Honda pgm fi

Customizing our own PGM-Fi program

Customizing our own PGM-Fi program

Honda's PGM-Fi is world-famous. Created and perfected through years of top-level racing, including six years of total domination in Formula-1, PGM-Fi is crucial to the ultimate performance of Honda's super high-performance cars. Because PGM-Fi is an integral part of the entire engine package, enthusiasts who modifies their Honda should keep PGM-Fi and ensure that it is able to handle the new fuel and ignition needs. In stock form, PGM-Fi is able to handle the milder mods. But for heavier mods especially serious engine works like wild camshafts, stroke-up, and forced induction, fuel and ignition requirements become more than what PGM-Fi can handle in stock form. The solutions so far are complex and expensive. They range from add-on injectors and controllers, piggy-back fuel and ignition computer systems, and even straight replacement ECUs. But the best form of fuel and ignition control still remains PGM-Fi. Can anyone actually do better than Honda ?

Cracking PGM-Fi

The idea has been floating around for a long time though its implementation is not as straightforward and simple as it seems. This is the idea that since the stock ECU is in actual fact a microprocessor based computer, and thus PGM-Fi is actually a program, it is possible to de-assemble this program, ie PGM-Fi, and once having gotten access to the assembler codes, one can then endeavour to understand the working logic and consequently attempt to modify or even to improve on it.

Things are of course easier said than done and I myself am aware of many people who have been trying to do this for many years. Earlier pre-1990 PGM-Fi's were written using a set of INTEL-compatible instruction set. Zdyne have reverse engineered these earlier Intel-based ECUs and there are in fact many development tools for it. But Honda changed to OKI microcontrollers since the late 1980s, starting with the VTEC models. So, the instruction set became proprietry. This made it difficult to derive the program logic. In addition, a program is actually made up of instruction codes and data. Now, there is no easy way to separate the data from instructions in the de-assembled codes. And even if they are successfully separated, it is still no mean task to decipher what the data means and how they are used. Most importantly though, thinking about actually 'improving' the logic of PGM-Fi will certainly be delusions of grandeur. Honda evolved PGM-Fi over many decades and fine-tuned it in their race-cars. This includes the winning Formula-1 McLaren-Honda cars in the late 1980-early 1990s, the TAKATA-DOME/CASTROL-MUGEN NSX'es that is currently dominating the all-Japan GT-Championship as well as the current F1 season's BAR/Honda and Jordan/MUGEN engines. Look at this list. The question begs : how can one actually think of doing better than Honda ?

HONDATA is a brand new product from New Zealand. When its founders Doug Macmillan and Derek Stevens first approached me some time ago, it was for the purpose of eventually announcing their acheivement to the whole world and that is they have finally done what others couldn't do. They have 'cracked' the PGM-Fi code and now, their work is finally available to the world.


While cracking the PGM-Fi code is what I would rank as one of the most significant feats of recent times with regards to our ability to modify our Hondas, more importantly, it is after cracking the code that the real difficulties begins. Doug and Derek took what I would call the 'sensible' approach after they have cracked the PGM-Fi code. The source of their approach actually stems from their own requirements - Doug and Derek each races their own EF-CRX in New Zealand. So, what they did was to leave the actual logic of PGM-Fi alone and only to add new functions on top of it, functions which enhances the car -and tested- in their races. They also decided to make their work available to Honda enthusiasts by marketing it under the HONDATA brand-name.

HONDATA was initially available for the PR3/PW0 ECU used in the EF8/EF9 Civic/CRX SiR and DA6/DA8 Integra XSi/RSi but just recently also became available for the P30 ECU used in the EG2, EG6 and EG9 CRX DelSol/Civic/Civic Ferio (and the US domestic market's Del-Sol). Hondata will also be available for the P28 ECU used on the USDM Civic EX (1.6l SOHC VTEC). Hondata uses the base PGM-Fi codes and data at the minimum, and add varying degree of modifications and new functions on top of it. As explained, these functions are derived from actual racing requirements and experiences.

The HONDATA Approach

The PR3/PW0 ECU 1 - microprocessor, 2 - 256 ROM

Hondata is based on modified PGM-Fi, ie Hondata modifies both the codes and the data. But Hondata limits the code modifications to only the bare minimum necessary to implement its unique new functions. This is the most important and powerful feature of Hondata. PGM-Fi and the stock Honda ECU is an extremely powerful computer and is very flexible. The most important components of the stock Honda ECU are the main microprocessor chip (typically OKI or NEC) and a program chip, a 256Kb ROM. The 256 ROM contains the PGM-Fi codes and data. These data will be the fuel and ignition timing maps together with various operating parameters. The main ECU motherboard of course contains a lot of other circuitry, including a 'limp-home' mode back-up processor. The ECU also regulates acccessories such as air conditioner and alternator to keep battery voltage constant and is programmed for tasks like " open idle speed control valve when air conditioning on". Replacement computers have very few of the wide range of functions, refinement and emissions the stock computer has. This is why Hondata have chosen to reprogram the stock computers when adding their new functions. As Doug explained to me in very clearly, the stock Honda ECU is extremely complex and is top-notch. Expecting to replace it is a fool-hardy endeavour.

