Why Is My BMW Losing Power?

BMWs are high-performance vehicles and have consistently been updated with upgrades in technology over the years to improve horsepower and torque. Updates in engine technology and electrical accessories do have a negative side and that is that BMWs have become more complex machines with more components that could potentially fail.

There are a lot of potential causes as to why a BMW is losing engine power. There may be a mechanical problem like a clogged fuel filter or low cylinder compression. There could also be an electronics problem such as a faulty sensor, wiring, or a bad fuel pump. So, what are some of the common reasons why my BMW is losing power?

A BMW can lose power due to the following common reasons:

  • Low Cylinder Compression
  • Clogged Fuel filter
  • Dirty Air filter
  • Faulty Camshaft sensor
  • Faulty Mass Airflow sensor
  • Damaged fuel injectors
  • Faulty fuel pump
  • Worn spark plugs and ignition coils
  • Faulty turbo
  • Electrical fault

Read on to learn the most common causes why a BMW may lose power and how to repair the problem. Please keep in mind that this is a non-exhaustive list, as an exhaustive list of potential faults causing lost power could make up an entire book!

Low Cylinder Compression

BMW Cylinder Block

Let’s take a look at the worst possible cause first. Low cylinder compression is never a good sign on any vehicle. It equals either an expensive repair or a troublesome DIY.

Good cylinder compression is essential for the engine to produce adequate power. If the compression in one or more cylinders is low, the engine power output will be significantly reduced. This may be due to the following:

  • Blown Head Gasket
  • Stuck or damaged intake/exhaust valve
  • Crack in the cylinder head

What Causes Low Compression Problems in BMWs?

It’s no secret that BMW has an excellent reputation for building superb engines, I have owned a number of 3 Series BMWs and have yet to have an engine fail. That being said, one of the most infamous fail points on most BMWs is the coolant system. A failed water pump or leaking coolant hose can very quickly overheat your vehicle.

Once your BMW has begun to overheat you might only have seconds before permanent damage is caused to the engine. The most common result of a severely overheated engine is a blown head gasket, however, I have also seen BMW engines develop cracks in the cylinder head due to overheating.

How to Test For Low Compression?

The main way to identify a low cylinder compression issue is by using either a leak down or a compression tester. These testers can typically be picked up as rentals at your local auto parts store. Here is a great video on testing BMW cylinder pressure.

Fuel Filter Clogged

The fuel filter is situated between the fuel pump and the fuel injectors.  The fuel filter screens the fuel for any contaminants before entering the engine.  If the fuel filter is extremely clogged or blocked, it will restrict the amount of fuel sent to the engine. That being said, fuel filters rarely get filled up enough with gunk to restrict fuel flow to the fuel rail.

The issue here is that fuel filters should be changed around every 15,000 miles on most BMW models. However, fuel filters are a highly overlooked part and they are often changed significantly later than every 15,000 miles.

How to Identify and Replace a Failed BMW Fuel Filter

The easiest way to test whether a fuel filter is bad is by making use of a fuel pressure tester, which can also be picked up as a rental from a local auto parts store. Here is a great video on checking the fuel pressure.

Fuel filter replacement is extremely simple and easy. DIY time should be well under an hour. The only part of replacing a fuel filter that makes this job annoying is the chance that you will get bathed in a little fuel since you will need to get under the vehicle to change it. Here is a video that I created on replacing a BMW fuel filter.

Dirty Air Filter

Dirty engine air filter

The Air filter on a BMW cleans the air from larger particles such as insects, dust, and moisture that may cause damage to the engine if they are allowed to enter.  An internal combustion engine needs air and fuel to be mixed in the correct ratio to produce sufficient power.  A clogged or dirty air filter will restrict the amount of air entering the engine.

A dirty air filter will increase fuel consumption to make up for the loss of power.  But this can only be sustained for a while if you have a very dirty air filter. If the BMW is losing power and you notice that the fuel consumption increases, it would be worth your while to pull the air filter and inspect it. The air filter is extremely cheap to replace (under $40) and it takes less than two minutes to remove from the engine bay.

Malfunctioning Camshaft Sensor

The camshaft sensor sends the camshaft’s speed to the ECM (electronic control module).  This is needed so that the correct fuel injection and ignition system can work in sync to produce power.  If the sensor is faulty, it will significantly impact the engine’s performance. 

Replacement of the camshaft sensor will vary depending on the model BMW but typically the sensor will be located at the front of the engine, just below the valve cover. The camshaft sensor is usually relatively simple to replace, however, the difficulty will vary by model.

If you decide to DIY the camshaft sensor, be sure to only purchase OEM! These are extremely sensitive and I had to do the job twice on my E36 after replacing the first one with a non-OEM sensor.

Symptoms of A Failed Camshaft Sensor

  1. Check engine light reflecting camshaft sensor error
  2. The engine will stall and/or take longer to start
  3. Noticeable decline in engine power

Mass Airflow Sensor Malfunction

Dirty air flow sensor

The mass airflow sensor processes the amount of air that flows into the engine and relays this information to the vehicle’s powertrain control unit (PCU).  The PCU uses this information to calculate the engine’s load during driving.

