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Fuel Injectors Need TLC Too

Fuel injection and computerized engine management systems have not only given us less emissions, and more mpgs, they have also vastly improved drivability. Drivability refers to engine performance problems, or hopefully the lack thereof, such as stalling, hesitation, rough idling, poor fuel economy, and hard starting. Fuel injection systems are a big improvement over carburetors. Senior drivers will probably remember, though not fondly, the days of flooded carburetors, pumping the accelerator, hard starting on cold mornings or hot afternoons, re-jetting for different altitudes and vapor lock. These drivability problems have virtually disappeared with the advent of fuel injection. However, fuel injection is not infallible, and gives its own set of drivability problems, though more infrequent, if not cared for. As a bit of trivia, the 1990 Subaru Justy was the last car sold in the U.S. with a carburetor.

Today, most engines use port injection. Here there is an individual injector at each cylinder, usually located so that it sprays fuel right at the intake valve. Ideally, the injectors spray a fine mist of fuel so it vaporizes almost instantaneously. Vaporized, not liquid fuel, is required for combustion, and the finer the spray, the more efficient the combustion.

Dirty fuel injectors are the biggest problem with fuel injection systems that can lead to drivability problems. Dirty injectors don’t produce the fine spray needed for complete combustion. They can stick close 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 distribution - too much to some cylinders and too little to others - can result in misfiring. In today’s computerized engines, one missing cylinder can affect the other cylinders causing the engine to run even rougher. That’s because when a cylinder doesn’t fire, the unused oxygen goes out with the exhaust. The oxygen sensor then detects this excess oxygen and thinks the engine is running lean. Thus, the computer signals the injectors to stay open longer to add more fuel compounding the misfiring problem and increasing emissions.

Fortunately, today’s gasoline is designed for fuel injection systems so they are usually very clean. Also, filters in the fuel system trap virtually all the larger dirt particles and most of the smaller particles down to the 10-micron size. However, some dirt can get pass the filters especially in vehicles driven at low speed for long periods when the low fuel flow rate doesn’t cleanse out dirt from injector tips.

Like dirt, gum deposits can also result in drivability problems. When a hot engine is turned off fuel the injectors are “heat soaked”. Now, fuel can evaporate on injector nozzle tips leaving a gummy residue that can cause an uneven or off-center spray pattern leading to drivability problems.

There are a couple of ways to clean out deposits in injector nozzle tips. Sometimes, an “Italian Tune-Up” will work. Find an open stretch of highway and do a few full throttle accelerations.

If that doesn’t work, there are many commercial fuel injector cleaners on the market. Most recommend adding one container to a full tank of gasoline. Don’t add more than recommended since they contain chemicals that can damage rubber components in the fuel system. For preventative maintenance, periodically add the correct amount of cleaner to the fuel tank as recommended in your owner’s manual or on the container. These additives will help keep injectors clean especially if you do most of your driving in gridlocked traffic. Most gasoline today has some additives to help prevent and remove deposits, but it is still a good idea to use a quality fuel injector cleaner.

If this doesn’t work, you take your vehicle to a shop that specializes in servicing fuel-injection systems. Here the fuel injector lines are disconnected from the rest of the system, at the engine, and connected to a tank containing a cleaning solution. The engine is run on the concentrated detergent solution that usually cleans the injectors. It also removes carbon deposits off the backside of the intake valves allowing the air-fuel mixture to enter the cylinders better.

Next, the injectors can be removed from the engine and cleaned. If this doesn’t solve the problem, the injectors will have to be replaced. You should replace all the injectors, since if one has problems, it is likely others will have to be replaced sooner than later. Often, it is more cost effective to replace injectors in the first place rather than having them cleaned, only to find that they have to be replaced.