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EFI System Input Sensors
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Before we delve into the tables that control engine operation, it is important to understand what the
computer sees. The old saying, “garbage in, garbage out,” applies directly to EFI systems. More
often than not, the cause for a poor-running car lies not in a bad calibration, but rather in a bad
calculation. This is to say that engine output controls are formed based on inputs and calculations.
A perfectly good calculation on a bad input parameter drives just as poorly as a poorly tuned car.
Although not all sensors are absolutely critical to engine function or drivability, there are a handful
that the EFI computer can’t live without. Likewise, sometimes we have redundant sensors where
only one really impacts the final calculation of engine output controls and others are merely
monitors.
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Throttle Position
The throttle position sensor (TPS) is one of the most critical inputs for any EFI system. Think of it as
the volume knob on the stereo in form and function. The TPS tells the computer exactly where the
throttle blade is so that it can be determined whether the driver is attempting to idle, cruise at a
steady state, accelerate, or decelerate. Additionally, the rate and direction of change of this sensor
helps the computer determine if the driver is attempting to change states. Most TPS sensors are
basically a rotary potentiometer that varies output based on position around a dial. The further up
the dial, the longer the electrical path gets through a set of resistors. We usually read output in a 0
to 5-volt scale with 0.5 to 1.0 v usually indicating closed throttle and 4.5 v or greater indicating wide
open (WOT).
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Mounted directly to the
throttle shaft, the TPS
sensor (arrow) reports
actual blade angle to the
PCM. (Nate Tovey)
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It is important to know exactly what the threshold is between closed throttle (C/T) and part throttle
(P/T) for calibration to ensure that the computer actually uses the idle tables when the driver’s foot
is off the pedal. It is a common mistake for a car owner to open the idle screw on the throttle body
without checking TPS output. If the blade is opened beyond the C/T threshold to prevent stalling,
the TPS must be readjusted to reflect the new closed throttle position. Likewise, a stretched cable
or bent linkage may prevent the computer from seeing WOT even though the blade is 99% open.
Since the effective flow area changes so little between 70% and 100% blade opening, many
systems consider anything over 70% or so to be wide open depending on RPM.
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Coolant Temperature
Temperature of the engine itself is another extremely important monitoring point. This is a two-way
street. Engines have a relatively narrow temperature band in which they operate most effectively.
Too cold and fuel has trouble atomizing before the combustion process. Too hot and preignition in
the chamber has almost identical negative effects to knock or expansion and distortion risk, warping
critical sealing surfaces. Actual desired operating temperature depends upon desired engine
usage. Most current OEM systems are thermostatically controlled to about 200 degrees F to allow
for ideal combustion and emissions. Typically, a 20-degree drop to about 180 degrees F nets
cooler chamber temperatures and allows those few extra degrees of spark advance that make more
horsepower. Much like the mechanical choke on a carburetor, EFI systems allow for enrichment and
added idle speed based at cold temperatures. Going too cool on the thermostat opening
temperature can keep many OEM processors in the warm up routine skewing target fuel delivery
and idle speed. A skilled calibrator can change the parameters that determine what is “warmed up”
to avoid excess enrichment. However, intentionally running a cold engine and head temperature is
usually reserved for drag race applications where emissions and cylinder wash from excess raw fuel
are not a concern.
Knowing how much enrichment to add depends directly upon actual temperature. This comes from
a sensor in either the coolant path or mounted directly in the cylinder head itself. These sensors
are typically a basic thermistor with a resistance that varies directly with contact temperature. Most
ECT sensors are of the negative temperature coefficient (NTC) type. NTC thermistors reduce in
resistance as temperature increases. With a steady input voltage (usually 5 v) to the thermistor,
increasing temperatures are read as higher return voltages from the sensor as a result of the
dropping resistance thanks to Ohm’s Law.
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Intake Air (left) and Coolant
(right) Temperature sensors
are usually NTC thermistors
with slightly different housings
to accommodate their
installation environments.
