TCFI Twin Cam Fuel Injection
Why is the TCFI auto-tuning
capability superior to competitive products?
Competitive systems such as the
and the new Dynojet®
claim to have auto-tuning capability. Prospective customers should ask whether
a given system meets two important criteria:
auto-tuning real-time and continuous? Real-time means that the system makes
immediate air/fuel ratio corrections based on oxygen sensor feedback.
Continuous means that the system makes corrections whenever it is running.
2. Can the user monitor, control, and override the
Any "feedback" system using a sensor to make corrections is subject to
operating regions where instabilities or errors exist.
system fulfills the first
criteria, it does offer
real-time and continuous auto-tuning. The new Power Vision®
system is neither real-time nor continuous. The user must log operating data
while the engine is running, download the data to a PC, apply the air/fuel
ratio corrections to a tuning file, and then reflash the engine control
module (ECM) with the modified tuning file.
Only the TCFI system meets
both criteria. 30 seconds after engine start, when the oxygen sensors have
warmed up, the TCFI system continually updates independent front and rear
cylinder air/fuel correction tables, referred to as the block learn
multiplier (BLM) tables. The BLM tables have the same cells (RPM rows and
throttle position columns) as the air/fuel ratio command table. Correction
values are in percent units. A value less than 100% means that fuel is being
taken out to correct a rich condition. A value greater than 100% mean that
fuel is being added to correct a lean condition. An actual BLM table is
shown below. Most of the values are between 90% to 110%, showing that the
system is now well tuned and just making small corrections. The user can
download the setup file from the TCFI at any time and monitor the BLM
Part of the second criteria listed above
is the ability to control and override the auto-tuning corrections. Only the
TCFI system offers this capability on a cell-by-cell basis. You will notice
cells highlighted in blue with values 0 and 1. Closed loop feedback is
disabled in any BLM cells with value 0. This is useful in operating areas
where exhaust reversion effects may cause incorrect sensor readings. The
table has the value 0 in cells corresponding to decel (RPM above idle and
closed throttle) where reversion effects are most pronounced. BLM update,
but not closed loop feedback, is disabled in any BLM cells with value 1.
This means that the system always starts with 100% fuel in these cells. In
this table, the value 1 is used in the range of 750 to 1,500 RPM and 0% to
5% throttle position (TPS) to compensate for the unstable cold start
characteristics of a particular engine combination that includes an
aftermarket throttle body. Please refer to the TCFI Idle Tuning Tech Note
for more information on this subject.
BLM Table Showing Special Values
What is the difference between
the Gen 4 and previous Gen 3 TCFI versions?
The TCFI Gen 4 is identical to
the previous Gen 3 (TCFI III) version with the exception of the housing and
wire harness hookup. The Gen 4 version has a lower profile housing that allows
installation on Sportster®
applications. For Twin-Cam applications, the WEGO IIID wide-band exhaust gas
oxygen sensor interface now conveniently mounts on top of the TCFI module. The
WEGO IIID wire harness has been simplified to allow easy plug-in connections
for power and ground using the existing Harley-Davidson four terminal
The same setup files and software can be used
interchangeably with Gen 3 and Gen 4 product versions.
Typical TCFI Gen 4 Installation on Twin-Cam Model
Gen 4 Installation on Sportster®
with Remote Mounted WEGO
Easy Plug-In Installation of WEGO
How does the new TCFI EX version
differ from the standard TCFI?
The TCFI EX is 50 states street
legal (ARB E.O. No. D-641-5) for 2001-2006 88 CID Twin-Cam with 36 pin Delphi®
system, excluding 2006 Dyna®
models with original equipment oxygen sensors. The
TCFI EX is recommended for all street driven applications and allows retrofit
of closed loop oxygen sensor technology to earlier models. There are only a
few limitations compared to the standard version. User changes
to the air/fuel ratio table are only allowed above 2750 RPM or 35% throttle.
The range below this is shown in red and locked out. But as you can see from
the actual table below, the values are still optimized for performance
applications. There are also some limits on the range of user changes to the
spark advance table. The programmable user input and output functions are not
Refer to the
TCFI EX Installation & Tuning Manual
TCFI EX Air/Fuel Ratio Table
What special considerations apply
to 2006 and later models?
2006 and later models use a new
throttle body with smaller injectors (rated 3.91 gm/sec versus 4.22 gm/sec for
2001-2005 models). The smaller injectors limit maximum power to about 90 HP.
