Diagnostics and maintenance of engines with direct injection

The family of French engines with the HDI designation has become very popular in recent years, among others thanks to their use in many companies, not only French. 1.6 HDI and 2.0 HDI engines were commonly used in passenger cars. Due to the global plan to implement exhaust emission standards, the French company, like all other car manufacturers, had to respond with technology that would meet the prospective, stringent approval requirements. The French answer was a new generation of engines marked “BlueHDi”, with capacities of 1.5, 1.6, 2.0 and 2.2 [l].  

The 1.5 and 1.6 BlueHDi engines use the Bosch Common Rail injection system. The 1.6 engine is equipped with a CP4S1 pump, operating at a maximum pressure of 180 MPa and driven by the timing belt in a 1:1 synchronised manner. Correct positioning of the pump during installation is crucial in this case for two reasons. First of all, it helps to reduce pressure pulsations in the fuel rail by synchronising the opening of the injectors with the pump compression stroke. Second, the pumping unit of the pump is single-section and has a large piston stroke, therefore with high load there are stress jumps that must be compensated by another load (e.g. the timing system). Overlapping loads on the belt cause its premature wear and, as a consequence, even its breaking. The high-pressure accumulator has no fuel outlet, and the pressure control strategy using the ZME metering valve (German: Zumesseinheit) is characteristic of CP4S1 pumps (without control, the ZME metering valve is open). On popular information platforms you can find a diagram of the fuel system, which is presented in the figure below. 

 With this configuration, for an open electrical circuit fault on the ZME metering valve, it was necessary to use a start-up interlock and disable the injectors. In the previous generation 1.6 HDI engines, equipped with a CP1H pump, the operation was reversed, i.e. in the de-energised state, the ZME metering valve was closed, which resulted in a pressure drop with the ZME valve circuit open. The low pressure system is powered by an electric fuel pump located in the tank, while the pre-charge pressure of 3.5 to 4.1 bar is regulated by a relief valve located in the high-pressure pump. The pre-charge pressure measurement can be performed with a scan tool using the parameter of the sensor that is mounted in the circuit between the filter and the pump.

A slightly different principle of operation is used in the 1.5 BlueHDi engines, which are prepared for future emission standards and are to replace the 1.6 unit in the future. In this engine, the latest generation CP4S1 high-pressure pump is used in the fuel system, with a function called eSV (German: elektrisches Saugventil). A similar solution can also be found in VW and Renault engines. While the low pressure system is not significantly different, there are significant modifications to the high pressure system.  

As you can see in Figure 2, the eSV pump does not have a typical ZME metering valve; it has been replaced with an electric suction section valve located in the upper part of the pump cylinder. Unlike the ZME valve, which throttled the fuel flow, the eSV valve is mechanically open and can be closed at any time by the engine controller. During the intake stroke, fuel flows in, and during the compression stroke, fuel flows out. High pressure is generated only when closing the eSV in the final phase of compression, but the angle of its closure determines the flow rate of the pump. This solution makes it necessary to precisely synchronise the pump with the timing system, and incorrect installation will result in too low or no fuel consumption. Another change concerns the fuel rail, which in this version is equipped with a PLV (pressure limited valve) drain valve located at its end. The PLV valve serves here as a mechanical protection against too high pressure.

When testing this fuel system, you should remember that a potential leak may occur not only in the injectors, but also in the pressure accumulator. In the first versions of the 1.5 BlueHDi engines, CRI2-20 edge valve injectors were used, which work at a maximum pressure of 2000 bar, while the latest solutions use CRI2-22 injectors working at a pressure of 2200 bar. Injectors of this type are characterised by high leakage resistance and high hydraulic efficiency, which is why their overflows during idling tests do not exceed 5 ml/min. Possible leaks resulting from operation are compensated by the pump output. The advantage of the eSV type pump is the ability to set the exact compression angle by the pumping section, which is regulated and targeted at the moment of opening the injector. The eSV valve signal is clocked relative to the engine RPM and the duty cycle determines the flow. At light loads, the computer can manipulate the use of the pump cam, which reduces the pulsation of the timing belt loads.  

The 2.0 and 2.2 Blue HDI engines use a Delphi Technologies fuel system. This system is powered by an electric fuel pump built into the tank module and an integrated control valve that maintains the pressure in the system at 4.5–5.5 bar. As with smaller engines, there is also a fuel pressure and temperature sensor in the low pressure circuit after the filter. On popular information platforms, we can find a diagram of this fuel system (Figure 5).  

The mounting position of the fuel temperature sensor is justified by the fact that in this system the fuel is heated using an electric heater located in the fuel filter. The high-pressure system is equipped with a PLV valve, which is designed to limit the pressure in the CR rail to a value of 2250 bar. Due to the lack of an electric valve on the accumulator, the reduction of pressure from high to low takes place here by the principle of “pressure digestion by injectors” and this is typical of Delphi systems.

