Starting and Flooding
Source: RX8Club.com - New and Potential Owners START HERE! Author: RIWWP
Flooding — What It Is and How to Fix It
Another major complaint about the RX-8 is the tendency to "flood".
What Is Flooding?
Flooding, per the rotary engine term, is when there is too much gasoline in the combustion chamber. This really only happens when driver attempts to start the engine, but the engine doesn't immediately start. The ECU is pumping fuel while the engine is cranking, and if the engine doesn't start up quickly enough, all this fuel just soaks the plugs, washes around in the housing, and keeps the ignition from actually firing.
Flooding is only a concern if you have a weak ignition system, failing compression, failing battery, and/or failing starter.
Every single flood I have seen reported ended up coming down to one of these failing: Battery, Starter, Coil(s), Plug Wire(s), Plug(s), and/or Engine Compression. (RX8Club)
- If it's the battery that failed, the starter can't spin the engine fast enough, so the engine won't get good enough compression, and the air/fuel mixture won't ignite with any force.
- If it's the starter that failed, the starter can't spin the engine fast enough, so the engine won't get good enough compression, and the air/fuel mixture won't ignite with any force.
- If it's the engine compression that has failed, the engine won't get good enough compression, and the air/fuel mixture won't ignite with any force.
- If it's the coils, plug wires, or plugs that have failed, it doesn't matter what compression you can achieve, what engine speed you can reach, you need a spark to light the air/fuel mixture!
Stay on top of the maintenance (long term included!) and you will wonder what all the fuss was about. Coils, plugs, and wires, should be replaced every 30,000 miles, possibly sooner if you detect something starting to fail, since people have had them fail as early as 8,000 miles or 15,000 miles, though that's rare. You can replace them for as little as about $200.
You don't want to shut off while it's cold simply because when the engine is cold, the ECU dumps more fuel into engine to help it warm up, and it leans back once the engine is warm. This extra fuel can make it harder to start an ignition, which a healthy ignition system is perfectly capable of overcoming. Weaken the ignition with failing plugs, coils, wires, alternator, starter, or battery, and you have a flood on your hands, and all the associated problems from that.
How to Fix Flooding?
There are many methods, but the method you should always try first is what Mazda has built into the ECU logic:
- Hook up another running car to the RX-8's battery with jumper cables to keep the battery from dying.
- Hold the gas pedal to the floor (this signals the ECU to stop all fuel injection while cranking).
- Crank in 5-10 second intervals, waiting the same amount of time between each to let the starter cool down.
- Repeat this 10 times.
- Then take your foot off the gas pedal and try to start normally.
- If it won't start, repeat the series of cranking with the gas pedal to the floor.
If it still won't start, do a search on the forums for deflooding DIYs, and pick ONE of the other methods to try at a time. (RX8Club) Don't mix methods, that can cause it's own problems.
How Do I Shut Off an RX-8?
This somewhat ridiculous question keeps popping up recently. Other than the obvious "turn the key counter clockwise and remove", there is literally nothing special that you have to do. You will find people that insist that I am wrong in making this statement, but no, it is just that they are taking one symptom and extrapolating preventative measures even further off base than they already were. For example, you will find people that swear by reving the engine to 4,000rpm in neutral and cutting the key out there, with the revs up. They are doing this under the assumption that the faster spinning rotors will help sweep excess fuel out of the rotor housing, to prevent a flood. The problem with this idea is already explained in the Flooding section above. If your engine is already warm, there is no excess fuel being dumped in! (Except perhaps the fuel needed to rev to 4,000rpm). Shutting it off at 4,000rpm is no different in terms of fuel than shutting it off at 750rpm. If your engine is currently cold, then this could only POSSIBLY have an impact if your ignition or starter or battery is failing, in which case 'yes', it might help prevent a flood. But a flood is a symptom of another issue anyway, and only happens on START, not on SHUTDOWN.
Weak Starter (2004-2005)
On 2004 and early 2005 models, the starter was pretty weak. Mid 2005, Mazda upgraded the starter that they use, and it works pretty well, and lasts quite a while. The 2004 and some 2005 starter upgrades WERE free, but the owner had to do something about it with the dealer. It was NOT a recall. So if you have a 2004 or 2005, it is entirely possible that you still have the original, and very weak, starter. (Wikipedia)
The starter is an electric motor that accepts 12v power from the battery to power it, and a gear that engages the flywheel to spin the engine when the engine isn't running under it's own power.
If the starter can't spin the engine fast enough, there will be starting problems. The faster a starter can spin the engine, the more immediate the engine fire-up will be. Starters, like any other electric motor, slow down over time and will eventually wear out.
The starter is easily reached under the car (picture), and replacement is very simple to DIY (DIY Starter Change/Swap for Dummies).
