Car Repair – Diagnosing A Bad Fuel Injector

The carburetor used to be the go-to solution for mixing air and fuel in a car’s engine but it has been almost completely been phased out by electronic fuel injection systems, due to fuel injection being much more reliable and offering better performance over carburetors. While fuel injection systems are more reliable, they still aren’t 100% fail-proof and diagnosing a bad fuel injector is much easier than many people think.

How a Fuel Injector Operates

To understand how a fuel injector can fail, it’s important to know how they operate. The fuel in your gas tank is pumped from the tank to fuel lines that lead to injectors. Some high-performance cars, such as the Golf GTI, will have a secondary fuel pump in the engine bay. This ensures that the fuel in the fuel rail is of high enough pressure that it can be sprayed into the combustion chamber as a fine mist by the injector’s nozzle.

Of course, having fuel constantly spraying into the engine isn’t ideal. Fuel injectors are designed with a solenoid plunger. When your car’s ECU (Electronic Control Unit), which controls engine timing and fuel-air ratio in the engine, sends a signal to the injector, a solenoid activates in the injector, pulling the plunger backward, and allowing fuel to spray into the engine. When the ECU stops sending the signal, a small spring in the injector pushes the plunger forward and prevents any fuel from escaping the injector.

Signs Of a Bad Injector

Fuel injectors go bad when the solenoid or the spring fails. Cheap fuels can also cause the injectors nozzle to degrade over time preventing the plunger from stopping fuel flow. Cheap fuels, along with carbon build-up, can also clog or block the injectors nozzle. A bad injector has the following symptoms.

• Fuel Leak

  A part of the injector sits outside of the engine and connects to the fuel rail. Damage to this section will cause fuel to escape through the injector and leak inside the engine bay. If you open your hood and you can either see or smell gasoline, your injector may be cracked.

• RPM Variation

  If a fuel injector is badly corroded or is jammed in the open position fuel will constantly be spraying into the engine, causing your RPMs to fluctuate when the car is at idle or with a constant load.

• Misfires

  A blocked injector, or one where the plunger is stuck in the closed position, will cause the engine to misfire. A misfire occurs when there’s too little or no fuel in the combustion chamber and the spark plug ignites nothing. This leads to a decrease in performance, fuel economy, and causes a delay in acceleration. However, there are several other reasons misfires occur.

• Engine Vibration and Rough Idle

  When the engine does not get the right amount of fuel for each cycle, the cylinder is not able to fire. This causes a drop in your RPMs at idle and can cause the car the engine to vibrate more. If your idles drop low enough the car will stall out instead of idle.

Repairing an Injector Issue

There are three ways to repair an injector problem. If your injector has failed due to a blockage, injector cleaner can be added to fuel to help clean out the injector and free the blockage. In more severe cases a professional will need to remove the injector and clean it with kerosene or similar cleaning materials.

Some injectors are serviceable, which means the solenoid, plunger, and electrical contacts can be removed. Once removed these parts can be further cleaned, or have parts that have failed, such as the solenoid, spring or plunger seal, replaced. Where fuel or age has corroded or cracked an injector, its recommended all of the injectors be replaced. It is also wise to request your mechanic flush your fuel tank and lines so that your new injectors operate properly.

If you suspect one of your injectors has failed, and you’re unsure of how to proceed, pop into our Pompano Beach Automotive repair shop, and one of our friendly performance shop pro’s will happily assist you.