I have the Duratec 24valve V6 engine

KICKBACK

MEMBER
2000 MERCURY SABLE
41,000 MILES

I have the Duratec 24valve V6 engine. This apparently is an electrical problem that involves both the radio & the CD changer. When I start the car up in the morning and turn on the radio, I hear crackling coming from all the speakers and also does it if I switch to the cd changer to play a cd. If I turn off the engine but leave the key in accessories, the crackling is not there and the sound is great. On the other hand, if I start up the engine and put it in drive and drive the car around the crackling stops but anytime I go to press on the brake pedal to slow down or leave my foot on the brake when stopped, it still crackles. I drive 20 miles on the freeway to work every morning and when i'm on the freeway, I seldom if any, have to step on thwe brake pedal so the sound system is good until I pull into the parking lot at work, which requires the brake pedal to be used and reverse to back into the parking space and at that time the crackling returns until I shut off the engine then the sound is fine. I did disconnect the belt to the alternator and started the engine but the crackling was still there. Any other suggestions would be appreciated:o)

1 Reply

CARADIODOC

MECHANIC
33,908 POSTS

I suspect you are on the right track with the generator but there may be more to the story. If I'm right, the problem should occur when you turn on the head lights or heater fan too. The problem could be due to low system voltage. If you're not having trouble with run-down batteries, suspect there's one bad diode in the generator. A professional load-test will verify that. The generator will only be able to develop exactly one third of its rated output of typically around 90 amps. The electric fuel pump only runs when the engine is running, and that draws about 8 amps. Add in the fuel injection and ignition systems, all the computers, and a few other small loads and you're past the 30 or so amps the generator can produce. The battery has to make up the difference and that's when system voltage starts to drop.

In addition to a bad diode, or instead of that, a weak battery can cause system voltage problems. The battery is the key component in helping the voltage regulator maintain a steady system voltage. As it ages, it loses its ability to smooth out the "ripple" that all AC generators produce. That can cause radio noise but unplugging the generator or removing the belt, as you did, will uncover that problem. There won't be any ripple when the generator is disabled. Since you still had noise with it inoperative, low voltage or a defect in the audio system are the suspects. I ruled out the audio system because the radio has two or four audio output channels, depending on which part you look at, and the amp has four channels. All of them aren't going to work properly and act up at the same time unless it is something they all have in common, and that something is something you have control over meaning turning on additional loads and drawing down system voltage.

What I would start with is measuring the battery voltage with the engine off, then with it running. At engine-off it must be 12.6 volts to be fully charged. If it's around 11 volts it has a bad cell and must be replaced. 12.2 volts indicates it's good but discharged. With the engine running the battery voltage must be between 13.75 and 14.75 volts. If it is low we know we have a problem. Even if it is within that range, see what happens as you turn more and more things on like head lights and heater fan. If the voltage drops, suspect a bad diode inside the generator. You'll see that with a professional load test, and it will show that ripple is very high.