Electronic Fuel Injection Made Simple: Basics Of H-D EFI - Baggers Magazine
01. The ’09 Harley-Davidson FLHTC Electra Glide Classic on the lift awaiting an ECM transplant.
01. The ’09 Harley-Davidson FLHTC Electra Glide Classic on the lift awaiting an ECM transplant.
03. The ECM fuse was removed next by carefully gripping the fuse by hand and gently pulling it straight out.
04. Each of the stock, narrow band oxygen (O2) sensors had to be removed from each header pipe. An O2 sensor socket that slips over the wiring loom or a crow’s foot extension make this job easier.
05. On ’09 and earlier models, the O2 sensors are at the top of each pipe close to the head. If the sensors have been in for a while adding a few drops of throttle body choke and carb cleaner to loosen them up. We used a crow’s foot attached to a 3/8-socket extension to remove the sensors.
06. A close-up of the stock, narrow-band O2 sensor.
07. The threads on the new ThunderMax wideband O2 sensors were dabbed with anti-seize compound to prevent corrosion between the sensors and pipes.
08. The wideband sensors were installed into each pipe.
09. The front sensor wires were routed across the brace in front of the engine and along the lower frame rail on the right side of the motorcycle and connected to the autotune harness plug.
10. The rear lead was routed between the transmission top cover and the starter then beneath the ABS caddy (under the right side cover) and connected to autotune harness
11. The factory O2 sensor to ECM connectors were capped off and not used.
12. Next, the factory ECM was removed by spreading the plastic latches on either side of it and lifting up and to the right to release it.
13. To release the main wiring harness from the ECM the release button (top arrow) was pressed and the grey locking bar moved to the full rearward position until the bar locked into the rear detent (bottom arrow). Care must be taken to make sure the bar is in the full rearward position to release the connector’s internal latches; then we removed the connector from the ECM.
14. The main harness connector was cleaned and the rubber gasket (arrow) checked for damage then coated in dielectric grease. We routed the autotune harness plug up the seat post past the battery towards the ECM holder.
15. The autotune harness plugged into the ThunderMax (arrow) with the logo facing up and secured with the two screws. Before plugging in the ThunderMax unit we confirmed the gasket was fully seated in the connector, and the locking bar was all the way open. To avoid damage to the ThunderMax it’s important everything slides into place smoothly and that it is all the way in before engaging the locking bar. The ECM fuse got a dab of dielectric grease and plugged back in.
Since electronic fuel injection (EFI) appeared on Harley-Davidson baggers in 1995, for many of us, the thought of a computer replacing the carburetor’s gas and air mixing duties has been a difficult proposition. The Harley faithful were leery of the electronic technology that replaced the venerable, easy-to-tune carburetor. As most of us know the hog-riding public, as well as the Factory, don’t always make hasty, potentially disastrous decisions. There’s a century’s worth of Harley products and tradition and it would be fair to say Harley isn’t much of a follower. Based on history, we riders love that approach. We embrace retro, whether it’s looks or choosing air-cooled, pushrod motors. However, the Motor Company, always looking further down the road than just the next model year, saw the writing on the wall. In order to comply with ever-tightening emissions standards and future environmental concerns, EFI was more than just an exercise in “what if” engineering and an option to check on bike orders. Carbs worked pretty well for close to a century, and the straightforward accessibility and diagnosis of fuel-related problems was well within the reach of the average mechanic.
If any of us want a non-EFI bagger, H-D’s last carbed Touring bikes rolled out of York, Pennsylvania, for the ’06 model year. Luckily though, the EFI system has been continuously refined over the years and the newest Electronic Sequential Port Fuel Injection (ESPFI) system is reliable and dare we say it—better than any carb ever made for the precise regulation of fuel delivery. Unlike a carburetor’s sole responsibility of passing gas and air into the motor, EFI is a part of a complete, computer operated engine management system.
