5 November 2008
Fuel Injection Systems
Injector TLC
Fuel injection systems have been used in most passenger vehicles since the early 1980s and have been dramatically improved over the years.
Some traditionalists would still rather have a carburetor today, but it’s heavier and takes more fuel to move— not good considering gas prices today. A carb may have slightly more power, but that’s only for those that really want extreme power. People with family vehicles are pretty content with the power they have. Fuel injection and computerized engine management systems have given vehicle owners lesser emissions (great for the environment), more kilometres per litre, and vastly improved drivability.
SFI
Today’s fuel injector system is electronic (EFI) with several injectors that can fire in groups, one at a time or all together. If they fi re all at once (the simplest way) there are two shots of fuel per combustion cycle. Sequential fuel injection (SFI) fires the injectors one by one—in fact, these injectors fire in the same order as spark plugs. OBDII and all 1996+ systems use SFI. The injectors are electronically controlled valves that are supplied with pressurized fuel by the fuel pump, so they open and close many times per second.
Fuel injection maintenance isn’t something you do frequently, but when your customer brings you a vehicle that’s hesitating, getting poor gas mileage, is sluggish, or having trouble starting, you must consider the fuel injection system; after all, it’s the “main artery” of the heart of the vehicle—the engine. It likely needs to be cleaned because deposit build up has occurred over time from the fuel injection process. When the injectors propel fuel into the engine’s combustion chamber, it mixes with air and is ignited by the spark plugs (combustion). This is a very heat intensive process and the burning fuel can leave carbon deposits on pistons, valves and injector nozzle heads. This causes fuel restriction and now needs servicing. Some TLC is needed for the injectors!
Dirty injectors
Dirty injectors can’t produce the fine spray needed for complete combustion. They can stick closed and not supply any fuel, spray more fuel in one direction than another, leak fuel continuously, or deliver different amounts of fuel to the individual cylinders. Uneven fuel can result in misfiring. One missing cylinder in today’s computerized vehicles can affect other cylinders, making the engine run rougher. When a cylinder doesn’t fire, the unused oxygen goes out with the exhaust. The oxygen sensor then detects the excess oxygen and thinks the engine is running lean. The computer then tells the injectors to stay open longer to add more fuel, thus making the misfiring problem worse and increasing emissions.
Today’s gasoline was designed for fuel injection systems, so they’re usually very clean and filters in the fuel system trap nearly all the larger dirt particles plus most of the smaller ones. Some dirt does get past the filters, but usually in vehicles driven at low speed for long periods when the low fuel flow rate doesn’t clean dirt out of injector tips.
Engine problems can also result from gum deposits. Turning off a hot engine leaves the injectors “heat soaked.” Fuel can evaporate on injector nozzle tips and leave a gummy residue that can cause an uneven or off-centre spray pattern.
Clean injectors
To fix the problem, the injectors need to be disconnected from the rest of the system at the engine, and then be connected to a tank filled with a cleaning solution. Running the engine on the concentrated detergent solution usually cleans the injectors. In addition, it removes carbon deposits off the backside of the intake valves. This allows the air-fuel mixture to enter the cylinders better.
You can also remove the injectors from the engine and clean them. If this doesn’t solve the problem, the injectors will have to be replaced. If one injector has a “problem,” you should change all of them because they’ll likely need replacing soon. You should tell your customer it’s more cost effective to replace injectors in the first place rather than having them cleaned, only to find that they have to be replaced. | 
