Fuel System - HPI (High Precision Injection) Information
SI B 13 06 06Fuel Systems
November 2006
Technical Service
This Service Information bulletin supersedes S.I. B13 06 06 dated October 2006.
[NEW] designates changes to this revision
SUBJECT
High Precision Injection (HPI) Information and Service Procedures
MODEL
E90 and E92 (3 Series) All models equipped with the N54 Engine
INFORMATION
High Precision Injection (HPI):
High precision injection allows precise metering of the fuel mixture and higher engine compression - ideal preconditions for increasing efficiency and significantly reducing fuel consumption. This is made possible by using new generation Piezo injectors, located centrally between the intake and exhaust valves. In this position, fuel is injected directly into the combustion chamber in a highly atomized tapered shape.
HPI Function:
Fuel is delivered from the fuel tank by the electric fuel pump at a "feed" pressure of 5 bar to the highpressure pump. Feed pressure is monitored by a low-pressure sensor. If this sensor fails, the electric fuel pump continues to run at 100% delivery with terminal 15 ON. The high-pressure pump is driven by the oil pump chain drive assembly. Fuel is compressed in the permanently driven three plunger highpressure pump and delivered through the high-pressure line to the rail. Fuel accumulated under pressure in the rail is distributed via the high-pressure lines to the Piezo injectors. Required fuel delivery pressure is controlled by the engine management system based upon engine load and engine speed. Fuel pressure is monitored by the high-pressure sensor and communicated to the engine control unit. Pressure is regulated by the fuel supply control valve located inside the high-pressure pump. Fuel pressure is programmed for the best possible consumption and smooth running of the N54 engine. Maximum programmed fuel pressure (200 bar) is only required at high load and low engine speed.
Limp Home Mode:
NEW If a fault is diagnosed in the system, such as e.g. failure of the high-pressure sensor, the fuel supply control valve is de-energized, allowing only 5 to 6 bar fuel pressure to the fuel rail. In the event of HPI limp home mode, turbo charging is deactivated by an opening of the waste gate valves. The Service Engine Soon light is illuminated and a fault will be stored in the engine control module memory.
HPI limp home can be caused by any of the following scenarios:
- Implausible high-pressure sensor values
- Failure of the fuel supply control valve
- Leakage in the high-pressure system
- Failure of the high-pressure pump
- Failure of the high-pressure sensor
SERVICE PROCEDURES
Fuel System Safety:
Working on this fuel system is only allowed after the engine has cooled down. The engine coolant temperature must not exceed 40 degrees C (104 degrees F) otherwise there is a risk of fire if the fuel comes in contact with a hot engine. Before opening the high-pressure portion of the fuel system it must first be depressurized. Removing the power supply for the electric fuel pump and allowing the vehicle to run until it stalls will depressurize the fuel system. Always wear protective clothing, safety glasses and Nitrile rubber gloves when working with fuel systems. When working on the high-pressure fuel system, take particular care to ensure conditions of absolute cleanliness. Even the smallest contaminants or damage to the screw connections on the high-pressure lines can cause leaks.
Fuel Injector and DME Replacement:
Replacing a fuel injector or DME requires the injector volume tolerance to be relearned. To perform this task a test plan has been created called "Calibrate Injectors". The test plan stores the injection volume tolerances for each injector in the DME memory if an injector is replaced. If the DME is replaced, all six injector volume tolerances need to be relearned. This procedure is not learned automatically, it needs to entered manually via the DIS Plus or GT1 diagnostic devices. Refer to DIS Function Description "Calibrate Injectors" for additional details.
The test plan can be found under the following path:
Function Selection - Service Functions - Adjustment Programs - Calibrate Injectors - Test Plan.
NEW If a fuel injector(s) is removed from an engine the Teflon seal is damaged and cannot be reused, the Teflon seal must be replaced with PN 13 53 7 557 550 or refer to EPC for parts information and quantities. Swapping injectors from cylinder to cylinder for troubleshooting is permitted but the Teflon seal must be replaced on all relocated injectors before completing final repairs. New injectors are shipped with a protective cap installed on the tip. This cap is installed to protect the injector tip from damage and to also retain the Teflon seal shape during shipping. If the protective cap is removed the injector must be installed into an engine within 10 minutes. If the protective cap is reinstalled on the injector damage will occur to the Teflon seal. Refer to TIS Repair Instruction RA 13 53 310 for proper procedures. Refer to SI B04 30 06 for applicable tools to perform this procedure.
WARRANTY INFORMATION
Information only
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