Vehicle and Tuning Index/ Glossary

Modified on Wed, 19 Oct 2022 at 11:37 AM

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 known as a Stoichiometric ratio. 


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.