I think I need a new alternator...


New Member
Jan 15, 2008
... Yes, i DID use the search function, but i wanted more specific advise on how to remedy my currrent situation...

well, i'm running an electric fuel pump off of my set up (a carbed 306)... however, i think my alternator is holding me back. i checked and charged the battery, even changed it out, but still no improvement...

basically, when i turn on my fuel pump, it's a lower-key hum. when i turn the car on, wait for it to idle, it idles and still makes the lower-keyed wine. when i rev the motor, however, it wines inconsistently, like a "WAH WAH WAH WAH WAH WAH WAH"... not just a straight "wahhhhhhhh"... my theory is that i'm not getting enough juice to the pump. so i took my car charger and hooked it up to the engine start setting (constant 200 amps to start).. the fuel pump, as soon as i turned it on, had a constant, high-pitched, better-sounding noise, and then when i turned it on, despite what rpms it was revved at, it never inconsistently wine.

furthermore, when i turn my headlights on, they dim in sync with the wah wah wah of my fuel pump. however, with the extra juice provided by the car charger, they were as bright as ever and do not dim in the slightest with the fuel pump...

so can anyone figure out my problem? i had it it figured for an alternator. if everyone agrees, can anyone point me in the direction of a cheap (and when i say cheap, please, for the love of god, as least costly as possible - i'm a full time college student, folks :() alternator that will give me all the juice i need...

... the way i see it, i cannot simply do with the incessant whining because this obviously means that at some point or another, my car is leaning out and is in needs of more fuel. i figure i'm losing some serious numbers on the top end because my alternator is ****tign out on the bottom end.

PLEASE mustang guru's, help me out here!
  • Sponsors (?)


Jun 11, 2005
Portland, OR
Well, I would try an aftermarket alt to put out more juice. How-ever, it doesn't really sound like you're overloading the system with much.

If that doesn't work, and you're half way decent with electrics, you could try a capacitor from a stereo store and run your fuel pump off that. It will help limit the pulsing by providing it's own battery source and constant flow of electricity.

But again, it doesn't really sound like you need any of this. Your not asking anything more than an efi setup. And it shouldn't have any problems.

It could be more that the fuel pump is bad and the alt is fine. The fuel pump could be wearing out causing it to draw more power from the system and causing the fluctuation in pump speed.


"How long does it take to get help in here?
15 Year Member
Nov 29, 1999
You could use your DMM to see what the actual voltage is at different times. And/or check the voltage drop to the pump.


Founding Member
Apr 22, 2002
A cheep test that may work is to get crazy with grounds. Put ground wires everywhere, body to motor, body to frame, frame to motor, etc. Most electrical problems I run into are ground issues.


Active Member
May 5, 2004
Waldorf MD
Pull that Alternator and have a shop test it. Auto Zone , advanced will test them for free. Are you running an in tank, stock type pump or an after market setup. You said you have a carb up and most carbs only need 6-8 PSI. A stock in tank fuel pump is go for over 40 PSI so I doubt your leaning out if you have a stock EFI pump.