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Mercedes Engine Misfire Problem

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srs warning lightEngine misfires are one of the most common problems we see in many Mercedes-Benz cars. To be honest, it is not because MB cars are weak in this area, but because most owners forget that spark plugs are wear items and need to be replaced at the recommended intervals. As soon as an engine misfire occurs on a Mercedes-Benz, you will notice poor engine performance and strange vibrations that in some cases can be felt even in the driver cabin. The first thing that comes to mind when you get an engine misfire is: “This is going to be expensive.” Take a deep breath because in most cases it doesn’t have to be. In this article, we discuss Mercedes Engine Misfire problems, what are the most common causes that trigger misfires and how to diagnose an engine misfire on a Mercedes-Benz cars.

What does it mean when you have Mercedes Engine Misfire

recommended mercedes spark plugUnder normal operation, the fuel and air mixture entering the combustion chamber of your Mercedes-Benz engine ignites. When the fuel/air mixture doesn’t get ignited one or more cylinders don’t provide any power to turn the engine which gets detected by the Engine Control Unit (ECU) which triggers an engine misfire code.

Common Engine Misfire Symptoms

Depending on the type of misfire and what caused it, you will notice one or more of the following misfire symptoms:

  • Engine Vibrations
  • Loss of power
  • Shaking / Vibrations Noticeable at Low RPMS and idle
  • Vibrations go away at high RPMS typically over 3000
  • Engine Stalls in some cases
  • Poor Engine Performance
  • Check Engine Light
  • Fuel / Gasoline smell from exhaust
  • Blinking Check Engine Light

How to diagnose Mercedes Misfire Problems

mercedes benz fault codesMany mechanics and car owners don’t like to work on Mercedes because they believe that MB cars are difficult to diagnose due to the large sensors and electronics. In our opinion, if you have the proper tools diagnosing Mercedes cars is easy. Luckily for you, the misfire codes are stored in the ECU and are very easy (and inexpensive) to retrieve. To diagnose an engine misfire on a Mercedes all you need is a generic OBD II code reader that can be bought in some cases for under 20 at your local auto parts store or on Amazon’s Best Selling OBD II scanners list. If you would rather invest in an advanced OBD II scanner for Mercedes, then read our article on Top 10 Best Diagnostic Scanners for Mercedes Benz.

Steps to diagnose Mercedes Engine Misfire

1. Turn ignition to position II. All dash lights should be on. Don’t start the car.
2. Locate the OBD-II port under the dashboard.

OBD II Port Scanner Mercedes Benz Star Diagnostic
Location of OBD II port used to retrieve Mercedes-Benz fault codes.

3. Plug your OBD II scanner and let it turn on.

check engine light
Use an OBD II scanner to check why the Check Engine Light is ON.

4. Hit Read button to retrieve the fault codes from the ECU. You will get a code such as P0301. These are called diagnostic trouble codes (DTC).mercedes benz fault codes

For more help watch the following video.

 

Now what?

You most likely will get one of the following codes

  • If you are reading fault codes such as P0301 through P0312, that means that most likely the problem is with one of the cylinders misfiring. This is due to a bad spark plug, spark plug wire or ignition coil issue.
  • If you are reading a P0301 through P0312 code plus another code, let say P0100. It is very likely that the P0100 fault code which refers to a malfunction in the mass air flow sensor circuit is also causing the misfire codes and even a limp home mode. Lime home mode means the transmission gets stuck in gear, typically in second gear.

The bottom line is that you need to research all the codes that your OBD-II scanner retrieves from the ECU. Now let’s talk about some of the most common reasons that cause engine misfire and check engine light on in a Mercedes-Benz car.

Common Causes of Mercedes Engine Misfire

Spark Plugs

mercedes spark plug engine misfireThe #1 cause of Mercedes engine misfire is old spark plugs. Spark plugs don’t last forever. They are wear and tear items. Standard copper spark plugs last up to 30k miles while iridium and platinum spark plugs can last over 60,000 miles. If your Mercedes-Benz has over 80,000 miles and still has the original spark plugs, it makes sense to change the spark plugs before you pour money on any other repair. New spark plugs will make your engine run smoother, and you will even see an improvement in gas mileage. Rember that Mercedes-Benz V6 and V8 engines utilize two spark plugs per cylinder. That is typical in Mercedes-Benz engines such as M112 M113 M272 M273 found on E, C, S, CL, CLK, ML, GL, G, R, SLK Class. For example, if you have an E320 (M112 engine) or E350 (M272) your car has six cylinders but requires 12 spark plugs.