Thus the HONDATA mod is based on (for the moment) a 256 EPROM (28pin DIP) which is an exact replacement for the stock PGM-Fi ROM. It contains exactly the same base PGM-Fi codes and data except for a minimum of codes modification for adding new functions. PGM-Fi stock size is below 256KBytes so it does not completely fill up the 256 chip. HONDATA utilized these empty slots to add codes that works in conjunction with PGM-Fi codes to implement their functions. Most of these functions makes use of an additional interface card. This card connects to the ECU via a 4-pin connector that will have to be soldered onto the ECU's motherboard. Interestingly the PCB for the PR3/PW0 ECU already has tracks for this connector, properly hooked up to the microprocessor and other circuitry. So installing the connector for the interface card merely entails soldering it onto 4 already available solder pads on the motherboard. It's almost as if the stock ECU were designed with the kit in mind...

The HONDATA Product Catalog

Doug and Derek currently markets Hondata in four stages, each with varying amount of functions added in.

Stage-1 is the simplest variation. A stage-1 HONDATA PGM-Fi chip contains the exact stock codes and data but with the logic to enforce the standard 180kph speedlimiter bypassed. Thus a HONDATA equipped EF8 will work exactly like the stock car but will be able to accelerate beyond 180kph. An additional feature is that the check engine light will flash at 7600rpm and serves as a shift-light. Finally, the rev-cut which is around 8100rpm stock is moved slightly higher to 8500rpm. The Stage-1 package comes with a properly programmed PGM-Fi 256 EPROM and a high intensity red LED (with wires and connector clips). This LED is meant to be spliced into the check-engine light wire and a relay wire in the ECU wiring harness and will be able to function as a super-bright shift-light that can be located at any location convenient to the driver.

Stage-2 adds the capability to dynamically change three useful rpm points. The interface card is introduced in this stage and the 4-pin connector will need to be soldered to the ECU motherboard for hooking up the card. This interface card also has a connector for a push-button and this is used in conjunction with the foot-brake for the custom rpm changes. The rpm points that can be changed are the VTEC changeover, the shift-light, and the rev-cut. Each rpm point can be changed to any value, with a resolution of 100rpm, within a sensibly impossed range. Eg, the rev-cut rpm can be changed from 5000rpm to 9000rpm (the range higher than the stock limit will be changed at the owner's risk !). The changed data are stored in the interface card and the rpms can be changed using either a dynamic method (with engine running) or static method (with engine off but ignition on). An additional feature in Stage 2 is the air-cond cut-off function. Codes are added to PGM-Fi that switches off the air-cond compressor clutch when the engine revs are above 5000rpm or the throttle is pushed beyond 50%. What this does is to automatically disengage the aircond for high-throttle sprints and automatically re-engages it when the throttle is released - without intervention from the driver ! An extremely intelligent function.

Stage-3 is where the serious stuff comes in. Exploiting their racing experiences, Doug & Derek added two new important functions in this stage. The first is the 'full-throttle shift'. Full throttle shift is where one keeps the throttle pedal bottomed (ie WOT) when executing a gear-shift. For the uninitiated, this can be a rather unsettling experience since the engine will bounce wildly against the rev-cut once the clutch is disengaged at red-line for the gear shift. A shock always follows when the clutch is dumped back on after the gear shift since the engine rpm is now incompatible with the speed & gear the car is travelling at. Hondata's full-throttle shift introduces a new refinement to this process. Using a special switch that is attached to the clutch pedal, Hondata implements a lower rev-cut when the clutch pedal is depressed. This new rev-cut is usually set at around 6000rpm, ie the rpm point at the next higher gear which corresponds to the red-line rpm for the current gear. What happens at WOT and clutch disengagement is now the engine will bounce against a lower 6000rpm. This allows smoother shifting to the next gear since there is a better match of rpm against gear speed. More importantly when the clutch is dumped, what happens is a very smooth engagement since there is near perfect match of rpm and speed for the selected gear.

Building on this function, Hondata Stage-3 also implements a full-throttle launch control. For standing start drag races, experienced drivers will be well aware of the difficulty at having to modulate the throttle in order to maintain the correct launch rpm. Then when the clutch is engaged, one has to quickly dump the throttle so as to avoid bogging down. Launch control is a variation of the full-throttle shift. When the car is stationary, Hondata actually implements a second, separate rev-cut on the engine when the clutch pedal is depressed. This second rev-cut limit is set initially at 3000rpm, which is very optimal for launching B16As. So, with clutch disengaged, one can be at WOT and the engine will be bouncing against the 3000rpm point. Launching is now simply dumping the clutch. For stock B16As, minimal wheelspin will occur and the car will quickly hook up. There is no need to modulate the throttle, the right foot is fully against the floor all the while.

The interface card for stage-3 now allows modification of two additional rpm points. These two are for setting the rev-cuts for the full-throttle shift and the launch control respectively.

