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Isuzu NPR75

Isuzu NPR75 1

Without keyword

I’ll tell you about a recent malfunction.

ISUZU (NPR75, Euro 4), equipped with a 4HK1 engine (155l / s) and a variable geometry turbocharger (VNT).

For turbochargers with variable geometry, this malfunction is typical: DTC P0045 – Malfunction in the circuit of the boost pressure control solenoid valve.
– MIL indicator lights up periodically or continuously
– the engine does not develop full power
– when you press the accelerator pedal incompletely, the speed increases slowly or does not increase at all
– the car responds to pressing the accelerator pedal with a delay.
– a malfunction can occur at any speed.

Currently, a malfunction does not occur, but a trouble code (DTC) has been registered and saved as a freeze / frame in the memory of the engine control unit.

The following information can be extracted from the stop / frame we received (data snapshots, stop / frames are provided for storing information that should help in identifying a malfunction):
· How often was DTC P0045 recorded (5 times)
· Design load
· How long has the MIL lamp been lit (9.5 hours)
· Mileage since the occurrence of the malfunction (417km.)
· That the exhaust gas recirculation system (EGR) is disabled, etc..

After analyzing the freeze / frame data and considering that it is impossible to repeat (provoke) the fault at the moment, it was decided to check the VNT actuator using a scanner.

To check the turbine blades for jamming, we will test the actuator

– a higher percentage indicates that the shoulder blades are shifted towards the opening
– a lower percentage indicates that the shoulder blades are closing.

Unfortunately, this is the only turbine test test declared on the list by the manufacturer of the G-IDSS diagnostic tool. In a nutshell – how the blades (nozzles) in question look like, how VNT works and why this is needed:

Along with fuel supply, the ECU controls the change in the geometry of the turbocharger.

The cross section through which the exhaust gases of the engine enter the turbine wheel of the turbocharger changes.

At low load, a small deflection angle is set for the VNT turbocharger drive, so the shear value of the working plate connected to the control rod is relatively small.
Moreover, the nozzle openings are quite wide (A). The flow rate of exhaust gases passing through the nozzles is low, so the turbine shaft rotates at a low frequency.
With a large load, an increased deflection angle is set for the VNT turbocharger drive, so the shear value of the working plate connected to the control rod increases. In this case, the nozzle openings narrow (B). The flow rate of exhaust gases passing through the nozzles increases, and the turbine shaft begins to rotate faster.

When it is necessary to quickly accelerate a turbocharger (for example, when you press the accelerator pedal sharply), the computer reduces the flow area and thereby increases the gas velocity.

A controlled change in the geometry of the turbocharger avoids the “turbo-hole” – the effect of delaying the increase in boost pressure with increasing load.
With a decrease in the flow cross-section to the turbine wheel, the gas flow is throttled (i.e., a decrease in pressure when flowing through the narrowing). In turn, in this case (according to Bernoulli’s law), the gas velocity increases. those. guide vanes – work like nozzles.

Step by step, we found out that the movement of the blades (nozzles) is limited by excess deposits (carbon deposits), and this malfunction is nothing but a jamming (sticking) of the blades.

When a malfunction of the DC motor, position sensor (or abnormal voltage in the system) is detected, the VNT control unit sends a message to the engine control unit (ECM). At the same time, a diagnostic code (DTC) is written to the ECM.

To summarize: we checked the nozzle unit (synchronizing ring, guide vanes) for mechanical damage, etc. – It remains to get rid of excess deposits (soot). In a previous article, we washed EGR coolers from carbon deposits and used a rather effective solvent PK-5300YP for this. In this case, we will try to wash the nozzle apparatus in an ultrasonic bath. For comparison, the details before washing:

And here is the result after washing:

After installing the turbocharger, you must:
– Delete fault codes from ECM.
– When you turn the key in the ignition switch to the “ON” position, the VNT unit will conduct internal diagnostics and calibration of actuators.

– Run a test for forced activation of a turbocharger geometry change drive

– Perform turbocharger boost pressure test.

Example of boost measurement on an ICE 4M50T5 (Fuso-Canter Euro4) using a mechanical pressure gauge (in the x.h. mode)

The video shows that the boost pressure is practically absent. We measure the boost pressure on the same car, using the scanner scan function and see in the video that the pressure is increasing.

Unfortunately, such a function for testing on ISUZU (N-series Euro 4) is not provided in the G-IDSS diagnostic system. Below is the only possible way to measure boost:

Checking the boost is carried out when the car is moving, under load and various modes of engine operation.

After making sure that the pressure values ​​are normal and that there are no DTCs, you can consider the work to be fully completed.


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