referring to fig1 , the major components of a modern electronic fuel injection ( efi ) system are shown . these are common components for gasoline engines in operation today . outside of a brief description , a detailed functional description of the system will not be taught here but rather the system is presented to form a basis for the first embodiment of the present invention shown in fig2 . the heart of an efi system is the engine control module ( ecm ) 10 . the ecm 10 typically contains a microcontroller that receives information from a variety of sensors such to control the operation of the engine . the ecm 10 controls the operation of the engine by controlling the timing of the firing of the spark plug ( s ) 130 and by metering the consumption of fuel via the fuel injector ( s ) 100 . the ecm also controls other aspects primarily related to the engine &# 39 ; s exhaust emissions . other important parts of the system are the fuel pump 55 that moves fuel from the gas tank ( not shown ) to the engine ( not shown ). the battery 20 is used to provide electrical power needed to start the engine . the ignition switch 30 is used to control the starting and stopping of the engine . most efi fuel systems use a fuel pressure regulator or sensor 190 to maintain system fuel pressure . the fuel systems are typically either return style and thus have a return fuel line to the tank or they are returnless ( deadhead ) style where the fuel is not returned to the gas tank . the ecm 10 receives signals from a variety of engine sensors . typical sensors are : engine coolant temperature ( ect ) sensor 40 , knock sensor 25 , manifold absolute pressure ( map ) sensor 65 , throttle position sensor ( tps ) 75 , manifold air temperature ( mat ) sensor 85 , mass air flow ( maf ) sensor 115 , exhaust gas oxygen ( o2 ) sensor 110 , and the crankshaft sensor 90 . two other sensors shown in fig1 , oil pressure 45 and vehicle speed 120 are used for diagnostic purposes . one other sensor read by the ecm 10 is the exhaust gas re - circulation valve position ( evp ) sensor 95 which lets the ecm know the exhaust gas recirculation ( egr ) valve 105 is either opened or closed . the function of the egr valve 105 is to reduce exhaust emissions . with ever tightening emissions standards through the 1970s and 1980s , efi systems gained in popularity . one reason for this was the efi systems ability to maximize the efficiencies of the catalytic converter 180 . the catalytic converter 180 was first introduced in the us in 1975 . efi systems built in automobiles since 1996 additionally have on board diagnostics ( obd ) 60 . obd 60 enables service centers an expedient way to check the operation of the components in the efi system . service technicians connect their diagnostic equipment to obd via the test connector 50 . obd is an important feature to aid with the regulation of exhaust pollution as motor vehicle ages . in fig2 , the major components of the flexible fuel engine control system according to the present invention are shown . these components consist of the flexible fuel electronic control unit 150 , the flexible fuel composition sensor 145 , the flexible fuel injector driver circuit 135 and the flexible fuel ignition module 140 . the flexible fuel injector driver circuit 135 and the flexible fuel ignition module 140 are shown internal to the flexible fuel electronic control unit 150 but either one or both could be external modules . the sole function of the flexible fuel electronic control unit 150 is to control the timing of the firing of the spark plug ( s ) 130 and to meter the consumption of fuel via the fuel injector ( s ) 100 in accordance with input from the flexible fuel composition sensor 145 . the flexible fuel electronic control unit 150 receives fuel and ignition input signals from the ecm 10 and then modifies those signals based on the input from flexible fuel composition sensor 145 . the flexible fuel electronic control unit 150 sends the modified signals on to the spark plug ( s ) 130 via the distributor 125 and on to the fuel injector ( s ) 100 . in some vehicle platforms with efi it may be necessary to replace the oem fuel injectors with larger capacity injectors , as higher concentrations of alternate fuels in the fuel mixture require a greater amount of fuel injected per mass of air . it is also possible that other components in the fuel system may need to be replaced . for example , the efi fuel pump 55 and the fuel lines ( not shown ) may need to be replaced either for capacity or compatibility reasons . the most desirable feature of flexible fuel control system of the present invention is that the system does not interfere with any of the engine &# 39 ; s original sensors or emission control devices including obd 60 . this is important for two major reasons . one reason is the ease of epa approval for the installation of the conversion system and the other is the lack of redundancy among component use . in total these translate into an inexpensive conversion for the consumer . fig3 refers to a typical modern carburetor fuel system found in engines prior to the advent of efi . although the carburetor itself is not modern , the fuel system contains modern emission control devices similar to those shown in fig1 . emission control devices common to efi and modern carburetor systems are : egr valve 175 , evaporative emissions canister 185 and the catalytic converter 180 . carburetors are historically simple devices that do not require a variety of sensors to meter the fuel . carburetor have been replaced by efi systems as they are unable to accurately control the required air to fuel ratio commonly referred to as stoichiometric . without being able to maintain stoichiometric , the catalytic converter 180 is unable to operate at its highest effectiveness to remove harmful emissions from the exhaust . because the carburetor 160 uses fixed jets to meter the fuel it cannot by itself properly deliver the correct amount of fuel for varying fuel mixtures