Fortunately, Screamin Eagle®
offers a high performance throttle body that comes complete with larger 4.89
gm/sec injectors for under $400.
2006 Dyna® and all 2007
and later models are factory
equipped with front and rear oxygen sensors. The Delphi®
controller operates in closed loop under part throttle conditions. This system
uses 2-wire narrow band oxygen sensors that maintain the air/fuel ratio (AFR)
near 14.5. If you attempt to install an "add-on" device such as
Power Commander® that changes the injector pulse width, the Delphi®
system will compensate within a few miles and return to the factory
programmed AFR values. The only solution is to completely replace the
factory system with a unit such as our TCFI. And you won't have to weld in
oxygen sensor mounting bosses, as H-D®
has already done that for you.
Does the TCFI system fully
support the new 96 CID engines introduced in 2007?
Yes. Installation is very
easy since the exhaust already has provision for oxygen sensors. The ECM
controls the 6th gear light. The new engine requires less spark advance. We
have new firmware and setup files for 2007 and later models. The TCFI does not
support the active intake and exhaust used on some international models, as
these are usually removed for performance applications.
Can the TCFI system be
used on 2008 and later touring models with electronic throttle control?
No. Due to the integration of
additional functions such as ABS brakes and cruise control along with links
to the infotainment systems, replacement of the original equipment ECM would
involve a level of complexity (including setup and tuning) beyond the
capability of most aftermarket installers. For these models we suggest using
Tuner in combination with the
Scan II Plus Tuning Aid.
Are there any special
considerations that apply to the new 2007 and later models with CVO 110 CID engine?
No, the new TCFI Gen 4 fully
supports the ACR system.
What is the advantage of
replacing a 2007 and later ECM with your TCFI system?
All 2007 and later models use
narrow-band oxygen sensors and closed loop control to maintain the AFR at
14.6 during idle and cruise. Our TCFI system with wide-band sensors allows
closed loop control under all conditions including wide open throttle. You
can set the AFR to any desired value from 10.5-15.0 in every RPM and
throttle position cell. Other add-on systems such as the Power Commander®
must either entirely disable closed loop control or restrict fuel
modifications to wide open throttle cells.
What is the difference between wide-band
and conventional oxygen sensors?
(narrow-band) exhaust gas oxygen sensors have been widely used in automotive
applications since 1981. Conventional sensors have one to four wires and can
only sense air/fuel ratio over a relatively narrow 14.5 to 15.0 range.
application is maintaining AFR near the 14.6-14.7 range required by
catalytic converters during idle and cruise.
range of narrow-band sensors is inadequate for performance tuning. While
originally developed for lab and specialized automotive applications, wide-band
sensors are ideal for tuning. The 5-wire Bosch LSU 4.2 sensor used with the WEGO
operates over a range of 10.3 to infinite air/fuel ratio and can be used for
closed loop operation under all conditions.
For more information about
wide-band oxygen sensors including the Bosch LSU 4.2, we suggest that you visit
the Tech FAQ on the Daytona Sensors website at
How long does it take to
install and tune the TCFI for a typical application?
The TCFI is a simple plug-in
that will take about 15 minutes to install. On 2001-2006 models, you can
expect to spend about 2-3 hours installing the WEGO sensors as this requires exhaust
removal and welding of mounting nuts for the oxygen sensor. Starting with the
models, the WEGO sensors fit in place of the stock narrow-band sensors. Initial tuning of the TCFI will
probably take about 1-2 hours, with another hour spent doing final checks after the customer has logged some time on the system. If you are doing
your first installation, you will need some time to familiarize yourself with the system. If you encounter problems with an
aftermarket throttle body or wiring issues on a custom bike, additional time may be required to complete the installation.
What skills and resources do I need to
successfully install and tune this system?
You need to make a realistic
assessment of your skill level. We have encountered issues with customers
that simply lacked the requisite PC literacy and resources to be successful
with the TCFI. If you have never worked with H-D®
EFI systems, the TCFI is not the place to start. Tuning the TCFI
requires competency in PC operation, using Microsoft Windows based
programs, and basic engine tuning and fuel injection mapping concepts. The TCFI installer is assumed to be familiar with the Delphi®
fuel injection system and to have access to basic test equipment and
factory service manuals. We suggest that you download the
Installation & Tuning Manual,
study it, and make sure you feel comfortable with it before purchasing the
If you have experience with
the Screamin Eagle®
Race Tuner (SERT), you should have no difficulty transitioning to the TCFI.
