General Precautions of EFI System Maintenance
F-94
124. P2178 Air-Fuel Ratio for Self-Learning Value under Closed-Loop Control
Exceeding Lower Limit (Medium Load Area)
Description about Principle and Malfunction Cause:
In order to optimize the integrated transformation efficiency of catalytic converter to HC, CO, and NOx, the
air-fuel ratio of the mixed gas shall be controlled at 14.7:1. If it is found the deviation in manufacture of parts,
the sedimentation of colloidal matters in gasoline on the fuel injector, the air intake pipeline, or the back of
valve, and air leakage exists with intake and exhaust system, all these factors will give rise to a deviation from
14.7:1 in the air-fuel ratio to different degrees (rich or dense), which will lead to deteriorated emission and
reduction in engine performance.
The engine control system is able to make amendments and self-learning on fuel injection volume according
to the degree and characteristic of deviation in air-fuel ratio. The self-learning of deviation in air-fuel ratio is
divided into “Self-learning in Small Load Area” and “Self-learning in Medium Load Area”. The system will
determine it to be the malfunction of rich mixed gas, when self-learning in medium load area reaches the
lower limit value set by the system (rich mixed gas, and the system continuously decreasing the fuel injection
volume up to the minimum value).
Malfunction Diagnostic Guide:
Required Equipment: (Diagnostic Instrument with EOBD Diagnostic Function)
Step I: Use diagnostic instrument to read the malfunction information
Read Result I Read Result II
MIL Lamp On P-CODE Present MIL Lamp Off P-CODE Present
P2178
P2178
Maintenance tips:
The malfunction has been confirmed, and the
following problems may possibly exist
1) Colloidal matter present inside fuel injector
slowing down the turn-off of fuel injector and
cleaning required
2) Air leakage with intake valve
3) Deviation in valve clearance
4) Deviation in parts of engine
5) Fuel pressure too high
Maintenance tips:
The malfunction has not bee finally confirmed, and
wait for system to fulfill diagnosis.
125. P2187 Air-Fuel Ratio for Self-learning Value under Closed-Loop Control
Exceeding Upper Limit (Low Load Area)
Description about Principle and Malfunction Cause:
In order to optimize the integrated transformation efficiency of catalytic converter to HC, CO, and NOx, the
air-fuel ratio of the mixed gas shall be controlled at 14.7:1. If it is found the deviation in manufacture of parts,
the sedimentation of colloidal matters in gasoline on the fuel injector, the air intake pipeline, or the back of
valve, and air leakage exists with intake and exhaust system, all these factors will give rise to a deviation from
14.7:1 in the air-fuel ratio to different degrees (rich or lean), which will lead to deteriorated emission and
reduction in engine performance.
The engine control system is able to make amendments and self-learning on fuel injection volume according
to the degree and characteristic of deviation in air-fuel ratio. The self-learning of deviation in air-fuel ratio is
divided into “Self-learning in Small Load Area” and “Self-learning in Medium Load Area”. The system will
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