Replacement spark plugs for your Mercedes-Benz can be purchased on Amazon if you are looking for a way to save money on parts.

Ignition Coils

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Location of Mercedes ignition coil packsIf you replaced all the spark plugs but are still getting an engine miss fire code, then the next item to check are the ignition coils. Mercedes uses one coil per cylinder. In some cases, each coil may power two spark plugs. Ignition coils are easy to replace, and you don’t necessarily need to replace all of the ignition coils if one has failed. Replacing the ignition coil is very straight forward. You will need to unplug the coil, remove the bolt, disconnect the spark plug wires and reinstall in reverse order. If you need a replacement coil, you can get them on Amazon for much less than the dealer.

Mass Air Flow Sensor

mas air flow sensor engine misfireMass air flow sensor is one of the most critical sensors in a Mercedes-Benz car. It is responsible for measuring the temperature and volume of air entering the engine. This is crucial because if the mass air flow (MAF) sensor is bad or failing not only will you have poor fuel economy and performance but you may also get misfire problems and other symptoms. Pay close attention to the codes and also look for the following codes related to the MAF sensor.

Fault Codes related to MAF sensor

If you do find out that the MAF sensor is defective, don’t panic. It is not an expensive repair if you are willing to get the hands dirty. You can get an aftermarket sensor, but we recommend sticking with OEM MAF sensor whenever possible.

 

Spark Plug Wires

spark plug wireWhen we talk about spark plug wires, you may be thinking spark plug wires are a thing of the past. My Mercedes doesn’t have a distributor. But hold on! Mercedes uses wires between the ignition coil and spark plug on most V6, V8 and V12 engined. You don’t have to worry about spark plug wires if you have an engine that utilizes ignition coil installed directly on top of the spark plug.

While spark plug wires fail less often, we have seen a few cases where those short spark plug wires were either defective or damaged during improper removal. Keep this in mind especially if you change the spark plugs in your Mercedes and you are still getting an engine misfire.

Fuel Pressure

test fuel pressure at schrader valveFuel pressure can cause engine misfire as well. We haven’t seen too many cases where the fuel pressure was the cause of the misfire Generally when Mercedes owner’s experience fuel related problems it is because the fuel pump has failed. If that’s the case, your Mercedes won’t even start to get that fixed first before you start throwing parts and money on your Mercedes.

If you are suspecting fuel related issues, checking the fuel pressure on a Mercedes is very easy. You will need to connect a fuel pressure gauge to the fuel test port as shown in this picture.

The Actron CP7818 Fuel Pressure Tester Kit works very well. It has Schrader fitting required to connect to MB fuel test port.  It allows you to tests fuel pressure regulator, weak fuel pump and leaking injectors.

Bad Catalytic Converter

damaged catalytic converterA catalytic converter that is clogged and is restricting the exhaust gasses from leaving the engine can also trigger multiple cylinder misfire. If your catalytic converter is clogged you will notice a drastic drop in fuel efficiency and real struggle getting your Mercedes to accelerate. If the cat is completely clogged your car won’t even start.

Bad Car Battery

The car battery on your MB is very critical and if it fails you can experience a list of electrical malfunctions including engine misfire in some cases. If you have to jump start your MB on regular basis, it is time to get the battery replaced.

Internal Mechanic Issue

Mechanical engine problems can also cause an engine misfire. Burnt valve or blown cylinder head gasket can definitively trigger misfire code and symptoms. If a particular cylinder is not generating the required compression, the fuel mixture on that cylinder may never get ignited. Here you will need to perform a compression test and pay attention to any unusual engine noises.

Conclusion

If your Mercedes-Benz has developed an engine misfire always scan the codes via the OBD-II port. In most cases, a cylinder misfire is caused either due to old spark plugs that need to be replaced. A failed ignition coil or a bad spark plug wires. If none of the above fixes your misfire problem carefully analyze the fault codes, it is possible that misfire may be indirectly caused by another problem in the engine.

Please use the comments section below to report your engine misfire symptoms. If you already fixed this problem let our readers know what the cause and solution was in your case.

 

One comment

  1. My 2000 E55 developed a misfire and threw a code about 10000 miles after a dealer tuneup. I swapped the coils and it still would occasionally throw a code. Decided to do plugs and wires. Turned out that one of the rear plugs that threw the code was loose from when the dealer had done the previous tuneup.

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