Case 1
Failure phenomenon: a 2009 1.6 L models Beijing Hyundai Elantra sedan, mileage 14000 km. According to reflect the user, the normal vehicle starter, with occasional flame, low-speed slow acceleration, / h or higher and the acceleration is normal when the traveling speed reaches 50 km, engine failure does not light up.
Check Analysis: Use first fault diagnostic detection, no fault code storage engine system. Road test and the same user description, but is generally confirmed stall occurs when the accelerator pedal is released after the end of acceleration, and engine speed fluctuations at times before the stall. Maintenance personnel without measuring fuel system pressure, fuel pump is determined empirically fault, so the replacement fuel pump core, a simple test feeling after troubleshooting, then the user to observe the PDI. The next day the vehicle into the plant again, the fault persists.
The author next car, using the first fault diagnostic check engine system, this has been detected a fault code P0068 (MAFS / MAPS relationship error). The engine control unit ECU determines an idle throttle position sensor by the TPS (throttle closed), part-load, the acceleration / deceleration and wide open throttle operating conditions, the air flow meter MAFS or intake manifold pressure sensor signal MAPS and TPS adjusting the duration of fuel injection signal and an ignition timing. If the input value is lower or higher than the TPS input limit value MAFS / MAPS above 300 s, ECU will record the fault code P0068, but not light warning light with TPS, MAFS / MAPS ECU malfunction and possible fault cause or related line connection is bad.
FIG 1
For the car, the intake system is used in the MAPS, without the use of MAFS. Connection failure diagnostic check the incoming data stream, the opening degree of the throttle position sensor was observed and the voltage changes at light throttle pedal, no abnormality. Start the engine, there is no jitter idle state, only after the rapid acceleration of the engine speed fluctuates more powerful, and exhaust comparison smoked. At idle, the engine several groups observed important data stream (FIG. 1), the data flow analysis can be found doubt: oxygen sensor’S B1 / SI feedback voltage is too high, hardly moves around 0.8 V, belonging to the state of the combustible mixture concentrated rage; fuel correction value -26.3%, severe than the standard value (plusmn; 10%), belonging to reduce spray oil; the MAP sensor voltage is 2.2 V, the voltage in the normal idling state should be around 1.2 V, at which point the opening degree of the throttle position sensor is 0.0%, the voltage was 0.3 V, the normal value, the engine speed is 648 r / min, is in an idle state. Whereby preliminary conclusion can be drawn, the MAPS in the engine idling state of the engine control unit to the signal exceeds the standard many values, fuel injection pulse width after the engine is correspondingly increased, but at the moment the throttle valve is closed, the air to give less than the corresponding increase in mixture is too thick, the feedback voltage to the oxygen sensor in the engine control unit to display a very rich state, the ECU will be corrected by reducing the amount of fuel, so it was -26.3% of the fuel injection quantity correction. Thus failure phenomenon also reasonable, weak acceleration at low speeds, because the voltage signal to the ECU MAPS allowed, due to the mixture too thick. When the vehicle speed rises to a certain extent, with the increase of the throttle opening degree, the air entering the engine to meet the error signal is supplied MAPS under fault conditions, even slight discrepancies, because of high vehicle speed or at high load conditions and the negligible. When the accelerator pedal is released, closing the throttle, the engine enters the idling condition, and the feedback signal to the ECU MAPS case the signal is not in the idle state, the engine speed fluctuation arises even stall phenomenon. Mixture is too thick, incomplete combustion, it will surely be excessive exhaust smoke people.
After the above determination analysis, which can be identified in the fault MAPS.
FIG. 2
troubleshooting: After replacing MAPS, observed again the standard value of the engine MAPS data stream (FIG. 2), are restored to the idle state in , road test engine as usual.
Case 2
Failure phenomenon: a 2009 models Beijing Hyundai Yuet 1.6 L sedan, mileage 30000 km. Say users, sometimes cold start of the vehicle engine rotation speed does not drop down, the engine braking rpmSpeed fluctuations can sometimes be increased to 1 500 r / min or more, if the flame immediately started again, the engine speed can be returned to normal. This phenomenon will not occur every day, but there will always be several times a week, has a relationship with the temperature of the engine, the state will not be hot car, vehicle acceleration performance and found no abnormalities.
check analysis: the advent of the car has some chance of failure, the vehicle for the first time to shop maintenance staff can not capture the failure phenomenon, so in accordance with the general solution to the problem, the first of the basic vehicle checks. Each system has no fault code storage, the main data stream of the engine system are normal. Check the vacuum booster pump and a hose connected to the phenomenon of air leakage is not checked and the main parts of the engine and the main body of the engine wiring harness connector, no problems.