From a software standpoint, the SERT Tuning Mode corresponds to our PC Link
TCFI and the SERT Data Mode corresponds to our TCFI
Our tech support is limited
to TCFI and engine tuning issues. We cannot provide tech support for PC or
Windows related issues. You need
broadband Internet access to download software and firmware updates and an
email account to send us files for tech support purposes. You will also
require a program such as PKZIP or WinZIP to archive files prior to
attaching to an email.
One often overlooked resource
is time. When you are first starting with the TCFI, you will probably
require 1-2 hours to read the instructions and practice with the software.
Can the TCFI be made to work with
every possible combination of engine parts?
Mixing engine parts from
several different vendors involves some risk. Sometimes you get very
lucky and come up with a combination that wins the dyno shootout, most of
the time the system can be tuned to give good performance and drivability,
but on a few rare occasions it just can't be made to work. At this point in
time, the industry doesn't have enough of a knowledge base to accurately
predict what parts will or will not work together. The problem has been
around for years, but was masked by the forgiving nature of carburetors.
Sloppy engine building techniques such as not bothering to CC heads and
calculate the compression ratio or selecting parts for cosmetic appeal
compounds the risk.
What level of tech support does
Daytona Twin Tec offer?
We have staff available to take
tech support calls during normal business hours. If an initial telephone
conversation cannot resolve the issue, we will ask you to email us the current
setup file and a data logging file exhibiting the problem. We will try to get
you a solution within 24 hours.
Please do not ask us to read
you the instruction manual, lead you through basic PC or Windows operations, or fax you pages from H-D®
service manuals. We do offer an extensive
FAQ on engine
tuning principles and we will gladly offer advice on specific tuning
Most tech support calls involve
tuning issues that can easily be resolved. A small percentage of applications
have underlying mechanical or parts compatibility issues that cannot be
resolved by tuning alone. The most common issues encountered include
inappropriate exhaust systems,
mechanical/thermal problems with aftermarket or modified throttle bodies, and inadequate starting systems for high
We do not offer any
installation, tuning or diagnostic
services at our facility. We do offer a free TCFI training course at our
facility and conduct seminars at major trade shows (please call for scheduling
details). We also offer a
FAQ on diagnostic
tools and suppliers.
Can you recommend some books that
cover basic automotive electronics and engine control systems?
have listed a few suggested volumes that are available at Amazon (www.amazon.com):
Automotive Electronics (Sixth Edition) by W. B. Ribbens (highly recommended
- covers control system theory)
Fuel and Emissions Control Systems by J. D. Halderman (used by many
community colleges for ASE certification programs - much of the material is
directly applicable to motorcycle EFI systems)
to Tune and Modify Engine Management Systems by J. Hartman (automotive
oriented - material in first 15 chapters is generally applicable to
motorcycle EFI systems).
What is the difference between
speed-density and alpha-N fuel injection control systems?
The OE Delphi®
system is a speed-density control system. It remains a speed-density control
system even when devices such as the RevTech DFO, Dynojet® Power Commander®,
or Screamin Eagle®
Race Tuner are added. The TCFI is an alpha-N control
calculates air flow (and consequently meters the correct amount of fuel to
attain the desired air/fuel ratio) based on engine RPM (the speed term) and
manifold pressure and temperature (the air density term). Once calibrated,
speed-density systems can accurately meter fuel as long as the manifold
pressure is well behaved. Speed-density system are somewhat forgiving
for minor vacuum leaks and inconsistent throttle body behavior. However,
speed-density control cannot cope with the erratic manifold pressure
characteristic of long duration, high overlap camshafts.
Alpha-N systems are typically
used in racing applications where the camshaft characteristics preclude
speed-density control. Alpha-N control calculates airflow based on throttle
angle (the alpha term) and engine RPM (the N term). In addition, most
alpha-N systems make a correction based on air temperature. The accuracy of
an alpha-N system is highly dependent on consistent throttle body behavior
and is adversely affected by any vacuum leaks. Adding closed loop feedback
from a wideband exhaust gas oxygen sensor greatly improves the accuracy of
an alpha-N system. The major advantage is that alpha-N control has no
dependence on manifold pressure and is able to tolerate radical camshaft
Speed-density versions of the TCFI are
available for special applications where alpha-N control is not suitable,
such as motorcycles with turbo or supercharger installations.
What is the difference between
open loop and closed loop fuel control?
