Needs to be jumped every time

  • 1 POST
  • 6 CYL
  • FWD
  • 170,000 MILES

This car has many issues. We replaced the transmission in March with a rebuilt one we also replaced the plugs and wires at around the same time. Soon after that we were having trouble with it starting on occasion and it has been diagnosed as a fuel pump going bad. We have to turn the key to on 5 or 6 times in order to prime the pump. Then it may start or it may take a second cranking of the engine for it to start. Now, it has gotten to where the battery will try to crank it a few times before you hear the starter clicking. At first this was happening overnight. We would jump the car and it would be fine getting me to and from work but the last few times I drove it, it had to be jumped every time I try to start it. I've taken the car back to different auto parts stores to have the battery checked and they all find that the battery needs to be charged but otherwise tests as good and the alternator and starter are both testing good. Even after driving the car for an hour before parking it, I had to get a jump start in the morning. I've made sure that the radio, lights and A/C are all off before shutting off the car.
I understand the issues with the fuel pump but don't understand what is happening to the battery. Could priming the fuel pump really be draining the battery that much?

Do you
have the same problem?
Saturday, July 11th, 2015 AT 7:20 PM

1 Reply

  • 29,775 POSTS

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.

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Saturday, July 11th, 2015 AT 11:52 PM

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