A few days later, the same fault as the user again into the plant. I repeated step after the engine is started in the morning and observing the brake pedal of the engine speed, the cold car to 1 200 r / min or so, hot car was 800 r / min or so, everything is normal. After several cold test, the failure phenomenon, as long as the brake pedal, the engine speed will fluctuate time, an amplitude of approximately 2 00 r / min, then down to 900 ~ 1 200 r / min, and this when the engine has been working for some time, has reached normal operating temperature, after the end of the high back to normal idle speed should be 750 ~ 800 r / min, but when the engine speed is 900 ~ 1 200 r / min. Fault detection is the use of diagnostic trouble code is not stored, the main observation of dynamic data flow of the engine system: 30.5% duty cycle idle valve; coolant temperature sensor 87 deg.] C; degree of opening of a throttle position sensor 0.0%, a voltage 0.3 V; the engine rotational speed 1 237 r / min; MAP voltage of 1.4 ~ 1.9 V, the intake pressure 32 ~ 48 kPa, with the rhythm and fluctuate the rotational speed of the engine brake pedal constantly changing. In this analysis, because the fluctuation of the engine speed caused by an anomaly in the signal of the MAPS, the analysis will focus on the aspects of the brake. Thus quick disconnect hose vacuum booster pump in an idle operation state is then blocked, the brake pedal, fluctuation of the engine tachometer is observed after one stop at 1 000 r / min does not move a position near, orNot return to normal idle speed. It seems the brake pedal can increase the chance of failure, but a failure of the brake is not directly related, certainly not caused by the braking area.
Let’s look at a fault diagnostic apparatus MAPS data voltage of 1.46 V, pressure of about 42 kPa, I feel these data some of the problems, but because of the speed and the load pressure of the engine in the intake manifold relationship, (engine rotational speed 800 r / min, the opening degree of a throttle position sensor 0.0%, the voltage 0.3 V) data can not be simulated by comparing the data of the other vehicle in the normal state of the vehicle such that only parts replacement experiment.
Figure 3
troubleshooting: After replacing the MAPS (FIG. 3), the engine can be seen that normal data stream. Due to the fault will disappear after each restart, it can only track return visits to determine whether troubleshooting. A week later came the message user feedback, since the replacement of MAPS, engine speed fluctuation there have been no failures, and it feels smoother and more fuel, thus determining the fault completely resolved.
summarizes Description: Although the fault has been resolved, but Case 2 was worth considering. Although the same for MAP’s fault, but Case 2 Symptoms appear contingency and particularity increases the difficulty of analysis and judgment, and furthermore no fault codes and no special status in the standard data stream can refer to, but also to diagnose some not start . Recalling the repair process must start MAPS up the structure and working principle analysis, it may explain why MAPS of failure will cause the above-mentioned special malfunction.
the intake manifold pressure sensor detecting MAPS is an indirect way to the engine intake, also called a pressure type or D-type, usually installed in the intake manifold buffer. The structure has a silicon diaphragm MAPS reference pressure chamber, for detecting the absolute pressure inside the buffer (negative pressure) and sends an analog voltage signal proportional to the pressure ECU. If MAPS silicon diaphragm due to the quality problems caused by the deformation of the vehicle in a poor return cold state, but will consume an intake manifold negative pressure when the brake pedal, pressure change, change is less than the pressure normally MAPS pressure to affect changes, but this time in the cold start itself MAPSPoor return after deformation, resulting in the brake pedal silicon diaphragm pressure sensor of the intake air becomes large deformation is further based on the original, the voltage rises, the engine speed will fluctuate. Turn off the heat and, since the intake manifold negative pressure is completely eliminated, the intake pressure sensor diaphragm return the magnitude of change is relatively large, the return light can be overcome failure of the silicon diaphragm. When starting the engine again, the previous since the silicon diaphragm deformation returned to normal, it can be accurately feedback pressure inside the intake manifold, and also to restore the vehicle to a working state. Only such an analysis can explain the phenomenon of the failure from the principle.
(Beijing Hyundai Auto Sales & Service Co., Ltd. Hubei Xin Rui Zhougui Ming)