like e85 or m85 . since the physical diameter of the jets needs to be changed in order to change the air to fuel ratio , the carburetor cannot by itself be used in a flexible fuel system . so the carburetor must either be replaced or supplemented with an electronic system that is fuel flexible . the conversion of a carburetor system into a system that is fuel flexible can be accomplished in several different ways . one method is to remove the carburetor and install a complete efi system with flexible fuel capability . the result of this modification is shown in fig4 and the main components of the conversion are : the flexible fuel control unit 150 containing the fuel injector driver ( s ) 135 , exhaust gas oxygen sensor 110 ( either narrowband or wideband type ), and ignition module 140 and the flexible fuel composition sensor 145 . in this embodiment of the present invention , the flexible fuel control unit 150 receives inputs from a variety of sensors and controls the operation of the engine . the flexible fuel control unit 150 controls the operation of the engine by controlling the timing of the firing of the spark plug ( s ) 130 and by metering fuel to the engine via the fuel injector ( s ) 100 . the flexible fuel control unit 150 also controls other aspects of the engine like the ecm does in fig1 . in the same spirit as the conversion shown in fig2 , the conversion in fig4 does not modify or replace any of the emission control devices used in the carburetor system . however since the flexible fuel engine control system will operate the engine at air to fuel ratios near stoichiometric , the exhaust emissions of the converted engine will be greatly reduced . for proper operation the sensors , ect 40 , map 65 , tps 75 , mat 85 and the exhaust gas o2 sensor 110 are added to the engine . the addition of the sensors often requires that the intake manifold of the engine be mechanically changed to allow for mounting of the sensors . similarly the intake manifold is modified for the addition of the fuel injector ( s ) 100 . the installation of the exhaust gas o2 sensor 110 often requires modification to the exhaust system . fig4 also demonstrates control of the ignition timing with the flexible fuel ignition module ( 140 ). the stand - alone stock ignition system shown in fig3 is however quite usable and continual usage reduces the cost of the additional components . one advantage of adding the ignition module 140 is the module &# 39 ; s ability to adaptively change timing . this would allow the engine to use fuels with different octane ratings and still avoid engine knock in high compression ratio engines . another advantage of the ignition module 140 is to advance timing to increase the power of the engine and thus reduce the vehicle &# 39 ; s fuel consumption . a further use of the flexible fuel system would be in conjunction with a turbocharger or supercharger where the amount of alternate fuel in the fuel mixture would be used to determine the amount of boost the system could tolerate . fig5 shows an alternate method of converting a carburetor fuel system into a flexible fuel system . in this embodiment of the present invention , the carburetor 160 is not replaced but is supplemented by the addition of the flexible fuel control system . one or more fuel injectors 100 are mounted about the carburetor 160 and are controlled by the flexible fuel electronic control unit 150 . the flexible fuel electronic control unit 150 receives a variety of sensor inputs similar to the oem ecm in fig1 and also receives input from the flexible fuel composition sensor 145 and / or an exhaust gas oxygen ( o2 ) sensor 110 of either narrowband or wideband type . if a significant percentage of alternate fuel is present , the carburetor 160 will no longer be able to maintain a proper air to fuel ratio for combustion . the flexible fuel electronic control unit 150 will sense the presence of the alternate fuel and / or its associated lean mixture and then compensate by adding fuel into the combustion process via the fuel injector 100 . it is envisioned that the fuel injector 100 will typically be placed either in the air stream prior to the air entering the carburetor 160 or be placed under the carburetor 160 similar to the method in which nitrous oxide is introduced into racing engines . as a result the carburetor 160 and the fuel injector 100 will work together to provide the proper amount of fuel required by the engine . although not shown in fig5 the fuel flow from the gas tank ( not shown ) would normally be drawn to the carburetor 160 by the fuel pump 56 . the fuel pump 56 in most carburetor fed engines is a mechanical pump attached to the engine block and driven by the engine &# 39 ; s camshaft . mechanical fuel pumps are rather inexpensive when compared to efi fuel pumps and are generally capable of supplying the additional fuel needed by the fuel injectors 100 but not at the appropriate pressure . therefore the efi fuel pump 55 could be fed in series by the mechanical pump 56 and used as a booster pump to provide the high pressure typically needed by the fuel injectors 100 . the efi pump 55 when used in a return - less ( deadhead ) system could be controlled via pulse width modulation ( pwm ) by a control circuit in the flexible fuel electronic control unit 150 . to maintain proper fuel line pressure the flexible fuel electronic control unit 150 would monitor the fuel pressure sensor 190 mounted inline with the fuel injectors 100 and then pwm the fuel pump to maintain the fuel pressure needed by the injectors . the invention has been described in detail with particular reference to certain preferred embodiments thereof , but it will be understood that variations and modifications can be effected within the spirit and scope of the invention . accordingly , it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention . reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims , which themselves recite those features regarded as essential to the invention .