referring now to fig1 , an electric fuel pump 10 has an inlet 11 for receiving fuel within a fuel tank and an outlet 12 for connecting to a fuel line to a fuel rail or fuel injectors of a vehicle engine . a pumping chamber 13 containing an impeller is connected to a motor armature 14 . a commutator 16 is mounted to the opposite end of armature 14 and has commutator bars 17 disposed thereon . commutator bars 17 are in mechanical contact with brushes 18 under the influence of springs 19 for maintaining the close contact of brushes 18 with commutators 17 . brushes 18 are electrically connected to a power circuit 20 . power circuit 20 receives electrical power at terminals 21 and operates according to a control signal received from a controller 22 . fig2 shows a front view of commutator bars 17 on commutator 16 . fig3 is a side view showing a filming layer 25 that has built up between commutator bars 17 and brushes 18 . in accordance with the present invention , it has been found that boosting the voltage supplied to the fuel pump motor to a sufficiently high voltage can reverse ( i . e ., either reduce or remove ) the filming action . the boosted voltage results in electrical arcing between the commutator bars and brushes which removes the film and restores their electrical conductivity . since the higher voltage level to be used is greater than what is desirable for typical pump operation , the present invention employs a clean - up cycle that is periodically initiated for very limited times so that the filming is minimized to a sufficient extent . fig4 shows a voltage waveform 26 which is applied to a fuel pump motor according to one preferred embodiment of the invention . the pump motor has a nominal voltage rating dictated by its particular design . the nominal voltage rating is indicated on the vertical axis in fig4 and may have a value of about 13 volts for a typical automotive fuel pump . waveform 26 shows that at time t = 0 which coincides with the vehicle being started ( i . e ., turning on of an ignition key ), the pump voltage rises from zero to a normal operating voltage , wherein the normal operating voltage is less than or equal to about the nominal voltage rating of the motor . the power circuit provides this normal operating voltage to the pump motor to implement an ordinary run cycle of the pump for providing normal pump output . the ordinary run cycle could also include operating regimes wherein the motor voltage is modulated to lower levels in order to reduce the amount of fuel flow , as is known in the art . in order to periodically reverse the filming on the brush - commutator interface , one or more clean - up cycles are provided wherein a boosted voltage is supplied to the pump motor by the power circuit . the boost voltage is greater than the nominal voltage rating and may preferably be in the range from about 16 to 20 volts . the power circuit provides the boost voltage during a clean - up cycle for a limited time that is sufficiently short to avoid damage to the pump motor from exceeding the nominal voltage rating and is sufficiently long to create arcing at the brush - commutator interface that reverses formation of the film . the actual boost voltage level and the length of time that the voltage is boosted can be optimized for different brush and commutator materials , different pump speeds , different motor currents , types of vehicle operation , type of fuel , and other factors . by way of example , a pump having a nominal voltage rating of 13 volts that has been operated in e10 fuel for 1 , 000 hours can have the resulting film almost completely removed by running the pump motor at 16 volts for about 90 seconds . there are many potential ways of obtaining an appropriate frequency of clean - up cycles to keep filming in check while simultaneously avoiding motor damage from excessive boost voltages . for example , the clean - up cycle may occur once during each time a vehicle is operated ( i . e ., between engine starting and stopping ) and have a duration of about 90 seconds . alternatively , the clean - up cycle may occur several times during a driving session such that each individual clean - up cycle may have a duration between about 5 to 10 seconds . to minimize the risk of motor damage , it may be preferable to limit the occurrence of boost cycles during any particular intervals ( e . g ., one driving session or a period of 24 hours ) to less than or equal to about 90 seconds . one concern related to fuel pump operation at a higher voltage concerns the increased noise output from the fuel pump that may be audible to occupants of the vehicle . in order to mask the added noise , it may be preferable to conduct the clean - up cycle during times of other increased noise from the engine such as during a hard acceleration . accordingly , fig5 illustrates an embodiment wherein pump motor 30 is driven by either an operating voltage or a boost voltage as provided by a dc - dc converter 31 . a powertrain control module ( pcm ) 32 is connected to dc - dc converter 31 for selecting either the normal operating voltage or the boost voltage as appropriate . pcm 32 is connected to an ignition switch 33 for determining when the key of the vehicle is on ( i . e ., in the accessory , run , or start position ). pcm 32 is also connected to many other sensors and input control elements such as a throttle for determining engine operation . when the key is on , pcm 32 activates dc - dc converter 31 to convert a regulated vehicle system voltage + v to the normal operating voltage of pump motor 30 . one known typical pump motor has a nominal voltage rating of 13 . 2 volts , in which case the regulated vehicle voltage of about 14 volts may be converted by dc - dc converter 31 to an operating voltage of about 13 . 