(Nate Tovey)
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If the sensor is placed in the coolant path, it is important that no air pockets are present. It is a
common error to register a relatively cold input signal when the sensor is actually sitting in a steam
pocket out of contact with actual engine temperatures. Since most EFI systems have safeguards in
the code to allow for higher idle speed (more coolant circulation), increased electric fan activity, and
richer fueling conditions at high engine temperatures, this input can be an engine saver. A cylinder
head temperature sensor mounted directly to the casting reduces the chance of this error. The
thing to keep in mind here is that cylinder head temperatures are typically 8 to 15 degrees F
warmer than coolant temperatures at any given time due to conductivity.
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Transfer function of several
different ECT sensors. Note the
logarithmic scale for resistance
that yields large changes with
temperature.
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Air-Inlet Temperature
Air temperature has a direct effect on density as well as burn rate. As air is heated it gains volume
and loses density. In speed-density systems, this measurement is critical to determining exactly how
many oxygen molecules are available for combustion in the current cycle. Since the engine
displaces the same amount of manifold air in any given cycle, temperature directly affects the
density (number of available oxygen molecules) actually making it into the chamber. On mass air
measurement systems, air-inlet temperature does not directly adjust calculated charge fill for fuel
calculations, but it is still used as a modifier to control burn characteristics. Inlet temperature is
directly proportional to allowable spark advance assuming constant fuel delivery. Colder inlet
temperatures mean more timing advance can be used, resulting in more available horsepower.
Conversely, much hotter inlet temperatures (often a result of supercharging) require reduced timing
to avoid the knock that comes from the increased burn speed.
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The IAT sensor (arrow) should
always be installed in a location that
best represents the temperature of
the air entering the cylinders. In the
case of a supercharger, this means
placing it after the compressor to
measure any heat soak as seen on
this turbo Toyota Supra engine.
(Nate Tovey)
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Most inlet-temperature sensors are very similar in design and function to NTC coolant-temperature
sensors. Since air density is so much lower than coolant density, sensor elements can be
unshielded without risk of damage, making for faster response to changes in conditions. It is
important for the calibrator to understand where the inlet temperature is being monitored on forced
induction applications. While some OEM supercharged applications actually employ two inlet-
temperature sensors to monitor both ambient conditions and actual inlet-port temperature, most
systems only have one such input. Ideally, these sensors should be placed as near to the cylinder-
head intake port as possible so that the computer sees actual charge temperature. This allows for
tighter control in supercharged applications where charge temperatures vary from 90 degrees F
ambient to over 300 degrees F in non-intercooled vehicles. Again, a skilled calibrator can
compensate in the tune for a supercharged engine with an inlet-temperature sensor installed
ahead of the compressor with a shift in the temperature compensation function. By shifting this
function and leaving an appropriate safety margin, everything can work just fine, but it’s easier to
relocate the sensor for a more accurate signal.
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Manifold-Surface Temperature
Some systems add another sensor to monitor manifold-surface temperature. This allows for an
additional routine in the computer to model heat transfer from the intake manifold to or from the
intake charge immediately ahead of the cylinder. Again, this effect is more pronounced on
speed-density systems where the actual air mass entering the cylinder must be calculated and
temperature plays a bigger part in required fuel delivery. These sensors are usually almost
identical in design and construction to the NTC coolant-temperature sensors.
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Mass Air Flow
Since internal combustion engines are so sensitive to air/fuel ratio, it is important to know exactly
how much of each component is entering the engine at any given time. The best way to ensure
accurate fuel delivery is to have accurate air measurement before calculating anything.
Speed-density systems are constantly making calculations of estimated airflow based on pressure,
temperature, and engine speed. Mass air systems employ a sensor that directly measures air mass
flow into the engine. Basically, the more air molecules moving past the sensor, the more the signal
changes.
Early units used spring-loaded doors that were pushed further open by the force of the incoming
air. The density and velocity of the incoming air is proportional to the force on the door. The doors
of these sensors were then attached to a rotary potentiometer much like the throttle position
sensor. The drawback to these units is the lack of temperature compensation. These early sensors
require further calculation based on inlet temperature to determine the actual air mass.
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Previous | Next
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This has been a sample page from
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Engine Management: Advanced Tuning
by Greg Banish
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As tools for tuning modern engines have become more powerful
and sophisticated in recent years, the need for in-depth
knowledge of engine management systems and tuning techniques
has grown. Tuning engines can be a mysterious art, as all
engines need a precise balance of fuel, air, and timing in order to
reach their true performance potential.
