Intro to Datalogging
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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
This lets us see what speed the engine is moving at in Revolutions Per Minute. Additionally, conditions of acceleration, deceleration, and maintaining a steady speed will all cause variations in the fueling, ignition timing, and boost.
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. It 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.
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Monitor Name | What is it? | What can it Tell Me? | Normal Expected Behavior |
|---|---|---|---|
Advance Multiplier | A multiplier applied to the final ignition timing to add or remove power based on driving conditions/fuel quality | Typically a good indicator of overall engine health. It can move around a little under normal driving conditions, if it’s very low it could mean something is wrong with the car (it may just need a tune up), or your fuel is not good enough or contaminated. We recommend Top Tier Fuels https://www.toptiergas.com/fuel-stations/ | 0.7 - 1.0 |
Fuel Trim Short Term B1 | A correction based on current fueling error | The values shown are a percentage correction being applied. Positive values mean that more fuel is being injected and negative values mean less. These corrections are called trims. Their purpose is to adjust fueling in order to help the engine 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 as a part of normal behavior. Consistent corrections under similar conditions will be learned by the ECU and applied as AF Learning (See Below). Excessive trimming at idle or cruise may indicate an intake tract leak, bad sensor, or using the incorrect intake for specific mapping | Light Throttle: +/- 10%30% Heavy Throttle: 0% |
Fuel Trim Long Term B1 | Learned Corrections based on AF Corrections needed in the past. | Just like Fuel Trim Short Term, these are percentages added or subtracted to fueling. The values are learned slowly over time and are often referred to as long term trims. Short and Long term trims are added together, and then applied as a total value to the cars final fueling. 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% would result in a -3% trim. Generally, over time both trims will then get smaller as the ECU continues learning. Excessive long term trimming may indicate a mechanical issue. | +/- 10%7% |
Coolant Temp | Temperature of the engine coolant. | A measure of engine temperature. The car will typically alter timing and fueling at different engine temperatures. Can also let you know if the car is overheating or not fully warming up which could indicate issues with the cooling system or a faulty sensor. Above 225F you’ll see the RPM limit reduce from COBB Engine Safety | <225F |
Engine Oil Temperature | How Hot your oil is | Hot oil is bad for the engine and can significantly shorten engine lifespan. It’s a good idea to keep it under 230F for more consistent oil pressure and life span. Once it gets higher than ~260F you need to start worrying about severe engine wear. If you’re going to drive the car hard or live in a hot area, a good oil cooler is strongly recommended. Above 257F you’ll see the RPM limit reduce from COBB Engine Safety | <257F |
Gear | Current transmission gear. | It helps to provide a context of how the vehicle is being driven during a datalog. | R,1,2,3,4,5,6. If you manage a 10 or higher I’ll be impressed |
Intake Air Temp | The temperature of the air charge going into the intake. | As 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. | Relatively similar to outside temperature however it will be higher as it is measured in the engine bay. |
Knock Correction (Retard Amount AK) | Measure of current adjustment to ignition timing based on current knock (detonation) | Your car is knocking. If you’re outside the normal range you could have bad fuel, something could be wrong with the engine, you may need to let it cool down, or the 10mm you dropped into the engine bay is hitting the engine block just right | 0 to -3, occasionally more negative during an aggressive shift or when transitioning the accelerator pedal to another position. |
Knock Correction (Fine Learned) | A learned memory of previous consistent knock from Knock Correction | Typically any point where the ECU sees knock consistently it will apply a knock correction to keep it from happening in the future. This includes where there are consistent gear changes. It can also correct with positive values to increase timing in areas where the engine is running well and happy. | -3 or higherto +10 |
RPM | Engine revolutions per minute | This is a measure of how fast your engine is spinning. Inconsistencies at idle can indicate faulty sensors or vacuum/boost leaks. When looking at a datalog or graph under acceleration, seeing erratic values can be an indication of misfiring due to spark plug, coil pack, grounding issues, a fuel supply issue, or even a clutch or transmission slip. Looking at it against vehicle speed can indicate breaking tractionor a slipping clutch | Hopefully below ~7500 where the rev limiter is. Money shifting is not recommended for this application. |
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