Fuel System Monitoring

FUEL SYSTEM MONITORING

GENERAL DESCRIPTION

Mixture Pilot Control
The air mass taken in by the engine is measured. The signals are used to calculate an Injection signal. This mixture pilot control follows rapid load and speed changes.

Lambda-controller
The ECM-controller compares the oxygen sensor signal of the sensor upstream of the catalyst with a reference value and calculates a correction factor for the pilot control.

MONITORING STRUCTURE







Adaptive pilot control
Drifts and faults of sensors and actuators in the fuel delivery system, as well as unmetered air leakage, influence the pilot control. This causes increasing deviations of the air/fuel ratio. The adaptive pilot control effects the controller correction in three different ranges.

Ranges of Learning Correction Coefficients tra, fra and dtv







Lambda deviations in range 1 are compensated by an additive correction value multiplied by an engine speed term. By this an additive correction per time unit is created. Lambda deviations in range 2 are compensated by a multiplication factor. A combination of all three ranges will correctly be separated and compensated. Each value is adapted in its corresponding range only. Each adaptive value corrects the pilot control within the whole load/speed range. At the next start the stored adaptive values are included in the calculation of the pilot control just before the closed loop control becomes active.

Abbreviations for the fuel delivery system

Qu1 upper air flow threshold range 1
NU1 upper engine speed threshold range 1
TLARN upper engine load threshold f(n) range 2
TLL2 lower engine load threshold range 2
tra additive per time unit learning correction coefficient (range 1)
TRADN lower diagnosis threshold of tra
TRADX upper diagnosis threshold of tra
fra multiplicative learning correction coefficient (range 2)
FRADN lower diagnosis threshold of fra
FRADX lower diagnosis threshold of fra
DTVDN lower diagnosis threshold of dtv
DTVDX upper diagnosis threshold of dtv
QL2 lower air flow threshold range 2

# Range III not activated

Diagnosis of fuel delivery system
Faults in the fuel delivery system can occur which cannot be compensated by the adaptive pilot control. If the adaptive values leave a predetermined range, or if the adaptive values are outside a plausible range, then the MIL is illuminated and a fault is stored.

Flow chart of the fuel system monitoring function # Range III not activated