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Fine Tuning EFI Systems
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At this point, most of the work is complete. If all the steady state values are correct, the vehicle
should operate fairly well. The final phase of calibration is improving drivability. This should be
thought of as finely polishing a sculpture. Where we were using a chainsaw earlier, we are now
using sandpaper. There shouldn’t be any need for drastic changes anywhere. If large changes are
needed at this point, chances are that the earlier modeling is not correct or the vehicle has
hardware issues.
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Integrating Fuel Maps
During the mapping phase, lambda was set to 1.0 for all but wide-open throttle. During WOT
testing, an ideal lambda was found that makes the best power without knock. It now becomes time
to blend the map for smooth transition between cruise and power. For the majority of the base fuel
map, lambda remains around 1.0 for emissions and fuel economy. If the engine is to operate at l =
0.85 at 90% load at WOT, some sort of blending needs to happen between there and the cruising
region. Since light acceleration is usually acceptable at l = 1, the enrichment should usually start
above 50 to 60% load. Try even increments between 1.0 and 0.85 for the cells leading toward
stable WOT operation. If engine or exhaust temperatures get too hot when the engine is held in this
transition region, more enrichment can be added. If response is still crisp and temperatures are
acceptable, slight enleanment in the transition area may help improve fuel economy. This map
should look like a smooth function when viewed in 3D. Sharp breaks in commanded lambda usually
indicate a cover-up for some other issue such as insufficient acceleration enrichment or improper
ignition tuning.
For supercharged engines operating above 100% load, a reasonable estimate of target lambda
should be used for the same engine without boost for the 70 to 100% load regions. This means that
a supercharged engine operating at l = 0.80 at WOT (130% load, 150 kPa) should still have a
target of l = 0.87 at 80% load (100 kPa). It is recommended that target lambda remain fairly
consistent under boost, but there should still be a smooth ramping of fuel values between cruise
and 100%. In some cases, it may be desirable to tune the base fuel map for extra enrichment
above a standard boost level. This can be done by ramping in more enrichment relative to load (in
the base commanded fuel map) above the calibrated WOT line to provide more cooling and knock
resistance during over-boosted conditions.
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Integrating Spark Maps
Much the same way the base target fuel map was blended, a similar operation must be done with
the base spark map. The areas between cruise and WOT should be smoothly blended. This table
should also look like a smooth function if viewed in 3D. Remember that supercharged engines
usually tolerate the same spark advance as their naturally aspirated counterparts at approximately
80% load. If the engine is supercharged with a lower static compression ratio than the typical
aspirated counterpart, more timing is necessary at lower loads to compensate for the reduced
cylinder pressure. The idea is to run the engine close to MBT timing in these transitional regions in
order to extract maximum efficiency without knock.
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A smooth commanded air/fuel ratio
table is shown using the Cobb
ProTUNER software. This table shows
the stock values for a Subaru STI that
have a progressive enrichment as
speed and load increase.
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Drivability improvements are done largely by adjusting the transient controls to provide smooth
changes between steady state conditions. The first transient to be refined is acceleration
enrichment (AE). Adjustment of this parameter can be highly subjective. The object is to supply just
enough extra enrichment to allow smooth transition to power without dumping excess fuel and
hurting economy and emissions. When calibrating AE, it is helpful to think about how much of the
wall film is being evaporated due to the increased airflow and add just enough fuel to keep t
constant. A quick stab at the throttle pedal momentarily shows a lambda leaner than the
commanded value for high load. The acceleration enrichment multiplier should be increased until
the wideband goes directly to the targeted steady state lambda at the higher load. The larger the
camshaft, the more aggressive this function needs to be. Acceleration enrichment is usually
adjustable relative to throttle position, so this should be checked with tip-ins starting at idle, part,
and medium load. More AE is necessary at closed throttle because of the large amount of area
increase when rotating the blade here. Fine-tuning of this function should be done under normal
driving conditions with typical tip-in rates. If the vehicle stumbles, then picks up and goes, more AE
is likely needed and the wideband should show lean during the stumbling. Adding fuel makes tip-in
smoother, but too much can foul plugs, hurt economy, or increase emissions.
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Even more accurate calibration of the AE can be done with high speed logging of wideband lambda
and target ratio. While performing a tip-in with a known load change, but at a constant target
lambda, AE requirements can be shown. This is best performed at part load where target l = 1. A
change from 15% load up to 50% load should not incur a change in the delivered lambda. By
logging the actual lambda during this transition, AE requirements can be determined. If the
wideband shows a momentary lean condition during load change, more acceleration enrichment is
needed. Likewise, momentary rich conditions indicate excessive AE. This process assumes that all
static airflow and fuel mapping has already be done with a high degree of accuracy. In OEM level
calibrations, this process is repeated for a large array of speed, load, and temperature points to
provide the best possible lambda control for emissions under all possible conditions.
