Vehicle | Tuning Index

    Terminology

    A/F 

    Air to fuel ratio. An air to fuel ratio of 14.64 to 1 is used by manufacturers

    as the optimum setting for minimizing emissions. This you will see expressed

    as 14.64, but what it means is, there is 14.64 parts of air to one part of

    gasoline. The ‘parts’ mentioned is generally weight and another way of saying

    weight is ‘mass’. Optimum wide open throttle A/F is anywhere from 12.5 to

    13.5 for a naturally aspirated vehicle and from 11.5 to 12.0 for a power adder

    vehicle. The optimum A/F ratio is discussed in this book.


    AC 

    Air conditioning.


    ADVANTAGE

    “Advantage” is the name of the tuning software released by Derive Systems


    ACT

    Air Charge Temperature sensor. This is a crucial sensor that measures

    and reports to the PCM the actual temperature of the air going into the engine.

    This sensor provides input that may modify how much timing and fuel go into

    the engine. It is VERY important in a car with a supercharger or turbocharger

    that the ACT be located after the blower and/or intercooler. In other words,

    you will want the ACT to measure the temperature of the air after the air has

    been compressed. This is critical because it is a law of physics that whenever air

    is compressed, it is heated. SCT takes this into account in the value files and

    base files for a blown car. Not locating this sensor after the blower could result

    in severe engine damage. This also can be referred to as the IAT sensor.

    Ambient – This is the air temperature that the engine will be ingesting. If the

    car is outside on a 75º day, then the ambient temperature is 75º.


    Batt

    The car’s battery voltage (normally 12 volts DC.)


    BAP

    Barometric air pressure sensor. Used on older EEC IV cars to measure

    barometric pressure of the atmosphere. This was eliminated in later models.

    This data is now inferred from the MAF readings.


    Boost

    This is simply a measurement of pressure in pounds per square inch. It

    applies to a blown car and is normally measured in the intake manifold. Boost

    by itself really doesn’t mean much, except as a rough guide as to how much

    extra air is being forced into the engine and is being heated in the process. An

    engine is a big air pump. The more airflow it can generate, the more power the

    engine will make.


    CCS

    Converter Clutch Solenoid used in an automatic transmission to control

    lockup of the clutch that is inside the torque converter.


    CEL

    Check Engine Light. This a light that comes on when there is an emissions

    failure or a sensor failure. If this light comes on, then a diagnostic trouble

    code has been set and action needs to be taken to resolve this issue. This can

    also be referred to as an SES light, Service Engine Soon.


    Closed Loop

    When the engine is using input from the oxygen sensors and the

    MAF to control the engine to 14.64:1 air-fuel ratio.


    DCL

    Data Communication Link –This is a protocol used in later EEC IV

    processors that allow viewing of some real-time sensor data.


    DIS

    This is a Distributor-less Ignition System. This type of ignition system

    has no distributor but only has a small number of magnets on the crankshaft,

    exactly half the number of cylinders the engine has. This system needs a camshaft

    sensor to properly synchronize the ignition system. This type of system

    was mainly used on 3.8L SuperCoupes and some 2.3L Mustangs/Rangers.


    EEC, ECM, ECU

    Electronic Control Module/Unit, the car’s computer or

    PCM.


    ECT

    Engine Coolant Temperature sensor. This is a crucial sensor that measures

    and reports to the PCM the actual engine coolant temperature in the

    engine. This sensor provides input that may modify how much timing and fuel

    go into the engine.

     

    EDIS

    Electronic Distributor-less Ignition System used in later Fords. This is

    an ignition system used in Ford vehicles that do NOT use a distributor. This

    type of ignition system uses a 36-1 tooth wheel on the crankshaft to pickup

    engine speed.

     

    EFI

    Electronic Fuel Injection.

     

    EGO

    Exhaust Gas Oxygen Sensor – also referred to as a 02 sensor. This sensor

    provides feedback as to whether or not the system is either rich of 14.64:1

    air-fuel ratio, or lean of 14.64:1 air-fuel ratio. It does not, and cannot provide

    data as to the actual air-fuel ratio.

     

    EGR

    Exhaust Gas Recirculation – This is an emissions component that recirculates

    exhaust gas into the engine. This reduces combustion temperatures and

    at the same time reduces nitrogen based emissions from the vehicle. It is only

    used at part throttle on a warm engine. It is shut off by the PCM at WOT. The

    EGR valve does not hurt performance at all and even increases fuel economy.