Hondata's ROMEditor (low cam ignition map in 3D editing mode)

Stage-4 is for the serious enthusiasts and is also what a Hondata dealer will be equipped with. Stage-4 Hondata adds a ROM editor and the HondaLogger. The ROM editor is a windows based editor that allows the fuel and ignition maps in PGM-Fi to be customized (attempt only with the help of a dyno and accurate wide-band air-fuel ratio sensor !). Various other important parameters are also modifiable using the editor including idle speed, VTEC changeover, air-cond cut-off rpm, etc. There is also an injector modifier value, something new introduced by Hondata. This modifier is used for injector sizing. The stock PGM-Fi fuel maps are calibrated for stock injectors. Any attempt to obtain greatly higher power (20% and higher) and the injectors will need to be changed to larger capacity models. When this is done, the fuel map values are no longer useable since they are opening durations for a lower flow rate injectors. Running in this condition will cause the car to over-fuel and lose power. The modifier value is used as a global multiplier to lower any values read from the maps by a fixed factor to account for the higher flow rate of the new injectors. A brilliant feature !

HondaLogger's digital dash

HondaLogger is a windows based software that communicates with the Hondata Stage-4 modified PGM-Fi program via the interface card. This interface is through the serial port. The Logger records and plays back practically all the engine sensors that the ECU reads, including the O2 sensors, air-temperature sensor, even the knock sensor (available on the 1st generation B16A). All data captured are recordable onto a file. But there is also a 'digital dash' which is a windows-based program that dynamically displays all recorded sensors on a specially designed 'dashboard'.

Stage-4 would be invaluable for the enthusiast who is forever modifying his engine. However, for those who does a one-time big project and then basically leaves the engine alone for long periods of time (typical of most of us), an alternative would be to purchase a Stage-2 or Stage-3 Hondata chip from a Hondata dealer who would be able to supply it as a complete package together with dyno-tuning. Thus the extra cost of Stage-4 which is due to the ROM editor and Logger can be used instead to partially pay for the dyno-tuning, to set the custom maps.

The Boost Option

However, what I would consider the most significant feature of Hondata would be the Boost Function. As most enthusiasts might know, when turbo-charging or super-charging a Honda engine, the ECU will throw a check engine condition and go into the back-up mode when boost is reached. The reason for this is because the fuel and ignition maps in PGM-Fi are calibrated only up to atmospheric pressure since Hondas are generally NA. Thus as a safey check PGM-Fi has codes to check that the MAP sensor signal is within operating parameters which is about -700mmHg to just slightly above 0-bar. If the MAP signal goes above 0-bar, Honda coded PGM-Fi to go into back-up mode since such a condition for the stock engine will mean a defective MAP sensor.

Pictorial representation of stock PGM-Fi Hondata PGM-Fi with boost option

Hondata deals with this condition in a very unique way. First Hondata added new fuel and ignition maps into PGM-Fi, utilizing the empty memory slots left in the 256 ROM. Next the upper limit for the MAP sensor signal is moved to a higher value at 0.9 bar of boost. The new maps are of sized to accomodate this amount of boost, with resolutions of approximately 0.1 bar. Along with moving this limit, Hondata changed the codes so that when the MAP sensor reads boost, PGM-Fi now refers to the new boost maps for the injector and ignition timing values.

The full-throttle shift function available in Stage-3 will be extremely beneficial for a turbo-charged or super-charged Honda since it functions as an anti-lag device. The ability to keep the throttle fully floored keeps the turbo or super charger spinning at speed and maintains boost to the engine even during gear shifts. This is an extremely powerful function.

Thus with a single code mod, Hondata has created a PGM-Fi program for forced-induction - Turbo-charged and Super-Charged Hondas ! Fuel and Ignition needs for turbo-charging our Honda are now met by simply adding a Hondata PGM-Fi ROM with the Boost Option. A Hondata equipped turbo-charged Honda will have absolutely no mods to the MAP sensor, wiring harness or the ECU. The only change, which will not be always visually obvious, would be a new 256 EPROM and the interface box.

Getting Hondata for your car

Readers who are interested to learn more about Hondata should visit the Hondata Web-Site . The site has more detailed information including descriptions of the 4 stages. An especially worthwhile section to go to on the site would be the Downloads where readers can download working demos of the HondaLogger and ROMEditor to play around with. There are also sample manuals and brochures in Acrobat format (PDF files) and even some videos, including the one where Doug launched his CRX to the New Zealand 1.6l class land speed record (240kph).

Readers with heavily modified Hondas must seriously consider using a Hondata chip for their fuel and ignition timing management needs. There are two ways to get a Hondata chip. One method would be direct ordering from the web-site. Detailed instructions are available on the site and payment can be made via credit card though Doug and Derek have not yet implemented the secure web store. A much better alternative in the near future would be to get a chip from a Hondata dealer. Hondata is currently evaluating and establishing a network of dealers to market their product. Note that Stages 1 to 3 contains only the stock fuel and ignition maps. Enthusiasts who are considering a modified PGM-Fi ROM will almost never have a completely stock engine. Thus modified fuel and ignition maps would be certain requirements from Hondata chips. These are available from Stage-4 but, especially with addition of the Boost function, it is an expensive option. Furthermore Stage-4 will require professional dyno-tuning in order to properly modify the maps.

