Aftermarket November 2022

NOVEMBER 2022 AFTERMARKET 23 Pinpointing the cause As you can see if you refer to Fig.1, there were certain anomalies occurring within this cylinder. We can clearly see that the exhaust pocket is rounded, which indicates a slow change in pressure, over time, as opposed to a quick snap- open of the exhaust valve, which is what is desired. You will also notice the exhaust plateau is shifted to the right, indicating that the fault is related to a valve duration issue. Because the exhaust valve is slow to open, it is also slow to close, causing it to affect the intake valve event. The intake valve opening event appears delayed. Logic should make it impossible for the cylinder to draw into a vacuum if the exhaust valve is connecting the intake manifold to the exhaust via the still-open exhaust valve Knowing there are anomalies occurring in this cylinder I wanted to check a known-good, non-misfiring cylinder. So, I moved the test equipment from cylinder #5 to Cylinder #2, which was also on the opposite bank. As you can see from the idle, in-cylinder capture of cylinder #2 as seen in Fig.2, there is an obvious difference in the valve train events. The exhaust plateau is not shifted to the right, and we can clearly see that the exhaust valve event displayed a quick opening, which is desirable. Accurate analyses yield confidence Armed with this information we could then confidently inform the customer that there was an obvious valve train issue for cylinder #5. Before dismantling the engine, I connected a pressure pulse sensor to the intake manifold, and using a current clamp, synced to cylinder #2’s ignition coil event. I compared the intake pulls for each cylinder on this engine. This was simply to back up my diagnosis of a valvetrain-related issue for cylinder #5. If the exhaust valve is opening late and closing late, then this will affect the intake pull and valve overlap for that cylinder. As you can see in Fig.3 and Fig.4, there is a 7- degree difference in the intake pulls between a good cylinder and the misfiring cylinder #5. Please note that the valve overlap event is different on cylinder #5 compared with the other cylinders. This now confirms more so that there is a definitive exhaust valve train problem on this cylinder which is affecting the intake valve event. I then wanted to research this engine configuration to ascertain which type of valve train system Mitsubishi Fig.3 implemented. It was very difficult to find anything conclusive. Therefore, knowing the vehicle had a valve train issue, I advised the garage to remove the rocker cover and inspect the camshaft and lobes for any abnormalities. They reported back that the camshaft and lobes looked in good serviceable condition, with no excessive wear. At that point, it was very difficult to determine whether the valve spring or possibly the hydraulic tappet was causing the problem. I recommended that an oil flush should be carried out. If that rectified the issue, then we would know the problem was within the hydraulic tappet. However, if the fault remained then the issue would clearly lay with the valve spring or valve seat area. Committed to a correction After the oil flush and change was carried out, the customer stated that there was an audible ticking noise. However, this noise vanished shortly thereafter. With that, the misfire vanished as well, thus confirming that the issue was within the hydraulic tappet on this engine. The vehicle has run many miles since the flush was carried out and is no longer misfiring. I also took the liberty to check the Mode $06 misfire counters in EOBD data after the vehicle returned for its inspection. This also confirmed no misfires present. Sometimes we are limited in the information we have available to us, as technicians. Although this is an inconvenience, employing logic and understanding can lead to a hypothesis of the likely fault, paving the way for intelligent tests that can flush the fault to the surface for us. This proves, once again, that the most valuable tool a technician possesses is the one between his or her ears. Fig.4 The most valuable tool a technician possesses is the one between his or her ears ”