Fault phenomenon: a Mazda Bongo (engine type: RF turbocharged diesel engine), equipped with transmission: 5 speed manual transmission. Already running mileage: 99000km. Car owner Description: when the 4 gear accelerates, there is a strange noise, just like where to run gas like "prickle" to ring. Fault diagnosis: this car has been overhauled a year and a half ago, the symptoms of the time were also different noise, speculates is the connecting rod small axle bush different noise, in order to be cheaper, replace a Ford Spike type RF diesel engine, its supercharger is with the intermediate cooler. Two kinds of engine shape and exhaust volume are the same, after the change to do the driving test, no problem, again check the content of the operation, no abnormal, so the vehicle returned to the user. It was about 3 weeks, and there was another noise in the drive. In the previous maintenance, the engine lubrication system and the cooling system have been checked and confirmed, there is no problem, the idle speed is also very quiet, how can produce abnormal sound? But this time, it is overhauled on the basis of abnormal sound, and it is in the 4 gear acceleration to produce abnormal noise, that is to say, without a considerable load does not produce abnormal noise. Is the engine replaced by the rear engine abnormal noise? As a preventive maintenance, the timing belt and water pump have been replaced before. A road trial was carried out, and a "prickle" leak was found on the highway. It was presumed that the turbocharger was leaking. The pressure relief valve installed on the intake manifold is shown in Figure 1, and the boost control system is shown in Figure 2. If it is a gasoline engine, the throttle butterfly valve should be taken into account when the throttle valve is closed, but the pressure of the throttle valve rises sharply before the throttle valve, but the diesel engine has no throttle butterfly valve, the intake manifold is connected directly with the turbocharging system, and there is no sharp rise in the pressure like the gasoline engine. Turbocharger body is brought about by repairing and regenerating diesel engine. So does the exhaust channel control valve do not match the pressure relief valve? It's very suspicious, but it turns out that the engine's intake system parts have been thrown away and can't be compared. The difference between type RFT and RF turbocharger is that the former has an intercooler, and the latter has no intercooler. Remove turbocharger and confirm exhaust passage control valve according to data. Using self made static pressure box to do leakage test, it was found that the exhaust passage control valve began to leak at 80kPa, and 70KPa began to leak. The difference this 10KPa is the cause of failure? There are two questions: one is the actual working environment, the pressure should also have pulsation; two is the pipe diameter of the exhaust channel control valve 35mm, the diameter of the pressure reducing valve tube is 20mm, can the synchronization be guaranteed in time? Failure to remove the leakage of the coolant pipe when replacing the turbocharger The coolant pipe was replaced. Check the work area again, confirm that no road trip test is made after omission, acceleration is good, at the same time very quiet. No matter how heavy load, high speed and speed up, no leakage is produced. Reconfirm that oil and coolant are not leaking, troubleshooting.