-start enrichment (duration e.g. 2 seconds)

t3 Warming-up phase (duration in accordance with coolant temperature)

A Enrichment rate

a Start

b End of start, start of deactivation of post-start enrichment

c End of post-start enrichment, commencement of warming-up control

Idle speed control

When the engine is running at idle speed, it is primarily the efficiency and the idling speed which determine the fuel consumption. For this reason, it is beneficial to achieve the lowest possible idling speed.

Idle speed should be set, however, so that it does not drop excessively and, as a consequence, causes the engine to run irregularly or even to cut out, no matter what conditions exist, such as loads applied from the vehicle electrical system, air conditioning switched on, gear engaged on models with automatic transmission, power steering turned to full lock etc.

This correction is achieved by varying the ignition angle control which is activated by the control module. The idle speed control has to create a balance between the engine torque which is output and the engine load, and thus to ensure a constant engine speed.

In addition to the signal supplied by the crankshaft position sensor, the idle speed control also requires information from the pedal value sensor and from the coolant temperature sensor in order to be able to detect the idle speed condition. The control module defines an air mass in line with the data detected, and this is subsequently corrected in the closed-loop control mode.

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The input signals supplied by the air conditioning system or the automatic transmission, if fitted, ensure improved precontrol and thus assist the idle speed control.

Warming-up enrichment

Fuel precipitates against the cold parts of the engine during the warming-up phase.

This results in a leaner fuel mixture. The fuel-air mixture is enriched in order to compensate for this.

The additional quantity of fuel is metered to the engine in line with the map stored in the control system.

This is achieved by appropriately extending the injection time.

Warming-up enrichment is dependent on:

 Coolant temperature

 Intake air temperature

 Engine speed

 Engine load

 Idle speed/part load

 Correction programming with the HHT

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Part load/full load operation

When the engine is operating in the part load and full load, the respective quantity of fuel is metered to the engine in line with the map. An adjustment range of more than about 55 % at pedal value sensor, is defined as full load; approx. 10 - 55 % as part load.

Part load operation: together with the lambda control, ensuring optimum exhaust emission levels and good fuel consumption when the engine is at operating temperature.

Full load operation: ensuring maximum engine torque when the throttle flap is fully open. The injection time is extended accordingly for this purpose.

The fuel quantity is dependent on:

 Coolant temperature

 Intake air temperature

 Engine speed

 Engine load

 Lambda control

 Correction programming with the HHT

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Acceleration enrichment

If the throttle flap is opened rapidly when accelerating, a leaner mixture is produced for a short time. This may then result in jerky acceleration.

In order to prevent this, an additional quantity of fuel is metered to the engine in line with the map. The injectors are operated with additional pulses for this purpose.

Acceleration enrichment is dependent on:

 Coolant temperature

 Load change rate

 Engine speed

 Engine load

 Correction programming with the HHT

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Inertia fuel shutoff

Inertia fuel shutoff is intended to improve the emission characteristics in the deceleration mode, to increase the braking action of the engine and to reduce fuel consumption.

The ME-SFI control module shuts off the fuel injectors in the deceleration mode if

- coolant temperature > 50 °C

- engine speed > 1350 rpm

- throttle flap closed (recognized from actual value potentiometer of throttle flap)

- cruise control OFF

The fuel injectors are activated again once

- engine speed < 1100 rpm

- throttle flap opened (detected from actual value potentiometer throttle flap)

- cruise control ON

The ignition timing is briefly retarded in order to prevent a sudden increase in torque when the fuel injectors are activated again after inertia fuel shutoff.

Limiting maximum engine speed

The engine speed limiter is designed to protect the engine and drive train from excessive revs and to limit the maximum speed of the vehicle.

Engine speed is limited to 6200 rpm and, a further 10 seconds, is reduced to about 6000 rpm in order to protect the engine from the consequences of impermissibly high revs.

The ME-SFI control module detects the engine speed from the signal supplied by the crankshaft position sensor. The speed of the engine is limited by the ME-SFI control module by shutting off the fuel injectors.

Torque converter protection in selector lever position P/N

Engine speed is limited to approx. 4200 rpm in selector lever positions P and N (no power transmission) in order to protect the torque converter from excessively high static internal pressure.