6 Symptoms of a Bad Fuel Rail Pressure Sensor

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symptoms of a bad fuel rail pressure sensor

A few weeks back, I noticed that my Nissan became a gas guzzler. It suddenly raised its fuel consumption from 5 liter/100 km to 7 liter/100 km. Having driven it above 100,000 miles, I thought maybe it was time for an engine overhaul or new pistons rings. So, I took it to my local shop.

After inspection, the mechanic asked me if I felt sluggish acceleration alongside this poor mileage. I realized that, yes, the acceleration had been a little sluggish, and he said that the fuel rail pressure sensor of the car was near failure.

As someone who knows about cars, it instantly clicked that his diagnosis was correct. How could I miss these symptoms? That’s when I thought about writing this article.

In this article, I’ll walk you through the symptoms of a bad fuel pressure sensor in detail, so you can deal with this issue faster than I did!

Where is Fuel Rail Pressure Sensor Located?

fuel tank pressure sensor

Fuel rail pressure sensor is part of the fuel delivery system of a car. To explain it simply, you can say that it’s located on the high-pressure rail between the fuel pump and fuel injectors. (In reality, the chain is a lot more complex than this and contains other components like fuel filter, regulators, and a bunch of other sensors, but let’s not get into that)

How Does the Fuel Rail Pressure Sensor Work?

engine control unit

Like any other sensor, the fuel rail pressure sensor has the sensing element and the calibrated unit. The sensing element is usually a tiny dome-shaped diaphragm or bellow that elongates when pressurized fuel passes through it.

This elastic or mechanical sensing part is calibrated against a voltage-producing element. This element generates a voltage corresponding to the elongation in the sensing element. This energy is then amplified in the same ratio to make the voltage detectable.

A signal is generated and sent to the Electronic Control Unit (ECU) of the car, which regulates the amount of fuel injected into the combustion chamber accordingly.

Delivering the right amount of fuel is essential as it directly affects the engine’s performance.

The combustion process involves an air-fuel mixture. The ratio of both constituents in this mixture is referred to as AFR (air-fuel ratio). The AFR governs whether the engine is running rich or lean. If AFR is greater than one, more air is in the ratio than fuel, aka the engine is running lean.

The fuel rail pressure sensor sends the signal to the ECU in the form of voltage to adjust the AFR. For normal performance, the AFR of the engine is set at 14.7:1. To increase engine performance, the amount of fuel is increased.

When the fuel rail pressure sensor goes bad, or the signals are faulty, this mixing ratio is disturbed. As a result, you might feel engine stall or sluggish acceleration.

Symptoms of a Bad Fuel Rail Pressure Sensor

fuel system

Following are the main symptoms you would observe when the fuel rail pressure sensor goes bad:

  • Poor Fuel Mileage
  • Sluggish Acceleration
  • Problems in Starting
  • Stalling
  • Engine Check Light
  • Unburnt Fuel in Exhaust

1.      Poor Fuel Mileage

The first and foremost sign of a damaged fuel rail pressure sensor is a gradual increase in your car’s fuel consumption. When the fuel pressure sensor malfunctions, it delivers a higher amount of fuel than required for the combustion process.

This excess fuel remains unused during the engine cycle. It leads to other symptoms as well, which are discussed below, but poor fuel mileage is one thing that’s difficult to ignore. It becomes clear that some fuel delivery system components are not working correctly.

2.      Sluggish Acceleration

Sluggish acceleration is a result of incomplete combustion. When ports are not injecting the correct amount of fuel, the combustion process is compromised.

In this case, you’ll press your car’s gas pedal and feel like it’s not accelerating. Or if it is, the rate of acceleration is inadequate. This is often an indication of a bad fuel pressure sensor.

A not only can a faulty fuel pressure sensor can supply excess fuel, but it can also limit its quantity, starving the engine. This will cause the engine of your car to underperform.

3.      Problems in Starting

Starting an engine requires a higher amount of fuel. When the fuel rail pressure sensor isn’t working correctly, the necessary amount of fuel is not delivered. As a result, you might experience problems starting your car.

In SI (spark ignition or petrol) engines, the ignition coil provides voltage to the spark plug. The spark plug ignites the air-fuel mixture in the combustion chamber at the end of the compression cycle.

As opposed to that in CI (compression-ignition or diesel) engines, the air-fuel mixture is compressed to the point of self-ignition.

In both engines, receiving the right amount of fuel is critical. Without it, the engine will not start at all.

4.      Stalling

You might feel powerless while driving your car if the fuel rail pressure sensor goes bad. This is mainly due to the stalling of the engine.

The engine ceases to turn in between cycles. In a four-stroke engine, the processes take place as per following.

1.       The intake stroke

2.       The compression stroke

3.       The power stroke

4.       The exhaust stroke

For each cycle, you get one power stroke. When fuel is below the optimum level, you get low or no power during the power stroke.

Hence, the engine turns intermittently, and you get pulsating power at the output shaft.

