(most content from Larry Carley aa1car)

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, then performance, fuel economy and emissions are all going to suffer. Dirty fuel injectors can’t flow as much fuel as clean ones, and they can’t they delivery the correct spray pattern that is so essential for clean, efficient combustion and the horsepower desired. 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.

Troubleshooting can lead you to the fuel injectors needing to be cleaned, if an engine is experiencing any of the classic symptoms of dirty injectors, such as lean misfire, rough idle, hesitation and stumbling on light acceleration, a loss of power, and higher hydrocarbon (HC) and carbon monoxide (CO) emissions. Lean misfires can cause newer systems (OBDII) to read a misfire code or multiple codes depending on the effected injector(s).

Sometimes Fuel Injectors Clog and it does not take much for this to happen. Restrictions in the 8 to 10% range can cause a misfire or other classic symptoms of the injectors “failing”. When an injector is not flowing at an optimum rate it causes the o2 sensor to read the unburnt oxygen resulting in a lean condition. The computer compensates by increasing the “on” time of all the injectors in the older multiport systems where the injectors fire simultaneously. This can create an overly rich fuel condition in the other cylinders. In turbocharged applications engine damaging detonation can occur due to the overly lean condition caused by the dirty injector. When a turbocharged engine is at high RPM’s and under positive pressure (Boost) it requires a much more accurate fuel flow than any other application. If the fuel injectors are dirty or out of balance at this time, your engine will surely be toast from the leaning effect of the dirty injector. Being proactive about this can save you a lot of money and headache in the long run.

In older pintle style injectors, the size and shape of the nozzle’s orifice would determine the amount of fuel and the spray pattern the injector would have, respectively. These pintle style injectors are more prone to injector cloging where the new style injectors, while still subject to clogging, are less vulnerable. Pintle style injectors have a much nicer cone (or “conical”) spray pattern to them while the latter injectors do not atomize the fuel as well.

Fuel itself is what causes deposits that lead to a fuel injector clogging. Gasoline is a mixture of many heavy and waxy compounds made up of different hydrocarbons, including oilfins. The heavier the hydrocarbon, the more energy it yields when it burns. Fuel injectors undergo a lot of heatsoak when the engine is turned off. The waxy oilfins are left behind when the fuel residue in the injector nozzle evaporates. While the engine is off there is no airflow to cool the injectors down or fuel flow to wash away the residue. This is what causes the oilfins to harden and cause deposits, clogging the injector(s) over time. Because this is a perfectly normal consequence of engine operation, detergents are added to gasoline to help prevent this as much as possible. When an engine is run hard or for very short trips, the deposits can build up faster than the detergents can help to wash them away. This is the same principle used with turbochargers and the use of a turbo timer. Turbo timers are primarily marketed to allow an engine to run for a period of time (usually specified by the end user) to allow the car to “cool” before stopping the flow of fluids.

Common sense would tell you that the location of the fuel injector in relation to the heat would lead one injector more prone to clogging than others. In a standard 4 cylinder application the number 2 and 3 cylinder / injectors are the hottest and more prone than the number 1 and 4 injectors. In a 6 and 8 cylinder engine, the middle injectors are also in the greatest risk. Primary injectors on a Mazda rotary engine (20B or 13B) are more at risk than their secondary counterparts placed higher up and in the intake manifold rather than in the engine block itself. Same goes for throttle body injection injectors.

Saving those few cents on buying cheap gas can only more matters worse and speed up the effects of the oilfins clogging the injector. Refiners have cut back on the amount of detergents and the quility / effectiveness of the detergents used to increase profit margins and be more competitive in the gasoline market. Deposit-control additives that are commonly used include polysibutylamine, polyisbutylene succinimide and polyisobutylene phenylamine. 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. These fluidizers can contribute to the formation of combustion chamber deposits that raise compression and the engine’s octane requirements. Polyetheramine is one of the best additives to keep 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. 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 $.01 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.

What are the Benefits of cleaning and balancing your fuel injectors? Its obviously will depend on the condition of the fuel injectors prior to the cleaning. Older more “clogged” injectors will notice a much larger improvement over injectors that are less accumulation of deposits. No matter the starting condition of the fuel injectors, an increase in performance and fuel economy will pay for the cleaning in a matter of no time. Most high-mileage engines and engines that are used mostly for short trip stop-and-go driving are the most likely prospects for injector cleaning. High performance applications are even more important to maintain and keep in balance. We recommend cleaning the injectors every 25,000 to 30,000 miles to keep them flowing at peak efficiency.

On car, or off the car cleaning. What do we recommend? It depends… there is a place for both.
The easiest thing to do is to clean them on the car as removing the injectors can be a real pain in the you know what… Running the cleaner on the car can clean the intake runners, combustion chambers, valves as well as other components. This is especially helpful when the engine is full of carbon deposits. You can usually tell the results within a few minutes. It is usually recommended that the fuel return line is capped off . This can cause engine codes to be thrown by the ECU.

Even though on the car cleaning is a much easier process, it is not always the answer. An injector that is very clogged will not pass enough of the cleaning fluid through it for a thorough cleaning. Even if an injector does break a deposit loose, the injector’s filter will catch this particle and may lead to another “clog” in the system. Here at Injector-Rehab when doing a full injector service with off the car method, these filters will be replaced. If on the car cleaning does not work the first time, multiple applications may be required. The chemicals used in these cleaners can also cause serious damage to other components in the car.

Injectors that are really dirty may not respond well to on-car cleaning. You may have to use a more powerful solvent and/or longer cycle time to loosen these baked-on deposits. Off-car injector cleaning is a more expensive service because of the labor involved to remove the injectors (which can be considerable on some applications), and it requires special equipment that can cost upwards of $15,000. Many shops charge between $25 and $35 per injector for off-car cleaning – which makes it more costly than on-car cleaning.

Here at Injector-Rehab we are currently charging $18 per injector for port injection cleaning. $25 for Dynamic injector cleaning. It also can save motorists a lot of money because off-car cleaning is a lot cheaper than replacing the injectors with new ones (which can cost hundreds of dollars a set!). Off-car injector cleaning can often restore dirty injectors that fail to respond to on-car cleaning. That is why we only do off-car cleaning. We do not want to have to clean the injectors twice. Off-car cleaning takes more time (typically 30 to 45 minutes after the injectors have been removed), and our machines have an ultrasonic bath that can be used to soak badly clogged injectors. Our machines also reverse-flush the injectors which provides an added measure of cleaning. Another reason for using off-car cleaning equipment is that the injectors are flow-tested after they have been cleaned to verify their performance. The injectors are mounted on a test manifold and energized to spray solvent into clear graduated cylinders. By comparing the volume of fuel delivered, it is easy to see if all the injectors are flowing evenly. As a rule, you should see less than 2% to 5% variation between injectors (We aim for 1% or less variation between injectors!). If an injector is not passing as much liquid as its companions, we do more cleaning. If it fails to respond to additional cleaning, there is no guesswork about which injector needs to be replaced. Flow-testing also allows us to compare the actual flow rate of each injector. If the flow is within specifications, we know the injector should perform properly when it is reinstalled back in the engine. Flow-testing also is a good way to make sure the injectors are the right ones for the engine (one or more injectors may have been previously replaced by someone else). A flow test on the cleaning equipment allows us to see each injector’s spray pattern. If we see a normal, cone-shaped mist then we know the injector is flowing properly. If we see streamers of unatomized liquid in the spray pattern, we know additional cleaning is needed or the injector needs to be replaced.