Datalogging Parameters - McLaren

This brief guide will provide you with descriptions of each logging parameter. Click on the parameter for an expanded view. Some helpful conversions are located at the end.

This is a measurement of how many revolutions the engine makes per minute.

Relative load is the bases for many calculations within the ECU from boost control to fueling. It is the result of airmass calculations. Typically 100% would be the airmass ingested by the engine at STP. It is not uncommon to see a relative load of 200+ in turbocharged applications.

Ignition timing is an offset measurement in degrees of engine rotation from TDC (Top Dead Center) at which the spark plug is fired. Positive timing values are degrees before TDC, negative values are after top dead center.

This is the absolute pressure inside of the intake manifold. This is a direct pressure measurement from the sensor located on the top of the intake manifold.

  • This is absolute pressure, to calculate boost pressure subtract ambient pressure from this value.

    • e.g. 2500hPa Manifold Absolute Pressure - 1003 hPa (Ambient Pressure) = 1497hPa of boost pressure.

  • To convert hPa to psi multiply hPa by .0145.

    • 1497.00hPa x .0145 (psi/hPa) = 21.71psi

This measures the air pressure after the intercoolers on each bank. They are direct measurements from the pressure sensors located on the intercooler outlet. These can be used for diagnosing large boost leaks as well as compressor surge.

  • This is measured in absolute pressure.

This value is the direct measurement of the air temperature inside the intake manifold. This value can be significantly higher than the Pre Throttle Temperature sensor due to heat soak at low loads and idle.

This is a direct measurement of the air temperature between the intercooler and throttle body.

Ambient pressure is the measurement of the atmospheric pressure. Higher elevations result in lower ambient pressures. Typical ambient pressure at sea level is 1013.25 hPa or 14.7 psi. This is a useful monitor to determine your actual boost pressure. See Manifold Absolute Pressure for how to calculate boost pressure.

This is a measurement of the accelerator pedal position from 0 - 100%.

This is a measurement of the actual throttle position from 0 -100%. The throttle is used to modulate torque in many situations (load control, traction control, etc…) and can close even when the pedal position is 100%. Throttle closures are normal and generally not indicative of an issue.

Lambda is a measurement of the actual air/fuel ratio divided by the stoichiometric air/fuel ratio of the fuel used. Typically you will see this value hover around at 1.00 λ while at idle and low load situations. For turbocharged vehicles under heavy load this value will range anywhere from .77 λ to .85 λ depending on load and the octane of the fuel used. Under deceleration lambda will be greater than 1.00 λ and this is normal as fuel injection is cut off, but engine continues to pump air. The higher the lambda value the leaner the mixture and vice versa. Lambda values can read deceivingly lean under heavy load if traction control or launch control is active. This is due to cylinders being systematically cut to manage engine speed or torque.

Short term fuel trims (or STFT) are an instantaneous correction to the fuel model to keep your actual lambda value near your target lambda. They will be constantly adjusting while fuel is injected. These can swing drastically during transient events but should typically stay between +/- 10% under steady state operation. If your short term fuel trims are consistently adding or subtracting fuel they will eventually be transposed into long term fuel trims (or LTFT). Fuel trims are often confused with lambda. If your STFT is .95 it does not mean your car is running rich. It is simply removing fuel to achieve the commanded lambda. STFT & LTFT are multiplied together to give you an overall fuel trim.

Long term fuel trims (or LTFT) are learned corrections to the fuel model to keep your actual lambda value near your target lambda. Fuel trims are often confused with lambda. If your LTFT is .95 it does not mean your car is running rich. It is simply removing fuel to achieve the commanded lambda. STFT & LTFT are multiplied together to give you an overall fuel trim. If these values drift too far from 1.00 you will typically receive an engine fault for system to rich/lean.

Fuel Temperature is vital in estimating fuel mass for fuel injection. This value can creep up under low load or idle as the engine heat soaks. Typically this value will range from 30-80*C depending on ambient temperature and driving conditions.

This is the measurement of intake air temperature. It is a modeled temperature which takes into account coolant temp, air temp, and mass airflow.

This is a measurement of the engine coolant temperature in the head.

Measurement of engine oil temperature.

This is the measurement of the actual absolute fuel pressure in the fuel rail. This value should generally always be at or near your fuel pressure setpoint value. If this value is unable to achieve the setpoint pressure it may be indicative of a fuel pump issue or a pressure loss in the fuel lines, perhaps due to a clogged fuel filter. If you have significant upgrades you may be pushing the fuel pumps passed their operational limit.