The option of getting a Hondata chip from an approved dealer is the best way to get customized fuel and ignition maps together with the functions desired but without the expense of getting the full-blown Stage-4 chip. Furthermore Hondata dealers will be knowledgeable in modifying Hondas. They will of course be equipped with the ROM-Editor and the HondaLogger and will be able to arrange for proper dyno-tuning sessions to customize one of the 'lower' stages, either Stage-2 or Stage-3 (Stage-1 does not come with the interface card so will not be offered with customized maps).

Most enthusiasts with modified Hondas would go for one or two turn-key projects done individually over a period of time. The key requirements for us would be driveability and to enjoy the car. Getting a Hondata chip from an approved dealer would be hassle free with minimal mods to wiring and ECU, and will be the best option for such requirements. Enthusiasts on the other hand who regularly modifies their engine will want to get the full blown Stage-4 Hondata chip. Whichever way an enthusiast goes, the Hondata chip provides the ultimate in flexibility and power for modifying our Hondas.

WongKNAugust 2000&copy Temple of VTEC Asia.

Honda Worldwide | Technology Close-up

The development of an ECU-integrated throttle body module for an electronic fuel injection system for small motorcycles


Honda has a goal to reduce the total emissions of HC (hydro-carbon) from new vehicles to approximately 1/3 and to further improve the average fuel economy by approximately 30% (both from 1995) by the year 2005. To realize the goal, we at Asaka R&D Center considered that the small motorcycles used in many countries in the world should be improved further for clean exhaust gas and low fuel consumption. Accordingly, we have started development of the PGM-FI system for small motorcycles with engines of 125cc or smaller, including air-cooled engines.Honda has a goal to reduce the total emissions of HC (hydro-carbon) from new vehicles to approximately 1/3 and to further improve the average fuel economy by approximately 30% (both from 1995) by the year 2005. To realize the goal, we at Asaka R&D Center considered that the small motorcycles used in many countries in the world should be improved further for clean exhaust gas and low fuel consumption. Accordingly, we have started development of the PGM-FI system for small motorcycles with engines of 125cc or smaller, including air-cooled engines.

To ensure clean exhaust gas and high fuel economy, the control of combustion through an accurate fuel supply is a must. As the conventional FI system (electronic fuel injection system) applied to motorcycles is bulky and costly, its application has been mostly in large motorcycles using multi-cylinder engines. In the newly developed PGM-FI, in order to apply to small displacement models, the obstacles have been eliminated by fully using Honda's techniques to down-size components as well as making maximum use of the FI techniques attained from the large motorcycles. The compact PGM-FI offers new benefits such as the reduction of released environmentally detrimental substances and the improvement of driveablity, economy, etc.

*PGM-FI is a registered trademark of Honda Motor Co., Ltd.

The compact PGM-FI has been realized through the ultimate modularization of components.

To attain clean exhaust gases and high fuel economy, an electronic fuel injection system that permits accurate control of the air-fuel ratio should be applied. The development team at Asaka R&D Center consolidated the functions into the size of a conventional carburetor through the ultimate modularization of components, thus developing the ECU-integrated throttle body for an electronic fuel injection system for small displacement engines.

Important points on the development

The future of this system is in such a construction that combines the two modules, i.e., the throttle body module having several kinds of bore sizes in the series, and the ECU module in that the ECU, sensor and the idle air control device are packaged in a compartment. Eliminating complex wires and pipes to allow a compact system, the compact fuel injection system applicable to a single cylinder engine from 50cc to 250cc has been developed.

For global environment protection

In 1992, Honda addressed to the world the "Honda Environment Declaration", in that declaring "Actively be involved in the retention of personal health and preservation of global environment, and maintain advanced characteristics in such activities."

And based on such principles, to have the products used by more people and to further contribute to the preservation of global environment…, the first model "Pantheon" using the newly developed PGM-FI has been marketed in the 125cc class, which is the most popular class in Europe.

Then, in an attempt to apply the technique to the Asian market where demands are high for motorcycles, the new model "Wave 125i" having the PGM-FI has been introduced for Thailand.

Models using the compact PGM-FI
The scooter "Pantheon/Pantheon 150" (for Europe) having a water-cooled 125/150cc engine equipped with the PGM-FIThe PGM-FI (electronic fuel injection system) applied to the stylish, Super Cub type "Wave 125i" motorcycle using an air-cooled, 4-stroke, single cylinder 125cc engine (for Thailand)

History of Honda's PGM-FI development for motorcycles

Honda started more than 20 years ago to develope a FI system to constantly provide the optimum air fuel ratio required by the engine using electronic control techniques. Since then, Honda has been actively promoting the application of FI to motorcycles as a technique to realize environmental performance and high level driveability.

