Clean fuel injectors are a must for peak engine performance, fuel economy and emissions. If the injectors are dirty and can't deliver their normal dose of fuel, performance, fuel economy and emissions are all going to suffer. Dirty injectors can't flow as much fuel as clean ones, nor can they delivery the correct spray pattern that is so essential for clean, efficient combustion. The fuel feedback control system will compensate for the leaning effect once it is in closed loop, but it can't correct the underlying condition that is causing the problem.

Where do the deposits come from? Mostly from the fuel itself. Gasoline is a mixture of many different hydrocarbons, including oilfins, which are heavy, waxy compounds. The heavier the hydrocarbon, the more energy it yields when it burns. When the engine is shut off, the injectors undergo heat soak. Fuel residue in the injector nozzles evaporates, leaving the waxy oilfins behind. Because the engine is off, there is no cooling air flow through the ports and no fuel flow through the injectors to wash it away, so heat bakes the oilfins into hard varnish deposits. Over time, these deposits can build up and clog the injectors.

The formation of these deposits is a normal consequence of engine operation, so detergents are added to gasoline to help keep the injectors clean. But if a vehicle is used primarily for short-trip driving, the deposits may build up faster than the detergents can wash them away.

Now here is the potential problem with purchasing cheap petroleum. To save a few pennies per gallon and to increase the competitive and/or profit margin of gasoline, some suppliers have cut back on the amount of detergent they add to their fuel or have switched to cheaper and less effective additives.

Commonly used deposit-control additives include polysibutylamine, polyisbutylene succinimide and polyisobutylene phenylamine. But these same additives also can build up on intake valve stems causing them to stick. To prevent this from happening, additional additives called "fluidizers" must also be added to the fuel. But, over time, these can contribute to the formation of combustion chamber deposits that raise compression and the engine's octane requirements.

Dirty injectors lean out the fuel mixture and contribute to lean misfire, hesitation and even detonation. Cleaning should restore like-new performance.

One of the best additives is polyetheramine. It keeps injectors, valves and combustion chambers clean without the help of any additional fluidizers - but it costs more than twice as much as the other commonly used additives.

How much additive does it take to provide an adequate level of protection? Industry sources say the recommended level is about 1,000 parts per million (ppm) of dispersant-detergent in the fuel - which costs the gasoline supplier less than a penny a gallon. Even so, as much as 85% of the gasoline that is being sold contains only one-tenth of the recommended dosage, or only 100 ppm of additive. Consequently, using cheap gas contributes to the formation of injector deposits.

The benefits realized by injector cleaning obviously will vary depending on the condition of the injectors prior to cleaning and how badly they were clogged. Injectors that are really dirty should show more of a noticeable improvement in performance than ones that have only a light accumulation of deposits. Either way, performance, fuel economy and emissions should all be better after a cleaning.

Most high-mileage engines as well as engines that are used mostly for short trip stop-and-go driving are the most likely prospects for injector cleaning. Some experts recommend cleaning the injectors every 25,000 to 30,000 miles to keep them flowing at peak efficiency.