     

    EGT

    Exhaust gas temperature.


    EPC(S) 

    Electronic Pressure Control Solenoid. This is a solenoid in an automatic

    transmission that regulates line pressure. This can also be referred to as a TV

    solenoid.


    EVP(S)

    EGR Valve Position Sensor. This provides feedback to the PCM as to

    what level the EGR valve is operating at.


    HEGO

    Heated Exhaust Gas Oxygen Sensor, also referred to as a 02 sensor.

    This sensor provides feedback as to whether or not the system is either rich of

    14.64:1 air-fuel ratio, or lean of 14.64:1 air-fuel ratio. It does not, and cannot

    provide data as to the actual air-fuel ratio.


    HEI

    High Energy Ignition.


    IAC

    Idle Air Control. This valve uses feedback from the PCM to automatically

    vary the amount of air going into the engine at idle to control idle speeds

    as set by the PCM. This can also be referred to as an ISC valve.


    IAT

    Intake Air Temperature, see ACT above.


    IMRC

    Intake Manifold Runner Control - It is a device that allows the intake

    manifold to switch from a long runner to a short runner and vice-versa. Typically,

    a longer runner makes more low RPM torque and a shorter runner makes

    more peak horsepower (HP). Having two runner lengths allows a broader, flatter

    torque curve. Normally, the longer runner creates more swirl in the combustion

    chamber and therefore the combustion chamber becomes a faster burn

    chamber, requiring less overall timing for peak HP. When the IMRC opens

    the shorter runner is utilized. This results in a slower burn rate combustion

    chamber and requires more timing to produce peak HP. The PCM controls the

    amount of spark that gets added when the IMRC opens.


    ISC

    Idle Speed Control, see IAC above.


    KAM

    Keep Alive Memory. This is an area in the PCM’s memory where data

    is stored that will allow the PCM to adapt and change settings to allow for

    changing conditions. This area is kept powered up even when the vehicle is not

    running.


    Load

    Load can also be called volumetric efficiency. It is usually expressed in

    a percentage, such as 50% load. Load or volumetric efficiency is actually the

    measurement of how much air is flowing into the engine. If a 4.6L engine

    sucks in 4.6L of air in two engine revolutions (it takes two engine revs for all

    the cylinders to go through their different strokes) then it’s load is 100%. If it

    only sucks in 2.3L of air, then it’s load is 2.3/4.6 or 50%. On a blown car, you

    can force more air into the engine than it’s displacement, so load will go above

    100%. Load is VERY important because as you will learn, load is used on

    many of the tables for a variety of critical engine controls. Load is calculated in

    the PCM based on input from the mass air meter.

    You can calculate load mathematically:

    ((MAF reading (lbs/min) X 2) / (RPM X 8)) / engine_displacement

    Here’s an example: ((40 lbs min X 2) / (6000 X 8) ) / 0.00155 = 1.075, or .5%


    LTFT

    Long-term fuel trims. These are values that are stored in the PCM that

    tell the computer the trends for correction made by the PCM, using feedback

    from the oxygen sensors (EGO/HEGO) to correct for conditions that cause the

    fuel control to vary from 14.64 A/F at idle and part throttle.


    MAF

    Mass Airflow Sensor. This is the most critical sensor in a car. It directly

    measures airflow with an electronic hot wire sensor. The sensor resides in a

    small ‘sample’ tube that is in the incoming air path. The sample tube size is

    calculated to be a certain proportion of the larger inlet tube. The wire is heated

    to a specific temperature and the PCM tries to keep it at a certain target temperature.

    As airflow increases, the sensor cools, the PCM responds by adding

    more voltage to keep the sensor’s temperature constant. The meter can output

    up to 10 volts or more, but the PCM will only acknowledge a maximum of 5v.

    As engine airflow increases, the voltage increases signaling more air to the PCM.

    If the meter is of insufficient capacity and goes past 5v, this is called pegging or

    saturating the meter. We will discuss this in detail later. The PCM determines

    the air mass from a software function in the PCM. This is called the MAF

    transfer function. The transfer function is a series of points on a graph that

    shows a specific air weight at 30 voltage points. There is a lengthy discussion of

    this in this book.