In 1982, Honda marketed the first-in-the-world, fuel injected motorcycle CX500TURBO, which attained both better acceleration performance than the CB900F and better fuel economy than the base model CX500. In 1998, the environmentally friendly sport tourer model VFR800FI was marketed. This model, using the PGM-FI and the newly developed three-way catalyst, attains 1/30 CO emissions and 1/10 HC+NOx emissions from the EURO1, which is the European exhaust emission regulation enacted in 1999. And now, the racing machine "RC211V" has been dominating the MotoGP races. The "RC211V" uses the PGM-FI, which aids in allowing the overwhelming power output of the RC211V to be controlled for efficient use by the rider. Honda always keeps improving the fuel injection system at the highest level of technical competition.

The first motorcycle equipped with an electronic fuel injection - CX500TURBO

In the late 1970's, Honda R&D was filled with enthusiasm towards attaining "core technologies that would lead to the development of new technologies in the 1980's". Through discussions on what should be the core technologies, "turbo charging" was choosen, and the CX500 was selected as the base model. Honda defined the purpose of "turbo charging" not merely as a boost of extra power output from a large displacement engine, but an increase of specific power from a small displacement engine, and an increase in thermal efficiency by reducing the frictional losses per output. Simply stated, it was to attain both an increase in power output and a reduction in energy loss. Most critical in the development were the turbo charger and the fuel injection control systems. The CX500TURBO eventually made the first step of innovation into the 1980's with its acceleration performance better than the "CB900F" and fuel economy better than the base model "CX500".

Computer controlled fuel injection

One of the features of the CX500TURBO was the practical application of the computer controlled fuel injection system. Instead of using the then-conventional air flow meter, the computer-controlled fuel injection system calculated the injection volume using the two control maps, i.e., one for the boost zone where the basic injection volume was determined by the engine revolutions and the boost pressure, and the other for the throttle zone where the basic injection volume was determined by the engine revolutions and the throttle opening. The actual injection volume was adjusted by the intake density compensation, the intake air pressure and/or intake air temperatures, the supplement for acceleration, warming up, starting, the compensation for battery voltage, etc. Also incorporated in the computer-controlled fuel injection system was a self-diagnosis system that activated the warning lamp and the backup system to keep the engine running when a failure occurred in the system.

The racing machine of the 21st century - RC211V

In the world of championship motorcycle road racing, the machine regulations of the pinnacle 500cc class underwent a drastic reform, and changed its name to "MotoGP" in 2002. The machine regulations changed from a 2-stroke, 500cc engine to a 4-stroke, 990cc maximum displacement, and the name of the class was modified to "MotoGP". The Honda RC211V is the machine that was developed to meet the new regulations. Honda has developed a unique engine having the V-5 configuration. After dominating the races in the debut year 2002, the RC211V keeps winning in an overwhelming manner in 2003.

FI control ensuring superb driveability

The MotoGP machine uses fully closed or partially opened throttle conditions way more frequently than the Formula 1 race cars, for example. Compared to the Formula one cars which use fully opened throttle frequently, the controllability of the power output is more critical than the maximum power output. Honda developed and applied new techniques to provide superb driveability for the PGM-FI used in the RC211V.

Twin injector

Providing the deflecting multi-hole levigation injectors before and after the throttle valve, and having each one take care of the low load zone (after throttle) and the high load zone (before throttle), both the driveability and the high power output have been realized.

Variable fuel pressure control

The accurate control of fuel supply and throttle controllability are attained by the ECU continuously controlling the fuel pressure.

Predictive control of residual injected fuel

When the throttle is opened or closed (fully opened, fully closed, not when kept at a partial opening), the "amount of fuel sticking" on the inlet port walls and flowing into the combustion chamber during the following combustion cycle is predicted and applied to the control to ensure the most suitable air fuel ratio for improvement in driveability and fuel economy.

List of Honda motorcycles equipped with a PGM-FI

The PGM-FI is one of the core technologies to attain the goals of clean exhaust gas and fuel economy. An inevitable next goal is to extend the application of the innovative technique to models in various categories that respond to a larger number of users. Through the newly developed compact PGM-FI, Honda increases the application from large touring models, to the super sport models, and the models targeted towards a larger number of people.

Development of the ECU-integrated throttle body module

To allow for application to a small motorcycle, the FI system had to be simplified and down-sized considerably from the conventional one. The development team packed various functions into the compact yet simple system that could be installed in the place of a conventional carburetor by modularizing the throttle body, various sensors, and the engine control unit (ECU) into an integral unit.

Aims of integrating and modularizing the throttle body and ECU

In conventional motorcycle FI systems, the ECU is mounted to the vehicle body. Also, various sensors for detection of the control information are located at various places in the engine or vehicle body as an independent component. Because of that, many wire harnesses are required to connect various sensors to the ECU. Consequently, the conventional system is complex, and difficult to apply to a small motorcycle having a 50cc-125cc single cylinder engine. In an attempt to practically apply a compact PGM-FI in place of a carburetor, the throttle body, which controls the intake air volume, and the ECU module, which controls engine operating conditions, have been integrated into one unit. With the wire harnesses eliminated, the size of the module has been reduced to the same size as a carburetor.

