Fuel injectors play a critical role in a car engine’s fuel delivery system. It receives and sprays diesel or gasoline into an engine through the form of a high-pressure mist. If a fuel injector doesn’t work properly, it can lead to a variety of problems such as starting issues, poor performance, failed emissions, and increased fuel consumption. Given these problems, it’s important to know when it’s time to replace a fuel injector. Here are some of the top signs that indicate your fuel injector needs to be fixed or replaced.
If your fuel injector has a restriction of around 8% to 10%, it can lean out the fuel mixture and potentially cause a misfire. During a misfire, unburned oxygen will enter the exhaust and make the O2 sensor read lean. In the case of older multiport systems that simultaneously fire the injectors, the computer compensates for that by increasing the “on” time of the injectors. As a result, a rich fuel condition is created in the other cylinders. Remember that direct fuel injectors have more sensitivity to restrictions because of the exact amount of fuel that they inject into the combustion chamber.
- Turbo troubles
When using a turbocharged engine, dirty injectors can have a leaning effect that potentially leads to your engine being damaged by detonation. Particularly when your engine is under boost and operating at a higher rpm, it needs as much fuel as possible from the injectors. When the injectors are dirty and unable to meet your engine’s demands, the fuel mixture leans out, and detonation occurs. As a result of the leaning out, your car may experience turbo failure and higher than normal exhaust system temperatures.
- Heat soak
Fuel injectors go through heat soak whenever your engine is turned off. In the injector nozzles, fuel residue is evaporated, and waxy olefins are left behind. As a result of the engine being off, cooling airflow isn’t moving through the ports, and there’s no fuel going through the injectors to wash away the waxy olefins. The heat ends up baking the olefins into hard varnish deposits. The deposits build up and clog your injectors over time. Keep in mind that this can occur even in vehicles with low mileage because of short drive cycles and increased heat soaks that clog the injector. Gasoline can have detergent added to it to help keep car injectors clean.
Nonetheless, if you’re only using your car for short-trip drives, deposits can build faster than the detergent is able to wash away. When looking for build-up in your fuel injectors, remember that the middle cylinders of your engine are always the hottest, and will get clogged faster than the cylinders on end. If you have throttle body injectors, they’ll likely be less susceptible to heat soak since they’re located above the intake manifold. If you have direct-injection injectors, heat soak will potentially affect them because of their placement in the head.
- Longer crank times
Whenever your fuel injector leaks, it causes the rail to lose pressure when your vehicle is sitting. This loss of pressure results in a longer crank time because the rail needs more time to pressurize. In a diesel common-rail injection system, a normal crank time is three to five seconds. The common-rail pump will take this long to build fuel pressure to the threshold. At around 5,000 psi is when the fuel rail pressure for cranking starts to occur. When idle, common-rail systems can operate at 5,000 psi, and when at wide-open throttle, they can get up to 30,000 psi.
- Balance test failure
Injector balance tests can identify the bad injector if you suspect one of them is malfunctioning or clogged. The way the test works is that scan tools will disable injectors and isolate one of them for diagnostics. An effective diagnostic method you can use is observing the voltage changes from the O2 sensor. Be aware that even when your injector is disabled, dead injectors or leaky injectors can still be missed. Additionally, other problems with the mechanical components and ignition system may not show an RPM loss at the time you have the injector turned off. A sign that your fuel injector is in good condition is when the voltage from the O2 sensors drops to around 100 mV. If the problem has been a dead injector, long-term fuel trims possibly compensated for it so that the voltage wouldn’t change.
An additional test you can try is measuring the pressure loss in the fuel rail whenever each injector pulses for a set period. You can perform this test with an electronic pulse tester. You can monitor the drop in fuel pressure when each injector is energized through a fuel pressure gauge. The electrical connectors to all of the other injectors have to be removed to isolate the injector you’re testing. You want to ideally have each injector drop the same amount of pressure when opened. If there’s no drop or a very low drop, this may indicate that the tip or orifice is restricted. If the pressure drop is higher than normal, this can indicate a rich condition caused by a worn pintle or stuck plunger.
- Lack of resistance
At the top of your fuel injector is the solenoid. The solenoid is responsible for pulling up the injector pintle whenever the injector is energized. If the magnetic field isn’t strong enough to overcome the fuel pressure and spring pressure above the pintle, the injector may not open all the way. Solenoids will often short internally when an injector is failing, and that causes a drop in resistance. If a fuel injector only measures 1 ohm when a specification calls for 3, more current will be pulled by it than the other injectors. An excessive amount of current flow to one injector can cause the driver circuit to shut down and kill the other injectors that share that driver circuit. Be sure to check your injectors with an ohmmeter regularly.
A fuel injector that isn’t working properly can lead to many problems in your car. Be sure to look out for all of these signs to know if it’s time to fix or replace your fuel injector. You can learn more about fuel injectors at Goldfarb inc.