    MAP

    Manifold Absolute Pressure sensor. This measures the pressure inside

    the intake manifold.


    MIL 

    Malfunction Indicator Lamp – the same as a check engine light.


    MLPS

    Manual Lever Position Sensor. This is a sensor on an automatic transmission

    that tells the PCM what position the gearshift lever is in. This is also

    referred to as a TRS, Transmission Range Sensor.


    NA

    This means naturally aspirated. A power adder (nitrous or blower) is not

    being used.


    OBD

    On-Board Diagnostics.


    O2

    Oxygen.


    Open Loop

    When the engine is running without direct input from the oxygen

    sensors.


    PCM

    Powertrain Control Module, the car’s computer.


    PCV – Positive Crankcase Ventilation.

    PIP – Profile Ignition Pickup. This sensor is located either in the distributor (if

    so equipped with one) or is calculated from a crankshaft position sensor. The

    PIP signal is used by the PCM to determine engine timing and injector operation.

    Power Adder – Either a supercharger, turbocharger or nitrous oxide. Used to

    provide more air and fuel to the engine.


    PSI

    Pounds per square inch. This is a measurement of pressure that can also

    be designated with a ‘pound’ sign such as 5#.


    ROM

    Read Only Memory.


    SEFI

    Sequential Electronic Fuel Injection.


    SPOUT

    Spark Output signal. This is a signal that is output by the PCM to

    either the TFI module (on distributor cars) or the EDIS/DIS module. This

    signal contains the information required for the module to output the spark at

    the correct time.


    STFT

    Short term fuel trims. A ‘trim’ is a correction that is applied to a setting

    in the engine. STFTs are used at idle and part throttle. They are usually

    expressed as either a positive or a negative number. A negative number means

    the car is too rich and the PCM is attempting to ‘trim’ a percentage of fuel out.

    A positive number means it is running too lean and the engine is adding fuel. A

    STFT of (-10%) means that the PCM is pulling 10% fuel to get the engine to

    operate 14.64 A/F.


    Stoichiometric or Stoich

    This is the chemically correct air-fuel ratio, typically

    14.64:1 for gasoline.


    Target A/F

    We will refer to target A/F as the value we are targeting for when

    we are tuning the engine.


    TDC

    Top Dead Center. This is a measurement of the piston location in

    degrees of crankshaft rotation. This can be referred to as either BTDC, Before

    Top Dead Center, or ATDC, After Top Dead Center.


    TB

    Throttle Body.


    TOT

    Transmission Oil Temperature sensor. This is used in automatic transmissions

    to send transmission temperature data to the PCM.


    TP

    Throttle Position. This is a value seen in the Advantage software that tells

    the PCM when the car is in WOT mode. This is a parameter seen in Advantage

    software, the units used are AD counts.


    TPS

    Throttle Position Sensor. This sensor is attached to the throttle body

    and tells the PCM what the relative position of the throttle is. It is used to

    determine TP.


    VBAT

    Vehicle Battery Voltage.


    VIN

    Vehicle Identification Number.


    Volumetric efficiency

    see Load, above.

     Volumetric Efficiency can also be called Load. It is usually expressed in

    a percentage, such as 50% load. Load or volumetric efficiency is actually the

    measurement of how much air is flowing into the engine. If a 4.6L engine

    sucks in 4.6L of air in two engine revolutions (it takes two engine revs for all

    the cylinders to go through their different strokes) then it’s load is 100%. If it

    only sucks in 2.3L of air, then it’s load is 2.3/4.6 or 50%. On a blown car, you

    can force more air into the engine than it’s displacement, so load will go above

    100%. Load is VERY important because as you will learn, load is used on

    many of the tables for a variety of critical engine controls. Load is calculated in

    the PCM based on input from the mass air meter.

    You can calculate load mathematically:

    ((MAF reading (lbs/min) X 2) / (RPM X 8)) / engine_displacement

    Here’s an example: ((40 lbs min X 2) / (6000 X 8) ) / 0.00155 = 1.075, or .5%


    VSS

    Vehicle Speed Sensor. This sensor is attached to the transmission and

    sends the PCM information on vehicle speed, which is critical for automatic

    transmission shifting and in speedometer operation (99-up).


    WOT

    Wide Open Throttle.

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