A carb is a passive device in that it operates (discharges gas into the manifold) only when a pressure difference exists between the carb’s gravity fed float bowl and the engine. As the piston moves down the cylinder a vacuum is created and that pressure difference draws air into the carburetor. Air speed increases as it passes through the carb (venturi effect) and gasoline is drawn through the carb’s jets, mixing with and forming a fine mist (atomization) with the incoming air, eventually reaching the spark plug in the cylinder head and combustion occurs. A throttle cable opens the throttle plate (butterfly) and allows more air to pass into the carb. The farther you twist the throttle the clearer the path for air to flow in. A downside to this simplicity is that carbs are sensitive to weather related air pressure and altitude changes. A carb tuned at sea level would run rich if ridden at significant elevation with a noticeable loss of performance. If going from high to low elevation the fuel mixture would get lean, a potentially engine threatening situation. Obviously a simplistic explanation, but even the most sophisticated carbs operate on the same principles.
EFI’s main difference is that instead of low pressure induced airflow to draw and atomize the fuel, the gas is actively “sprayed” through injectors directly into the intake manifold. The basics of how it works on a H-D is the fuel pump located in the fuel tank supplies high-pressure (55-62 PSI) fuel to a fuel rail on the throttle body (induction module assembly connected to the cylinder heads). The fuel rail feeds fuel to the injectors, which spray fuel into the intake tract. One injector is located close to each cylinder head intake port. In addition to the throttle body and injectors, the electronic control module (ECM, the bike’s brain) uses multiple sensors to gather information about engine operating conditions, air temperature and manifold pressure. The ECM then uses a program (AKA, calibration map) to determine the timing and amount of fuel delivery to each injector. Of note, is the ECM is also responsible for ignition timing.
A butterfly is still present to control airflow into the intake, and through 2007 was controlled by throttle cables. For 2008, H-D eliminated throttle cables and introduced electronic throttle control (throttle-by-wire; fly-by-wire). Sensors inside the right grip communicate throttle position to the ECM, and based on the map, RPM, and engine load the proper amount of fuel and air are delivered to the throttle body. A motor opens and closes the butterfly to control airflow. The ECM is simultaneously controlling ignition timing as well.
Although we won’t delve into every aspect of how the ECM gathers and uses information, there have been two general ways EFI does its job, and Harley has used both methods. Through 2001, the Magneti-Marelli (MM) produced EFI is what’s called an Alpha-N based EFI. Throttle position and RPM determined the amount of fuel to deliver. Harley also added an intake air temperature (IAT) sensor within the throttle body to make adjustments to the fuel mixture. A problem with the sensor in the MM system was that the measured air temperature was not an accurate reading of what the intake temp really was. Relying on temperature close to a hot motor was not the best way to determine intake air temp. When the air enters the venturi of the throttle body, it speeds up, thereby changing its temperature. In addition, the throttle body sits right above the hot motor, compounding the problem of accurate air temperature measurement. Some of the problems reported with the MM EFI were hard starting, erratic idle, and difficulty in tuning. For performance motors, the dual-plenum throttle body, with independent runners feeding each cylinder, was too small to pass the required air into the engine. An advantage of throttle-based control is that there’s no dependence on intake-manifold pressure, which benefits motors with radical cams.
The next generation Delphi manufactured EFI uses a speed-density method to calculate how much fuel the motor needs. Speed-density systems use RPM and manifold pressure (via a MAP sensor in the intake manifold/throttle body) to determine the load on the motor and report back to the ECM for fuel changes. Again, H-D incorporated intake temperature but accuracy was improved by moving the sensor into the throttle body.
In summary and very generally, from ’95-01 H-D EFI used a throttle-position based system and from ’02 to now a manifold-pressure based EFI.
There are two other important EFI operating methods: an “open loop” and “closed loop.” In open loop (’95-06) the ECM uses preprogrammed maps to control EFI. Sensor data is “read” by the ECM and then matched to a map/table/database; the maps have instructions for the amount of time an injector is on as well as ignition timing. Since the maps are fixed (read only in computer terms) even small changes to airflow (pipes, airbox) require reprogramming the map and often requiring expensive dyno tuning.
