6 Symptoms of a Bad Fuel Injector (And Its Replacement Cost)

Today’s internal combustion engines are relatively complex in nature, featuring some critical components, none any less valuable than the last. The vast majority of these components, as well as the systems they make up, have evolved significantly from what there were just 20-30 years prior.

Perhaps no automotive system has undergone such substantial revision as that which pertains to fuel delivery. What once was accomplished through the use of a carburetor, is now achieved with cylinder-specific fuel injectors, which atomize the fuel into each individual combustion chamber.

While this method of fuel delivery is rather efficient, it does come with its own inherent issues. Injectors can fail or can become plugged, leading to a number of secondary issues, many of which can significantly hinder a vehicle’s drivability. To fix such issues, one must be able to identify symptoms related to injector failure as they are encountered.

Read on to learn more about the various symptoms associated with fuel injector failure, as well as the cost associated with remedying problems of this nature.

What Do Fuel Injectors Do?

As their name would suggest, fuel injectors deliver fuel into a defined space, in order to facilitate combustion. More importantly, fuel injectors deliver this fuel in an atomized form, which proves far easier to combust efficiently.

Furthermore, injectors deliver fuel in a precise manner, as specified per engine timing.

This form of fuel delivery differs from carburetion due to the fact that fuel is dosed in a cylinder-specific manner. This not only leads to increased combustion efficiency and horsepower but reduced emissions as well.

Where Are They Located?

fuel injectors location

Fuel injectors are traditionally mounted within an engine’s intake manifold, within close proximity to each respective cylinder head. As fuel is injected, it is mixed with incoming intake air, and pulled via vacuum through an open intake valve. This configuration is true of most engines currently marketed.

However, there is an exception to this rule as well. Direct injection engines feature head-mounted injectors, which make in-cylinder fuel/air mixing possible. This is an engine design that has become increasingly prominent over the past decade.

See Also7 Symptoms of Ignition Coil Failure

Dirty/Clogged vs Faulty Injectors

A fuel injector can fail to perform as intended for multiple reasons. However, such issues can be largely consolidated into two categories, electrical/mechanical failure or clogging. Each of these issues can prove problematic and can lead to a host of troubling symptoms.

The term “faulty” is typically used to describe any fuel injector that has experienced electrical/mechanical failure. In such cases, an injector’s electrical circuitry fails, causing an open condition, or the mechanical internals of an injector degrade.

On the other hand, a fuel injector can also become carbon-fouled, thereby preventing an injector’s tip from opening/closing completely. This often results in an irregular fuel stream or a persistent fuel flip. Under either of these circumstances, engine performance is sure to suffer.

Signs of a Bad Fuel Injector

The presence of a faulty fuel injector is often accompanied by a number of troubling secondary symptoms. Recognizing these symptoms is key when attempting to expedite repair wherever possible.

The following are several of the most common symptoms of a faulty fuel injector.

1. Consistent Misfire

The presence of one or more faulty fuel injectors will lead to a misfire condition that is relatively consistent in nature. This will often lead to a noticeably rough idle, vehicle shaking, or even a certain degree of hesitation under higher periods of throttle demand.

2. Reduced Fuel Economy

A faulty injector robs an engine of a certain degree of fuel efficiency. This problem only compounds with each additional fuel injector that fails. This will perhaps be most noticeable at the pump, as fill-ups become ever more frequent.

Read Also8 Ways to Increase Your Fuel Economy

3. Reduced Power

Whenever an injector fails, total engine output is reduced to a specific degree. While this is most noticeable in smaller four-cylinder engines, this reduction in power can also be observed in larger engines of a “V” configuration.

4. Stalling At Idle

As mentioned above, a faulty fuel injector is often to blame for a rough idle and shaking while stopped. However, in the most severe of cases, the presence of a faulty fuel injector can cause an engine to stall and die when coming to a stop.

5. Rich Fuel Smell

In certain instances, a faulty fuel injector can cause your vehicle’s exhaust to carry a rich smell of fuel. This is especially true if the injector in question is hung open, allowing fuel to be dosed at an excessive rate, or at inappropriate times.

6. Check Engine Light

In the vast majority of cases, the failure of one or more injectors will quickly cause a vehicle’s check engine light to illuminate, as all applicable DTCs are stored.

This occurs as a result of the ECM’s ability to determine relative cylinder contribution rates.

See AlsoWhy is the Check Engine Light Blinking?

7. Car Jerks or Stutters When Accelerating

When a fuel injector is working properly, it sprays a consistent mist of fuel into the engine’s combustion chamber, which is then ignited by the spark plug. However, if a fuel injector is clogged, it can cause a misfire which in turn can cause the engine to run rough and produce a jerking or stuttering sensation when accelerating.

Bad Fuel Injector vs Spark Plug

Today’s gasoline engines utilize both fuel injectors and spark plugs to facilitate efficient combustion. While fuel injectors dose fuel to each respective cylinder, spark plugs are used to ignite this fuel, thereby initiating a combustion event.

Similarly, the failure of either one of these components can easily lead to a misfire on one or more cylinders.

