Toyota Costa [Case Analysis of Two Faults of Toyota Crown and Costa]
Inspection and analysis: the maintenance personnel detected the engine control unit, and there was no fault code. Observing the data flow, 1 cylinder long-term fuel is revised to 19.5%, which is too high. This should be related to the high fuel consumption of the car.
When the fuel injection control state is in a closed loop, the engine control unit keeps the air-fuel ratio of the mixture in an ideal state at any time by correcting the fuel injection amount. The high fuel correction indicates that if the fuel injection is not corrected, the concentration of the mixture will be lean. So what is the reason for the high fuel correction? Considering that the problem occurred after replacing the air-fuel ratio sensor, we decided to start the inspection here.
Switch the air-fuel ratio sensor of 1 cylinder with the air-fuel ratio sensor of cylinder 2 (1 and the sensor of cylinder 2 are exactly the same). Observe the data flow of the engine after adjusting the air-fuel ratio sensor. After the engine was started, the data of two cylinders changed obviously. 30s from the start time, the long-term fuel correction value of 1 cylinder decreased from 19.5% to 14%, and the short-term fuel correction value increased from-1 .8% to -6.3% (Figure/kloc-0 The long-term fuel correction amount of double-row cylinders increased from 4.6% to 19.5%, and the short-term fuel correction amount decreased from 19.5% to 12.5% (Figure 2).
Judging from the signal changes after sensor adjustment, the reason for the high fuel correction is the poor signal response characteristics of the air-fuel ratio sensor (Figure 3). This can be judged from the phenomenon that the short-term fuel correction decreases after the installation of 1 cylinder air-fuel ratio sensor in cylinder 2. The judgment is based on the low sensitivity of the air-fuel ratio sensor, so that the engine control unit always gets the error message that the mixture is too rich. This error message will cause the engine control unit to continuously issue instructions to reduce the fuel injection quantity. In addition, due to the decrease of fuel injection quantity, the long-term fuel correction quantity finally increases.
In order to further determine whether the fuel consumption of the car is high. Find a normal vehicle for comparison. The results show that the air intake and fuel injection of the faulty vehicle are slightly larger at the same idle speed (table 1). It can be seen that the quality of the newly replaced air-fuel ratio sensor does have problems.
Troubleshooting: After replacing the air-fuel ratio sensor, compare it with the normal vehicle again. At the same idle speed, the air intake and fuel injection of the two cars are the same. Test run and confirm troubleshooting.
Fault 2
Symptoms: A 2007 Toyota Costar bus in Sichuan, equipped with 2.7L2TR-Fe engine, has a mileage of 70,000 kilometers. The user reported that the engine fault light of the car was on, and the problem could not be solved after repeated maintenance.
Inspection and analysis: the maintenance personnel detected the engine control unit, and the fault code was p 0 17 1- The mixture was too lean. Check the oil supply and ignition system, everything is normal.
After the engine control unit obtains the information of lean mixture through the oxygen sensor, it will automatically increase the fuel injection quantity to maintain the correct concentration of the mixture. However, when the fuel injection quantity increases more than 35% of the normal fuel injection quantity, the closed-loop control state of the fuel injection control system will be disconnected, and the fault code of lean mixture will be generated. The current control state shows that there must be some factors in the fuel injection control system that make the air-fuel ratio of the mixture out of control.
First of all, fault diagnosis is carried out in a simple way. Replace the air flowmeter, and the fault still exists. Check the air filter to see that it is new and clean, so it doesn't need to be replaced. Check the exhaust system to ensure smooth exhaust. When the air-fuel ratio sensor is replaced, the state of the mixture does not change. Next, clear the fault code and analyze the data.
Let the engine run at idle speed and observe the data related to mixture control (Figure 4). When the idle speed increases to 2 13 1r/min, the sum of long-term and short-term fuel corrections has exceeded 35%. At this time, although the fuel control is still in a closed-loop state, it has exceeded the critical point of switching to open-loop control. Put forward gear to accelerate the vehicle. When the engine speed reaches 1057 r/min and the load rate reaches 56%, the fuel control is turned into an open-loop state (Figure 5), and the fault light is on at the same time.
Observing the data of engine at idle speed and partial load, it is found that they have a similar abnormal phenomenon-low air pressure in front of throttle. In both cases, the pressure in front of the throttle should be close to atmospheric pressure, but at this time it is nearly 30kPa lower than atmospheric pressure. The engine corrects the data of the air flowmeter according to the air pressure in front of the throttle. Obviously, if there is an error in the air pressure data before the throttle, then the corrected air flow data must be too small, which is the direct cause of the lean mixture. So, what caused the air pressure data before the throttle to be wrong?
Looking at the circuit diagram, it is found that the car is not equipped with an intake pressure sensor alone. It is speculated that the intake pressure sensor should be calculated from the air flow and throttle opening. In order to confirm this, remove the air filter and open the air inlet channel in front of the air flowmeter to make the pressure on the sensor equal to the atmospheric pressure. Let the engine idle and make the throttle opening close to the value before removing the air filter. At this time, it is observed that the air pressure in front of the throttle valve is close to atmospheric pressure (Figure 6), the air flow and idle speed are obviously increased, and the long-term and short-term fuel correction amounts are close to ideal values. This shows that the problem lies in the air filter, which brings additional intake resistance to the intake system and makes the air pressure data in front of the throttle valve wrong.
Troubleshooting: Test run after replacing the air filter. When the vehicle accelerates, the air pressure in front of the throttle valve does not drop significantly (Figure 7), indicating that the new air filter works completely normally. Repeated trial operation, confirm that the fault is completely eliminated.
Review and Summary: After the event, the performance of two kinds of air filters was compared and tested. The test found that the fuel consumption of vehicles increased by nearly 25% when using inferior air filters. This case reminds maintenance personnel that the role of air filter in engine control system cannot be underestimated.