Example of conventional FI system for motorcyclesCut model of FI for small motorcycles
Outlines of system

The newly developed compact PGM-FI system has a two-split configuration consisting of the throttle body and the ECU module. This configuration allows for replacement of a throttle body having a bore size suitable for a particular engine displacement, thus realizing a FI system applicable to various models with a high level of application freedom. The throttle body and ECU module incorporating various sensors are connected with 4 bolts. The idle air passage is grooved on the mating surface, and by sealing with an O-ring, the idle air passage is formed, thus contributing to the integration and down-sizing. The ECU module unit consists of the plastic box (device body), ECU board, and the cover. Various sensors are housed in the device body, and the ECU board is connected directly to the input and output terminals of the sensors. Applying the cover from above, the inside is packed with potting resin to secure the internal parts and to prevent water entry.

Layout of sensors

The throttle body module has 3 sensors in the device body.

  1. Intake air temperature (Ta) sensor:To allow measurement of intake air temperature, the sensing tip of the sensor is exposed in the intake air passage before the throttle valve. For down-sizing, the sensor terminals are directly mounted on the ECU board.
  2. Throttle position sensor (TPS):Located on the end of the throttle shaft, directly detects the throttle opening. The throttle shaft and the sensor rotor are connected via a spring to eliminate a hysteresis in the operation. The TPS is directly fit into the device body and sealed from outside by potting.
  3. Manifold vacuum (Pb) sensor:The sensor terminals are directly mounted on the ECU board, and connected to the connecting passage provided after the throttle valve in the throttle body.
ECU module component
ECU board

The ECU board used in the PGM-FI system for small motorcycles is exclusively designed for single cylinder engines. The size is reduced by providing an injector driver circuit and an ignition circuit for one cylinder, allowing mounting on the side of the throttle body. The CPU used for the controller is a 16bit CPU. The large parts such as the power supply condenser are located in the space between various sensors in the device body, contributing to reduce the overall width to the same level as a conventional carburetor. The ECU board is a 4-layer structure to reduce the surface area for various circuits. In addition, the harness connector, which takes a large amount of space in a conventional ECU, has been down-sized to approximately 1/2 from the conventional one by using a terminal-to-terminal pitch of 2.6mm·32 pin design. The reduction of terminal-to-terminal pitch becomes possible by using an adhesive gel sheet to seal the connector from water. To allow application of additional function such as an immobilizer, the number of pins is set at 32.

Idle air control device

Compared to a large motorcycle, less volume of intake air has to be controlled for a small displacement motorcycle engine. To cope with the stringent exhaust emission regulations, delicate control capabilities are also required. At the same time, to make an FI system applicable to small motorcycles, down-sizing is the key. To satisfy these demands, the slide-valve-type air control valve (SACV) driven by a stepping motor is applied to the PGM-FI system for small motorcycles. In conventional direct drive type, a stepping motor of ø20mm was required to maintain the operating torque to overcome the intake vacuum. In this system, the size of the stepping motor has been reduced to ø14mm by using the slide valve design.

Comparison of idle-air control valve
FI system control

The PGM-FI system for small motorcycles controls the fuel injection volume, injection timing and the ignition timing based on signals from the throttle position sensor (TPS) in the ECU module, the manifold vacuum (Pb) sensor, and the crank position sensor that detects the rotation angle. The fuel injection volume, the injection timing and the ignition timing are further compensated by the engine temperature, intake air temperature and the atmospheric pressure to ensure optimum controls under various environmental conditions.

Fuel injection control

For the control of fuel injection volume, two kinds of maps are stored in the ECU and an appropriate map is selected and used depending on the throttle opening and the engine revolutions.

  1. When the loads are low, the delicate changes in throttle opening are detected by the manifold vacuum, and the manifold vacuum map determined by the manifold vacuum and the engine revolutions is used.
  2. When the loads are high, the throttle map determined by the throttle opening and the engine revolutions is used.
Ignition timing control

For ignition timing, the map control determined by the throttle opening and the engine revolutions is executed to control the ignition timing at the optimum timing.

O2feedback control

To efficiently use the 3-way catalyst in the exhaust muffler, the feedback system using an O2sensor is applied to control the mixture near the stoichiometric ratio.

Control of idle air control device

The idle air control valve regulates the intake air volume depending on the operating conditions such as the starting, warming up and idling. When starting, the intake air is supplemented by opening the idle air control valve depending on the engine temperature for easy starting. The opening of the air control valve is regulated depending on the increase of the engine temperatures to control the intake air volume at the optimum level. After the engine reaches the prescribed temperature, the intake air volume is controlled to maintain idling at a constant speed by the revolution-feedback control. This feedback control eliminates the conventionally required idle speed adjustment, thus eliminating the need of maintenance to compensate for the secular distortion.

