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Direct Petrol Injection (DPI)

Issues and Diagnosis.

With over 2 million vehicles on road in Australia and New Zealand fitted with a direct injection petrol engine it is evident that this technology is seen as the way forward by vehicle manufacturers. Improvements in fuel economy as well as increases in engine torque and horsepower make the use of direct injection technology a no brainer when it comes to driving your fuel dollar further and providing more power from smaller capacity engines. The benefit of lower exhaust emissions is also another by-product of this process.

What is direct petrol injection and what are the benefits and drawbacks to using this technology?

Direct Petrol Injection engines go by many names including GDI (Gasoline Direct Injection), DI and FSI amongst others and these engines are now used by such manufacturers as Mazda, Toyota, Audi, BMW, Volkswagen, and Kia to name just a few. The basic mechanics of this process sees the fuel injector mounted on the cylinder head to spray fuel directly into the combustion chamber to provide greater efficiency and power using the same amount of fuel. This direct injection results in a more complete combustion and the cooler temperatures provided by the injected fuel allow for a better compression ratio inside the cylinder thereby generating the greater power. Improvements in the range of 10-15 per cent for horsepower and as much as a 50 per cent improvement in torque show that with the increasing price of fuel this technology provides gains far superior than the old method of port injection.

What are some of the downsides that come from having a vehicle that uses less fuel for greater horsepower?

On certain direct injection engines, the back of the intake valves and their ports can become coated with carbon deposits. Carbon is the hard-black soot like substance that is produced from burnt fuel and is generated by hydrocarbons, metals and additives contained within the fuel. Over time, and if enough carbon builds up, it can cause rough idling, stumbling on acceleration, stalling, check engine lights, increased fuel consumption and a general lack of power.

Its predecessor, port injection or multi point fuel injection, had the injectors mounted in the intake manifold and the fuel spray was directed at the back of the intake valves prior to entering the combustion chamber. The side benefit of this method of injection was that along the way to the cylinder, the injected fuel provided the additional benefit of serving as a solvent that cleans the intake port and intake valve. Even in relatively new engines there will be some degree of oil lubrication that will make its way past the valve stem seals and down into the intake port whilst the engine is running. Over time and combined with heat, this oil will bake onto the valve and accumulate as carbon build up. Without the solvent effect of the fuel providing this cleaning, the carbon can form into deposits that break off and become jammed either on the intake valve seat or make its way into the cylinder and score the bore causing further oil burning and carbon build up. Both of these issues can be related to fuel economy and performance because the intake valve can’t close properly.These problems become more evident on vehicles that are only ever driven on short trips or do not reach optimum operating temperature for any significant period of time.

What can be done to fix these problems?

In a worst-case scenario, the engine’s cylinder heads may have to be removed to perform manual cleaning and de-coking which involves significant cost.

What happens if I run an injector cleaner with my fuel?

Running an injector cleaner fuel additive with your fuel will assist in cleaning your injectors but this will not alleviate the carbon build up on the intake valves as the fuel and additive does not come into contact with these areas.

Does running better fuel help keep my engine clean to eliminate carbon build up on my direct injection engine?

Vehicle manufacturers will always specify the preferred octane rating for their engine to maximise performance and assist in long service life. Running a high-quality modern fuel contains specific detergents and cleaners that will minimise carbon build up and maintain power. This however still does not clean the intake valves and ports but does assist in cleaning the combustion chambers as a step in minimising carbon build up and cylinder scoring and further oil burning. Many carmakers also issue new engine management software to help alleviate this problem by changing the amount of time the intake valves are open and adjusting the ignition timing. Newer calibrations can also help solve wear problems and driveability issues associated with the high-pressure fuel pump (HPFP) and updating these may save you from replacing the pump used on a direct injection engine.

Are there any products that can clean the cylinder head while still on the engine?

There are a number of upper cylinder head cleaner and detergent products that, with one or multiple applications, effectively clean the intake manifold and components as well as the intake valves and valve seats. Products such as the 3 Bond Super Engine Conditioner in either Petrol or Diesel variants are effective in providing solvents to the intake components that do not receive the cleansing effects of the fuel intake.

What are the benefits of regular oil changes on my direct injection engine?

Regular oil changes are highly recommended by manufacturers as the detergents contained in modern engine oil help break down and wash away carbon build up. These oil changes also assist in keeping valve control mechanisms working freely and effectively to ensure proper metering of fuel to maintain performance and fuel economy.

Many of the components in a high pressure direct injection setup will also benefit from regular oil changes and using an engine oil with the correct viscosity and friction modifiers as directed by the vehicle manufacturer. One of these critical components in this system are the high-pressure fuel pump (HPFP), as this main component is responsible for compressing the fuel, supplied by the electric fuel pump, to the pressure required for high pressure direct injection. The HPFP is mounted to the engine and mechanically driven by the camshaft and governed by the ECU to be able to vary the fuel output to match the load or power requirements of the engine.

If regular oil changes are not maintained this can cause wear between the camshaft lobes and the HPFP follower, in addition to carbon build-up in the intake. This carbon and sludge build up will prevent the HPFP from generating enough piston movement, therefore reducing the fuel pressure, in turn contributing to poor fuel economy and lack of power. This issue may be diagnosed as Fault codes being logged in the ECU and the malfunction indicator light (MIL) will illuminate. If incorrect engine oil is used this will adversely affect the HPFP and may cause premature failure due to inadequate lubrication of the camshaft and HPFP cam follower.

If the seals on the HPFP also fail this can allow lubricating oil to enter the fuel side of the intake when the engine isn’t running. Numerous rich fault codes will be logged in the ECU in this scenario.

As one of the premium suppliers to Repco, GOSS now provide a range of high-pressure fuel pumps as well as an extensive array of fuel and ignition components to ensure your vehicle runs to its optimum potential. GOSS are an iconic Australian automotive parts supplier and have been sourcing the best quality automotive equipment and components for over 75 years, so they know what goes into great replacement parts for your car. Goss offers a true genuine alternative often at a fraction of the price of the OEM.

So as can be seen, the benefits of direct fuel injection are numerous but not without potential downsides that may be difficult to alleviate if left unchecked. As with the operation of any vehicle it is vital that periodic maintenance is carried out in accordance with the manufacturer’s recommendations. In the case of direct fuel injection engines, the best method to eliminate issues are to run both high quality fuels and perform oil changes as required to ensure that carbon build up is reduced. The many additives and detergents contained within both modern fuels and modern engine oils do an effective job in cleaning and limiting carbon build up during operation. It is also beneficial to drive your vehicle for sustained periods to ensure the engine has a chance to heat up and burn traces of carbon that accumulate more frequently in daily and stop/start driving.

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