The Delphi Technologies high-pressure pump is also made as a single-section, and the variable flow is regulated by a metering valve, in this case the IMV (Inlet Metering Valve). The solenoid valve is responsible for the pump output, so if we have a fault involving incorrect pressure regulation, we can first indicate it as a potential cause. There is a filtering material on the solenoid valve, so after removing it, it is worth checking if there are no filings or other impurities in the system. A significant amount of swarf means that we are dealing with a serious pump failure consisting in the wear of the cam and guide roller in the pump. In this case, the entire fuel system including the accumulator and injectors is contaminated and must be checked and cleaned and the high-pressure pump must be replaced.     

In the 2.0 and 2.2 BlueHDi engines, the pump is not driven by the timing belt, but by a drive gear (multiplier) driven by the exhaust camshaft. The transmission used doubles the RPM making the pump speed match the engine speed. The gear ratio is important because of the synchronisation of the pump compression with the injectors, which has already been described.  

At this point, you should pay attention to the correct installation of the pump, as sudden load spikes imposed on the roller loads can damage the multiplier module or cause damage to the timing belt. The correct positioning of the pump during its installation can only be achieved by following the correct installation procedure. There is a mark in the form of a dot on the gear wheel of the pump, which must be aligned with the mark on the housing, as shown in Figure 9. When inserting the pump, the engine must be in the pump installation position and not in the timing belt installation position. This setting can be achieved by removing the timing locks and turning the engine approximately 50° past TDC. Note the locking of the camshaft sprocket which has two locking holes at 8mm and 6mm. The 8mm lock is used to mount the belt and the 6mm lock is used to mount the high-pressure pump (Figure 10). Installing the pump with an 8mm lock is a common cause of premature timing belt failure. In Figure 8, the arrow shows the inspection plug. If there is a plug, it means that in this version there is an automatic spring compensation system for clearance and before removing the pump, you should unscrew it and insert the locking pin there.     

What does this procedure entail? The DFP6.1 pump does not have a lock as in the 1.5 and 1.6 engines. For this reason, setting it to TDC of the engine would require setting a specific position where the spring of the pumping unit pushes against the cam and rotates the pump shaft. The installation of the pump in this case would be very complicated, therefore the designers have developed a procedure for installation in the post-TDC position of the engine. Another important element you should pay attention to are the injectors. As with the high-pressure pump, there are some technical details you should keep in mind when servicing the injector system. Replacing injectors requires a specific procedure for bleeding and starting. After installing the injectors, screwing the high-pressure lines and connecting the overflows, it is recommended to vent them by creating pressure in the fuel rail without controlling the injectors. This can be achieved by turning the starter motor several times on the disconnected electrical connectors of the injectors. Before doing this, it is worth running the electric fuel pump several times using a diagnostic proof point. During the operation of the electric pump, the fuel flowing from the overflow of the high-pressure pump creates negative pressure in the return circuit of the injectors. This effect is very helpful in venting and is characteristic of this fuel system, because the manufacturer from the very beginning uses a Venturi nozzle in the return circuit of the pump and injectors. In BlueHDi engines with the Delphi system it is located in the return port of the high-pressure pump. Improper bleeding can cause the injector valves to jam, resulting in the inability to start the engine or its uneven operation. The installation and bleeding itself is not the end of the procedure, because additionally, the injectors must be coded (20-character codes), and then calibrated while driving. The calibration process is automatic and the engine controller performs it automatically after coding the injectors. To do this, after starting the engine, let it idle until it warms up, then make a test drive using the so-called “engine brake mode”. Adaptive values are determined at different pressures, for instance 230, 400, 800, 1000, 1200, 1600 bar and the following conditions must be met:

 

• engine temperature >70°C
• fuel temperature >0°C
• accelerator pedal not pressed
• engine braking profile
• vehicle speed >50 km/h

 

Auto-adaptation can be fully carried out after driving as many as 200–500 kilometres.

To sum up, stringent environmental standards force manufacturers to constantly modify existing control systems. The concept and principle of operation of popular diesel engines generally remains the same, but the system configurations of subsequent generations differ in the details. The continuous change of operating parameters, such as e.g. injection pressure, number of injections per engine stroke, or expansion of exhaust gas treatment systems require design changes that can be a serious challenge for repair workshops. Lack of knowledge of the specification, specific configuration and dependencies of individual system components can cause huge diagnostic difficulties. 

The article presents selected issues related to the range of BlueHDi series engines which, in practice, will help workshops to improve the process of servicing, diagnosing and repairing these popular drive units.