Starter Motor Revisions (All by Mitsubishi)
The Renesis requires a minimum cranking speed of approximately 250 RPM to start on a perfectly healthy engine. Mazda released four successive starter motor revisions:
| Revision | Part Number | Power | Cranking RPM | Notes |
|---|---|---|---|---|
| Original (2003) | N3H1 | 1.2 kW | 220-250 RPM | Soon proved insufficient; Mazda issued a service bulletin for free upgrade |
| Rev 1 | N3H1-A | 2.0 kW | 260-280 RPM | Longer body than N3H1; very durable, lasting tens of thousands of miles |
| Rev 2 (~2006) | N3Z1 | 2.0 kW | 260-290 RPM | Revised internal components; slightly less durable than N3H1-A but more readily available and cheaper |
| Rev 3 (Series 2) | N3R3 | 2.0 kW | 290-330 RPM | Additional tooth on pinion gear; fastest cranking speed. Can start engines well past their serviceable life |
The N3Z1 and N3R3 are popular upgrades for older cars. The N3R3 is particularly effective at masking low compression, but this can delay necessary engine rebuilds. (Source)
The Cold Start Cycle and Flooding Mechanism
The cold start cycle is designed to bring the catalytic converter up to operating temperature quickly for emissions compliance. During this cycle, the ECU pours excess fuel into the engine (similar to a choke) while a secondary air injection pump (located on the left side of the engine bay under the bonnet) feeds additional oxygen into the exhaust manifold, giving the unburnt fuel a second chance to ignite and heat the catalytic converter.
If the engine is switched off during this cold start cycle, the unburnt fuel remains in the combustion chambers and soaks the spark plugs, causing a flood. The air-fuel mixture becomes too rich to ignite via the spark plugs alone.
Continued cranking attempts on a flooded engine will only worsen the flooding and can cause significant damage to both the engine and the starter motor.
(Source)
How to Jump Start Your RX-8
If the battery is too low to crank the engine, you can jump start using a donor vehicle:
- Open both bonnets. Remove the RX-8's engine cover and battery cover
- Connect Red (+) jump lead to the positive terminal on the RX-8 battery, then to the donor's positive terminal
- Connect Black (-) jump lead to the negative terminal on the RX-8 battery, then to the donor's negative terminal
- Start the donor car's engine and have the driver hold a steady rev
- Wait for the RX-8's ignition to settle (turn key two notches), then attempt to start
- If nothing happens, re-check all four connection points
- Once started, disconnect leads in reverse order (negative first, then positive)
- Drive for a minimum of 30-45 minutes to sufficiently recharge the battery before switching off
(Source)
Official Mazda TSB: Engine Cranks No Start (TSB 01-015/08)
Source: TSB 01-015/08 (PDF) — supersedes TSB 01-048/06
This 16-page Mazda TSB covers 2004–2008 RX-8s that crank but won't start. (TSB 01-015/08 PDF) It addresses two root causes and provides detailed repair procedures.
:::info Warranty Coverage This repair is covered under warranty for 8 years / 100,000 miles from the original warranty start date, whichever comes first. :::
Root Causes
The most common trigger is starting the engine cold and moving the vehicle a short distance without reaching operating temperature (e.g., moving the car to wash it, stalling then restarting). This causes:
- Cause A: Fuel-flooded spark plugs — the plugs are soaked with fuel and cannot ignite
- Cause B: Low compression from apex seals locked in the rotor groove due to carbon accumulation
Repair Procedure A — Flooded Spark Plugs (0.5 hrs)
- Remove all 4 spark plugs
- Purge fuel from the cylinders (crank engine with fuel pump relay removed)
- Install new spark plugs (do not reuse flooded plugs):
- Leading (2x): Mazda part
0000-18-N3Y8(NGK RE7C-L) - Trailing (2x): Mazda part
0000-18-N3Y1(NGK RE9B-T) - Full set reference:
N3Y3-18-S30-9U(TSB 01-015/08)
- Start the engine
- Leading (2x): Mazda part
Repair Procedure B — Carbon-Locked Apex Seals (1.6 hrs)
If Procedure A does not resolve the no-start, the apex seals are likely carbon-locked:
- Inject approximately 30 cc of 5W-20 engine oil per rotor through the vacuum ports (to free the stuck apex seals)
- Attempt to start the engine
- If it starts, proceed to the full carbon removal procedure below
- If it still won't start, repeat the oil injection and attempt again
Carbon Removal Procedure
This procedure uses Mazda Engine Cleaner (part 0000-77-A86, 1 can = 2 cleanings):
- Warm the engine to operating temperature
- Spray engine cleaner through the intake manifold vacuum ports:
- Spray for 10 seconds while cranking the engine (do NOT start)
- Wait 30 seconds
- Repeat
- Let the engine soak for a minimum of 1 hour (longer is better)
- After soaking, start the engine and:
- Rev to 6,000 RPM — repeat 20 times
- Connect the MOP (Metering Oil Pump) simulation tool and set to position 60 for 15 minutes at idle
- Perform a compression test after the procedure
:::warning Compression Test Required After Procedure B, a compression test is mandatory. If compression is still low, engine replacement may be necessary (determined via Mazda's MXConnect system). :::