Maintaining your EFI – Part 3 of How to keep your car always new?


The benefits of EFI systems for improving efficiency and drive-ability have now been universally recognized. In Pakistan, these systems are also in widespread use, but due to the variable quality of the fuel and the service conditions, some special considerations will be presented in this short article.

Let us start by considering the structure of a typical fuel injector and basic operation.

As shown in the diagram, there are only a few parts to a fuel injector. The pressurized fuel rail supplies fuel which passes through a small and very fine fuel filter. This filtered fuel is held up in a plunger assembly that is opened by a solenoid when an electrical signal is received from the ECU. A spring shuts the plunger when the signal is removed. The fuel goes to the tip, which then sprays it in a fine atomized mist to help create the air:fuel mixture in the intake tract of the cylinder just upstream of the intake valve.

Understanding this structure is the key to keeping it working as well as possible.

The first requirement is good fuel supply;

This means clean and cool fuel at the correct pressure. So the main fuel filter in the tank must be kept clean and the pump in good condition. One thing to note is that electric fuel pumps use the petrol they pump as a cooling aid for themselves, so it is a good idea to keep at least one-quarter tank of petrol in the tank at all times. Running low as a matter of habit can cause overheating of the pump, leading to a shortened service life. The fuel lines should be kept away from all moving parts and those at high temperatures, specifically exhaust components. This hold true in the engine bay as well. Lastly, the pressure in the fuel rail to which the fuel injectors are connected must be at the specified pressure. There is a connection port to which a pressure gauge can be attached to check pressure. It is to be noted that the fuel rail holds this pressure even when the engine is switched off. This is maintained by a anti-drain back pressure valve on the supply side and the fuel injectors themselves on the output side, and slow leaks at either end can cause a loos of pressure after standing for a few hours, and this can be one of the causes of difficulty in starting.

The second requirement is a good ECU signal;

This means that all the sensors that feed their signals to the ECU must be in good working order. Those sensors will be the topic of a future article but suffice it to say here that the air filter/MAF sensor and timing signals from the crank/cam position sensors are among the more important signals needed by the ECU. For purposes of this article, the electrical connection to the fuel injector is important. Each injector has an electrical connector and this should be checked for corrosion and good contact between terminals. Also, this part of the wiring harness passes over the head and other hot components and  care should be taken with proper routing of the wires with all clips and heat shields in place. Any deterioration or chafing must be addressed as appropriate.

The third requirement is a good spray pattern;

This means that the tip of the nozzle must be kept clean. Buildup of varnish and sludge due to poor quality fuel can greatly disturb the spray pattern, as shown in the figure. This leads to poor atomization and causes poor economy. If the spray pattern of the injector is disturbed to the point that part of the spray hits the cylinder wall, it will wash of the film of lubricating oil from that portion, and greatly increase wear and can even lead to burnt or broken rings, drastically reducing the service life of the engine. The periodic use of a fuel injector cleaning agent can be a good remedy for poor quality fuel. While there are many additives available in the market, two of the better ones that can be recommended are by Chevron (containing Techron) and Gunk (containing Regane).

With this background we can now see that taking care of the fuel injectors is straightforward. In spite of this, if the problems develop that can be traced to the fuel injectors, it is possible to service these injectors with an available service kit. These service kits contain a new micro-fuel filter, and replacement O-rings, plus any model-specific parts.

Even if a specific rebuild kit is not available, fuel injectors can be removed and thoroughly cleaned and tested for good operation. Soaking in a cleaning solution overnight is a good start, followed by blowing with compressed air to remove loose contaminants. The solenoid can be operated by supplying a 12 volt signal to the connector while running a cleaning solution through the injector. It is important to note that the 12 volt supply must not be continuous since that will burn out the solenoid quickly and also that they are not designed for continuous operation. Rapidly switching the signal on and off gives the best results. Dedicated test benches are available, but these are too costly for the average PW enthusiast. However, these results can also be achieved using simple DIY equipment. It is also important to note that no abrasives should be used during this entire process, specifically at the tip of the injector. Also, all O-rings should be coated with a small amount of oil before installation, and all removing/installation should incorporate a twisting motion to prevent damage to the O-rings.

A properly operating fuel injection system gives superior drive-ability compared to the older carburetor technology, and if these systems are maintained properly as outlined above, durability is also much superior, even in the difficult operating circumstances prevalent in Pakistan.