The 2009 Harley-Davidson FLHTC Electra Glide Classic strapped to the mobile ThunderMax lift awaiting an ECM transplant.

When: 1995

What: Electronic fuel injection (EFI) debuts on Harley-Davidson Baggers

Where: Italy & Milwaukee, Wisconsin

Why: Tightening of emissions standards; engine management; improved engine performance, especially with variable atmospheric conditions, e.g., heat, altitude

For many of us, the thought of a computer controlled throttle body replacing the gas and air-mixing duties of the carburetor was a difficult proposition. The Harley faithful were leery of the electronic technology that replaced the venerable, easy-to-tune carburetor. For years to come the carb vs EFI debate may have been the biggest backroom biker bar debate since the black box ignition module began replacing points ignitions. 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, Harley 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 environmental concerns, EFI was more than just an exercise in "what if" engineering or 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 2006 model year. The H-D EFI system experienced continual refinement 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 its precise regulation of fuel delivery. Unlike a carburetor’s sole responsibility of passing gas and air into the motor, EFI is a partner to a complete, computer operated engine management system.

A carb is a passive device in that it operates (by discharging gasoline into the manifold) only when a pressure difference exists between the carb’s gravity fed float bowl and the engine. A piston moving down the cylinder creates a vacuum (negative pressure) and that pressure difference draws air into the carburetor. Air speed increases as it passes through the carb (venturi effect) drawing gasoline 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. Combustion of this mixture occurs if the ratio of air and fuel is in the proper range and spark is delivered at the right time. Throttle cables linked the right twistgrip to the carb opens the throttle plate (butterfly) and allows more air to pass into the carb. The farther you twisted 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 (smaller air:fuel; “air to fuel ratio”) if ridden at significant elevation, and produces a noticeable loss of performance and power. This is due to reduced oxygen levels available for combustion and the air actually weighs less. If going from high to low elevation, the fuel mixture gets lean; too lean a mixture is a potentially engine threatening situation producing excess heat and detonation (pinging). Obviously, a simplistic explanation, but the most sophisticated carbs operate on these principles.

EFI’s main difference is that instead of using low-pressure induced airflow to draw and atomize the fuel, the gasoline 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 (for late model Twin Cams,) 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, such as air temperature, engine rotation and manifold pressure. Over the years, H-D refined its EFI to incorporate more sensors for better fuel metering. The ECM then uses a program (AKA, calibration map) to determine spark timing and amount of fuel delivery to each injector. Of note, is that the ECM controls ignition timing as well.

Like a carb, a butterfly is still present to control airflow into the intake tract, and through 2007 controlled by throttle cables. Since 2008, H-D eliminated throttle cables on Baggers 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 (preprogrammed “amount” of fuel delivery), RPM, and engine load the proper amount of fuel and air are delivered to the throttle body. A motor opens and closes the butterfly (throttle plate) to control airflow.

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 adjust  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 communicate with the ECM to determine fuel requirements. Again, H-D incorporated intake temperature and 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: “open loop” and “closed loop” EFI systems. 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. Maps are specific to engine size and such add-ons as pipes, air box and cams and have instructions for the duration an injector is on (spraying) as well as ignition timing. Since the maps are fixed (“read only” in computer terms), for optimal performance even small changes to airflow (pipes, airbox) require reprogramming the map, often requiring expensive dyno tuning.

A closed loop system also has preprogrammed maps but can be modified (read/write) through feedback from sensors on the motorcycle. Oxygen (O2) sensors located in the exhaust pipes continuously monitor the spent gas to determine and maintain the proper air:fuel 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 engine heat to operate correctly. For ’10 to present, smaller, heated O₂ sensors are utilized and located before the catalytic converter, under the transmission area. Other than size, an advantage of the heated sensors is the ability to control emissions when the engine is cold.

In closed loop mode, changes in airflow or poor gasoline quality can be overcome by the ECM but due largely to environmental concerns, air and fuel ratios are varied only 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 generally work well with performance modifications. For government compliance the stock air:fuel ratios fall 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.

Closed and open loop systems can be remapped as well as using add-on modules to modify air:fuel that work in conjunction with the factory ECM. While adding aftermarket wide band 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 each time you make a change.

