Symptom: a Mercedes-Benz C280 sedan paragraph 95, in the process of moving, accelerating weakness, close to full throttle, the speed can not exceed 3Okm / h, even when the high-speed failure rarely occurs, mainly after the stop, start, and then accelerate process and intermittent. Usually turn off the engine after the ignition switch is turned off, then turn the ignition switch, start the engine, the fault disappears, accelerate normal cars with twenty-three days failures will reproduce. This car had some manufacturers repeatedly checked and replaced the temperature sensor, crankshaft position Multidiag Pro sensor and oxygen sensor straight and other components, the failure was not ruled out.
Maintenance process: using red box SCANNER diagnostic check, enter the OBD-Ⅱ diagnostic mode, first read the engine system fault code is displayed as PO000, no fault codes; then enter the numerical analysis, start the vehicle road test, driving all normal at the beginning of and then brake, parking, hard acceleration times of trial and error approach to make a failure, road test more than one hour later, the failure to reproduce the phenomenon, the speed throttle in the end is still below 3OKm / h, and then read the red box SCANNER no fault is still P0000 fault, the analysis of the value found two clues:
(1) when the normal driving, i.e. after starting IGNADV ignition advance angle is 5.5 °, when the engine is 300Or / min to 38 °, normally a strong acceleration; When a fault occurs, idling, acceleration of ignition advance angle showed a negative angle, and sometimes as -6 °, sometimes -2 °, but as long as the ignition switch off, turn off the engine, and then start the ignition advance angle back to 5.5 °, accelerate to normal.
(2) during normal driving, the fuel control system FUEL SYS normal value changes, cold car for OL (open-loop control), hot car for CL (closed loop control), hard acceleration display OL DRV, which is a positive instruction is executed by the engine automotive diagnostic tool computer normal program concentrated injection, when the failure occurs, hard acceleration weakness, the display OL FLT, which is the meaning of the fuel control system damage.
Impact of delayed ignition timing signal mainly KS knock, ECT cooling water temperature, IAT intake air temperature, CKP crankshaft position sensor signal. After testing these signals were normal, but which does not make a bad signal the engine control computer after normal driving twenty-three days before the implementation of the standby function, so we must consider the possibility of damage to the computer. Originally open-loop control, closed-loop control, gear reduction oil, gear oil and rapid acceleration off-enriched fuel trim, etc. These models are controlled by the engine computer. Symptom reflect a sudden change in motion car fuel correction mode, a sudden change in the ignition advance angle, indicating that the engine computer has poor control. This failure to completely rule out the replacement engine control computer.
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