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Picture of a bad and good fuel pump amperage draw Posted by SWEDECAR [Email] ![]() ![]() ![]() In Reply to: Fuel pump intermittant - how long do I have doc?, 97 aero auto, Tue, 20 Jul 2004 07:57:48 Members do not see ads below this line. - Help Keep This Site Online - Signup |
I bet that if we hooked up a lab scope and milliamp clamp to your cars fuel pump power feed it would something like the left picture.
It have a couple of the commutator plates burned and when one of the brushes ends right on top of that burned area, the pump won't start again.
Each dip (burned spot) represents one full turn of the fuel pump on left picture (6 revelutions) but because of a faster time base on the right picture the good pump is only showing less than one revelution. Each hump on right picture is when the brush passes over to the next plate on commutator.
What you are doing by knocking on the tank is to shake the pump motor enough to make the brush contact commutator to make it turn again.
Each and every time you turn off the car, you risk stopping the pump right on that burned spot again.
It also doesn't work being by yourself not having someone cranking the car while knocking on the pump (gas tank).
It needs to be a combination of power going to the pump at the same time as the shaking occurs.
Theorethically, if you don't mind being stranded somewhere, you could go on driving the car hoping the pump won't stop at the bad spot again for awhile, people have done that.
But I advice you to have it replaced soon, especially if your wife drives the car, they don't have the same understanding of a car stalling sometimes (at least my wife doesn't).
Anders
posted by 67.122.16...
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