2 volts . in response to information relating to the throttle position and other factors , pcm 32 detects whether a sufficiently large acceleration of the vehicle is taking place so that sufficient engine noise is present to mask the added fuel pump noise to conduct a clean - up cycle . in response to detection of such an acceleration event , pcm 32 commands dc - dc converter 31 to generate the boost voltage which may be in the range of about 16 - 20 volts . fig6 shows in greater detail a control circuit for generating a control signal to limit the times that a clean - up cycle may be performed during any particular time interval ( such as a 24 hour period ). an acceleration event signal as determined by the pcm is provided to a timer 35 for measuring the limited time for an individual clean - up cycle , preferably less than about 10 seconds . a high logic level signal from timer 35 determining the limited time for an individual clean - up cycle is provided to one input of an and gate 36 . the timer output signal is also provided to an input of an accumulator 37 which keeps a running total of the durations of clean - up cycles over a predetermined interval . the predetermined interval is defined by consecutive reset signals provided to accumulator 37 . the reset signal may be obtained from a clock in the pcm for measuring a predetermined interval such as 24 hours , for example . the accumulated total time of all clean - up cycles during the current interval is provided from accumulator 37 to an inverting input of a comparator 38 . the non - inverting input of comparator 38 receives a threshold signal defining a maximum amount of time for conducting clean - up cycles during the predetermined interval . the maximum threshold and the predetermined interval between reset signals are coordinated in order to insure that the limited time for the clean - up cycles are sufficiently short during the predetermined interval to avoid damage to the pump motor while being sufficiently long to reverse formation of the film . for example , a maximum threshold of 90 seconds during a predetermined interval of 24 hours may be appropriate depending upon brush and commutator size , dimension , and materials and other factors . each individual clean - up cycle is sufficiently short ( e . g ., less than 10 seconds ) in order to prevent obsessive heating or other stresses when operating the motor over its nominal voltage rating . the output of inverter 38 provides a high logic level signal to the remaining input of and gate 36 unless the accumulated amount exceeds the maximum . thus , and gate 36 functions as a transmission gate for the timer signal until the repeated periods of the clean - up cycle have accumulated to the maximum during the predetermined interval . a method according to another embodiment is shown in fig7 . in this embodiment , the predetermined interval corresponds with a driving cycle from the time a vehicle is started , driven , and turned off . when the ignition key is turned on , the accumulated time is reset in step 40 . in step 41 , the pump motor is run in its ordinary run cycle at its normal operating voltage . a check is made in step 42 to determine whether an acceleration event is in progress . if not , then the pump motor continues to run in the ordinary run cycle in step 41 . if an acceleration event is detected , then a check is made in step 43 to determine whether the accumulated time is greater than or equal to the maximum allowed time . if it is , then a return is made to step 41 for continuing to run the pump motor in its ordinary run cycle . otherwise , the pump motor is put into its clean - up cycle at the boost voltage in step 41 for a predetermined number seconds ( designated as x seconds ). in step 45 , the amount x is added to the accumulated time and after the current clean - up cycle time expires a return is made to step 41 to return the pump motor to its ordinary run cycle . fig8 shows yet another embodiment for generating clean - up cycles . this embodiment does not depend upon a connection with a powertrain control or engine control module . pump motor 30 is driven by a dc - dc converter system 50 that receives system voltage ( i . e ., the regulated voltage from the voltage regulator such as 14 volts ). a converter circuit 51 which may comprise an integrated circuit has an input receiving the system voltage and an output for providing either an operating voltage ( e . g ., 12 volts ) or a boost voltage ( e . g ., 18 volts ) to pump motor 30 . converter circuit 51 has a select input receiving a control signal from a controller 52 . controller 52 receives the system voltage in order to be able to detect the key - on status of the vehicle and to coordinate the occurrence of a clean - up cycle or cycles during a particular driving cycle . for example , a clean - up cycle may be conducted at a fixed time interval after the key - on signal is received . a clean - up cycle could be conducted a few seconds after receiving system voltage or could be a longer delay in order to wait until engine operation and the electrical system voltage have stabilized . alternatively , the clean - up cycle could be initiated at key - off when the system voltage drops back to zero , provided there is sufficient stored energy in the dc - dc converter or provision is made to provide additional power to the dc - dc converter . system voltage may typically be provided through a fuel pump relay as is known in the art . the pump motor of the present invention may be sized for efficient operation at the normal operating voltage of the vehicle electrical system . for example , the pump motor may be run directly off of the vehicle system voltage so that the dc - dc converter is only activated during the clean - up cycle in order to provide the boost voltage . therefore , the pump motor design may be optimized for its ordinary run cycle . nevertheless , the pump motor may be safely operated at a boost voltage greater than the motor &# 39 ; s nominal voltage rating by limiting the time of the clean - up cycles by any suitable method including but not limited to the methods shown herein .