10 Symptoms of a Bad Fuel Injector
Most vehicles from the 1980s onwards have modern electronically injected engines (instead of carburetors). A key part of this system is the fuel injector. Even if your fuel injector never had any problems, sometimes it can become dirty, clogged or fail completely and need replacing.
Below are the most common symptoms of a bad fuel injector and the average cost to replace (if cracked) or clean (if clogged).
Common Symptoms of a Bad Fuel Injector
Here are some of the most common signs of a fuel injector problem: Be aware that the fuel injector in question may simply be clogged, so don’t automatically assume it needs replacing.
A bottle of fuel injector cleaner may help. Before spending money on new injectors, it’s even better to give them a thorough cleaning with a fuel injector cleaning kit.
1) Rough Idling or Engine Stalling
The vehicle is not getting enough fuel or the fuel delivery is uneven, causing the idle speed to fall below optimal levels, resulting in a rough or even rough idle. If the RPM is too low, the car may actually stall and you will have to restart. This issue is especially noticeable when the engine is cold or when stopped at a traffic light.
2) The motor vibrates
A bad fuel injector can prevent certain cylinders from firing properly, causing noticeable engine vibration. You may feel a rhythmic shuddering or hiccup-like sensation (from the seat or steering wheel) while driving, especially when traveling at a certain speed.
This occurs because the affected cylinder does not receive the proper amount of fuel, disrupting the engine’s normal ignition sequence. The intensity of the vibration may vary depending on which injector has failed and the severity of the failure. You may also notice that the vibration is more noticeable at certain speed ranges.
3) Engine misfire
Engine misfires occur when a cylinder doesn’t fire properly, often due to a clogged or defective fuel injector. You’ll probably notice a hesitation or wobble when accelerating, as if the engine is momentarily losing power. In some cases, you may feel a slight twitch or shudder.
Fuel injectors aren’t the only cause of misfires, but they are often the culprit, so they should be the first thing you check if you experience this symptom. If your engine’s air-fuel ratio is out of whack, you’ll need to fix the problem right away.
4) Check Engine Light Comes On
The most obvious sign of a problem with your car is when the “Check Engine Light” comes on on your dashboard. This can mean a variety of things, but a faulty fuel injector (indicated by a code like P0201, P0202, P0203, or P0204) could be one of them.
When the injectors deliver less fuel than required (and sometimes more), engine efficiency decreases and the check engine light can come on. Use an OBD2 scanner to check for the problem.
5) Fuel Leaks
When a fuel injector actually breaks or cracks due to damage or aging, it will start to leak fuel. You may notice moisture in the fuel rail area, and in severe cases, a puddle of gasoline on the floor below.
Most of the time, the leak is caused by a damaged injector seal. But no matter how severe the leak is, you’re dealing with fuel that poses a serious fire hazard. Get it repaired as soon as possible.
6) Fuel Smell
This will come with a fuel leak, but if your injector is damaged or stuck and you have gasoline that won’t burn, you’ll smell gasoline. Sometimes it may be due to a problem with the fuel lines or a faulty sensor that tells the ECU to inject more fuel than necessary. Either way, you need to find out what is causing the fuel smell and fix it immediately before it becomes a serious fire hazard.
7) Overloaded Motor
When the fuel injectors inject too much fuel into the engine cylinders, it overloads the engine. You may feel like your car is accelerating and decelerating slightly while maintaining the same throttle position. This uneven performance is especially noticeable when driving on the highway. Engine judder can also manifest as speed fluctuations under a constant load, instead of maintaining a constant speed.
8) Poor fuel economy
Just as a bad fuel injector won’t give you enough fuel, it can also give you more fuel than you need. One of the most obvious signs of this is having to fill up your gas tank more often than normal.
Your car’s computer may make the situation even worse by injecting even more fuel in an attempt to make up for the perceived fuel deficiency. Not only is this excess fuel consumption hard on your wallet at the pump, it’s never good for the environment either.
9) Failing Emissions Tests
And speaking of the environment, defective fuel injectors can cause uneven or incomplete combustion of fuel, leading to increased emissions. This means a much greater chance of failing an emissions test, and a guaranteed failure if the check engine light comes on.
In some cases, a leaking fuel injector can cause the mixture to become too rich, eventually burning out the catalytic converter.
10) Uneven Cylinder Temperatures
- If you have access to an infrared thermometer (Klein Tools makes a great, inexpensive one), you can use it to measure the temperature in the exhaust manifold.
- If the engine is running properly, each cylinder should be at the same temperature.
- If you notice a large temperature difference between the cylinders, you may have uneven fuel distribution. A likely cause for this is the fuel injectors, which are often accompanied by a decrease in engine performance. However, you should also look at the spark plugs.