FAW Mazda 6 Car Engine Fault 2 cases

Case 1

a 2007 annual output of FAW Mazda 6 2.0 L sedan, equipped with 5-speed manual / automatic transmission from one type, mileage is 31,000 km. Reflect the user vehicle dashboard engine failure warning light warning the normal traveling, the engine idling and acceleration performance but unaffected, normal vehicle travel. Users say the car 15 days before the pit stop had repaired once, when maintenance personnel will clear the trouble code test failure did not occur again, put the vehicle be delivered to the user. But after a period of use of the vehicle, engine failure warning light again.


After receiving the car, I Connect the diagnostic sense WDS engine control system is detected, the device displays the fault code ldquo; P0420mdash; mdash ; low catalytic reaction efficiency rdquo ;. Now seen maintenance manual, a PCM monitoring, signal voltage value after the oxygen sensor, and calculates the curve> 0.5 V ratio of the number of times, if the ratio is less than the standard value 5.5, it is determined that a three-way catalytic reactor decreased efficiency. The failure cause code appears includes a front oxygen sensor (FIG. 1) failure, an oxygen sensor fault (FIG. 2), catalytic reactor damage, and damage to the engine PCM poor working conditions.

FIG. 2

decided to first check the front and rear oxygen sensor. Then the engine control system of the first observation data stream (Table 1) using a fault diagnostic apparatus.

Table 1

From the above value change situation, the output signal of the oxygen sensor is normal, the engine control system may determine normal. After I also checked before and after the oxygen sensor in response to changes in air-fuel mixture. Modified human throttle, before the oxygen sensor signal 3.35 mA ~ 325mu; change between A, after a change in the oxygen sensor signal 0.5 ~ 0.7 V, the test is repeated three times, changes are consistent. Front and rear oxygen sensor signal value changes with the air-fuel mixture to be responsive, indicating that it is working properly.

Since the front and rear oxygen sensor is working properly, it will not be a three-way catalyticProblems in the reactor itself it? If the oxygen sensor signal voltage prior to> 0.5V and the number of oxygen> 0.5V times the ratio ge; 5.5, show that catalytic reactor is working properly. Observed after prolonged oxygen sensor signal voltage found, when the engine is idling, sometimes of a relatively stable amplitude, is maintained at about 0.2 V; occasionally changes in 0.2 ~ 0.6 V, lasts approximately 10 s. Under normal circumstances, the voltage signal of the oxygen sensor curve flatter and less than 0.2 V. The inspection vehicle of catalytic reactors see, I determined that the initial conversion efficiency of three-way catalytic reactor difference. In order to determine whether the three-way catalytic reactors work, I decided to engine exhaust emissions are detected by the engine exhaust gas analyzer. 5 by using the exhaust gas analyzer of exhaust emissions when the engine idling condition is detected, as its value (Table 2).

Table 2

According to the measurement results, the CO emissions percentage reaches 0.324, indicating that the catalytic reactor is not functioning.

The author of the subsequent three-way catalytic reactor were examined. After careful observation of their appearance, no external damage can be determined. In order to determine the performance of the catalyst inside the catalytic reactor, the author uses the infrared thermometer measured three-way catalyst inlet and exhaust temperature, nearly equal, may be determined catalytic reactor failure (for which car and words, normal vehicle operation when the engine is idling for a long time, the catalytic reactor outlet temperature of about 270 deg.] C, inlet temperature of about 240 ℃).

After replacing the catalytic reactor, again using the exhaust gas analyzer for detecting the engine exhaust emissions, exhaust emissions back to normal, after a long monitoring the oxygen sensor signal, the normal range of variation, troubleshooting.

Summary: less this vehicle mileage, but catalytic reactor before damage can be determined that the car should be added inferior gasoline long, so that early ldquo catalytic reactor; poisoning rdquo; failure. When troubleshooting the car, the oxygen sensor signal the magnitude of change in the voltage curve is not obvious, it is also sufficient to determine catalytic reactor failure, which requires the aid of other aids, such as the temperature difference before and after the catalytic reactor,Exhaust gas emission values ​​common diagnosis. In addition, the new car with the old car, PCM works in monitoring the efficiency of the catalytic reactor is basically the same, but slightly different. Old car before and after the oxygen sensor using a common oxygen sensor, the oxygen sensor monitored before and after the PCM signal voltage profiles> 0.5 V ratio of the number of times, if the ratio> 5.5, the catalytic reactor is considered working properly. New car before the oxygen sensor using the new broadband oxygen sensor, PCM need to convert the current signal into a voltage value monitored.