Simplified block diagrams for
engine control modules with open and closed loop fuel control are shown
above. The open loop system has inputs for RPM, throttle position (TPS), and
cold start related variables (such as engine temperature and elapsed time
since engine start). Fuel lookup tables translate these inputs into a
predetermined fuel injector pulse width. The fuel injectors then deliver
fuel to the engine. The overall accuracy of the system is dependent on the
lookup tables and the fuel injectors. If the lookup tables are not correct
or the fuel injectors become clogged with deposits over time, engine
operation will suffer.
With a closed loop fuel
control system, a feedback path is added to allow the system to make
corrections. In the case of the TCFI system, wide-band oxygen sensors
measure the actual engine air/fuel ratio (AFR). The system compares the AFR
command from the fuel tables to the measured AFR from the sensors. The
difference between the AFR command and the measured AFR is referred to as
the AFR error. The system slowly makes corrections to the injector pulse
width to drive this AFR error to zero. These corrections are stored in a
block learn multiplier (BLM) table organized into RPM and TPS cells. The BLM
table is continually updated. When engine operation shifts to a new cell
(for example the RPM changes), the system can use the BLM value last saved
in this cell as a starting point for further corrections. Over time, the
system will learn the BLM value required for every cell in order to drive
the AFR error to zero. This process is referred to as auto-tuning. With the
use of wide-band sensors, closed loop control is possible throughout the
range of 10.5-15.0 AFR.
The 2007 and later Delphi®
systems are similar, except that they use narrow-band oxygen sensors that limit
closed loop fuel control to 14.6 AFR. H-D®
uses the terminology "error integrator" in place of BLM.
The block diagram above shows
how closed loop fuel control is implemented in the TCFI. An initial
estimate of horsepower and injector size (flow rate) is used to calculate a
base injector pulse width. Base injector pulse width corresponds to the
amount of fuel required to generate a stoichiometric mixture (14.7 AFR) at
wide open throttle (WOT), 6,000 RPM and standard atmospheric conditions.
Base injector pulse width then corrected for intake air temperature (IAT)
and barometric pressure. At any given RPM and throttle position (TPS), the
corrected base injector pulse width is multiplied by the values in the
Alpha-N table (main fuel table), AFR table (the AFR command), front cylinder
trim table (only for the front cylinder), and block learn multiplier (BLM)
tables. The BLM tables store closed loop correction factors based on
feedback from the WEGO system. Independent BLM tables are used for front and
rear cylinders. The BLM tables are continually updated whenever the system
is operating in closed loop (generally 30 seconds after engine start). The
BLM tables are updated based on the AFR error (difference between AFR
command and actual AFR read by the WEGO system). Additional cold start
enrichment fuel is applied based on engine temperature and elapsed time
since engine start. Priming fuel is injected when the run/stop switch is
cycled on. A fixed pulse width injection is also used during cranking (RPM
< 400). Two tables set the priming and cranking pulse widths based on
engine temperature. Separate control loops are used for the front and rear
How does the block learn
multiplier (BLM) value respond to AFR changes?
The figure above shows how a
closed loop fuel control system such as the TCFI responds to a disturbance.
AFR is the air/fuel ratio measured by a wide-band oxygen sensor. The
measured AFR value is initially equal to the AFR command (zero error) and
the BLM value is 100% (no fuel correction). A disturbance reduces the
measured AFR to about 12.5. The system responds by lowering the BLM value to
remove excess fuel and thus reduce the AFR error. After several seconds, the
error is again zero with measured AFR equal to the AFR
How does the TCFI closed loop
idle speed control work?
The output of the idle RPM
control loop is idle air control (IAC) stepper motor position ranging from
0-127. A higher IAC value allows more air flow and increases engine RPM. A
table sets the idle RPM command as a function of engine temperature. This
allows a higher idle RPM while the engine is cold. Closed loop idle RPM
control is only enabled when vehicle speed is zero and TPS is less than the
idle TPS value (usually 1%). Under open loop conditions (such as the
motorcycle being driven while the engine is warming up), IAC position is
continually adjusted based on engine temperature and elapsed time since
engine start. When the engine is fully warmed up, the system assumes that
the IAC position will be close to a nominal value (usually 30). Additional
idle air (IAC > nominal IAC value) is considered the same as increasing
TPS since the effect on airflow is identical. Under cold start conditions,
when the IAC value is high, the system may be using the 2.5% or 5% TPS rows
in the fuel tables even when the throttle is closed.
Do I need a load control dyno
with exhaust sniffer?
