Fuel injection cleaning and testing - Jebs Performance Engineering

We´ve all seen the classic symptoms of dirty injectors: lean misfire, rough idle, hesitation and stumbling on light acceleration, a loss of power and higher hydrocarbon (HC) and carbon monoxide (CO) emissions. And the older the vehicle, as a rule, the worse the driveability symptoms.

It doesn´t take much of a restriction in an injector to lean out the fuel mixture. Only an 8% to 10% restriction in a single fuel injector can be enough to cause a misfire. When this occurs, unburned oxygen enters the exhaust and makes the O2 sensor read lean. On older multiport systems that fire the injectors simultaneously, the computer compensates by increasing the on time of all the injectors, resulting in an overly rich fuel condition in the rest of the cylinders. HC emissions shoot up because of the misfire, and CO emissions rise because the computer is overfueling the engine.

All vehicles are vulnerable to injector clogging, but the ones that are most vulnerable and most likely to experience such driveability and emission problems are older vehicles with pintle-style multiport injectors.

In the early pintle-style injectors, a solenoid in the top of the injector lifts the pintle valve up off its seat. Pressure in the fuel line then forces fuel to spray out through the nozzle. The shape and orifice size of the nozzle determine how much fuel flows through the injector and the shape of the spray pattern. Most pintle-style injectors are designed to produce a cone-shaped spray pattern. But if fuel deposits accumulate in the nozzle area, it can restrict fuel delivery and break up the spray pattern causing a lean fuel condition and many of the problems just mentioned.

Read the full article Fuel Injector Cleaning - Unclogging a Common Condition, Larry Carley, Underhood Service, December 2000.

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