1. Failure phenomenon
A 2010 Volvo S80L car, equipped with a B5254T inline 5-cylinder engine, has a cumulative mileage of approximately 105,000 kilometers. The car was brought to the factory for maintenance due to oil leakage from the front of the engine. The maintenance personnel replaced the intake and exhaust camshafts and the front oil seals of the crankshaft and then re-tested the car. The engine fault light was abnormally lit, and the engine would occasionally turn off automatically when the engine was cold. It was detected with a fault detector. The engine control unit has a fault code in terms of engine timing. The maintenance personnel repeatedly checked the assembly process and used special tools to check the positions of the intake and exhaust camshafts. No abnormality was found, so I asked the author Technical Support.
Two, fault diagnosis
The car's engine is horizontal, and the engine support on the passenger side must be removed to have room to check the engine timing. The maintenance personnel felt that it would be troublesome to disassemble and assemble the engine support back and forth, so they simply did not install it and used a jack to support the engine oil pan. In this way, it is impossible to go out for a road test, only to lightly step on the accelerator pedal to test the car.
Start the engine, the engine idling runs relatively smoothly, but the engine fault light on the instrument cluster is always on. Using a fault detector, it was found that the engine control unit stored the fault code "P001762 crankshaft position/camshaft position relationship (cylinder group 1, sensor B)-algorithm error-signal comparison failed" and the fault code "P001662 crankshaft position/camshaft" Position relationship (cylinder group 1, sensor A)-algorithm error-signal comparison failure" (Figure 1); clear the fault code, the fault code can be cleared, but the fault code reappears after the engine runs for a while.
Figure 1 The fault code stored in the engine control unit (screenshot)
Fault code P001662 and fault code P001762 are two common fault codes. Fault code P001662 means that the position of the intake camshaft relative to the crankshaft is incorrect, and fault code P001762 means that the position of the exhaust camshaft relative to the crankshaft is incorrect. The intake and exhaust camshafts of the car adopt variable valve phase technology. The engine control unit continuously monitors the timing positions of the two camshafts through the intake and exhaust camshaft position sensors, that is, checks the timing between the camshaft and the crankshaft. Relative position, if the relative position deviation is too large, the fault code P001662 and the fault code P001762 will be stored.
This engine is driven by a timing belt. The method of correcting the timing is very simple. Align the vertical line mark on the crankshaft drive pulley with the mark on the cylinder block, and then align the vertical line marks on the two camshaft adjusters. The mark on the cylinder head, and then install the timing belt. The crankshaft drive pulley and the front end of the crankshaft are connected by a spline, and there is a wide positioning tooth in the spline to ensure the uniqueness of the assembly position. The two camshafts have flat grooves at the rear end (transmission side). Special tools can be used to fix the two camshafts. The flat groove opening is designed very cleverly. The special tools can only be inserted when the two camshafts are in a certain position at the same time.
According to the description of the maintenance personnel, he first turned the engine to the timing position, fixed the rear end of the camshaft with special tools, then removed the crankshaft drive pulley and camshaft adjuster, replaced the oil seal, and reinstalled the components in sequence. It seems that this operation should not cause engine timing faults, but the engine control unit stores the engine timing fault codes. Therefore, in order to eliminate this fault, the problem must be analyzed from the perspective of the engine control unit. The engine control unit checks the position of the camshaft and the crankshaft through the intake and exhaust camshaft position sensors and the crankshaft position sensor, so I decided to measure the signals of each sensor with a pico oscilloscope, and then combine them for analysis.
Figure 2 Connect pico oscilloscope
Connect the pico oscilloscope (Figure 2) to measure the signal waveforms of the intake and exhaust camshaft position sensors and the crankshaft position sensor when the engine is idling (generally called the combined waveform "engine timing waveform"), as shown in Figure 3.
Figure 3 The engine timing waveform of the faulty car (screenshot)
The analysis shows that the camshaft position sensor of the car's entry and row is Hall type, and its signal target wheel has a "2 wide and 2 narrow" structure, that is, there are 2 wide teeth and 2 narrow teeth on the signal target wheel; crankshaft position The sensor is a magnetoelectric type, and its signal target wheel has a "58+2" structure, that is, there are 58 teeth and 2 missing teeth on the signal target wheel. The space between the two dashed lines in Figure 3 represents 1 working cycle of the engine, the crankshaft has rotated 2 revolutions, and the camshaft has rotated 1 revolution. Because the engine timing fault code is stored, the variable valve phase system is in the off state at this time, so Figure 3 reflects the basic timing state of the car's engine. Theoretically speaking, it is necessary to find a car of the same model and compare the engine timing waveforms to accurately determine whether the car’s engine timing waveforms are normal. However, after further analysis of the car’s engine timing waveforms, the author inferred that most of the cause of the car’s failure The position of the crankshaft drive pulley is installed incorrectly for the following reasons.
(1) The failure occurs after the oil seal is replaced, and improper assembly may cause failure.
(2) The fault code involves the intake and exhaust camshafts at the same time, and the possibility of the two being installed incorrectly at the same time is very small.
(3) The waveforms of the intake and exhaust camshaft position sensors are exactly the same. If the camshaft is installed incorrectly, it would be too coincidental. This should be the design of the original car.
(4) The maintenance personnel mainly disassembled the camshaft adjuster and the crankshaft drive pulley, and once the crankshaft drive pulley is installed incorrectly, the engine control unit will store the fault code P0016 and the fault code P0017 at the same time.
After listening to the author's analysis, the maintenance personnel will be suspicious, because the crankshaft drive pulley and the front end of the crankshaft are splined, and the position is the only fixed, it is unlikely to be installed incorrectly, but there is no other idea, so they had to remove the crankshaft drive pulley for confirmation. After pulling out the crankshaft drive pulley with the pull claw, the problem was found at a glance. As shown in Figure 4, the position indicated by the green arrow is the wide positioning tooth that matches the crankshaft drive pulley and the front end of the crankshaft. It was installed by mistake to the position indicated by the red arrow. It was originally a convex tooth, which was flattened during installation. . In the process of reverse thrust failure, after removing the right front wheel and inner lining, the maintenance personnel squatted on the side of the vehicle to work. Due to the position and light, he could only put the crankshaft drive pulley on the front end of the crankshaft by hand, and then use a hammer to drive the belt. The wheel knocked in place, and the crankshaft drive pulley was installed in the wrong position during this process.
Figure 4 Crankshaft drive pulley
Three, troubleshooting
Use a file to repair the strained position, re-install the crankshaft drive pulley and repeat the test. The engine is running normally and the fault code no longer appears. The fault is eliminated.
Four, fault summary
After troubleshooting, measure the engine timing waveform again (Figure 5), and use the rising edge of the second wide tooth of the camshaft as the reference to calculate the deviation angle between the crankshaft position sensor and the signal waveforms of the intake and exhaust camshaft position sensors. Compared with the normal state, the state is about 6.5 crankshaft signal target gear teeth, one tooth is about 6° crankshaft angle (360°÷60=6°), and the crankshaft angle is advanced by about 39° (6.5×6°= 39°). The crankshaft drive pulley has a total of 27 teeth per revolution, and one tooth is about 13.3° crankshaft angle (360°÷27≈13.3°). Because the crankshaft drive pulley is installed with a deviation of 3 teeth, the deviation is about 39.9°crankshaft angle (3 ×13.3=39.9°). It can be seen that the data calculated by the above two methods are basically consistent, which shows that the engine timing waveform can accurately reflect the engine's mechanical valve timing.
Figure 5 The engine timing waveform of a normal car (screenshot)