Servicing Fuel Injectors: On-Car versus Off-Car

SERVICING FUEL INJECTORS
Adapted from various articles and research papers


The Problem

When fuel injectors get dirty, they restrict the necessary fuel flow and do not deliver the correct spray pattern necessary for optimal combustion. The fuel feedback control system will compensate for the leaning effect once it is in closed loop, but it cannot correct the underlying condition that is causing the problem.

Injectors should be serviced when: an engine exhibits lean misfire, rough idle, hesitation and stumbling on light acceleration, a loss of power, and/or higher emissions. Lean misfire may trigger a misfire code and trip the Check Engine light on newer vehicles with OBD II systems.


Fuel Injector Clogging

A restriction in fuel flow of 8% to 10% in a single fuel injector is enough to cause a misfire. When this occurs, unburned oxygen enters the exhaust and makes the O2 sensor read lean. On older multi-port systems that fire the injectors simultaneously, the computer compensates by increasing the on time for all injectors. This can cause the mix to the other cylinders to be too rich. Fuel flow restriction in turbocharged engines can damage the engine. When the engine is under boost and operating at higher rpm, proper fuel delivery is critical. If the injectors are dirty and the fuel mixture too lean, engine damaging detonation can occur.

Older vehicles with pintle-style multi-port injectors are most susceptible to clogging. In the early pintle-style injectors, the nozzle shape and orifice size determines 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. So that fuel deposits accumulating in the nozzle area can restrict fuel delivery and disrupt the spray pattern causing a lean fuel mixture.

Fuel Injector Deposits

Gasoline is a mixture of a variety of hydrocarbons including olefins 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 olefins behind. Because the engine is off, there is no cooling airflow through the ports and no fuel flow through the injectors to wash it away, so heat bakes the olefins into hard varnish deposits.

Another more recent culprit is the addition of ethanol. Ethanol absorbs water and gums up gas engines, particularly outboard motor engines. Over time, elements of the fuel you use to power your engine will clog the injectors. Detergents are added to gasoline to help keep injectors clean but detergents provide limited protection, especially if the vehicle is used in stop and go, short distance driving. All cylinders do not clog equally. The ones in the hottest location on the motor will clog faster due to heat soak.


On-Car versus Off-Car Cleaning

On-Car Cleaning

The easiest way to clean fuel injectors is on the car because you don’t have to remove them. You can run cleaner through the injectors while the engine is running and be done in 15 minutes but preparation takes time and the process is risky and imperfect.

Drawbacks to On-Car Cleaning
Pressurized equipment must be used to feed the solvent directly into the fuel rail while the engine is running

Disabling the fuel pump and plugging the fuel return line or installing a U-tube so fuel recirculates back to the tank can be messy and time consuming.

Disabling the fuel pump can set a fault code on some cars

Badly clogged injectors that are not thoroughly cleaned in one cycle must be done again.

Testing fuel injectors after cleaning is difficult and time consuming while still on the car.

Effective reconditioning requires a less than 10% power variation between cylinders; only an off-car injector pressure drop test will confirm this.

If the on-car cleaning was not entirely successful, you will still have to remove the injectors for more thorough cleaning or replacement.

Concentrated cleaning solvent is difficult to regulate while feeding through the fuel system under pressure.

Solvent can damage fuel system components.

Feeding high pressure, highly flammable solvent into the engine while it’s running is risky.


Off-Car Cleaning

When performed by qualified technicians in a shop equipped with the proper equipment, off-car testing and reconditioning is the most thorough and cost effective method.


Advantages to Off-Car Cleaning
:

The cost to the customer per injector for off-car cleaning is typically between $25 to $40 compared to $100+ for each new injector.

The process is thorough, often restoring dirty injectors that fail to respond to on-car cleaning.

All Fuel Injector, Inc. Optimizers™ come with an ultrasonic bath to clean badly clogged injectors.

All Fuel Injector, Inc. Optimizers™ reverse-flush the injectors, providing added cleaning.

Off-car machines can flow-test injectors after cleaning to verify performance.

Optimal functioning (5% to 7% variation between injectors) can be verified and the malfunctioning injector precisely identified for additional cleaning or replacement.


The Importance of Flow Testing

Flow-testing allows you to compare the actual flow rate of each injector to factory specifications. If the flow is within specifications, you know the injector should perform properly when it is reinstalled back in the engine. Flow-testing also lets you verify that the installed injectors are the right ones for the engine and not incorrectly replaced on a previous occasion. Performing a flow test with a Fuel Injectors, Inc. Optimizer™ allows you to see the spray pattern of each injector. If you see a normal, cone-shaped mist, you know the injector is flowing properly. Streams of un-vaporized liquid in the spray pattern indicates additional cleaning is needed. An injector that fails to respond needs to be replaced.