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Gasoline Direct Injection issues – Who or what is to blame?

By autotech-nath on May 24, 2023

Vehicle owners, workshops and vehicle manufacturers are seeing issues with Gasoline Direct Injected engines that cannot be put down to one fault. What’s behind the problems and what are the consequences? More importantly, what’s the solution? GDI specialist Phil Ellisdon of ASNU delivers his findings within a three-part series of articles.

Phil Ellisdon, CEO of ASNU, has been in this field for nearly 50 years. Back in 1989, he became the ASNU distributor for Europe, gained Lucas and Bosch homologation, and eventually bought the ASNU business in 2000, shipping the manufacturing from Australia to Bushey in the UK.

The family business services thousands of ASNUs in over 60 countries worldwide through their distributor network and the equipment can be found in most vehicle manufacturer technical centres. In this article, Phil shares details of the symptoms, causes, consequences, and solutions on GDI issues that you need to be aware of…

Let’s start at the beginning. The concept of Gasoline Direct Injection, or GDI, is not new – the first direct injection engine to use gasoline (amongst other fuels) to reach production was the 1925-1947 Hesselman engine, built in Sweden for truck and bus applications. As a hybrid between an Otto cycle

and a Diesel cycle engine, it could be run on a variety of fuels including gasoline and fuel oils.

So, if the design is perfect, the performance is fantastic and the reliability is outstanding, why are we seeing issues with GDI vehicles that cannot be allocated to anyone or any one thing? For those of you reading this and saying, “We don’t see problems with GDI”, you will understand more later in this article.

The GDI vehicle in use…

The perfect driving conditions for a GDI engine are as follows: Using top grade fuel (as advised in the vehicle manual from the manufacturer) you start the engine and head out to the motorway without traffic and without stopping. Drive 20 miles or whatever number of miles at the national speed limit up the motorway to your destination. Come off and drive without stopping, park up for the duration, then complete the same journey home.

The same scenario can be applied to the Diesel engine as well. If there were such a perfect condition, this would be it.

The reality is you start the engine and head out in the work/ school traffic to the M25 motorway in a Stop/Start enabled vehicle, so the engine automatically shuts off when stuck in the traffic and then starts and stops again 10 yards down the road when the traffic grinds to a halt again. This stop/start behaviour continues for the duration of the journey in the traffic. Then you hit the motorway and as its morning/evening the traffic is heavy and the stop/start process begins again. So, what is the problem we are seeing with GDI?

The answer is carbon build-up in the combustion chamber.

What causes carbon build-up?

It’s not any one entity, so let’s take a look at the contributing factors.

1. Fuel quality

The vehicle manufacturers stipulate that to maintain maximum engine efficiency with the minimum exhaust pollution a GDI engine must use the top-grade fuel. Now where fuel has an Ethanol content, the quality of fuel will vary from country to country, some owners prefer to use cheaper fuels as they have a cheaper car.

2. Driving conditions

The roads today are seeing more congestion than ever before, even clear roads have lower speed limits, and with engines encased in a much smaller location with smaller airflow access, the modern engine runs extremely hot, this heat quickly dries any residual fuel on the injector tip, it also dries any residual fuel in the combustion chamber creating the start of a carbon build-up.

3. Emission control

Emission control is the single one factor that EVERY vehicle manufacturer must comply with and although the GDI engine is by far the most emission-efficient produced, does produce more particulates than a Port Injected Engine. To ensure their vehicles produce a minimum carbon footprint, the VM’s Engine Management System, EMS, uses an automatic engine Stop/ Start system that switches off the engine when in traffic.

4. Fuel trim adjustment

In addition, the EMS also has Short- and Long-Term Fuel Trims that can add or reduce the amount of fuel the engine requires, controlled by various combustion performance sensors located on the engine. Unfortunately, this system has a flaw – it cannot see the injectors’ spray pattern and therefore cannot determine if the spray is good or bad, which could result in bad combustion, leaving residual fuel in the combustion chamber.

Are you now understanding where I am coming from?

5. Injector performance

The GDI Injector is the single most important component in the delivery and control of the fuel
that is delivered directly into the combustion chamber; one of the harshest environments on the engine. It has the finest tolerance of any mechanical part on the vehicle, it has a 30-micron filter in the fuel inlet neck and it is required to deliver a very specific amount of fuel in a very specific spray format and droplet size in milli second durations. All this precision in one component and yet nowhere in the lifetime of the vehicle is the injector filter recommended to be replaced or the injector tested or serviced. We change the air filter, oil filters and fuel filters, but not injector filters, why not?

Individually, these contributing factors may cause issues in the long-term running of the vehicle, but only the petrol will cause the carbon build-up. An efficient engine driven in perfect conditions will prove to be trouble-free but collectively these contributing factors can cause short- and long-term problems that will require a diagnosis and fix but, in some cases, damage the engine beyond economical repair.

Keep an eye out for Part Two in the June issue of Autotechnician where ASNU will be looking at the consequences.

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