The Mazda 2.3 DISI Turbo engine earned a spot on Wards 10 Best Engines list in 2006 for good reason. It makes big power with lots of torque from a small displacement. Mazda went to great lengths to ensure that this power was not at the expense of reliability. There are multiple safety features in the ECU including overrev protection, overboost protection, overload protection, sensor failure protection, etc. It's a very well engineered system.
The ECU has rpm controls for normal and fault mode rev limits in addition to secondary sanity checks for rpms. When rev limits are exceeded, the ECU cuts fuel to protect the engine from catastrophic damage.
The ECU uses load as its primary power output control metric. Load is calculated as a function of Mass Air Flow (MAF) sensor reading, engine displacement, and current RPM. A load of 1.0 means that the current mass air flow is equal to the engine running at 100% volumetric efficiency. In the ECU, engine power output is managed based on load targets. There are many controls that regulate engine load. I have detailed these controls in my article titled Mazda MZR DISI 2.3l Turbo Load Targeting Logic. The ECU has two levels of overload protection. When the operating load exceeds the defined operating load limit, the ECU reduces the wastegate control solenoid duty cycle until load falls below the defined limit. This is to provide a gentle reduction of slight overload conditions. If load exceeds the secondary limit, the ECU cuts fuel to protect the engine from catastrophic damage.
Engine intake manifold pressure is measured by the Manifold Absolute Pressure (MAP) sensor. The turbocharger is used to create boost pressure. Boost pressure is the pressure in the intake manifold in excess of atmospheric pressure. Boost pressure is what allows a 2.3l engine to produce 263 HP compared to a normally aspirated 2.3l engine that produces 160 HP. The ECU has two layers of overboost protection. The first layer is throttle reduction. If the primary defined boost limit is exceeded, the throttle is opening is reduced in an effort to gently lower boost. If the boost continues to climb and exceed the final overboost limit, the ECU cuts fuel to protect the engine from catastrophic damage.
How do you know when you are experiencing fuel cut due to overboost or overload conditions? It is not subtle at all. Engine power output goes from 100% to 0% in a fraction of a second. The car will shudder for a half second and resume full power. It's not healthy for the engine or the drivetrain, and should be avoided. The ECU will record a P0234 DTC when an overboost condition occurs. You can log injector pulsewidth with VersaTuner. When fuel cut occurs, you will see injector pulsewidth briefly drop to zero in the log.
The ECU has multiple rev limit checks in multiple code paths for redundancy.
The ECU employs overboost protection in addition to overload protection as a redundant safety measure. These are independent safety checks based on separate sensors and code paths. If any one sensor fails - MAF or MAP - the ECU can still protect the engine from excessive cylinder pressures.
Make sure that the values you set are reachable by the sensors. For example, 260 kPa will never be seen by the stock MAP sensor which can only read up to 255 kPa. If you set the boost limit higher than 255 kPa with the stock MAP sensor, you have effectively disabled it. If you need to run more than 255 kPa, install a 3 bar or 3.5 bar MAP sensor so that you can retain the safety of overboost protection.
The ECU will reduce power if the MAF sensor output exceeds 4.9 V. If you are seeing MAF volts over 4.6 V, install a larger MAF housing and re-calibrate your MAF sensor.
VersaTune recommends setting overload and overboost limits to rational values. Rational values are slightly higher than you expect to see in normal operation. With a proper margin above normal operating values and well tuned overload and overboost reduction tables, you should not hit fuel cut unless something is really wrong.
These controls are there to protect your engine, and by extension, your wallet. Use them! If you are regularly hitting fuel cut due to exceeding the overload or overboost limits, modify your tune. All of these parameters are configurable in VersaTuner.
Wishing you safe motoring,
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