Regardless of what some
people may claim, it is impossible to properly tune a fuel injection system
on a modified engine without some means of covering the entire engine load
range (from decel to wide open throttle) and exhaust gas analysis. If you
use a system like the Dynojet® Power Commande®, you had better find a
shop with the DynoJet® Model 250 load control dyno and optional air/fuel
You can accomplish the same
result with the TCFI and WEGO by simply riding the bike for several hours. As you run through different engine loads and RPM levels,
the system auto-tunes the fuel tables.
What applications has the TCFI
been tested with?
We have tested and qualified
the TCFI with engines up to 145 CID capable of producing 170 HP. With a dual
independent runner throttle body and 6.0 gm/sec injectors, the TCFI
can support engines up to about 195 HP.
How do I set up and tune the
TCFI for a particular application?
We provide setup files for
common applications based on using the WEGO for auto-tuning fuel tables. We
suggest that you download the
Installation & Tuning Manual for more details.
Do I need to spend time on a
Auto-tuning under actual
riding conditions with the
WEGO generally gives better results because the operating conditions are
more realistic. Do the auto-tuning first. Then, if you want to get
maximum horsepower at wide open throttle, do dyno runs to fine tune the
ignition advance and air/fuel ratio.
What are the limitations of the
stock throttle body?
The stock throttle body is
inadequate for performance engines and will not flow sufficient air above
4500 RPM. Maximum power
will be limited to about 105 HP (injector flow rating may impose an even
lower limit). Our tests have shown that boring out the
stock throttle body is ineffective. An aftermarket throttle body greater
than 50mm is required for maximum power. The stock air cleaner is
grossly restrictive and must always be replaced for any performance
You can easily verify air
flow restrictions with the TCFI Log data logging software. Examine manifold
pressure (MAP) at wide open throttle. If MAP drops off as RPM
increases, you know you have a problem.
What aftermarket throttle
bodies have been tested with the TCFI?
Aftermarket throttle bodies
fall into two categories: single throttle body with siamesed runner (same
configuration as the stock Delphi®)
and dual independent runner. We have tested the 53mm single throttle
body system from
Inc. We have also
Cycle VFI Tuned Induction
that is a dual independent runner configuration. There was
no measurable difference in performance at high RPM and wide open
throttle between any of these systems on our 95 CID engine. However, part
throttle operation between 1500 and 3000 RPM was smoother with the dual
independent runner system.
When a dual independent runner
intake is combined with a dual independent exhaust (no crossover or 2-into-1
collector), the V-twin engine now operates as if it were two single cylinder
engines. Problems with fuel distribution between cylinders, normally
aggravated by the odd 315° and 405° firing intervals, are almost entirely
eliminated. This greatly reduces the potential for tuning headaches.
What issues have been encountered
with aftermarket or modified throttle bodies?
You must budget some time to properly adjust the idle
setting and idle stop. Throttle blade, linkage or cable binding are often
encountered with installation of an aftermarket throttle body. Our customers
have also encountered thermal problems, where a mismatch in thermal
expansion between the throttle blade and throttle body results in idle
instability as the engine heat up. Improper installation or faulty throttle
shaft seals can cause intermittent vacuum leaks that are difficult to
diagnose. Note: please refer to the section on idle air control (IAC)
actuator issues when changing throttle bodies on 2006 and later
Will the exhaust system affect
Yes. The choice of exhaust
system has a very significant effect. Unfortunately, many exhaust systems
have been designed without any consideration of gas flow dynamics. This is true of both OE and aftermarket systems. The
worst example is the OE exhaust used on “bagger” style motorcycles,
where two pipes split off near the rear cylinder and then run to each side
of the bike. At part throttle, air is actually sucked into the left
tailpipe, wreaking havoc with oxygen sensor readings. The only solution is
to install a true dual type performance exhaust.
Our customers have reported
that some aftermarket 2-into-1 systems, such as the Thunderheader can cause
significant tuning headaches, whereas others such as the Supertrapp, Vance & Hines
Pro Pipe and White Brothers E-series seem trouble free. The problem with the
Thunderheader appears to be over-scavenging around 2500 RPM with some
camshaft combinations. Customers have reported that bending the ends of the
so called "flow director" to increase backpressure at low RPM
appears to help.