If the sensor is not working, it will cause a significant change in the engine power, especially at higher RPM.  This sensor is positioned just past the air filter and before the intake manifold.

If you have a bad mass airflow sensor you will likely get a check engine code reflecting a problem with the sensor. Mass airflow sensors are extremely easy to replace, but they are relatively expensive parts. My advice is that if you have a problematic sensor, try cleaning the sensor first instead of replacing it.

Here is a video on cleaning the mass airflow sensor.

Clogged Or Damaged Fuel Injectors

Fuel injectors serve a critical role in the proper performance of any engine. The fuel pump sends fuel to the fuel injectors, the fuel injectors then spray the fuel into the intake manifold. Air and fuel are then compressed in the combustion chamber and ignited to power your vehicle.

The ECU controls the injectors, and as the engine demands more power, more fuel is sprayed into the manifold. If an injector is clogged, not enough fuel can enter the cylinder, and a decrease in power will be noticed.

Symptoms of Failing Injectors

  1. Decreased power
  2. Difficulty starting
  3. Misfiring, knocking
  4. Rough idle
  5. Check engine light

How to Fix a Failed Fuel Injector

Your BMW will have one fuel injector for each cylinder, this is important because the fuel injectors rarely fail all at the same time. If you know you have a fuel injector problem, the first thing to do is to confirm whether the fuel injector is clogged by sediment or whether a fuel injector seal has failed.

If the fuel injector has clogged, you can either replace it or send it to a specialty shop to have the fuel injector reserviced. If you choose to send the injector to a specialty shop you should go ahead and have all of the injectors looked at and serviced.

One surefire way to tell that a fuel injector seal has failed is that you will notice a gasoline smell in the engine bay. This type of problem should be resolved as soon as possible, as gasoline is obviously very flammable. Luckily, fuel injector seal kits are sold separately from the injectors and can be purchased for under $50.

Faulty Fuel Pump

The fuel pump is found in the fuel tank of a BMW which is typically accessed via the back seat.  It is there to pump the fuel from the tank to the engine under the correct pressure.  If the pump is not bringing the fuel at the correct pressure, it could lead to fuel starvation.

The best way to identify a fuel pump problem is using the same method that I mentioned above to test the fuel filter, with a fuel pressure tester. Alternatively, one method that I have found to be very useful is to pop the back seat in your BMW and listen to whether the fuel pump turns on when you attempt to start the car. Here is a video that I made on diagnosing a fuel pump.

Symptoms of a Faulty Fuel Pump

BMW fuel pumps rarely fail gradually. When your fuel pump fails, you may have a short period where you will notice a steep decline in engine power. Be forewarned, once a BMW fuel pump begins to fail, you will have a very short amount of time before it dies completely and your BMW will be stuck in place. This happened to my brother once and we got stuck in the middle of the street on a busy road.

Worn-out Spark Plugs And Ignition Coils

Dirty spark plugs

The spark plugs are what essentially makes the engine go bang.  They ignite the air and fuel mixture producing the power of the engine.  If a cylinder is not receiving a large enough spark, it can not ignite the mixture.  This will result in a significant power loss in the engine.  Spark plugs are inexpensive and easy to replace (unless you are buying iridiums!).

The ignition coils convert 12 volts to 20,000 volts; the spark plugs require this high voltage to produce the spark.  If the coils are faulty, they will not supply a high enough voltage to the spark plugs and there will be no spark. The ignition coils are easy to replace but are significantly more costly than spark plugs.

You can check out this article here to learn the ins and outs of spark plug replacement intervals and how to do it.

Leaking Turbo Charger Tubing

The turbo forces air into the engine within the high RPM range. Not every BMW has a turbo, but BMW produces more and more cars nowadays with stock turbos. If there is a leak in the tubing, not enough air will get to the engine. This will result in power loss within the high RPM range. Leaking turbocharger tubing can be relatively easy to spot as the escaping air will produce a loud whistling sound.

Turbochargers are very dependent on oil for cooling, so ensure that these systems are working correctly, as a damaged turbo is a very costly repair.

Faulty Electrical System

All BMWs are packed full of electronics and sensors, and they rely on a constant supply of voltage to keep them functioning.  A loose wire may cause the sensor to stop working or have it switch on and off.  If the check engine light, temperature gauge, or oil pressure light illuminates faulty, it will cause the car to go into a safe or limp home mode.

This can happen even if there is no mechanical problem.  Still, the computer received faulty information, restricting the engine’s power output.  An electrical problem can easily be rectified if found, but it’s better to have a professional look into the problem or purchase diagnostic equipment yourself to identify the issue.


There are many reasons why a BMW may suffer from a loss of power; this could be due to a mechanical or electrical fault.  The common causes for loss of power are bad or dirty filters, clogged injectors, or faulty sensors. It is recommended to take the vehicle to an accredited BMW dealer for approved repairs or purchase diagnostic equipment so you do not end up going down a rabbit hole searching for the problem. 




Stephen Metellus

I am a BMW enthusiast and owner of abetterbmw.com! I have been repairing, flipping, and parting out BMWs for nearly ten years. I love these vehicles and I hope you will find my articles and YouTube channel helpful for whatever BMW project you have in store!

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