Failure phenomenon: a 2003 annual Honda Odyssey wagon, mileage 180 000 km. Users reflect the car unstable idle speed, high fuel consumption. Failure nearly two weeks, the idle valve cleaning process has been done, the injector and the throttle, and the replacement of the spark plug, but the fault persists.
inspection and analysis: First, fault maintenance staff confirm. This car is slightly difficult to cold start, the normal temperature, engine shake clear, idle instability, but the normal acceleration, the fault does not light.
FIG 1
of the idle valve, the fuel injection amount, fuel injection spray, cylinder pressure, timing, and the valve clearance for catalytic converters the inspection found no abnormalities. HDS dedicated fault diagnostic data flow measurement (FIG. 1), found that the intake pressure fluctuations and high MAP, fuel trim ST unstable, unstable idling control IAC. Alternatively idle valve, an intake pressure sensor and an oxygen sensor, could not bear fruit.
FIG. 2
carefully observe data flow when idling (FIG. 2), we found MAP, EGR high signal values. MAP normal value should be 29 kPa, 45 kPa current value during idling. EGR during idling normal value should be 1 V, the current value is 1.89 V.
3
whether the EGR system failure related to it? First look at works EGR system (Figure 3). EGRmdash; mdash; exhaust gas recirculation system is exhaust gas of the engine to reduce nitrogen oxides (NOx) is provided. Exhaust gas introduced into the intake manifold, and incorporated into the mixed gas to reduce combustion temperatures. When the ECM determines the circulation amount of EGR, EGR control solenoid valve is opened, the intake manifold vacuum acting on the poppet EGR valve diaphragm, the diaphragm connected to the opening, the exhaust gas flowing into the exhaust pipe into the intake manifold. EGR valve lift is equipped with a sensor, whose output voltage is proportional to the lift amount. It is the actual lift amount of feedback to the ECM, the target lift amount for comparison, a closed loop control system. To ensure the performance of the engine, when cold idling, deceleration and high load, the EGR is not working, then lift sensor (no-lift) Voltage value should be 0.95 ~ 1.50 V.
Figure 4
According to the principle of the analysis, when the engine is idling EGR valve should be closed, but this time the data of the EGR valve is open, which is clearly unusual. Find relevant information in accordance with the EGR valve position (FIG. 4), remove the EGR valve (FIG. 5) check valve bottom found more coke, refitted after washing, a significant improvement in engine idling.
Figure 5
troubleshooting: After replacing the EGR valve, failure to completely eliminate. Observation data stream (FIG. 6), MAP, EGR data properly and smoothly.
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reviewed: fault diagnosis to master the normal value at each measurement point, in order to identify problems in a timely manner. For abnormal data to be analyzed carefully, and strive to find out the cause of the malfunction. This case means at the beginning of the scan tool has been measured to high MAP, ST, IAC unstable, but there is no time for numerical analysis, but replacing the pressure sensor, an oxygen sensor and the idle valve according to take a detour surface phenomenon. If you think inlet leak from the high MAP, lift high at idle from the EGR valve, I think this is the root cause of the leak, then it is entirely possible by means of numerical analysis to find the point of failure.
(Lide Guo, Fu Yanwei)