General Motors Company's 3800 engine is a V6, 3.8-liter engine. Produced between 1995 and 2008, the GM 3800 was installed in over six-million vehicles. The 3800's fuel injectors are positioned three on each side of the V engine. The fuel injector sprays pressurized fuel into the combustion chamber when charged solenoid opens a valve in the injector. Failing injectors commonly trigger and engine code that turns on the "Service Engine" light in the instrument panel. A scan tool may be used to read the engine code to determine which cylinder requires fuel injector testing.
Unplug the fuel injector electrical connection from each of the 3800's six fuel injectors.
Adjust the multimeter to measure ohms resistance. Place the metal ends of the red and black multimeter leads into the fuel injector plug terminals. The leads can be touching either side of the plug, but both sides must be touched at the same time to properly test the resistance.
Read the ohms measurement on the multimeter. Mark down the cylinder number and the resistance measurement associated with the cylinder.
Repeat the resistance test on the remaining five fuel injectors, noting each value with the associated cylinder.
Compare the ohms measurements. Individual measurements should approximate all the other measurements. If one cylinder's fuel injector is producing a significantly higher or lower resistance measurement, the injector has likely failed, or will fail soon.
Replace any injector that fails the resistance test.
Turn the ignition key to start, but do not start the engine.
Disconnect the fuel injector electrical connection. Move the electrical plug into a position you can insert the multimeter leads into the plug.
Adjust the multimeter to measure voltage. Insert both leads into the electrical plug, one in each side. It does not matter which colored lead is in each side.
Monitor the voltage output on the multimeter. The voltage should read approximately 12 volts.
Replace any fuel injector receiving 12 volts that fails to operate.
Touch the tip of a long-handled screwdriver against the flat plastic top of the fuel injector.
Press your ear to the handle of the screwdriver. Listen for a clicking sound. The clicking sound transferred through the screwdriver indicates the solenoid is operational, pulling the valve open.
Replace any injector which passes the electrical plug test but fails the solenoid and valve test.
Connect a scan tool to the OBD-II reader. On GM vehicles equipped with the 3800 engine, the OBD-II reader port is located near the driver's side kick panel under the dash.
Pull the codes from the engine's on-board computer.
Look up the codes in the scan tool's code reference manual. Fuel injectors failing to produce a sufficient flow of fuel may trigger a "lean" combustion code. Fuel injectors with broken valves or which allow too much fuel into the cylinder may trigger a "rich" combustion code. Failed fuel injectors may result in a cylinder "misfire" in the cylinder.
Replace failed fuel injectors. For injectors which may be incorrectly injecting fuel into the combustion cylinder, consider a fuel system cleaner which cleans fuel injectors.