For the reasons provided above, it is extremely important to take care when diagnosing a misfire concern. One can easily find themselves chasing fuel-related concerns that actually do not exist when a spark-related concern was the underlying issue at hand.

A trouble tree should be followed in its entirety, whenever addressing issues of this type.

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How Long Do Fuel Injectors Last?

faulty fuel injector

There are a number of circumstances that can directly affect the longevity of an engine’s injectors. This includes the frequency of engine maintenance, engine repair history, and overall engine operating demands. For this reason, it is impossible to predict the exact longevity of an engine’s injectors.

Nonetheless, most manufacturers specify that their fuel injectors should last for a total of 50,000-100,000 miles, without the threat of imminent failure. However, it is not unheard of for injectors to experience significantly greater lifespans than that which is specified by this general estimate.

Can a Malfunctioning Fuel Injector Damage the Engine?

A malfunctioning injector, if not cleaned or replaced in a timely manner, can indeed result in engine damage. This is due to the fact that irregularities surrounding the atomization and timed delivery of fuel can result in cylinder pre-ignition.

This term is used to describe a condition in which combustion takes place at less than optimal timing, or at a less than efficient rate. Prolonged instances of pre-ignition can result in damage to an engine’s combustion chamber, and the piston retained within.

Additionally, the excess downstream dosage of fuel into an engine’s exhaust can also lead to rapid deterioration of a vehicle’s catalytic converter. This often necessitates costly, and otherwise unnecessary repair.

Do Fuel Injector Cleaner Products Actually Work?

In certain instances, the use of commercial fuel injector cleaners can prove helpful when attempting to renew carbon-fouled injectors or even help unclog a catalytic converter. However, the use of these products should not be considered a cure-all, nor a replacement for the removal and hand cleaning of dirty or clogged injectors.

Fuel injector cleaner is best used periodically as a preventative means of warding off carbon fouling. This tends to be a far more effective approach than simply attempting to treat the issue after it has already compounded to an unmanageable degree.

After carbon-fouling has reached a certain threshold, there is little chance of reprieve through injector cleaner use.

Fuel Injector Cleaning Cost

Fuel injector cleaning costs pale in comparison to that of total injector replacement and serve as a cost-effective means of remedying injector-related issues, assuming that no electrical or mechanical failure has taken place.

While injector cleaning is typically handled by professionals, those who are mechanically inclined can clean their own injectors at home, to a high degree of success.

The following are the average costs associated with fuel injector cleaning:

Professional Cleaning Cost

In the event that you choose to take your vehicle to a professional shop for a fuel system/fuel injector cleaning service, you can expect to pay somewhere within a range of $60-$150 for such services.

Cleaning severely fouled injectors is a far more pricey proposition, often costing nearly as much as fuel injector replacement, due to the extensive labor required. In such cases, one can expect to shell out approximately $350-$700.

DIY Cleaning Cost

If so inclined, one can also remove and clean their vehicle’s fuel injectors themselves, eliminating unnecessary expenditure along the way. In such instances, only those materials required to perform services per manufacturer are required.

In most cases, these supplies and materials total up to no more than $100. You simply need cleaning kit (like this one) which allows you to easily test and clean individual injectors, fuel injector cleaner (like Seafoam or B-12 Chemtool)

Fuel Injector Replacement Cost

The exact cost associated with fuel injector replacement differs from one model of vehicle to the next. Price fluctuations are also to be expected between dealership-based and private shop-based repairs.

For this reason, it’s always important to receive multiple quotes before determining where to have any such work conducted.

Though figures can differ significantly depending upon a number of variables, one can expect to pay approximately $400-$1,000 to have their vehicle’s fuel injectors replaced.

The lower end of this spectrum typically relates to smaller sedans featuring four-cylinder engines, while higher costs tend to be associated with V8-powered vehicles.

Is It Ok To Replace Just One Fuel Injector?

broken fuel injector

It is never advised to replace just a single injector. This is due to the fact that all of an engine’s injectors should be of a similar age, and should exhibit nearly identical wear/degradation.

Therefore, replacing just a single injector would likely prove counterproductive, necessitating further diagnosis and repair as other injectors of the same vintage begin to fail.

Furthermore, replacing just a single injector makes little sense, since it seldom takes much additional work to replace an entire set of injectors, rather than a single injector. In such instances, it is far better to be safe, rather than sorry.

Simply put, replacing just a single injector is more of a band-aid than an actual proper repair.

Steve Cooper

3 thoughts on “6 Symptoms of a Bad Fuel Injector (And Its Replacement Cost)”

  1. Leaking injectors after replacement. Spraying out around the injectors. Should you use any kind of lubricant on O rings on injectors to make sure of proper seating of injectors??

  2. Tim, I recently installed for fuel injectors in my daughter’s car. The attempt to put the injector into the fuel rail was difficult. I took a q-tip with a tiny tiny bit of Vaseline and did the inside of the fuel rail and I touched the little rubber ring that went into the rail and they slid right in perfectly. Prior to that, I attempted to install a different set and I tore the rubbers on two of the new injectors lesson learned.


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