A 2010 Buick Yinglang, engine model: LDE1.6L, driving range of 165090km. The car was due to damage to the thermostat caused by high water temperature, the inquiry the knowledge that the thermostat has been replaced in other repair shops, replaced the airflow sensor (MAF), intake pressure sensor (MAP), oxygen sensors, valve cover, the problem remains. Let’s see what the problem is!
Troubleshooting and diagnosis:
After picking up the vehicle, confirm that the engine malfunction indicator light is illuminated, and check the engine fault code P0171-00: Fuel Correction System Low Voltage.
Check the engine fuel correction data
I found that “the long-term fuel correction data is 26%”, according to the long-term fuel correction data is 26%, it means that the mixture detected by the oxygen sensor is diluted and is being adjusted to the trend of thickening, then what causes the mixture to be diluted? It is envisioned that the causes of the lean mixture are：
- Fuel contamination/low fuel pressure;
- Cracked, kinked, or improperly connected vacuum hoses;
- Injector failure;
- Vacuum leaks at the intake manifold, throttle body, injector O ring， and injector O-rings
- Incorrect operation of evaporative emission control system.
Since this car has been inspected many times at other garages, I’m sure all the usual tests have been done, so I decided to start with the easy ones. I proceeded to check the engine data and found that the MAF data at idle was 1.72g/s while the “Air Flow Calculated Value is 2.23 q/s”, a difference of about 0.5 q/s.
The engine module determines that the base fuel injection is determined by the MAF value of 1.72g/s while the actual air intake of 2.23 q/s is The engine module decides that the basic fuel injection is determined by the MAF value of 1.72g/s, while the actual intake volume of 2.23 q/s is calculated indirectly from the MAP and intake air temperature sensor data.
The engine module determines the base fuel injection quantity from the MAF value of 1.72g/s, while the actual air intake quantity of 2.23 q/s is calculated indirectly from the MAP and intake air temperature sensor data. If both the MAF measurement and the engine module value calculated indirectly using the MAP and intake air temperature sensor data are accurate, and combined with the 26% long-term fuel correction data in the above engine fuel data, the data matches perfectly, and then compared with the engine fuel data of a normal vehicle. Comparing the engine intake data of a normal vehicle, the intake volume measured by the MAF and the indirectly calculated intake volume by the engine module is consistent, so the direction of the fault is centered on the intake volume.
Inspection did not find the engine had obvious air leakage sound, check the oil dipstick 〇 type ring and oil filling port 〇 type ring, normal, did not find a broken phenomenon, test the charcoal canister was not found to have a stagnant phenomenon, will be leading to the charcoal canister solenoid valve of the vacuum hose unplugging, plugging the engine intake data did not change, to rule out the charcoal canister solenoid valve stagnation or leakage of air caused by this fault, car in a suspected leakage parts with the chemical detergent spraying, did not find the engine There is no change in engine speed. Preliminary ruled out the phenomenon of air leakage, check the MAF for the sub-factory parts to try to replace the MAF is ineffective, suspected that the air filter housing body grille installed incorrectly resulting in the uneven air intake will be disassembled and checked no abnormality found. To adjust the valve and try to pull all the crankcase ventilation tubes, the fault remains. Check the absolute intake air pressure sensor data at idle speed is 32kPa, showing normal.
I’m in a quandary at this point, everything related to air intake has been checked, so what else is wrong? Could it be a wiring problem? Measuring the MAF’s power supply and iron are both normal. Try in the MAF power supply pin and ground pin using a direct cross-wire way to rule out the airflow meter power supply and iron bad, the results of the fault are still day. Measure the resistance value between the signal line of MAF and ECU is 0.52, which is normal. To prevent line interference directly to the MAF miscellaneous ECM signal line cut off after the cross-connection, the fault remains.
Measurement of the engine module power and iron is normal, this failure from the data analysis to determine the amount of air intake problems caused by the reconsideration of the phenomenon that there is still air leakage, decided to remove the intake manifold to check, if the removal of the intake manifold to check the normal can only be replaced with the engine computer, remove the intake manifold to check the manifold gasket is normal, there is no rupture phenomenon, this time, found that in the intake manifold under the check valve appearance of some anomalies And there is a small crack, with a fingernail buckle will fall off a piece, check this check valve is installed in the intake manifold built-in vacuum storage tank, this vacuum storage tank is designed to change the intake manifold length of the vacuum valve to provide a vacuum source, replacement of the intake manifold after the vacuum check valve to view the engine data “air flow sensor” and “airflow calculated value”. Air Flow Sensor” and ‘airflow calculated value’ data are consistent, and the fault phenomenon disappeared.
This car in the water temperature is normal before the engine runs well, due to high water temperature and maintenance is completed after the emergence of a thin mixture of vapor which leads to the engine fault light, according to the shape of the one-way valve, thus determining the high temperature of the engine above is located in the lower part of the intake manifold one-way valve, close to the engine block is relatively close to the high temperature due to baking deformation and cracking lead to air leakage, due to the one-way valve in the lower part of the intake manifold is more hidden, so the There is no change in engine speed after spraying alcohol on top of the engine using a chemical cleaner.
Engine speed did not change above the engine spray wine, if the lower part of the engine intake manifold sprays cleaner engine speed will certainly change, so then such problems suspected one-way valve leakage can be used from the lower part of the engine to the intake manifold spray method to determine the existence of leakage of the one-way valve.
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