How to De-Flood a Mazda RX-8

The Mazda RX-8 and its 13B rotary engine made a great pair. The lightweight, high-revving sports car is quick and agile, making it fun on the track and on the streets. The 1.3L rotary engine, however, requires a lot of special attention and extra maintenance than a traditional piston engine would require. Thus, RX-8 owners need to learn about the 13B engine and its faults to be able to properly maintain and care for their vehicles.

One common RX-8 problem to be aware of is engine flooding. The 13B pumps a lot of fuel into the combustion chamber during start-up, which can cause the engine to become flooded with gasoline if you either turn it off too quickly after starting it or if you have weak ignition components that cause a long-crank and no-start condition.

This guide is going to discuss what RX-8 flooding is, why it happens and how to prevent it, as well as provide a DIY solution for starting and de-flooding a flooded 13B.

RX-8 Flooding: What is it, and why does it happen?

The 13B rotary engine in the RX-8 is a rather emissions un-friendly engine. It produces a lot of emissions when it is cold. To combat this, Mazda developed a cold start process with the purpose of helping the engine warm up quickly, therefore, reducing emissions.

When an RX-8 starts up cold, the fuel injectors pump a lot of fuel into the combustion chamber. At the same time, extra oxygen is cycled into the exhaust gases that are being recirculated into the engine. Therefore, the added fuel and oxygen result in hotter gases which help heat the catalytic converter up more quickly.

Flooding occurs in the RX-8 when too much fuel builds up in the combustion chamber, preventing the engine from starting. It predominantly happens for two reasons:

  1. If you turn the engine off too quickly after turning it off, the fuel doesn’t all burn, leaving a build-up of gas in the combustion chamber, preventing it from starting
  2. You have bad ignition components which cause a long-crank problem which results in excess fuel being injected, which then builds up and causes a no start

How to Prevent RX-8 Engine Flooding

We are going to cover how to deflood the 13B next, but first, there are a few steps you can take to make sure you never have to deflood it. The first cause of flooding is turning the engine off too quickly. Always let your engine run for at least a few minutes before turning it off. If you are just moving your car in or out of your driveway, take it for a lap around the street before parking it and turning it off. Getting the engine up to operating temperature is always good, but letting it run for a few minutes will do too. The colder it is outside, the longer you should let it run.

Secondly, spark plugs and ignition coils are other common RX-8 problems. When the ignition coils or spark plugs go are faulty, it can cause a long-crank issue, leading to a lot of fuel being poured into the engine, causing it not to be able to turn over. Therefore, keeping your ignition system well-maintained is important for preventing flooding. Additionally, the 13B has a weak starter, and continuous long cranks can cause the starter to fail too.

Overall, proper maintenance and knowledge of the engine are crucial to preventing flooding.

2004 Mazda RX-8 13B engine

How to De-Flood an RX-8 13B Engine

If you have flooded your engine, fortunately, it is a pretty simple process to deflood it. While “flooding” sounds bad, it really doesn’t have any negative consequences or other reliability issues that it causes. While it can foul the spark plugs a bit more quickly, this is about the extent of the damage it does. Additionally, it can put some wear and tear on your starter if you try to crank it constantly, but if you follow our steps below, you can get it unflooded with minimal harm.

There are a few different strategies for starting a flooded RX-8. The one we provide below is the easiest and safest option. We will recap at the bottom the other ways to do it, but we recommend following this procedure:

1) Remove the fuel pump fuse

Go to the fuse box inside the engine bay and remove the fuel pump fuse. Depending on the year of your RX-8, this is either fuse #20 or #22.

Pulling the fuel pump fuse will prevent the injectors from pouring any more fuel into the engine while you are cranking it and trying to burn off the existing fuel within the combustion chamber.

2) Fully press the gas pedal and crank the engine for 5-6 seconds

With the fuel pump turned off, the engine isn’t going to start. However, cranking it will burn off the fuel in the engine. Put your foot to the floor (gas and clutch, if manual) and let it crank for 5-6 seconds at a time only. Cranking the engine puts stress on the starter, so we want to give it time to cool down before trying again. Wait 30 seconds, and then let it crank for another 5-6 seconds. Repeat this process until the engine has cranked for 50-60 seconds in total.

To recap:

  • Turn the ignition on
  • Push the gas pedal to the floor (if manual, push the clutch in too)
  • Crank the engine for 5-6 seconds
  • Wait 30 seconds for the starter to recover
  • Repeat 8-10 times

Important: Doing this will drain your battery pretty quickly. We recommend hooking jumper cables up to another running car, or keeping a battery charger on it, while you perform these steps.

3) Put the fuel pump fuse back in

After 50-60 seconds of cranking, the majority of the fuel stuck in the combustion chamber should be burned off, allowing the engine to start. If you haven’t hooked your car up to a charger or another vehicle, it’s a good time to do it now, as we are going to crank it again to get it to turn over. If you don’t have enough battery power, it can prevent the car from turning over and potentially re-flood it if you let it crank for too long.

4) Crank the engine with the gas pedal to the floor

We are now going to get back in the car and try to start it. Before doing this, let your starter cool off for about 5 minutes. Keep your foot pressed to the floor again as you did during step 2. Turn the key and let it crank. If it doesn’t start in 5-6 seconds, stop cranking and let the starter catch its breath.

If it doesn’t start, try holding the gas pedal to the floor for 30 seconds with the ignition turned on (but not cranking). After 30 seconds, try to crank it again.

If you can’t get it to start, go back to step 2 and repeat the process.

5) Let the engine warm up once started

Once the engine fires up, let it run and warm up to operating temperature to prevent it from flooding again.

Alternative Strategies for Starting a Flooded RX-8

Our steps above should work 98% of the time. If it doesn’t work, then we recommend repeating the process. If it doesn’t work again after this, then you should replace your spark plugs and ignition coils. A flooded engine can foul the plugs preventing it from starting even after the engine has been unflooded. Therefore these could be the reason that this process isn’t working for you.

Some people have had success following this process without pulling the fuel pump fuse. If you want to try it this way, make sure you press down on the gas pedal for 30 seconds before trying to crank it. We recommend pulling the fuse since it takes only about 30 seconds to do and prevents additional fuel from entering the engine while you are trying to start it.

I have seen a few guides recommend pulling the fuel pump connector at the fuel pump. This is a waste of time, as pulling the fuse is so much easier and accomplishes the same thing.

Disconnecting the secondary air pump (it’s to the left of the oil cap) is helpful but not required.