Engine Management: Advanced Tuning explains how the EFI
system determines engine operation and how the calibrator can
change the controlling parameters to optimize actual engine
performance. This book takes engine-tuning techniques to the
next level. It is a must-have for tuners and calibrators and a
valuable resource for anyone who wants to make horsepower with
a fuel-injected, electronically controlled engine.
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Click below to view sample
pages from each chapter
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Author Greg Banish is a calibration engineer with extensive
aftermarket performance calibration experience. With over a
thousand unique calibrations performed over five years, he has
worked with enthusiasts and OEMs alike to improve the
performance and driving behavior of a wide range of vehicles.
The book contains detailed equations, graphs, and illustrations.
Also included are valuable and practical examples, including real-
world examples based upon the author’s experience that will help
more advanced readers apply this new information to situations
that are commonly seen during calibration.
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1 - Introduction to EFI
2 - Basics of Fuel Injection
3 - Carbureted Engines
4 - EFI System Inputs
5 - Fuel Injectors
6 - EFI System Fuel Control
7 - Ignition Systems with EFI
8 - Data Logging
9 - EFI System Calibration
10 - Idle Calibration
11 - Tuning for More Power
12 - Fine Tuning EFI
13 - Tuning EFI with Blowers
14 - Tuning Ford EFI Systems
15 - Aftermarket EFI Systems
16 - INCA OEM Calibration
17 - External EFI Controllers
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8-1/2 x 11"
Soft bound
128 pages
200 color photos
Item # SA135
Price: $22.95
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Click here to buy now!
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How to Build High-Performance Ignition Systems
The complete guide to understanding automotive
ignition systems. Covers components, systems &
subsystems for street & race applications. This book will
help you understand how your car’s ignition works, and it
will help you choose the right components for your cars
performance needs, whether it’s a 1965 289 or a 2003
Cobra with a 4.6-liter modular motor.
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Price:
$
22.95
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Tune and Modify Engine Management Systems
Drawing on a wealth of knowledge and experience
engine control expert Jeff Hartman explains everything
from the basics of engine management to the building of
complicated project cars. This book is updated to address
the incredible developments in automotive fuel injection
technology from the past decade, including the multitude
of import cars that are the subject of so much hot rodding
today.
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Price:
$
27.95
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Turbo High Performance Turbocharger Systems
This book is the most detailed and up-to-date resource on
turbocharging. You'll learn how turbochargers work, how to
choose the right turbo or turbos for your engine by reading
flow maps, and how to tune your engine to run perfectly with
your turbo system. Uses more than 300 photos and technical
information to help you make more horsepower. It also
discusses the various components of a turbocharger and
explains how to decode turbocharger model numbers,
compressor maps, other specifications and includes a
complete step-by-step turbocharger tear-down and rebuild.
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Price:
$22.95
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Turbochargers
How to select and install the correct turbo for big or
small
horsepower gains. Discusses turbocharger design,
sizing,
matching, controls, carburetion, exhaust,
ignition,
intercooling, marine and high altitude
applications. The most
comprehensive book available.
Turbo suppliers and kit
maker addresses are included.
“Everything you could possibly
need to know about
turbochargers for automotive applications
is in this
book.
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Price:
$
18.95
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Payment, Shipping & Sales
Tax: Iowa
residents must pay 7% sales tax. Items usually ship
within one
business day of receipt of payment! Standard shipping is a flat rate of
$4.95 to
anywhere in the United States with USPS Media Mail.
Priority Mail shipping is available for an
additional $3.00, or
$7.95 for shipping. Shipping is combined and discounted for multiple item
purchases as follows: first item regular shipping price, add
$1.95 for each additional item. For
purchases of 3 or more items
shipping is automatically upgraded to Priority for no additional
charge! We offer world wide shipping and ship to Canada and Mexico
with USPS Priority Mail
International for $14.95, and to most
locations in Europe, Australia, Asia, Japan and South
America for
$18.95. Satisfaction is Guaranteed. Our store has a NO HASSLE RETURN
POLICY
within 30 days of purchase.
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