WARNING: If you can
insert a broomstick through the mufflers, you have the equivalent of open
drag pipes and the WEGO sensors will not read accurate AFR values except
at wide open throttle.
note that if you use drag pipes or other open pipes, auto-tuning may not be
possible at idle or part throttle due to reversion effects. In this case,
you have three options:
Modify the exhaust to allow auto-tuning at idle and part throttle by
adding a restriction such as the washers shown in the figure below or some
other type of baffling. For race applications, you can remove the
restriction after auto-tuning the idle and part throttle cells and then
lock out closed loop operation by using the special value 0 in the BLM
tables for these cells.
Use a rubber hose to extend the exhaust length during auto-tuning at idle
and part throttle. For more information, please contact our tech support.
Manually tune the fuel tables for idle and part throttle cells. This
involves trial and error and is not recommended. Closed loop operation in
idle and part throttle cells must be locked out by using the special value
0 in the BLM tables for the affected cells.
You can reduce reversion
effects in open drag pipes and mufflers without restrictive baffles with the
modification shown below.
Exhaust Mod to
washers with an OD that is 2/3 to 3/4 the ID of the pipe (for example,
1-1/2” OD washers are suitable for pipes with an ID of 2” to 2.25”).
Weld ¼-20 socket head cap screws to the washers as shown. Drill holes at
the bottom of the pipes about 2” from the end and use decorative acorn
nuts to secure the washer assemblies. We suggest that you use stainless
washers will reflect positive pressure waves that will cancel out the
negative pressure waves reflecting from the end of the pipes. You can turn
the washers just like throttle blades to provide more or less restriction.
Dyno tests will show a significant increase in midrange torque and a small
drop in top end horsepower as the restriction is increased.
What is the effect of an open
exhaust on torque and horsepower?
engine tuners have known for years that while open drag pipes may make the
most power at high RPM, some exhaust back pressure is required for maximum
torque in the low to mid RPM range. Some years back, we ran dyno tests on a
2003 Fat Boy with a 95 CID engine and our TCFI system. The exhaust system
consisted of stock headers and Cycle Shack slip-on mufflers without a
crossover. Two dyno runs are shown in the figure below. Dyno run 10 (red) is
with the Cycle Shack muffler inserts removed, resulting in the equivalent of
open drag pipes. Dyno run 9 (blue) is with 1-1/2" washers installed near the
end of the pipes as described in the preceding section. At 3,500 RPM the
engine gained more than 10 ft-lbs torque with the washers installed to
provide some back pressure. At 5,800 RPM the engine gained almost 7 HP with
the open pipes. On the street, the bike felt much faster with the 12%
additional torque available when the washers were installed.
with Open and Modified Exhaust System
Should the WEGO be left hooked up?
Yes! Due to the inherent
limitations of sensing airflow by measuring throttle angle, Alpha-N fuel
injection systems cannot precisely control air/fuel ratio without feedback
from a wide-band sensor system. The TCFI is not intended to be used without
Can the TCFI solve starting
problems with high compression engines?
Probably not. We have also
encountered cases where the customer failed to CC the cylinder heads and
calculate the actual compression ratio - only to later discover that it is
much higher than expected. The stock starting system is inadequate for high
displacement, high compression engines. For these applications, you must
install compression releases and upgrade the starter, ring gear/pinion, and
battery. Based on customer feedback, the best available starting system is
the combination of a
Cycle 2.0 KW
tooth ring gear/pinion set, and
YuMicron CX battery.
How do you select the proper
size fuel injectors?
Single throttle body siamesed
runner systems usually require some tuning effort to balance fuel delivery
between the front and rear cylinder at part throttle. Fuel imbalance
problems become worse with more camshaft overlap/duration and with low
exhaust back pressure. Fuel injector duty cycle limitations must also be considered. The industry
is just starting to recognize the extent of this issue. If fuel cannot be
delivered to the correct cylinder, the trimming process will not be
Accepted engineering practice
is to use the smallest possible injectors (in terms of flow) for best
control at idle and part throttle. When fuel injector duty cycle exceeds
50% in a system with siamesed runners, fuel will be inducted into the wrong
cylinder. For example, at high duty cycle, the front injector will be
spraying fuel while the rear intake valve is still open.
The TCFI cannot correct
Dual independent runner systems do not suffer from this
type of fuel imbalance problem and the fuel injectors may be run upwards of 80% duty cycle. At high duty
cycles, fuel may puddle up in front of the intake valve but will ultimately
be inducted into the correct cylinder. Stock Delphi®
injectors are rated at 3.91 or 4.22 gm/sec flow depending on model year.