A closed loop system has preprogrammed maps but can be modified (read/write). Oxygen (O2) sensors located in the exhaust pipes continuously monitor the spent gas to determine and maintain the proper air:fuel ratio and ignition timing on the fly in real time. For ’07-09 the O2 sensors were located close to the cylinder head; the sensors needed the heat to operate correctly. For ’10 smaller, heated O2 sensors were used and located before the catalytic converter, under the transmission area. The heated sensors control emissions better when the engine is cold. Small changes in airflow or even poor gasoline quality can be overcome by the ECM but due largely to environmental concerns, air:fuel ratios are varied within a small range due to the stock narrow band O2 sensors. What narrow really means is the measurement range is small and the sensors don’t work well with performance modifications. For government compliance the air:fuel ratios fall more on the lean side. Leaner mixtures (larger A:F) get better fuel economy, have more complete combustion (clean burning) for better emissions and fuel economy, but generate excess heat. Richer mixtures have the opposite characteristics while delivering maximum power.
A closed loop system can be remapped as well as using add-on modules to modify air:fuel that work in conjunction with the factory ECM in the same way as open loop; tuning will still be limited by the narrow band O2 sensors.
While adding aftermarket wideband oxygen sensors allows a wider range of air:fuel monitoring, the stock ECM will still need remapping for changes in engine airflow, and for optimal performance require expensive and time consuming dyno tuning. Be extremely careful when choosing a dyno tuning technician; treat the situation like real surgery. Because of the relative complexity of EFI there are many hacks that capitalize on misinformed customers. It’s very easy for a tech with little experience to make your bike run terribly, then sell you more parts to try and “fix” what he messed up. It’s easy to get fooled into the next, best, black box, so do your homework and make sure you have referrals. It can get very expensive when your bike doesn’t run right. If you plan on any engine modifications try and have a plan and do the mods all at once if possible. That way each time one part is changed—pipes, airbox, cams, headwork, big bore kit, etc.—you won’t need to get a dyno tune.
Another option that largely avoids dyno tuning is the addition of a new ECM that is easily modified and can handle a wide range of performance upgrades. There are several on the market that after engine modifications can tune the EFI and ignition just by riding the bike. Ranges of tuning after performance modification vary by manufacturer but they all provide more and better control over the fuel and ignition system. They’re not for everyone, but if optimal tune and avoiding a lot of dyno time is your goal there is an option.
One such device is the ThunderMax ECM with integrated AutoTune that works in conjunction with two wideband oxygen sensors. Using either a stock or aftermarket throttle body the closed-loop system automatically adjusts fuel and ignition requirements due to performance upgrades such as pipes, airbox, and cams. ThunderMax can also add this same closed loop operation on your older Magneti-Marelli or Delphi systems. ThunderMax works with either throttle-by-wire or cable-operated throttle bodies.
The ThunderMax wideband, five-wire oxygen sensors thread into bungs located near the exhaust port, and are the same thread size and location as stock narrow band sensors used on ’08 and ’09 exhausts. For ’10-12, smaller oxygen sensors were used and located forward of the catalytic converter near the transmission. The ThunderMax sensors must be mounted in the ’08-09 location and on newer machines either new bungs will need to be added to the existing headers in the upper location (with the lower stock sensors removed and ports capped) or ideally order an exhaust system for a 2009 model (fitment is the same for ’10-12 models) and the ThunderMax sensors will install without modification. ThunderMax has all the info needed and detailed instructions and support.
To get a better look at the system and try it we ordered a ThunderMax TBW (PN 309-362) for ’08-12 throttle-by-wire H-D Touring models. The system includes a ThunderMax TBW ECM with integrated autotune module, two wideband oxygen sensors, USB communication cable, TMax tuner software, and ThunderMax TBW quick start guide.
We recently installed a ThunderMax ECM with an autotune module on a 96ci Twin Cam that had only airbox and pipe modifications. The bike ran well beforehand but afterwards the owner said he couldn’t believe it was the same bike. He reported a super-snappy throttle response and a cooler running motor, and while there was no dyno chart (he didn’t need to pay for one) he said the bike had much more seat of the pants torque.
The First Start
After a new module install or interruption of 12-volt power takes place perform the following procedures:
• Turn the ignition switch on and the handlebar switch to run for at least 20 seconds
• Cycle the ignition switch off and on and start the engine
• Let the motorcycle idle on its own for at least 15 seconds
• Turn off the ignition and then restart the motorcycle.
Normal idle speed should be attained depending on engine temperature. The warm-up cycle will have slightly higher idle speed until it reaches operating temperature.
Zippers Performance Products
(410) 579-2828 | Thunder-Max.com