Advantages of newly developed compact PGM-FI

In 1992, Honda addressed to the world the "Honda Environment Declaration", in that declaring "Actively be involved in the retention of personal health and preservation of global environment, and maintain advanced characteristics in such activities." The PGM-FI technology is aimed at improvement of practical fuel economy, driveability, etc. to a high level as well as contributing to the reduction of the release of environmentally detrimental substances into the global environment.

2005 goals of exhaust emissions and fuel economy

In 1999, Honda newly addressed "2005 goals of exhaust emissions and fuel economy". In that statement, Honda set the following two goals.

  • Reduce the total emissions of HC from new vehicles to 1/3 from 1995 by 2005
  • Improve the average fuel economy by 30% from 1995 by 2005

With regards to HC, the emission has been reduced to 24% from 1995 at the end of 2001, and the goal has already been accomplished. The average fuel economy has been improved by 18% at the end of 2001, and further efforts are being made to attain the goal. It can be considered that the PGM-FI for small motorcycles is a technology that contributes to the global level environmental protection by reducing the exhaust emissions and improving fuel economy.

Merits from clean exhaust gas

The graph in dark green shows the data from the conventional "Wave 125" (for Thailand) using a carburetor. The graph in light green shows the data from "Wave 125i" (for Thailand) equipped with the PGM-FI. The light blue graph in the background is the 4th emission control regulations in the Thai market up to 2003, the dark blue shows the 5th emission regulation to be enacted in 2004. The "Wave 125i" equipped with the PGM-FI emits CO approximately 1/3, and HC+NOx 1/4 of the 4th regulation figures, thus attaining a very high level of cleanliness. The figures are less than half of the 5th regulation figures to be applied in 2004.

Merits of high fuel economy

The "Wave 125i" maintains the same level of fuel economy in ECE40 mode as the Wave 125, which has accomplished the remarkable improvement of fuel economy from the Wave110. By accurately controlling the fuel injection volume in the practical revolution ranges, the fuel consumption is reduced, attaining approximately 6% less fuel consumption from the current Wave 125 in the actual driving tests in Thailand.

Honda R&D will continue to strive toward the major goal of offering products more valuable for each customer as well as protecting the global environment. As one of such measures, we will extend application of the PGM-FI to even smaller displacement motorcycles and to more countries to have the technology used by as many customers as possible.

PGM-FI for 4-stroke 50cc scooters

We would like to actively introduce environmental technology into the vehicles being used by many people. By so doing, we wish to contribute to the improvement of the global environment even if a little. Here is the basic stance of Honda for environmental technologies including fuel consumption and cleaner exhaust gas. Asaka R&D Center evolved PGM-FI technology developed for small displacement engines like the 125cc, and developed a new electronically-controlled fuel injection device, PGM-FI,suitable for use in 4-stroke, 50cc scooters, presently marketed by Honda as "Clean 4".

First in the World as Mass-produced 4-stroke, 50cc Engines

The electronically controlled fuel injection system, PGM-FI, with enhanced fuel consumption and cleaner exhaust gas has been developed for mass-produced 4-stroke 50cc engines for the first time in the world. Through this technology, further reduction of fuel consumption and cleaner exhaust gas will be promoted for 50cc class engines which comprise the greatest sales in the domestic market.

Technological Features

The most outstanding feature is the integration of the ACG starter control and the PGM-FI into one ECU through mounting a CPU as high as 32bits. In addition, new technologies were developed aiming at mounting on 50cc scooters, including new injectors; ultra-small fuel pumps and new circuit system for kick-starting. Additionally, the number of parts were reduced from 15 to 8 as compared with the PGM-FI designed for large models through the efforts of integrating various functional parts, consolidating sensing functions and new designs of major parts including fuel pumps. A low-cost, compact and lightweight electronically controlled fuel injection system was realized.

Function-integrated ECU

Functions have been consolidated to achieve low cost through adopting a high speed 32bit CPU and integrating PGM-FI control ECU with the ACG starter control ECU. As compared with the conventional 16bit CPU, processing speed was increased by 3.5times and memory capacity doubled, which enabled the integration of the FI control and ACG starter control into one ECU. Compared with ECU designed for conventional 50cc scooters, the size was reduced by 21%.

32bit New ECUPerformance of 32bit CPU
Compact Fuel Pumps

To maintain a flat floor for 50cc scooters, ultra-small fuel pump modules were newly developed, which could be housed in a flat gasoline tank located under the floor. Adoption of a 10µm primary filter of the highest density in the world resulted in a substantial reduction in the number of parts and in the realization of compactness and light weight. Furthermore, power savings and high efficiency were achieved resulting in a rating level of 1A.

New Injectors

The amount of gasoline required for combustion in small displacement engines like 50cc is extremely small and the small amount of gasoline must be burned as efficiently as possible. It is required therefore for fuel injectors to make a minute amount of injection consistent with the atomization of fuel spray. It has been general practice before to have multiple injection holes for the purpose of atomization. In the injector developed this time for 50cc engines, the world's highest level of atomization was achieved by optimizing the form of internal passage of the injector with two injection holes, to reduce the amount of injection to a level of 1/3 of 125cc scooters.