Larger injectors are available from Marren Fuel Injection (www.injector.com)
and RC Engineering (www.rceng.com). The following table lists
conservative rear wheel horsepower limits based on injector size and type of throttle body.
gm/sec (stock 2006-2010 P/N 27709-06A)
gm/sec (stock 2001-2005)
gm/sec (2006 Screamin Eagle®
If you significantly exceed these
recommendations, it may not be possible to balance fuel between front and
rear cylinders. The result may be a lean cylinder and possible engine damage
at high RPM wide open throttle.
On a final note, the S&S
Cycle VFI Tuned Induction is supplied with appropriately sized fuel
injectors that will support engines up to 150 HP.
Why is limiting the injector duty
cycle so important?
At low duty
cycle, fuel is injected while the intake valve is open and air flow
carries the fuel into the correct cylinder.
At high duty
cycle, both injectors are spraying simultaneously and there no
control over where the fuel goes.
How are injector requirements
The math is relatively
Injector flow = (HP x BSFC)
/ (Number of Injectors x Duty Cycle)
Injector flow is in units
HP is maximum engine
BSFC is brake specific fuel
consumption (assumed to be 0.45 to 0.50 lbs/HP-hour)
Number of Injectors is
always 2 for a V twin type engine
Duty Cycle is 0.8 (80%) -
the accepted industry standard (injector flow does not increase
appreciably above 80-85% duty cycle)
For example, a 135 HP engine
with 0.45 BSFC, two injectors, and 80% maximum duty cycle will require
(135 x 0.45) / (2 x 0.8)
= 38 lbs/hour
Injectors are commonly rated
for flow at 43.5 psi (about 3 bar). The injector flow rating must be
corrected based on the actual operating pressure. The Delphi®
system runs at approximately 58 psi. Flow varies as the square root of the
Rated Flow = Required Flow
Pressure / Actual Pressure)
our example, the injectors should have a nominal rating of:
/ 58) = 32.9 lbs/hour (at 43.5 psi)
companies rate injectors in lbs/hour, Delphi uses a metric rating of gm/sec.
The appropriate conversion constant is 1 gm/sec = 7.93 lb/hour.
to our example, we would require injectors with a metric rating of:
/ 7.93 = 4.14 gm/sec
2001-2005 model year stock injectors rated at approximately 4.2 gm/sec would be adequate for this
can use our fuel injector calculator to estimate your injector requirements.
Use a BSFC of 0.45 for normally aspirated engines and 0.60 for
turbocharged or supercharged engines. You can use a maximum duty cycle of
80% for most applications, but remember that fuel imbalance can occur in
siamesed runner intakes when the duty cycle exceeds 50%. Use the default
value of 43.5 psi for injector rated pressure. Unless you have changed the
fuel pressure regulator, use the value of 58 psi for the actual system
pressure. The calculator below will show the required injector flow rating in the
three most common units. Note that the calculation is based on engine
horsepower. Increase expected rear wheel horsepower figures (as would be
measured on a chassis dyno) by 10-15% to arrive at engine
and Screamin Eagle® Race Tuner (SERT) systems require input of injector flow
rate in gm/sec at the system operating pressure. If you have an injector rated
in a different unit or at some other pressure, you can use the conversion calculator
Are there known issues with the
injectors on 2006 H-D® models?
H-D® has issued
Service Bulletin M-1185. Most 2006 models have narrow 8° spray pattern
injectors (P/N 27625-06) that cause poor cold start, idle, and cruise. The
replacement injectors (P/N 27709-06A) have a 25° spray pattern. You must
verify that the injectors have been replaced. The TCFI will not operate
correctly with the original injectors.
What injectors and throttle
bodies are available for 2006 and later models?
The injectors and throttle
body changed in 2006. P/N 27709-06A stock injectors are rated at 3.9 gm/sec
– less than the 4.2 gm/sec parts used in 2001-2005. Screamin Eagle®
P/N 27654-06 injectors rated at 4.9 gm/sec are recommended for performance
applications. For applications over 100 HP, the 50mm Screamin Eagle®
throttle body (P/N 27623-05) is an unbeatable deal.
Can the new Screamin Eagle®
50mm throttle body be used on earlier models?
The 50mm Screamin Eagle®
throttle body (P/N 27623-05) has slightly larger port diameters and is
intended to be used with matching Screamin Eagle®
heads or modified heads. Kuryakyn offers adapter flanges (P/N 457) that
allow using the Screamin Eagle®
throttle body on earlier heads. However, if you use the throttle body on
2001-2005 models, you must rewire the idle air control (IAC) connector (see
details in following section).
