Datalog Guide: Honda Vehicles

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

    • 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 - APP (drive by wire cars only)

    • 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.

  • Barometric Pressure (when available)

    • A Measure of Barometric Pressure which is the air pressure at your location caused by multiple factors like temperature and elevation.  Different pressures have an impact on air density which in turn will impact the amount of fuel necessary as well as peak boost and the way in which the turbo spools.   At lower pressures (higher elevation) the turbocharger will have to work harder to achieve the same boost pressures.

Quick Reference Guide

Monitor Name

What is it?

What can it tell me?



Light Throttle

Wide Open Throttle (WOT)

AFR Actual

Measure air fuel ratio of the front (pre catalytic converter) oxygen sensor. Units used are Air Fuel Ratio where 14.7 is the “ideal” mixture of fuel and air.

This lets you know how rich the fuel mixture is in the engine at any given time. Under most conditions the car will run 14.7 and then get richer under heavier load when component protection kicks in, as a richer fuel mixture provides a cooling effect for both the turbocharger and catalytic converter

  • 14.7 +/- 0.2

  • 14.7 +/- 0.2

  • FK8

    • 13.0-11.3

Short Term Fuel Trim


Instantaneous correction to fuelling caused by the engine not hitting target AFR. This is based on how the car is running currently.

Based on the AFR measurement, if the ECU continually sees the car being either richer (a lower AFR number) or leaner (a higher AFR number), it will begin to add or remove (trim) the fuelling over time to compensate so the car goes back to hitting it’s target. Large numbers may indicate a leak in the intake tract where extra air is getting in. It can also indicate other physical issues with the car, or that some modification hasn’t been tuned for on your car.

  • -10% - +10%

  • -10% - +10%

  • -10% - +10%

Long Term Fuel Trim

Adjustments to fuelling the computer has learned over time are necessary for optimal engine operation/efficiency. Based on how the car has run historically

Typically based on the car continually making adjustments via STFT, these trims are added “permanently” but will gradually learn away if it sees STFT corrections in the opposite direction in that area.


  • -10% - +10%

  • -10% - +10%

  • -10% - +10%

Ignition Timing Cyl 1-4

Ignition timing for each cylinder (1-4). This is relative to when the piston is at top dead center (TDC) of the combustion stroke.

This is the angle during the rotation of the engine (for that cylinder) at which the spark plug will fire. Numbers above zero are the number of degrees before the piston hits top dead center of the combustion stroke. While negative numbers are numbers after the piston has hit TDC. Typically as the engine works harder (load increases, more airflow/airmass/boost pressure) ignition timing advance will decrease

  • -5° to 5°

  • 20° to 40°

  • 4° (low rpm) to 12° (high RPM) +/-2° based on fuel octane

Knock Retard Cyl 1-4

Adjustments retarding the ignition timing (reducing ignition advance, lower ignition timing numbers) when knock has been detected

Knock has occurred, this can happen as a result of inadequate fuel octane (either bad fuel or you’re running too aggressive a map for the fuel you have), high temperatures of outside air, coolant, or intake temperature. While very minor ignition adjustments are normal, consisten large events can be very bad. Knock is actually a very aggressive detonation creating high pressure in the cylinders and can result in damage to the engine.

  • 0° to -3°

  • 0° to -3°

ETC Angle Actual

Electronic Throttle Control Angle Actual. The amount of opening of the throttle body.

When you put the accelerator pedal down you’re essentially asking for an amount of torque to be produced. In response the ECU will open the throttle to allow airflow to meet the demand of this request. If you see the number go down from 100% when at full accelerator pedal down, it may be closing due to traction control coming in to play to reduce power so you can regain traction




HPFP Spill Valve Duty (Final)

Duty cycle from 0-100% of the spill valve opening.

As the high pressure fuel pump builds pressure it releases fuel and pressure via the spill valve in order to hit the pressure target. Typically if you start to hit 100% continuously, that means it is always closed, and you may not be hitting the fuel pressure or quantity target the engine needs. This can cause the engine to go lean and cause problems

  • 10-20%

  • 10-20%

  • 10-20%

Boost Pressure

The amount of pressure over atmospheric pressure in the intake manifold. Also called Manifold Relative Pressure

Current amount of pressure in intake manifold.
Boost=Manifold Absolute Pressure-Barometric Pressure.

  • -11 to 9psi

  • -5 to 15psi

  • 25psi peak reducing by redline.

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!

Engine Swaps

With thousands of cars around the world utilizing these engines, oftentimes swapping a used motor into your car can be a cost-effective alternative to rebuilding a tired or broken engine.  However there are many important things to keep in mind when doing this as not all engines are created equal.  Oftentimes foreign engines can come from the exact same model but have completely different hook-ups, sensors, or manifolds attached to the engine itself.  Harder to detect are the engines that have different cam specs or a different compression ratio (a common occurrence between United States (USDM) and Japanese market (JDM) vehicles).  This means that while getting it to fit can be a simple matter of just swapping a few parts over, getting it to run healthily and correctly is a different matter.  Due to the fact that none of the engine's sensors will detect any of these changes, or the potential for a difference in sensor to cause skewed values, you will need to get a custom tune when swapping your engine out for anything other than the exact same engine your car had initially with stock specifications.

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.  Similar to swapping for another stock engine, you'll need to get a custom tune in order to keep your engine running safe and in optimal condition.  An added reason for this is that when using aftermarket parts that are forged or billet, there are differences in how much expansion the materials will undergo when they start to absorb the heat of the engine running.  As a result when attempting to run a stock tune with a built engine, you'll probably see a lot of knock numbers from piston noise.  It's important to tune the car appropriately for that so that these false knock readings don't mask the ones which are real, just like brakes can help you avoid an accident and keep your car safe, a tune can help avoid detonation or running lean, and keep your new engine safe.

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.

Map Notes for GT-R - A link to the map notes for GTR.  This way you can determine what map you should be on for the parts equipped on your vehicle.

GT-R Data Monitor Support - A list of all data monitors used by the GTR platform

Customer Support

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


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