Check engine light is on, so you decide to read the fault codes. It turns out that you have multiple P0300 fault codes.
Further troubleshooting determines that all the diagnostic trouble codes are on one side of the engine.
In this article, we look at common problems that can cause misfire codes on only one block. Before we dive into this topic, it is essential to point out that if you have this problem after changing the spark plugs or ignition coils, make sure that the spark plug wires and ignition coil harnesses are not switched around.
One of the most common problems that will cause misfire codes on one side of the engine is a clogged catalytic converter. This issue only applies to vehicles that have two catalytic converters, one catalytic converter for each bank.
A catalytic converter that is completely or partially clogged will restrict the exhaust gases. Because the exhaust can not escape the cylinder, it builds excessive pressure, and that cylinder will not fire properly. Each catalytic converter is connected to all the cylinders on one side; you will end up getting several misfire codes plus the typical P0300 random misfire code.
A clogged catalytic converter can be verified by performing an exhaust backpressure test. You will need to remove the upstream oxygen sensor, connect an exhaust back pressure test gauge. Run the engine for a minute or crank it for a moment. To learn more, follow this guide on how to perform an exhaust backpressure test.
Comparing oxygen sensor values between the two catalytic converters can hint at a bad catalytic converter as well. Also, symptoms of a clogged catalytic converter include:
- Check engine light on or flashing.
- Sluggish acceleration
- The smell of rotten eggs from the exhaust
- Excessive heat, catalytic converter turning red.
If you have these symptoms, the chances that you have a partially clogged catalytic converter are high.
Low Engine Compression
Another possible problem that can cause misfire fault codes on only one side is low compression. A blown head gasket can cause low compression.
To find out if you have low compression, you will need to remove the spark plugs. Connect a compression gauge to the spark plug holes and crank the engine a few times.
Healthy engines should have compression over 120 psi per cylinder, with no more than 10 percent variation between the highest and lowest readings. Since the gasoline engine has a spark plug, only moderate compression is enough, requiring about 140-160 pounds per square inch (PSI). Depending on their size and application, some engines may require higher compression, such as 220 PSI.
A damaged wire harness from the ECU to the ignition coils can also be the culprit. Use a digital multimeter to test that you have power going to the ignition coil and a good ground connection.
Engine Control Unit
A faulty Engine Control Unit (ECU) can cause multiple random misfire codes. A bad ECU will most likely cause misfire codes on all cylinders, but it may affect only specific cylinders in a few rare cases. Symptoms include communication errors and random fault codes.
Mass Air Flow Sensor
In some cases, vehicles have two air intakes, one for each bank. This translates into one Mass Air Flow (MAF) sensor per bank.
If one of the MAF sensors fails, it will send the wrong air volume and temperature data to the ECU. Since the ECU has inaccurate data about the air entering that side of the engine, the ECU will calculate the air/fuel ratio incorrectly.
This causes the wrong amount of fuel to be sent to the cylinder on one side, which leads to misfire codes on one side of the engine.
Camshaft Position Sensor
The camshaft position sensor detects the speed of the well....the camshaft. The ECU uses this data to adjust the timing, timing of spark, and fuel injection. Having a bad CPS sensor can trigger misfire codes on one side of the engine.
This guide applies to all makes and models that utilize a V engine, such as V6, V8, V10, V12. These engines are found on many makes, including Acura, Audi, BMW, Honda, Toyota, Hyundai, Mercedes-Benz, Porsche, Subaru, etc.
It doesn't apply to vehicles with four-cylinder engines, inline 5 and 6, since they typically have only one catalytic converter. It will apply if your vehicle has two catalytic converters, such as is the case with BMW inline-six engines.