Sudden Loss & Regain of Power while Driving



[2000 Ford Mustang V6 3.8L] Today while driving to work on the freeway, my car’s radio suddenly shut off for a second, then came back on. I didn’t think anything of it. A few minutes later, everything shut off. Radio, lights, and I could feel the engine dragging as if it wasn’t running. This only lasted for a second before everything came right back on and the car ran fine the rest of the way to work. My genius deductive skills (lol, or rather, my common sense) says it’s something like the battery or alternator, but I’d like to see if anyone here can point me in the right direction. Thanks.


Your alternator is in its last death thoes, and will fail totally…VERY soon…possibly the next time you drive the car. Get it replaced today, before you wind up standed in the cold. It is also very possible that the battery will need to be replaced, along with the alternator.


It’s neither the battery, nor the alternator. The problem is caused by a lose of connection of the power supply cable / wires starting at the battery post and continuing on from there.
Battery CONNECTIONS can be intermittent. Start there. Disconnect and clean (wire brush) the battery cable terminals and the battery posts. With the engine running, wriggle the power supply wires from the battery to inside the car. If the engine stumbles, check that wire bundle further, Check grounds on the engine, body, connections.


Hellokit could well be correct.
However, my old Outback displayed the exact same symptoms as this Mustang about 30 minutes before the alternator crapped out. I had replaced the battery about 2 weeks prior to that, and had not realized at the time that the battery had likely crapped out after only a couple of years because of a bad alternator.

So–check into what hellokit described, but don’t forget about my theory.


Most parts stores can CHECK your alternator & battery on the car. Alternators have 3 large diodes, the “Diode Trio” that change the A/C to DC currant. If one of those diodes is weak, an “A/C Ripple” will get into your electrical system and raise havoc with all the computer functions…They can test for the A/C ripple in the system…But FIRST, check all the connections…



I will hope that it makes it back home from work today without incident, and test for these. I do know my car seems to be prone to heavy build-up on the battery terminals and it’s been a while since I last cleaned them, so that would not surprise me if it was the problem. I’ll also pull out my multimeter and make sure voltage goes up when the car is running to make sure the alternator is at least doing something productive.

I also remember now a sound that occurred both times immediately after the power loss happened, continuing for about 10 seconds until it went away. It was a high-pitched whine, which changed in pitch with change in RPM. The only other thing I can think of to describe it would be to say it sounded like a “smooth” whine, if that makes any sense at all, and it wasn’t all that loud. Barely noticeable, in fact, but it was definitely there.

Who knows, It may be a case of dirty terminals, sucky battery, and dying alternator all at once. I have taken this battery into a shop in the past (while diagnosing a different problem), and was told it had an abnormally low charge, although still quite usable, and they charged it up on their machine for me.


Was the “whine” coming from your radio? A SURE sign of a bad diode…


And, a bad diode would relate to my theory of a failing alternator.



I assumed it to be from the engine, but now that you mention it, if very well could have been. There’s a 2-second-ish delay between power-on and radio-on, and I didn’t notice it until after the radio was already back on. I didn’t think to turn the radio off to test to see where it was coming from. If it happens again before I get to my tools, I’ll cut the radio’s power and see if it persists.

And digging deep into my brain, I do remember one time many months ago when a whine with the same characteristics as this one was, in fact, coming from my radio (radio off = whine off, radio on = whine on). This only happened for a few minutes and didn’t happen again (until now), so I didn’t think much of it.


ok…I have the same car as you only a year older. A year ago I began having the exact same issue it continued to get worse. Come to find out…(when it finally broke and iI had no power or lights) it was my belt slipping. Have you ever had it replaced?



I haven’t had the belt replaced ever. I’ve figured I’d save a buck and not do it, since it’d be cheap to fix if it ever does break. Perhaps I’ll do this for good measure.

On another note, I cleaned battery terminals (which had absolutely horrible buildup on them) and replaced the alternator. The shop tested the alternator, and while it did pass, they tested it again, and started getting inconsistent results. They said it technically passed as a working alternator by that test, but wouldn’t trust it to “pass” every time in the driving world.
Since these, I haven’t had an issue. I plan to get a new battery and battery cables sometime soon anyways, just because they’re overdue to be replaced.