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Tip-In Ignition
While acceleration enrichment helps to ensure proper fueling during tip-in, it may sometimes be
necessary to take additional measures to prevent knock or driveline noise. Burst knock is a
phenomenon that can occur during sudden increases in engine load. The rapidly rising cylinder
pressures may lead to knock under what would otherwise be stable combustion at steady state
operation. Even without knock, the sudden onset of engine torque may lead to driveline noise as
the lash is quickly taken up. Many OEMs intentionally reduce the available torque onset to keep
noise low or prevent driveline component failure. Both of these functions are typically controlled by
momentarily reducing spark advance. If instant throttle response is desired, the spark retardation
can be set to zero. Added acceleration enrichment can be used to quench minor knock while
retaining full timing and better torque. If no specific function exists in the PCM being used and tip-in
retard is desired, the appropriate cells in the base spark map can be reduced. Since the engine is
not likely to spend any time cruising above ~50% load at low speed, it is usually safe to reduce
timing below MBT here to soften tip-in or reduce burst knock.
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This ECU is from a
Cadillac Northstar
engine. With an
advanced circuit board
design, the majority of its
surface area is filled by
the actual wire harness
connections.
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Deceleration
Dashpot adjustment can be checked at this point by simply lifting off the gas pedal from an elevated
engine speed. The same should also be done by cruising at a steady speed and pushing in the
clutch or shifting to neutral. The object is to find the balance between hanging at the elevated
speed for too long after lifting versus dropping too quickly past idle speed and stalling. If the engine
speed hangs, decrease the IAC position at the same engine speed or increase the decrement rate
of the IAC position. If deceleration tends to drop right past idle speed (and the closed throttle
position at idle is correct), the commanded IAC position at higher engine speeds should be
increased or the decrement rate should be reduced. Initial adjustments to this function should be
done in 10 to 20% increments to see enough difference in actual performance.
Some difficult engine combinations may not allow for a quick descent immediately to idle speed. In
these cases, the IAC position versus engine speed knee point can be moved to a few hundred RPM
above idle. This allows for engine speed to drop to a lower intermediate speed where stalling is less
likely and the idle controls can softly move toward the desired target with a softer landing.
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Deceleration enleanment (DE) can be adjusted next. Some PCMs have tables specifically for
deceleration enleanment. These tables allow for the adjustment of the turn on/off points based on
engine speed. These should be set well above idle to avoid stalling. The larger the camshaft
overlap and duration, the bigger the gap between idle and DE threshold should be. Many stock
engines that idle around 650 rpm can tolerate DE all the way down to 1,000 rpm or so. A modified
engine with high compression and overlap may drive better by only allowing DE above 3,000 rpm.
On PCMs without such tables, the same effect can be accomplished by adjusting the row or column
of base fuel map cells for high engine speed and low load (high vacuum). Since the only way the
engine could ever operate in these cells would be to have the throttle closed at high speeds, this
fills the definition of deceleration. Setting target lambda to an extremely lean value commands lean
operation in these conditions. A value of 0% VE also forces fuel shutoff and can be used in simpler
speed density systems to achieve the same result. Since normal combustion is not present and any
actual loads are very small, spark advance values for these cells can also be relatively high.
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DE feel to the driver is tied to dashpot as well. Dashpot should be the primary control of engine
torque and speed during deceleration with DE only activating in areas where very fast drops in
engine speed are desired. If a gentle drop in engine speed is desired at any point, DE should not
be used since it compromises the engine’s ability to produce consistent torque output.
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Closed Loop (or not?)
After airflow has been mapped correctly under most conditions, closed loop operation can be
considered. All modern OEM systems use closed loop operation to compensate fuel delivery for
weather conditions, part wear, and changes in tolerances. This operation is a very reliable method
of keeping the engine in stoichiometric operation as long as the system inputs (primarily from the
HEGOs) are reliable.
The timing of the HEGO signal is carefully adjusted in the factory PCM. The PCM makes
adjustments to delivered fuel based upon the amount of “flight time” or transport delay between the
exhaust valve opening and HEGO sensor measurement. When an engine is operating very close to
stoichiometry and only small adjustments are being made, it is important to adjust in the correct
direction at the proper time to avoid unstable correction conditions. If modifications to the vehicle
have forced moving the HEGOs further away from the cylinder head, it may be necessary to adjust
the transport delay functions in the PCM to compensate. Otherwise the fast adjustments being
made by the PCM during closed loop operation may become out of phase with the HEGO feedback,
forcing the learned values to diverge from ideal. Adjusting the transport delays can put these back
in synchronization, improving fuel economy and emissions. Typically, a change from a short
manifold to long-tube headers adds about 20 to 30% to the transport delay times due to sensor
location.
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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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Other items you might be interested in
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Performance Ignition Systems
Performance Ignition Systems is a comprehensive guide to
significant increases in power, mileage and overall engine
performance by custom tuning electronic or breaker point
ignition systems. Sections include increasing engine power,
efficiency, mileage and longevity using upgraded ignition
equipment, judging and troubleshooting ignition components,
including diagnosis and reading spark plugs, electrical wiring
problems and solutions, tech tips and custom wiring for the
ultimate performance ignition and much, much more.
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Price:
$18.95
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Building & Tuning High-Performance Electronic Fuel Injection
Provides specific, detailed info on what fuel injection is & how it works.
Covers buying and installing the proper system for your performance
application. After a description of what programmable EFI offers its
users, author Ben Strader (founder and senior instructor of EFI
University) gives a detailed account of what you want to accomplish with
your EFI system, then shows you how to get there.
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Price:
$18.95
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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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Shipping is combined and discounted for multiple item purchases!
Buy more and save on shipping!
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Thanks for your business!
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MRE
PO Box 47
Grinnell, IA 50112
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