A diesel light cargo came to repair at a time. The purpose is to replace the cylinder bed because the water tank is strong against water and insufficient power. After the completion, the anti water phenomenon is eliminated, the power is still insufficient, and the black smoke is very large (it turns out), the analysis may be the valve system gap is too large, open the valve chamber cover, find the valve wear seriously, to the adjustment limit. It is recommended to replace the valve. After the valve replacement, the phenomenon is weakened, but the smoke is still not very small, and the power remains unchanged. After testing, the valve leaks slightly. Inquire the car owner high pressure oil pump to check soon. Finally, consider the exhaust system. Remove the exhaust pipe and start the engine. There is no black smoke and strong engine power. It was caused by the unobstructed exhaust. After replacing the muffler, the fault is ruled out.