PWM fuel pump

[Greg Hermann]

>Jeffrey T. Birt wrote:
>
>> Hi all,
>>
>>     I'm new on this list so this is the first post that I have seen on
>>the subject
>> of controlling pressure via PWM of the pump.  It seems that trying to
>>control a
>> pump this way would cause premature failure of the pump.  Generally
>>starting a
>> pump (of any type) is much harder on it than continuos operation.  PWM
>>would stop
>> the pump and then restart it under load.  It would be much harder on the
>>pump to
>> start it with 30 lb or so of pressure
>> against it.
>
>> IMHO, the pump never stops, just runs slower....
>
>>    Next, picture this scenario.  Your tooling along @ 20 mph and your pump is
>> developing (x) lbs. of pressure.  You then mash the accelerator down and
>>the ECU
>> determines that you now need (x+y) lbs.  Currently the fuel system is
>>only @ (x)
>> lbs., when you accelerate you are effectively lowering the restriction
>>that your
>> pump is developing pressure against.  The duty cycle of you injector(s)
>>go up.
>> More fuel in the same time period equals less restriction.  The pump has to
>> compensate for the sudden loss of pressure (x) and try to build up even more
>> pressure (x+y).  This situation will lead to a lag in fuel pressure on sudden
>> acceleration.
>
>Hopefully, the pump will respond in milliseconds, the controller in
>nanoseconds - as
>fast as the injectors.
>
>Tom S

Yep--Tom is right---just don't put any kind of an accumulator downstream of
the pump!!

Regards, Greg