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EFI System Calibration
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Now that we have a good idea of what an engine needs to operate smoothly, it is time to actually
begin to construct the framework of the calibration. Before the engine is even started, the calibrator
must provide the PCM with some parameters that are close enough to the optimum setting to begin
checking operation. “Getting into the zip code” of the actual ideal settings can be one of the
toughest tasks in the whole process. Whenever possible, it is always easiest to start with a known
good calibration for the engine combination being tuned. If a similar engine combination has been
calibrated before, it saves a lot of time in the following steps. Making small changes to an existing
tuning file also reduces the chances for wholesale miscalculations and no-start, no-run conditions.
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Some software packages allow the calibrator a
head start with the necessary changes by
loading predefined tables. The SCT
Advantage package shown here allows the
user to select from a list of MAF sensors as a
starting point for the airpath model.
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The target air/fuel ratio is set to a
constant value in all areas where the
engine may operate during initial tuning.
This helps reduce the confusion
associated with trying to hit a moving
target when correcting the airflow model.
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Some aftermarket tuning packages have built-in tools that can often generate maps based on
engine component specs (port size, cam specs, compression ratio, etc.) that are close enough to
the optimum setting to get started. Other programs allow for changes to be made to a starting OEM
file to accommodate hardware changes (new injectors, different MAF sensor, addition of a
supercharger) providing the tuner with a closer estimation of what the engine requires in the
calibration. This is also the time to review all sensors to be used on the engine to ensure that their
outputs are properly recognized by the PCM. A quick key-on (turning the ignition to power up the
PCM) to compare ECT, IAT, and MAP values against ambient conditions prevents confusion after
startup.
Fuel injector parameters should also be checked at this point. Make sure that fuel pressure has
been set properly and injector size parameters in the PCM reflect the components used and current
rail pressure. This is also the time to double-check the voltage compensation curves and dead-time
characteristics of the injectors being used. Proper modeling of actual fuel delivery makes later
modeling of airflow much easier.
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One of the primary keys to properly calibrating any EFI system is the accurate modeling of engine
airflow. This is the most important point to remember. The majority of all fuel and spark calculations
is based upon airflow or engine load. If the PCM does not know how much air is passing through
the engine at any time, it has little hope of accurately metering fuel or controlling ideal spark
advance.
To begin calibrating airflow, it is usually easiest to start above idle, often 1,500 rpm or more. Idle is
one of the most difficult conditions for the PCM to control, so it is easier to skip right past this to get
things “in the zip code.” Running the engine at slightly elevated speed decreases the chances of
stalling as a result of less than optimal air/fuel ratio or spark advance. When first starting the airflow
modeling process, it may also be helpful to lock the timing to aid stability. The goal here is to build
maps representing what the engine does under stable operation. We will return later to smooth out
transitions. To accomplish this, the fuel tables are set to deliver a constant air/fuel ratio (usually l =
1) under a wide range of speeds and loads. With known fuel outputs, it can safely be assumed that
any deviation from the desired air/fuel ratio is a result of an error in measured airflow. If the target
ratio is l = 1, using a wideband air/fuel monitor makes this process easier.
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It has been my experience that it is easiest to perform initial fuel corrections in open loop. That way,
instantaneous lambda output equals the necessary correction factor needed for the current
operation point. The self-correcting action of the OEM lambda controller (closed loop operation)
often becomes more of a nuisance than tuning aid. If the stock HEGO is not providing an accurate
signal, the PCM’s correction may push against the calibrator’s initial changes. This can be more
prominent in cases where a larger duration camshaft is being used or header lengths have
required the HEGO to be moved farther away from the cylinder head.
Most PCMs can be forced to stay in open loop operation by adjusting the closed loop enable tables
to values at the extreme of their range. For example, minimum throttle for open loop can be set to
0% or minimum coolant temperature for closed loop set to 300 degrees. After the majority of airflow
modeling is complete and fueling errors are inside of a couple percent, changing back to closed
loop operation should not significantly change engine operation.
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It is possible to perform these corrections in closed loop, but it adds another multiplication step and
requires more data recording. In this case, both short- and long-term closed loop fuel trims must
also be monitored. These trims must be applied to the actual lambda before calculating the
necessary multiplier for airflow corrections. If the closed loop trims have enough authority to bring
the engine to l = 1, then these corrections themselves become the multiplier to be applied to airflow
for correction. This process works best on vehicles where the exhaust manifolds, camshaft, and
HEGO installations remain the same as stock. Since the PID (Proportional Integral Derivative)
control loop running the HEGO feedback and lambda trim in closed loop is rarely stable at 0%
correction, I often find it more useful to simply correct in open loop with a more stable delivered
lambda.
The bulk of the work in calibrating the airflow model should be done at nominal temperatures. The
engine should be warmed up and any startup enrichment routines should be expired before
proceeding. Coolant, oil, cylinder head, and intake air temperatures should be stable to avoid
interference from other multipliers while adjusting fuel delivery. Adjustments for cold start, varying
air temperatures, and other conditions are handled later in the process. This is simply the time to
model the base characteristics of the engine and its airflow measurement.
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Mass Air Flow Modeling
For engines that use an MAF sensor, airflow modeling means making sure that the transfer function
in the PCM matches the actual output of the sensor. The ideal method is to have data from the
exact MAF sensor to be used, as flowed with the exact intake tract from filter to throttle body, and
input this data directly into the PCM’s MAF table. Since this data is rarely available, the next best
thing to do is create this data by actual testing on a dynamometer. Something as simple as a
change in air filter design or MAF sensor clocking relative to bends in the plumbing can shift MAF
output to the PCM by 20% or more. Verifying actual performance on the exact vehicle in question
gives the best accuracy.
Actual MAF output calibration is best done by using the dynamometer to hold the engine exactly at
one of the calibration points of the MAF sensor, waiting for the engine to stabilize, and finding the
error. The calibration points in question may not necessarily line up with fixed RPM or engine loads.
All that is needed is a static airflow rate. This means that simply driving the vehicle in a single gear
on a chassis dynamometer can yield a wide range of calibration points simply by changing throttle
position and consequently speed. Once the engine stabilizes, the MAF table is adjusted at this
point and we move on to the next calibration point. This process is repeated for as much of the
MAF sensor range as possible, always waiting for the engine to reach steady state operation
before making an adjustment to the MAF table values. If it is not possible to adjust the MAF table in
real time, make a spreadsheet showing MAF calibration points, target l, actual l, and percent error.
(Figure 9-1) This makes for fast adjustments to the data tables and a quick return to the
dynamometer to confirm or adjust again until error is acceptable.
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A word of caution here is to monitor engine temperature and actual lambda. Stop testing if the
engine is operating at either high temperature or an excessively rich or lean condition. Running the
engine excessively rich (l > 0.8) for too long during this process can cause bore wash and ring
damage. Likewise, running too lean can generate high exhaust gas temperatures that may damage
valves, manifolds, or catalysts. This part of the tuning process is not intended to cover airflow
ranges approaching WOT. It should be possible to map the majority of airflow conditions without
exceeding about 60% engine load. This should keep temperatures safe.
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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 car’s
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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How to Tune and Modify Engine Management Systems
Drawing on a wealth of knowledge and experience and a
background of more than 1,000 magazine articles on the
subject, 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. Hartmans text is
extremely detailed and logically arranged to help readers better
understand this complex topic.
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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
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business day of receipt of payment! Standard shipping is a flat rate of
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