With the new emissions standards for all internal combustion engines getting tighter and tighter, never has there been so much emphasis and reliance on the fuel injection system.

If we are all to enjoy a cleaner environment then it appears that the emission levels of our vehicles need to change.

This chart shows the changes that are required for the diesel engines exhaust to comply with various 'Euro' stages. There are various laws that require engine manufacture's to meet these emissions levels by a certain year.

Meeting these emissions levels is only part of the problem for design engineers. This allows them to legally release the diesel engine into the market. The consumer, however, also have demands.

To achieve the demands of the modern day motorist, (such as high performance, good fuel economy, low noise levels), in addition to much cleaner exhaust emissions, there has been a wave of technology applied to the fuel injection systems on the modern engine.

Below is a basic overview of the changes that have occurred in the diesel fuel injection system, specifically to BOSCH.

You can see from this diagram that this system comprises of mainly a fuel filter, injection pump and injector. There is not one electronic component in this fuel injection system.

The fuel comes from your diesel tank, through the low pressure mechanical feed pump on the side and then through a fuel filter. From there, the fuel travels into the injector pump and high pressure is created by means of a camshaft, tappet assembly plunger and barrel.

The normal pressure used in this system is between 100-300 bar (1,450 - 4,300psi)

Fuel delivery is then metered by means of various designs governors that measure engine speed (by means of centrifugal force) against spring tension applied by the throttle lever.

Testing of these components took great skill, and involved a lot of individual components.

Although this is an overly simplified explanation, when we compare it to a common rail system, it highlights the difference we see in the modern diesel fuel injection systems fitted today

Here is an example of a generic BOSCH common rail system. Straight away you see the difference in the amount of components in this system. It is fully integrated into the vehicles ECU and calculates delivery based on many other sensors not mentioned in this diagram. For instance if the air conditioner is on and the engine is idling, more fuel delivery is required to maintain the same idle speed etc.

No longer is the fuel injection system a bolt on, and separate component on the engine.

These pictures show a closer view of the injection pump and injectors in their current form on a diesel common rail injection system. As you can see, this system is full of electronics.

The common rail pump (or high pressure pump) pressurises the fuel by means of mechanical plungers up to a staggering 30,000psi! This fuel is maintained at the desirable pressure within the 'common rail'. The injectors are directly linked to this rail and are constantly exposed the full pressure within the rail. (This is very different to a mechanical system where the injector is only exposed to the high pressure during it's injection cycle).

The common rail injector is then open and closed electronically (by means of a solenoid or piezo crystals). Even under this enormous pressure this injector can perform up to 7 injections per revolution.

Cleanliness is the most important factor in the common rail diesel system. On-vehicle filtration is normally 2 microns. Service centres that are authorised to repair these systems, such as Highway Diesel Service, have specialised diagnostic equipment and tooling. In fact to repair these injection systems requires a 'clean room'. This room is an enclosed, dust free and pressurised work area. As you can appreciate their technicians undergo extensive specialised training from the manufactures to repair these systems.

Common application diesel common rail pumps and injectors are now available at special internet only prices: (Please note: All prices are plus 10%GST and are on an exchange only basis and may differ slightly from the picture. Core charges vary between models and is refundable if the core is of repairable quality when delivered to our workshop)

Mercedes Benz Sprinter
Bosch Part number

Nissan Patrol ZD30
Part number

PLEASE NOTE: THESE ARE CODED INJECTORS AND THE CALIBRATION CODE MUST BE ENTERED INTO THE ENGINE ECU UPON FITMENT OF THESE INJECTORS.

Highway Diesel Service or your local Toyota dealer has the required tools for this job.