Is there an issue with the idle
air control (IAC) actuator when changing throttle bodies?
The IAC actuator and wire
harness connections changed on 2006 and later models. If you install an
aftermarket throttle body on 2006 and later models and reuse the original
equipment IAC actuator, you will not encounter any problems. If the
aftermarket throttle body requires the earlier style actuator, you must swap
the wires going to pins A and C. If you install the new 50mm Screamin’ Eagle®
throttle body (P/N 27623-05) on a 2001-2005 model, you must swap the wires
going to pins A and C on the IAC actuator. Incorrect IAC connections will
cause idle speed control to fail. This will result in erratic engine
operation and the ECM setting IAC related diagnostic codes.
Can the TCFI be adapted to work
on bikes with the older
Marelli fuel injection system?
A conversion harness that
allows TCFI installation on Twin-Cam 88®
engines with the Marelli fuel injection is available from Thayer Sales
(585-762-4705). Please contact Thayer Sales for details. The TCFI cannot be
adapted to earlier Evolution®
engines as these lack a crank trigger.
Conversion Harness for Marelli Fuel Injection
Will the TCFI work with the
fuel injection used on new Buell®
No, the TCFI is specifically
intended for use with 2001 and later H-D®
models with the Delphi®
ECM. The Delphi®
ECM has a 36 pin connector. Newer Buell®
models use a small ECM with two 12 pin Deutsch connectors. Check out our
Can I use the TCFI on a custom
If you start out with a fuel
injected Twin-Cam engine, you should
not encounter any problems. You must retain all the original equipment
sensors and actuators. Two areas that are often overlooked are the
instrument cluster and turn signals. Like the stock Delphi®
ECM, the TCFI requires a vehicle speed sensor (VSS) signal.
If you are using an aftermarket instrument cluster, you can connect the VSS
sensor directly to the TCFI. With the TCFI, you can eliminate the stock turn
signal/security module (TSM/TSSM) and use any aftermarket turn signal
controller. The Marelli conversion harness shown above can also be used as
an engine wiring harness for TCFI installations on custom bikes.
How can an aftermarket
tachometer or shift light be connected to the TCFI?
ECM and TCFI both have a tach signal available on pin 3 of the 36 pin ECM
connector. This is a one pulse per revolution (PPR) 12 volt square wave
signal with 50% duty cycle that is compatible with all standard tachometers
and other RPM activated accessories such as shift lights. 2004 and later
models use the J1850 data bus for communication with original equipment
tachometers, however the tach signal on pin 3 can still be used if you are
installing an earlier style H-D®
or aftermarket tach.
How can an aftermarket
speedometer be installed on 2004 and later models?
2001-2003 models have the
vehicle speed sensor (VSS) connected to the speedometer. A VSS signal is
routed from the speedometer to pin 33 on the 36 pin ECM connector. The J1850
data bus is used to send distance data to the turn signal/security module (TSM/TSSM)
for turn signal cancellation. On 2004 and later models, the VSS is connected
direct to pin 33 on the ECM. Speed and distance data is sent on the J1850
data bus to the speedometer and TSM/TSSM.
For all model years, the ECM
requires a valid VSS signal for idle RPM control and turn signal
cancellation. If you plan to install an aftermarket speedometer, you must
maintain the VSS signal to the ECM. For 2004 and later models, you can try
connecting the VSS input on the aftermarket speedometer to the existing VSS
signal on pin 33 (leave the existing VSS ground and power connections
undisturbed). After completing the hookup, you should test drive the
motorcycle, download data with TCFI Log software, check VSS data, and verify
that the ECM is still receiving a valid VSS signal. If the speedometer does
not function with this hookup, it is not compatible with a fuel injected
Are there issues with the
crankshaft position sensor air gap?
The crankshaft position
sensor used in H-D®
applications is a variable reluctance magnetic pickup manufactured by Delphi®.
The sensor output voltage is proportional to RPM and drops off sharply as
the air gap increases. The air gap must be .040 ±.005" for proper
system operation. If the air gap is greater than .045", the ECM may not
trigger correctly at low cranking RPM. The nominal clearance is .845
±.005" measured between the sensor mounting surface on the engine
crankcase and the top of the flywheel teeth. The nominal length of the
sensor is .800" from the sensor flange to the tip. We have encountered
several aftermarket crankcases with excessive clearance. You can easily
correct this situation by machining some material from the bottom of the
sensor flange to restore the correct air gap.