It can get pretty annoying, especially while driving on highways when you need instantaneous power and the engine doesn’t respond. You can conclude that the fuel rail pressure sensor is likely not working correctly.

5.     Check Engine Light

I usually don’t like mentioning this obvious symptom, but you would say that I forgot it!

Well, I don’t mention it because there is a list of about 150 different problems that can cause engine check lights to come on.

You will always need to look out for other symptoms if the engine check light is on. Only then can you narrow down the problem.

But, it is what it is. If the fuel rail pressure sensor goes bad, you will get the engine check light.

6.      Unburnt Fuel in Exhaust

When the fuel rail pressure sensor goes bad, more fuel is injected into the piston. Due to which some of the fuel remains unburnt at the end of each cycle. This unburnt fuel ends up in the exhaust system of your car.

The unburnt fuel in the exhaust has two major impacts:

1.   It is bad for the environment

Unburnt fuel goes into the catalytic converter and compromises its ability to limit emissions. Moreover, incomplete combustion can also produce some very harmful gases. A catalytic converter might not be able to stop all of those.

2.   It will choke your engine

Unburnt fuel is usually deposited inside the exhaust ducts. At the end of each engine cycle, when the piston pushes out the exhaust gases, these gases won’t have anywhere to go. As a result, the engine of your car will be choked.

Believe me; it can get serious quickly.

Therefore, if you notice fuel droplets leaking out of the muffler, it might be an indication of a bad fuel rail pressure sensor.

Cost of Replacement for Fuel Rail Pressure Sensor

Replacement of fuel rail pressure sensors is a costly affair. Depending upon the make and model of your car, it will cost you somewhere between $250 and $450. The breakdown of this figure will be:

·         Fuel Rail Pressure Sensor Cost: $100 to $200

·         Labor Cost: $150 to $250

Since the fuel rail pressure sensor is located deep inside the engine, many parts need to be removed to access it. This is the main reason why labor rates for replacement are so high.

For mass-produced and economy sector cars, you might be able to find spare parts at significantly lower prices. Luxury cars will cost you more.

Similarly, the mechanic shop doing the replacement will matter a lot in this situation. Dealerships tend to charge more than local workshops. The price difference is due to their highly skilled labor professionals specializing in dealing with all issues of that particular car or brand only.

Conclusion

Fuel rail pressure sensor is a highly critical component of the fuel delivery system in a car. If it stops working correctly, the vehicle owner has to cover the added fuel cost due to decreased engine efficiency.

Or, in the worst-case scenario, if it fails while driving, the delivery of fuel to your engine will be cut off completely, stalling your vehicle.

It can also lead to the complete failure of your exhaust system since unburnt fuel in the exhaust can negatively impact its performance.

Hence it is essential to watch for signs and symptoms of a damaged fuel rail pressure sensor. If you’re unsure about the signs (since the same symptoms can appear due to other problems), visit a vehicle care professional. Immediately replace the sensor if the mechanic suggests doing so.

Taking the plunge on a $300 fuel pressure sensor replacement may cost you thousands of dollars in expensive repairs of the exhaust system and engine.

FAQ’s

Can you clean a fuel rail pressure sensor?

Fuel rail pressure sensors cannot function properly when dirty. While it’s unlikely for a sensor to stop working entirely from dirt buildup alone, it’s best not to try your luck. For proper cleaning, you will need to visit a skilled technician. 

What is the average life of a fuel rail pressure sensor?

Fuel rail pressure sensor should last for the entire life of your car. But several issues can limit its life to 80,000 miles or less. Voltage fluctuations due to faulty battery failed alternator of the vehicle and other electrical system issues are among the leading causes limiting its life.

Can you replace the fuel rail pressure sensor yourself?

Yes, if you can make an atom bomb yourself, I reckon you can replace a fuel rail pressure sensor. 

Replacement of fuel rail pressure sensor follows a highly critical procedure. You need to remove many parts before you get to the sensor. Hence, I advise against attempting to replace it yourself.

Can a bad fuel rail sensor lead to a seized engine?

Yes, a bad fuel rail pressure sensor can lead to a seized engine. These are the two primary causes of pressure sensor-related engine seizing: 

1. Excess fuel delivered to the combustion chamber can lead to fuel deposits. These deposits can trap the engine heat. Gradually, the deposits increase, and so does the average temperature of your engine. It will first cause cooling system failure, and if left unchecked, it may lead to a seized engine.

2. The choking of the exhaust system can have a similar outcome—the temperature of pistons rise, which may lead to a seized engine.

How long can you drive with a bad fuel pressure sensor?

Until things escalate, you can continue to drive with a bad fuel rail pressure sensor (if absolutely necessary).

Essentially, if stalling happens once or twice every time you drive, you should be okay to continue for a short while, while you get the funds together to pay for the repair. If your vehicle stalls more than that or has other symptoms, you should visit a mechanic immediately.

The same goes for fuel mileage as well. If it drops 3-5 mpg, you can continue to drive. If it drops more than that, your vehicle requires immediate attention.

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