2. A second chemical method of cleaning the injectors is the use of a cleaner that is run through the fuelrails and injectors. This method allows a stronger mix of cleaning chemicals than you should put into the gas tank (the stronger mix of chemicals could possibly damage the fuel system). This cleaning method can do a good job, but again, it does not allow you to check the fuel-injector spray pattern, plus the fuel "filter" built into the fuel injector may become plugged with contaminants that may be washed into it.
3. Our preferred method for cleaning fuel injectors is with an ultrasonic fuel-injector cleaner/fuel injector flow bench, such as the ACE/ASNU unit we use. The ultrasonic cleaning method involves cycling the fuel injectors while the fuel-injector tips are immersed in an ultrasonic bath that uses an environmentally friendly cleaning fluid to clean the injectors. The flow-bench portion of this tool also allows a user to perform a flow test before and after cleaning, and it also allows the user to observe the fuel-injector spray pattern. This method is more labor intensive because it requires that the injectors be removed from the engine and installed on a test fixture to perform the testing procedure.
Checking the Fuel-Injector Flow
A fuel-injector flow bench, such as the ACE/ANSU unit, can be used to check the actual flow from the fuel injectors at any load condition or engine rpm (fuel injector on-time) you choose to simulate. The flow bench also allows the user to observe the injector spray patterns and actually measure the fuel flow from each fuel injector so the user can actually see if the injectors are truly flow matched.
Not all fuel injectors are created equal. Most new OEM fuel injectors are held to a +/- 2-percent production flow variance. Ideally, each fuel injector would flow exactly the same, but holding a production line to that standard would raise the cost of the fuel injectors substantially. The replacement aftermarket fuel injectors that you buy at your local auto parts store are in some cases not built to the same flow standards as the OEM fuel injectors are held to. Also due to part number consolidation, the aftermarket fuel-injector flow rate can vary as much as 25 percent when compared to the OEM fuel injectors that the computer in your Corvette was programmed for.
If the fuel flow and spray pattern are not the same from each fuel injector used on an engine, the air/fuel mixture delivered to each cylinder of the engine will vary. When the air/fuel mixture varies by more that 6-8 percent from cylinder to cylinder, the engine will have cylinders that are running too rich and cylinders that are too lean. When each cylinder of an engine does not have the correct air/fuel mixture, the engine's power output, drivability, and fuel-mileage potential will suffer. The fuel injectors should always be replaced as a set, unless you are confirming the replacement injectors flow volume and spray pattern are the same as the original injectors by flowing them on a fuel-injector flow bench.
The General Motors Multec fuel injectors that were used in the Corvette Tuned Port fuel-injected engines produced in 1985 through the early '90s had problems where the insulation on the fuel injector coil windings would deteriorate and then allow the injector coil to short circuit. The problems you may experience can vary from an occasional one-cylinder miss (caused by an intermittent short in the injector coil) to a totally dead cylinder (a shorted coil in the injector coil that no longer supplies any fuel to the cylinder). To test the Multec fuel-injector coil for an intermittent short circuit, we use the OTC/SPX No. 3397 fuel-injection tester (this tool checks the fuel-injector coil while it flows current through it) and/or by flowing the fuel injectors on the ASNU fuel-injector flow bench. If one or more fuel injectors have failed due to shorted coils, we would suggest replacing all the injectors because the coils in other fuel injectors will most likely short/fail in the near future.