Datalog Guide: Mazda Vehicles


Mazda Datalog Guide


Intro to Datalogging

Whether a stock daily driver or a dedicated track car, keeping track of how your car is running is vital to making sure your car will last without needing expensive repairs.  While monitoring gauges on your car can let you know what is happening with a few parameters at a given moment, it won't be able to give you a full scope of how the car is running.  In order to gain perspective over a wider range of time and parameters we run a datalog.

Here's a good reference on how you actually create a datalog
How To: Datalog



What is a Datalog?

A Datalog is where the Accessport or another system records a user-specified set of sensor data and/or information which the vehicle's computer is using to run the engine.  This can include things from simple data like coolant temperature, to how often the computer wants the fuel injector to be open during a given engine cycle.



Why Can't I Datalog Everything?

While each generation of ECU has different limitations there is generally a limit to the number of parameters you can select.  In most cases this is because the ECU needs to process the requests for data and output that information to whatever device is requesting it.  As a result the more monitors you request, the more work the computer has to do in order to keep up.  On some vehicles as you approach the limit you won't see any differences until it simply can't log more items.  However on other platforms you will see the approach to the limit show itself as a slow down in the logging rate, so if you are logging a bunch of different items make sure to keep an eye on the amount of time in between each sample to keep things in perspective.



Things Every Good Datalog Needs

A Map with no reference points is never going to help you get from one place to another.  There are a few parameters that do wonders for helping to put other monitors into context, as well as showing your environment and driving style.

  • RPM
    • Engine Revolutions per minute.  This let's us see what speed the engine is moving at.  Additionally conditions of acceleration, deceleration and maintaining a steady speed will all cause variations in the fueling and ignition timing

  • Throttle Position - TPS
    • How far open the throttle is open changes airflow to the engine and when combined with the RPM helps to give an indication of the amount of load the vehicle is under.

  • Accelerator Pedal Position - Accel. Pedal Pos
    • Measures the amount the accelerator pedal is pressed down by the driver.  Does not always equate to the same amount of throttle position and can give us additional information similar to what throttle position offers.




Quick Reference Guide




Normal Expected Behavior
Monitor NameWhat is it?What Can It Tell Me?IdleLight ThrottleHeavy Throttle
Actual AFRAir/Fuel ratioThis is the air/fuel ratio the engine is operating at. Since this vehicle has a stock wideband front O2 sensor, these values will be accurate as long as the sensor is in good working order and exhaust has no leaks.~14.7:1~14.7:1~11-12:1
BoostMeasure of intake manifold pressure/vacuumThis can help to diagnose failing turbos, boost creep and help make sure boost levels are appropriate.Varies with Map
Coolant TempTemperature of the engine coolantA measurement of engine temperature. The car will typically alter timing and fueling at different engine temperatures, it can also let you know if the car is overheating or not actually warming up which can indicate issues in the cooling system or a faulty sensor.<215 F<215 F<215 F
HPFP Act PresActual fuel pressure at the injectorsActual pressure should be within +/- 200 psi of desired fuel pressure


HPFP Des PresDesired fuel pressure at the injectorsThe fuel pressure the ECU desires at the injectors, under current engine conditions.


Intake Air TempAir temperature reading taken at the MAF (mass airflow) sensorAs atmospheric conditions change, engine efficiency and operation are affected. The ECU attempts to correct for temperature changes in various ways. Knowing the temperature reading the ECU was given provides context for other readings such as boost.Dependent on ambient temp
Knock RetardIgnition timing response to detonationBased on the severity of engine knock detected, the ECU reduces ignition timing advance by the amount this monitor indicates. More severe knock will result in larger values.00-30-3
Long Term FTLearned corrections based on AF corrections needed in the pastJust Like AF Corrections, these are percentages added or subtracted to fueling. These values are learned slowly over time, and are often referred to as Long Term Trims. Be mindful that you may experience long and short term trims which partially cancel each other out. For example, a short term trim of +12% and a long term trim of -15% may both seem large, but they're only causing a -3% total trim. Generally, over time both trims will get smaller as the ECU continues learning. Excessive long term trimming, like excessive short term trimming may indicate a mechanical issue like those mentioned above.-/+ 10-/+ 100
Short Term FTCorrection based on current fueling errorThe values shown are a percentage correction applied to the injector pulse width. Positive values mean more fuel is being injected and negative values mean less is being injected. These corrections are called trims. Their purpose is to adjust fueling to help the engien run at the currently desired air/fuel ratio. When you floor it, or lift throttle and coast, you'll notice trimming stops (0% correction). During throttle transitions, expect to see trims move around. This is normal. Consistent corrections under stable and similar operating conditions will be learned by the ECU and applied as LTFT (see below). Excessive trimming at idle or cruise may indicate an air intake tract leak, bad sensor or using the incorrect intake for specific mapping.-/+ 10-/+ 150
Throttle PosThrottle PositionThis value relates to throttle plate opening. Keep in mind, full throttle opening will read about 75%.0Varies with driver input~75% value is full throttle


Special Notes:

Custom Tunes

With a custom tune, keep in mind that since they're made to specifications other than what we use, normal values may vary.  For troubleshooting on a custom map reach out to the Protuner responsible for your tune and they should be able to help you out!



Built Engines

In the quest for ever more speed and power, eventually you come to the point of ordering up a built engine block, or even having one custom built to your specifications.  This is an incredibly exciting day, as you'll no longer be held back by the limitations of the stock bottom end and can explore the upper limits of what your car (and in some cases you) are capable of. Even if your external engine parts match a COBB Stage package, you will need to get a custom tune in order to make your built engine run safely and in optimally.





Links and Related Videos

How To: Update Accessport Firmware - Can provide assistance with getting your Accessport running the most up-to-date firmware.

How To: Change Datalog Monitors - Shows you how to adjust your datalog monitors so that you are viewing what you'd like to look at.

Calibration Map Notes for Mazda Vehicles- A link to the map notes for all Mazdaspeed vehicles.  This way you can determine what map you should be on for the parts equipped on your vehicle.





Customer Support

Have additional questions? Please don't hesitate to contact our Customer Support Team!

Email: support@cobbtuning.com

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