Nope; fuel pumps don't draw very much current.
If you're having the charging system tested at an auto parts store, that is only the first part of the test that tells you it's okay to proceed to the more in-depth tests. You need a professional load tester to test for maximum output current. You won't find those testers, (or mechanics), at auto parts stores.
Under that full-load test, you're going to get either very close to the maximum rating for that alternator, or exactly one third of that. One third is what you get when there is one bad diode of the six. Charging voltage, which is what they look at at the auto parts stores, will usually be perfect or even a little high with a bad diode, but if you can only get 30 amps from the common 90 amp alternator, that is not enough to meet the demands of the entire electrical system under all conditions. The battery will have to make up the difference until it slowly runs down over hours, days, or weeks as you're driving.
With a bad diode, "ripple" voltage will also be very high, and the professional testers check for that. If the maximum output current is close to what it should be, then you most likely have a drain on the battery. Testing for that gets rather involved now thanks to the multitude of computers on the vehicle.
Saturday, July 11th, 2015 AT 11:52 PM