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.