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 can self-tune the EFI and ignition just by riding the bike following any engine modifications. 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 these are an option.

One such device is the ThunderMax ECM with integrated AutoTune that works in conjunction with two wide band oxygen sensors. Using either a stock or an aftermarket throttle body the closed-loop system automatically adjusts fuel and ignition requirements responding to performance upgrades such as pipes, airbox, and cams. ThunderMax can also add this same closed loop operation on any older Magneti Mareli or Delphi systems. ThunderMax works with either throttle by wire or cable operated throttle bodies.

The ThunderMax wide band, 5-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 (Part # 309-362) for ’08-12 throttle-by-wire H-D Touring models. The system includes a ThunderMax TBW ECM with Integrated AutoTune Module, 2 Wide-Band Oxygen Sensors, USB Communication Cable, TMax Tuner Software and ThunderMax TBW Quick Start Guide.

The 96ci Twin Cam Electra Glide Classic had only airbox and pipe modifications. Although the bike ran well beforehand, 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.

Installation was very easy. Follow along as we take you through some of the steps

We removed the seat and side covers. Under the left side-cover resides the fuse panel. To cut power to the Engine Control Module (ECM), we located the ECM fuse location on the fuse box cover.

The ECM fuse (arrow) was removed by carefully gripping the fuse by hand and gently pulling it straight out. Sometimes a little wiggle action (of your hand) helps things along.

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 makes this an easy job. The sensors are fragile and need to be handled with care.

[photo 26590

A crow’s foot extension can also be used, with or without the socket.

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 carb cleaner or Liquid Wrench can help loosen them up. Here, we used a crow’s foot attached to a 3/8-socket extension to remove the sensors.

A close-up of the stock, narrow-band O₂ sensor.

The threads on the new ThunderMax wide-band O₂ sensors were dabbed with anti-seize compound to prevent corrosion.

The sensor port in each pipe was wiped clean and the threads were checked before we proceeded.

The wide band sensors were installed into each pipe.

We routed the front sensor wires across the brace in front of the engine and along the lower frame rail on the right side of the motorcycle and connected them to the AutoTune harness plug.

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 the AutoTune harness.

The factory O₂ sensor to ECM connectors were capped off and not used.

Next, we removed the factory ECM (residing under the seat) by spreading the plastic latches on either side of it and lifting up and to the right.

To release the main wiring harness from the ECM, the release button (arrow) was pressed and the grey locking bar moved to the full rearward position until the bar locked into the rear detent (arrow). We made sure the bar was in the full rearward position to release the connector’s internal latches; then we removed the connector from the ECM.

The main harness connector was cleaned of debris and the rubber gasket (arrow) checked for damage, and then coated in dielectric grease. We routed the AutoTune harness plug up the seat post past the battery towards the ECM holder.

The main harness from the bike plugged right into the ThunderMax module. Next, the AutoTune harness was plugged into the ThunderMax (arrow) 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 seated all the way in before engaging the locking bar. The ECM fuse got a dab of dielectric grease and plugged back in.

We fired up a laptop computer and launched the previously installed ThunderMax software from the included disc. Step-by-step installation instructions were easy to follow. Earlier we downloaded a base map that matched our engine configuration. The program gave us different map options and we picked the one that was closest to our setup.

We connected the supplied communication cable between the computer’s USB port and the ThunderMax data port (arrow; under the protective plug) to allow for map transfer. Then it was time to start it up and let the AutoTune work its magic.

The First Start

After a new ThunderMax module install or interruption of 12-volt power takes place a few simple steps need to be followed:

·       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.

That’s about all it takes to install the ThunderMax and AutoTune module. Now, the computer will adapt to other modifications done to the bike and be in a perfect state of tune. 

The ThunderMax is a very sophisticated unit and offers diagnostics as well. Street Legal (even California!) and Race Only ThunderMax units are available. Give Zippers Performance Products a call or check out its website for more information.

The ThunderMax products came from a joining of two industry forces: Zipper’s Performance Products and Thunder Heart Performance Corporation. Thunder Heart’s cutting-edge technology combined with Zipper’s expertise in performance yielded great results to provide the rider with the best products possible.

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Thunder Heart

ThunderMax

Zipper’s Performance Products