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midautoparts.com INJECTOR CLEANING

"Dirty" injectors are a commonly encountered problem. Dirty is actually a misnomer because the problem isn't dirt but rather a buildup of fuel varnish in the injector nozzle. The olefins (heavy waxy substances) in gasoline form deposits that gradually accumulate and restrict injector nozzles. When this happens, the injector's normal cone-shaped spray pattern develops streamers that inhibit proper fuel atomization. Deposits also restrict theRacing Fuel Injector size of the opening and reduce the amount of fuel that's delivered per squirt, which leans out the fuel mixture causing hesitation, lean misfire, rough idle and similar driveability symptoms.

Though dirty injectors can often be cleaned with fuel additives, by feeding pressurized solvent into the fuel rail to flush the injectors on the vehicle, or by removing the injectors and cleaning them on special off-car cleaning equipment, sometimes the injectors are too badly clogged to be fully restored by cleaning.

HOW TO TELL IF INJECTORS ARE DIRTY
If a vehicle ix experiencing driveability symptoms that would suggest a lean fuel condition (hard starting, rough idle, lean misfire at idle, hesitation or stumble when accelerating, poor performance, etc.) the following tests can be used to verify dirty injectors:
* Power balance test -- Compares rpm drop between cylinders to identify weak cylinders. If compression is the same in all the cylinders, a single weak cylinder would probably indicate a dirty or dead injector. If all the injectors are dirty, this test won't help much.
* Fuel pressure drop test -- Measures drop in fuel pressure after fuel line is pressurized and engine is turned off. A gauge is used to measure the pressure drop when each injector is energized for the same period of time (a few seconds). Any injector that shows less of a drop than the rest is probably restricted.
* Off-car flow test. Injectors are removed from the engine and mounted on a flow bench. The amount of fuel that flows through the injectors into calibrated tubes is measured and compared. Flow should not vary more than 5% cylinder to cylinder. Low flowing injectors need to be cleaned or replaced. Injector replacement is also necessary if an injector is worn (which is not uncommon in high mileage engines) or has failed electrically (shorted or open). A working injector will make a buzzing noise as it cycles open and shut, but a dead injector will remain silent.

Accurate diagnosis of injector problems is essential beforeFuel Injector Spray - harmful deposits can build up around the injector nozzle and inside the injector any parts are replaced to rule out other possibilities. A bad wiring connector or computer circuit can render an injector inoperative. Air leaks past the rubber O-ring seal at the base of an injector can also mimic the symptoms of a clogged injector.

WHAT CAUSES IT
The following are all factors that can cause fuel injector clogging and restrictions:
* Low quality gasoline -- Many discount brands of gasoline do not contain adequate levels of detergent to keep fuel injectors clean. 
* Injector soak time - Worst case scenario would be 15 minutes of running followed by 45 minutes of hot soak, what around-town driving does. Deposits don't form while the fuel is flowing: only when it stops.
* Injector design - Pintle style injectors are more likely to clog up than injectors with ball or disc style valves.
* Fuel system configuration and injector tip temperature - High tip temperature means the formation of deposits, and the hotter it is, the more rapid the progress. Low hood lines and tightly packed engine compartments don't help.
* Geographical considerations - Injector failure rate is higher where it's hot and dry.
* EGR and PCV - Deposits on injectors and valves are promoted by EGR and PCV gases present in the intake passages at shutdown, which condense onto sensitive surfaces. This appears to be a big part of the mechanism that plugs injectors.
* Poor intake filtration - Leaking intake housing seals and gaskets can allow dirty air into the intake system, increasing deposit formation.
* Fuel stress - The constant heating and pumping of fuel through the pressure regulator and return line in a typical multiport injection setup may cause subtle chemical changes that can contribute to deposit formation.
* Engine operating temperatures and thermal characteristics - Heat is a big part of the problem so the cooling system design and function are important.

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