Twin-hole injector Comparison of minimum amount of injectionAtomization performance of highest level in the world
Idle air control valve

The amount of minimum controlled air at times of idling, etc. also needs to be reduced to one third of 125cc scooters. In the air valves developed this time for 50cc engines, it has been made possible to control optimum amount of air for the conditions of engine operations like starting, warming up and idling by minutely operating a high-precision valve with an ultra small step motor in units of 30µm. As the result, a substantial improvement was realized in the ease of starting and idling performance and maintenance was made unnecessary for secular changes.

Control of kick-start

In starting conventional engines based on a carburetor system, the pistons were operated by cell motors or by kicks and the negative pressure and mechanical throttle actions sucked fuel out. In the electronically controlled fuel injection system, however, electric power is required to inject fuel for the start of engines. For small motorcycles like 50cc scooters, kick-starts are required in case of complete discharge of batteries after having been stoked for a long time. In the PGM-FI newly developed for 50cc scooters, engines will start with a small electric current created by kicking, which was difficult in the conventional FI system. Reliable engine starting was made possible by kicking even when the batteries have gone dead, by the development of a system to supply power generated by kicking in a fraction of a second to only the circuit required for starting and power saving fuel pumps.

By kicking, the ACG will generate power. The little power generated will be supplied with priority to the circuit for ignition and fuel injection, shutting off circuits to batteries and lights. The time effective for the purpose is approximately 0.2 seconds, which is equivalent to about a stroke of suction, compression, explosion and exhaust, or to 2.5 times of crank rotation by kicking.

Merits of PGM-FI for 50cc scooters

Engines equipped with newly developed PGM-FI for 50cc scooters have contributed to cleaner exhaust gas and a largely improved fuel consumption rate. According to data during the development stage, CO and HC exhaust gas achieved the level of half of domestic control and improvement was realized in fuel consumption equal to 7% in steady speed mode and 10% in actual drive mode*. Moreover, high power performance, reliable starting quality and idling performance were realized. *In-house test mode assuming actual conditions of use.

The Development Team of Asaka R&D Center promoted development efforts to achieve Honda's goal of "switching to fuel injection for 50cc scooters by the year 2005", which was made public in 1999 and the team successfully achieved the dream one year earlier than the original goal. The technology will enable Honda to install PGM-FI on all motorcycles Honda will market all over the world. Honda set new goals for "installing PGM-FI on all scooters sold in the domestic market by the fiscal year 2007" and "installing PGM-FI on majority of models over the entire world by the end of year 2010". Honda's motorcycles are loved by a great many people throughout the world. Honda hopes to contribute to environmental improvement of global scale through further refinement of his environmental technology. - PGM-Fi - Main Relay

Fixing your PGM-Fi Main Relay.

Problems starting the car, usually after a short run (when the interior is warm), though in bad cases the car may fail to start at any time. A classic time for the problem to occur is at the petrol station, or if you park for a minute to get something from a shop. If the car is parked for a long period, the interior usually has cooled enough for the joint to make contact again, and you won't notice a problem. As the cabin temperature is a major feature of this problem, it might appear worse on cold or rainy days when you have the heater running to clear the windows etc. Extremely cold temperatures can also cause the problem to be more apparent.

The engine will usually fire, run for a split second and then stall, as the remaining fuel under pressure is used up. When you turn the ignition key to position II (ignition on) you should see the PGM-Fi indicator on the dash light up and extinguish. Exactly timed with this lamp, you should hear a click and the fuel pump turn on and off. If you do not hear a click and the fuel pump, then the main relay is likely to be at fault. 

A collection of main relays.

The black relay is used around 1985-1991, the small grey type are used from 1992-1995 and the large grey relay is used from 1995-2000+

The later 1995-on relays rarely go wrong, they use a different design to the earlier version. Click here to take a look inside.



The problem is caused by dry joints in the PGM-FI main relay. This relay controls power to the ECU, and the fuel pump. Without power to the rest of the fuel-injection system, or fuel pump, you won't be going anywhere!

Below is a diagram of the PGM-FI system fitted to Honda's first fuel injected engine as fitted to the MK1 CRX. PGM-FI has constantly evolved over the years but the function of the relay is the same in all Honda cars - to supply power to the fuel pump, and fuel-injection components.

On recent cars such as the 2001 Civic the current draw by the main relay is monitored by the ECU, this way the ECU can tell if the main relay is faulty.  


Here are a few examples of what dry joints looks like. You can see the fine crack in the solder between the pin and PCB track - notice the others are OK.

Here we have a dry joint on relay #1.

And another on relay #2.

Notice that the other joints are okay, it is always the two joints pictured above that fail.

Dry joints are caused by vibration and changes in temperature cracking the solder round a joint which has not flowed correctly. They have a characteristic look, and sometimes are very hard to spot, even to a trained eye.

Remember it is not the actual relay itself that is at fault, just the soldering. To repair the fault all we need to do is remove the old solder and re-apply fresh.

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