Fuel injectors direct fuel spray at an engine's intake valve. When a fuel injector becomes clogged or ceases to operate properly, engine performance problems will occur.
Most fuel injectors have an electrical resistance of approximately 10 to 18 Ohms, but check your vehicle's service manual for the exact amount.
Test Fuel Injector
Step 1- Turn off the vehicle.
Shut off the engine and remove the keys from the ignition.
Step 2- Remove the fuel injector electrical connector.
Remove the corresponding electrical connector from the fuel injector you wish to test. Move the wire out of the way for now.
Step 3- Locate the injector's electrical contacts.
You should see two metal prongs (contacts) inside the fuel injector housing.
Step 4- Measure the fuel injector's resistance.
Set the multimeter to the Ohms (Ω) setting. Touch the red meter lead to either injector contact, and the black meter lead to the other contact. Since you are in the Ohms setting it does not matter which lead goes on which contact. Be certain not to touch the meter lead tips together as this will cause an incorrect measurement. Repeat this step for all the installed fuel injectors you need to test.
Note: You should read approximately the same resistance on all of the fuel injectors. If one injector is reading much higher or lower than the rest, then it is likely faulty. If you read an open (O.L.), or zero Ohms (shorted), then that injector is bad.
Bonus: If in doubt whether the injector is faulty or not, try switching the suspect injector with a known working injector.
Fuel Injector Cleaning
If all the injectors read correctly, and you still have engine fuel problems, then you might have a clogged injector. Clogged fuel injectors will require a cleaning or replacement. The two types of fuel injector cleaning are on-car cleaning and off-car cleaning.
On-car cleaning is cheaper to the consumer and can be performed by the average garage mechanic for around $100. The cleaning kits can be found in most local automotive stores.
Use your vehicle's service manual for the following procedure.
Note: These instructions are general in nature and should not be followed for all vehicle types. Consult your service manual and the cleaning product instructions for any variations.
Step 1- Stop fuel flow to the injectors.
You will need to stop the fuel flow to the engine by disabling or removing the fuel pump, and capping the fuel return line.
Step 2- Disconnect the fuel regulator.
Disconnect the vehicles fuel pressure regulator by using the instruction given in your vehicle's service manual. Cap any open lines and ports to avoid contamination.
Step 3- Connect the cleaning kit.
Connect the pressurized cleaning detergent onto the injector system fuel rail as instructed by the product. Do not open the product's valve at this time.
Step 4- Remove gas cap.
Remove the vehicle's gas cap to relieve extra pressure. Don't forget to reinstall once you are all finished with the cleaning.
Step 5- Test the engine fuel supply.
Try and start the engine, as it should not with the fuel pump disabled. Turn off the ignition.
Step 6- Dispense the cleaning product.
Open the kit's pressure valve slowly and fully until you reach your vehicle's specified pressure reading as instructed on the product. This initiates the injector system cleaning.
Step 7- Cycle through the detergent.
Start the vehicle and let the pressurized detergent run through the system. The engine will die after the detergent is depleted.
Step 8- Reinstall all disconnected parts and lines.
Reconnect all the items previously removed including the gas cap, and run the car for a few minutes to return fuel to the system. If the detergent was able to unclog some of the injector grime, you should notice the engine running smoother than before.
Off-car fuel injector cleaning is accomplished at an auto repair shop and will cost significantly more than on-car cleaning, but will offer a lot deeper clean.