This is the absolute fuel pressure setpoint. Your fuel pressure actual value should follow this value closely.

This value is the amount of ignition retard applied to each cylinder due to knock. Lower quality fuels are more susceptible to detonation. Knock become more worrisome as engine load increases. Occasional knock counts are bound to happen at low load, shifts, and high throttle transients. However if you are noticing that you are consistently seeing knock counts greater than -5* in multiple cylinders you may consider switching gas stations or trying a higher octane fuel for a tank or two.

This is the system voltage, this should generally be 11.5-12.5 volts while the engine is off and 13.0-14.5 volts while the engine is running.

This is steering angle in degrees of steering wheel rotation. Negative values are a left turn, positive values are a right turn

This is vehicle acceleration based off of the front wheel speed in meters per second².

This is the demanded advance of the intake cam. Negative values denote cam advance offset in degrees before top dead center (TDC), and vice versa. Intake Cam Angle Actual Bank 1 / Bank 2 should follow this value closely.

This is the actual advance of the intake cam for bank 1 and bank 2. Negative values denote cam advance offset in degrees before top dead center (TDC), and vice versa. These values should follow Intake Cam Angle Desired closely.

This is the demanded retard of the exhaust cam. Positive values denote cam retard offset in degrees after top dead center (TDC), and vice versa. Exhaust Cam Angle Actual Bank 1 / Bank 2 should follow this value closely.

This is the actual retard of the exhaust cam for bank 1 and bank 2. Positive values denote cam retard offset in degrees after top dead center (TDC), and vice versa. These values should follow Exhaust Cam Angle Desired closely.

These values are the actual wheel speeds as measured by the wheel speed sensors. This is a great monitor to watch for wheel slip or traction issues.

This is the general vehicle velocity.

This is a measurement of engine acceleration per cylinder. This is a great monitor to watch when trying to decipher a misfire or which cylinders are being cut during traction control, launch control, etc. Spikes in a cylinder often indicate a misfire or a cut. Typical values under normal operation will be +/- 20 Rev/s²

This monitor will provide data on the map slot you are currently running using our custom map switching. This is a custom monitor.

This monitor will show you when you are activating the Rolling Anti-Lag System. A value of 1 means you are currently activating the Rolling Anti-Lag feature.

This monitor will tell you if an engine safety is active. Engine safeties are a custom feature we integrated into the stock control strategy to help save the engine in case of a mechanical failure. If this value is 1 an engine safety has been tripped and the throttle has been limited. For information on which engine safety may have been tripped consult the Engine Safety Source Monitors

This value will give you a value which corresponds to which engine safety may have been tripped. It will be active as long as the safety is active and will revert to 0 when the safety is cleared. Below is a list of what each engine safety is and their corresponding number.

  • 0 = No safety is active

  • 1 = Overboost Safety (Delayed)

  • 2 = Overboost Safety (Immediate)

  • 3 = Differential Fuel Pressure (Delayed)

  • 4 = Differential Fuel Pressure (Immediate)

  • 5 = Knock (Single Cylinder)

  • 6 = Knock (Multi Cylinder)

  • 7 = Short Term Fuel Trims (Delayed)

  • 8 = Short Term Fuel Trims (Immediate)

  • 9 = Lambda (Delayed)

  • 10 = Clutch Slip

  • 11 = Misfire Safety

This value will give you a value which corresponds to which engine safety may have been tripped. It will store the last safety that was tripped. So if you are out and about and trip an engine safety when you aren’t logging you can reference this value to see which safety you tripped. Below is a list of what each engine safety is and their corresponding number.

  • 0 = No safety is active

  • 1 = Overboost Safety (Delayed)

  • 2 = Overboost Safety (Immediate)

  • 3 = Differential Fuel Pressure (Delayed)

  • 4 = Differential Fuel Pressure (Immediate)

  • 5 = Knock (Single Cylinder)

  • 6 = Knock (Multi Cylinder)

  • 7 = Short Term Fuel Trims (Delayed)

  • 8 = Short Term Fuel Trims (Immediate)

  • 9 = Lambda (Delayed)

  • 10 = Clutch Slip

  • 11 = Misfire Safety

  • hPa → psi = hPa · .0145 = psi

  • kPa → psi = kPa · .145 = psi

  • kPa → hPa = kPa · 10 = hPa

  • hPa → kPa = hPa · .1 = kPa

  • *C → *F = (*C · 1.8) + 32 = *F

  • km/h → mph = km/h · .6214 = mph

  • Boost Pressure (hPa) = manifold absolute pressure (hPa) - ambient pressure (hPa)