P0300

P0300 – Random/Multiple Cylinder Misfire Detected Audi R8

Shortly after buying the Audi R8 V8, the car developed a performance fault, when pushing the car to full throttle, the R8 would stutter or misfire between 4,000-5,500 rpm. This started as being intermittent, but after a while began to occur every time passing 4,000 rpm. The fault showing on the ECU most frequently was “P0300 – Random/Multiple Cylinder Misfire Detected”.

The engine management light and ECU would report the following errors codes during my experience of the fault over a month or two:

This engine is similar to a B7 Audi RS4 if that helps some people with the troubleshooting.

P0300

P0300 Code

Looking at any misfire issues there are a few basic steps. Here’s how you can start diagnosing a P0300 misfire…

1. Spark Plugs

A good step is to initially inspect the spark plugs and either clean or replace them. I replaced my plugs initially and cost around £12o for a set of eight good quality plugs. If the fault reoccurs you might want to look at the coils.

2. Coils

Remove and inspect the coils. Look for water damage or oil at the end of the coils. You can clean them with a contact cleaner and replace them. If the fault occurs with one specific cylinder swap two coils around and sees if the fault moves with the coil to a new cylinder. If this problem doesn’t assist then you might need to look at a compression test.

P0300

In my case, at this point, my car stopped showing the misfire errors and started to report P2293 – Fuel Pressure Regulator 2 Performance. This leads me to look at the fueling of the car.

3. VCDS

I logged into VCDS and set up VCDS to log my misfires, it gives a lot more accurate data. From this, I could see that there were more misfires than the ECU reports to the dash. All of the misfires were reported to occur on bank 2. This means it was unlikely to be a spark plug or coil issue.

P0300

From here I could use VCDS to look at my fuel pressures which were low once going over 4,000rpm.

4. Fuel Filter

I first replaced the fuel filter as this part is not scheduled for maintenance on this car at all. It has a built-in regulator and only costs around £25. This would be the first step for making sure the fuel is getting to the high-pressure fuel pumps without a restriction. The filter was holding a lot of dirt that I could see from when I drained the fuel back out of the dirty side of the filter.

P0300

5. High-Pressure Fuel Pump

Once the fuel filter was replaced, the issue was still occurring, just on bank 2. Next, I removed the high-pressure fuel pump on bank two (this is the left-hand side looking at the engine). Opening up the pump you could see a dark black build-up in the pump. I cleaned it the best I could using Redex and refitted it to the car.

Engine OBD codes diagnose diagnostics troubleshooting repair

The car then ran 90% better, but not perfect. This confirmed my fault. I needed a new high-pressure fuel pump.

What Could Cause A P0300 Code

The high-pressure fuel pump on bank 2 (left-hand side look at the engine from the rear). The pump appears to not put out the required pressure the car requires over 4,000 rpm. This starves the cylinders of fuel and displays it as a misfire.

How To Fix P0300 Code

To fix the issue I replace the high-pressure fuel pump on bank 2. The process is very simple and is accessible on top of the engine. I acquired a genuine pump for £305.

Engine OBD codes diagnose diagnostics troubleshooting repair

Here are some rough steps I took to replace the pump:

  • Disconnect the car battery.
  • Ensure the car is cold (a warm engine could increase the fuel rail pressure considerably).
  • Remove the fuel pressure sensor from the pump.
  • Wearing eye and hand protection very slowly releases the pressure from the pump by loosening the hoses
    • The low-pressure side has a clip that can be squeezed with pliers and the rubber tube slipped back.
    • The high-pressure side uses a 17mm nut, be very careful on this side to gently bleed the fuel pressure and ensure you catch the loose fuel with a rag and dispose of it safely.
  • Once the pressure has been released disconnect the hoses.
  • Use a Torx bit to loosen the bolts that hold the pump to the car.
  • Once the bolts are out the pump can be lifted off and the new one replaced.

It is worth inspecting the cam follower on the car if it shows wear or play it might be worth replacing. In most cases on these engines, it should be fine.

When you next start the car expect it to take a little longer to crank the first time.

After replacing the pump the misfire was completely removed from the car and the P0300 fault hasn’t come back since.

Frequently Asked Questions

If you’re still unsure about that P0300 error code, our FAQs here might help…

What Does Code P0300 Mean

P0300 is defined as there is a case of either randomized or numerous misfires occurring inside your engine. Oftentimes, misfire-related OBD error codes end with a number. For instance, P0301 tells you that your engine’s cylinder #1 is misfiring. Then, there’s P0302, P0302, P0304, and so on for cylinders #2, #3, and #4, respectively. It can keep going depending on how many cylinders your engine has – i.e. a V8 could feature P0308, while a V12 may feature P0312. However, the ECU might only note down misfires as P0300 under specific circumstances. Either, the misfire isn’t contained with just one specific cylinder and jumps around from one cylinder to another in an instance. Or, multiple cylinders are misfiring all at once.

What Could Cause A P0300 Code

A P0300 error code will appear if your engine has a misfire. Unfortunately, misfires can be caused by numerous failures within your engine, so diagnosing and narrowing down the true fault can be difficult. For example, intake gasket leaks or poor cylinder compression will compromise the combustion force of the engine, thus causing a misfire. Plus, a worn-out spark plug, burnt exhaust valves, failed fuel injector, poor fuel pressure, or a bad catalytic converter can all cause P0300 to appear, too. Other than that, bad wires that lead to the spark plug, ignition coil, or even the ground wire can all prompt misfires to occur.

What Is A Misfire In A Car

A misfire in your car means that there’s incomplete combustion within the engine. In short, one of your engine’s cylinders isn’t firing at all or was firing, but not thoroughly. Usually, misfires only impact one cylinder. But, if the situation worsens, you might experience misfires in numerous cylinders at once. You’ll notice a misfire when the engine feels and sounds rough, as one (or more) cylinders isn’t firing in unison with the rest. Moreover, other tell-tale signs that your engine is misfiring include poor performance or hesitation while accelerating. You might notice how it loses power momentarily, or that the engine shakes and rattles more pronouncedly. Leave it unfixed, and you’ll soon notice other long-term symptoms appearing, such as bad fuel economy and increased emissions.

Can A Bad Catalytic Converter Cause A P0300 Code

Typically, misfires are caused by issues within the engine, such as a bad ignition coil or a worn-out spark plug. However, you can certainly notice a P0300 error code appear if your car has a bad catalytic converter. Should the catalytic converter be clogged up too much, it’ll be harder for the exhaust fumes to exit the engine. Instead of them being exhausted, these exhaust fumes might instead get trapped inside the combustion chamber. Or, flow back into the combustion chamber, right in time for the following combustion cycle. In so doing, these carbon by-products of the combustion process would poison the combustion mixture. Remember, an engine ignites with oxygen and fuel. If other gases are introduced, they could poison this air-and-fuel mixture, causing incomplete combustion.

Can A Bad O2 Sensor Cause A P0300 Code

Your engine’s ECU (practically its central computer brain) gathers a lot of data from the O2 sensors. By understanding the oxygen content within your exhaust fumes, the ECU can better calibrate your engine. Thus, keeping its air-to-fuel ratio in balance, ensuring that the ignition timing is in order, and so on. If the O2 sensors fail or glitch out and send an erroneous reading to the ECU, it can impact how your engine runs. In particular, the faulty readings from the O2 sensor might force the ECU to throw the air-to-fuel mixture out of spec. With an improper AFR (air-to-fuel ratio), your engine is more prone to issues such as misfires, especially when it’s running lean. In other words, your engine has too little fuel to combust thoroughly.

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