Case 2

a 2003 annual output of FAW Mazda 6 2.3 L sedan, equipped with four-speed manual / from one of the automatic transmission, mileage to 200,000 km. Users reflect car engine failure warning light warning, normal vehicle travel, but sometimes accelerating exhaust pipe ldquo; chug rdquo; sound. This failure already exists a month, before overhauled in other repair stations, but did not identify the specific point of failure.

The fault symptom car, the author of the first basic engine visual inspection. After careful observation, found no correlation vacuum tubes, wiring harness plug off, engine running smoothly, accelerate the normal place, but the engine is running louder. After connecting to the engine control system fault diagnostic testing, fault code display device ldquo; P0012mdash; mdash; actual valve timing is retarded rdquo ;. Now maintenance manual apparent, when engine speed is below 4 000 r / min and at normal operating temperature, if the actual valve timing is retarded than the target for more than 5 deg ;, delay longer than 5 s, PCM will be determined variable valve timing system fault exists. I then took advantage of the fault diagnostic control system engine reads the data (Table 3).

Table 3

After observation of the data flow analysis, I suspect engine variable valve timing system do exist valve timing retardation phenomenon .

According to our experience in the maintenance of the family car determination generally results in the car timing actuator failures occur mdash possible reason for this failure include variable valve; mdash; jamming, the OCV valve (FIG. 3) Cards stagnation, PCPCM line fault and fault between M and valve OCV.

Figure 3

We decided first detected OCV valve and its associated wiring harness. The relevant circuit diagram can be seen, W thread color and stitch a main relay connected to a supply voltage of 12V (normal); BR \ Y stitch thread color and stitch turned PCM-2E, the measurement result is not a problem. It was measured using a multimeter OCV valve plug. When I use active test OCV measurement function valve, the valve chamber cover is opened, the valve OCV remove, turn the ignition switch into the data logger

Figure 4

[123 ] select ldquo; VTDUTY1rdquo; vary between (the intake camshaft cycle command signal) output adjustment signal (12.5 ~ 96.5 percentage percentage), whereupon the intermediate valve element can be seen along the valve OCV variation. OCV check result indicating good operation of the valve.

Figure 5

After the completion of the inspection, I repeated rotation of the crankshaft Check tags on the actuator after 2 rings, found flag has been misaligned (FIG. 4 ,Figure 5). After removing the test, compressed air was blown into the hole, no action actuator (normal hole for blowing compressed air should be, the operation of the actuator to be the most retarded position or the most advanced position). Replace the variable valve actuator, the actuator has been jammed, resulting in valve timing tolerance time. So it will be on the actuator was replaced, and re-proof positive. The data flow was observed after the car was found, the actual value of the target value 0deg ;, 0deg ;, 98 ℃ and the coolant and the engine speed is 710 r / min. From the point of view of the engine idling, the system as usual. When the actuator active test variable, when the output signal reaches a percentage of 90, variable valve timing and the target value of the difference does not change, remained stable idling. Normal: When the above percentage adjustment signal 60, engine speed drops, until the flame jitter significantly.

it will not be the executor catching it? However, the above factors have been excluded, as long as the OCV valve operation, the pressure oil should be injected into the actuator, the oil passage blockage do? (With the engine front cover oil screen, the effect isPrevent impurities from entering the actuator) in rare cases. Compressed air cleaning, it was confirmed that the oil passage patency.

Path lubricating oil: oil pump rarr; main oil rarr; chain tensioner rarr; front cover oil passage rarr; head rarr; OCV valve rarr; actuator.

In the premise of ensuring safety: the engine start (misfire). Under normal circumstances, you can see the oil hole head. This oil vehicle starting little hole, thereby connecting the hydraulic pressure gauge suspected insufficient, the normal temperature is measured at 0.35 MPa (3 000 r / min), normal value should be 0.4 ~ 0.6 MPa (3 000 r / min), apparently, the oil pressure is lower than the standard value, indicating that the variable timing system is normal. Not enough oil pressure to provide, causing the actuator does not operate. According to our experience in servicing the car, when low oil pressure, there may be damage to the oil pump. Once the lubrication system in the drainage situation, will lead to the main bearing wear.

After analysis and examination, found no significant bearing excessive wear phenomenon, this normal car maintenance, first replace the oil pump, oil pressure value measured up to standard again, the actuator initiative to do the test, everything is normal.

Summary: This car engine oil pressure is low, but not to the extent alarm, some negligence in the analysis and inspection.

(Wong Sin)

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