Kinda OT: Electrical Problem on New Ford

Most car parts places will test the battery for free. They also test alternators, but they have to be removed from the vehicle first.

Just a shot in the dark... likely a centrifugally induced, open alternator field winding... or brushes floating on the slip rings for some reason.

Were it mine, I'd slap on a rebuilt alternator.

If your not going to do it yourself, by all means avoid dealers, they're mega bucks. Pretty much any competent automotive shop should have no issue with this... (and/or check the phone book for an auto electric shop.)

Good luck!

Erik

Actually, what I think you are seeing is badly worn brushes, which start bouncing off the slip rings at speed, and thus are making contact only part of the time.

That is 12 years on that original set of brushes?

At 12 years -- the cheapest thing is to first pull the alternator apart and replace the brushes.

Do you have an oscilloscope? If the problem is what I suspect, you should see a steady output when running at an idle, and intermittent voltage at the higher speeds.

Good luck, DoN.

Take it to an Advance/Autozone/OReilly/PePBoys type auto place. They can toss a charging system tester on it in the parking lot and tell you if it's battery (not likely) or alternator. I'm betting the alternator is dying. Sounds like either a bad rotor or a bad slip ring. Either way it isn't a tough job to swap out.

Just played that game a month back with the van. Happened on a 1200 mile trip, finished it with the last bit of charge in the battery, no auto parts places open at 2 AM in the middle of nowhere. Like you, I wasn't sure whether it was battery, alternator or something in the wiring. Started with the obvious, pulled the alternator and had the parts place test it, didn't even make it to the diode test, was a deader. Mid-trip, the light would go off if I gunned the engine. Then, not. I was lucky, the alternator is on top of the engine, pull the belt, 4 bolts and it's free. Took longer to find the socket set than to get it off. So I'd check that first. HF sells a copy of a decent battery load tester, have one of those. Said the battery was OK, but I replaced it anyway. Pulled it for recharging and it had a "recycled" sticker at the rear, explains the lack of any stickers on it. Bubba was cheap-ass on maintenance.

So don't overthink this and spend hours on it. Get another buggy, throw BOTH alternator and battery in and head to the local parts place. You MAY need both, have had that happen, too. Alternator goes, takes out the battery, generally a regulator failure when that happens.

Stan

Firstly, if you are reading 14 volts than the alternator is working, at least at the moment you read the 14 volts.

As for reading less at higher RPMs it is very unlikely that it is other then an alternator problem as a healthy alternator will put out a significant amount of amperage and for the engine to use so much electricity that it reduces circuit voltage to 12 volts while the alternator is producing 60 amps would likely mean a direct short.... which would shortly become very apparent.

My suggestion would be to take the alternator off and see if you can find a shop that repairs them to have a look at it.

I once had an Isuzu diesel pickup that exhibited similar symptoms. Took it to the shop and never got to the end of my explanation before the mechanic said "bad brushes" :-)

Ditto

Gunner

The methodology of the left has always been:

1. Lie
2. Repeat the lie as many times as possible
3. Have as many people repeat the lie as often as possible
4. Eventually, the uninformed believe the lie
5. The lie will then be made into some form oflaw
6. Then everyone must conform to the lie

John B. wrote in news:jo4id8t3dad9i9dkkcoosq6g39u3ff8n16 @4ax.com:

That's my take on it too.

Check the brushes.

Bad brushes in the alternator - and possibly worn or out-of-round slip rings. The brushes are pretty common cause for the described problem. ALMOST guaranteed a new alternator will solve the problem if you don't want to fiddle around fixing the old one.

Den 24-12-2012 23:54, Tim Wescott skrev:

Most likely the fault is on the alternator. There are severeal faults that will give this indication.

Flea bay sells cheapo cigarette lighter voltmeters:

I have one in each car. You can easily tell if it's charging or not. I don't trust their accuracy, but you can see the trend.

Further, you can test an alternator by ear. At idle, load it with headlights, and rear-window defrogger. You can hear the engine slow slightly.

And the third one is a real long-shot.

Won't test for intermittent operation like the OP described.

You CAN however, test for bad diodes with a standard AC voltmeter. Bad diodes cause ripple, which is read as low voltage AC And of course a DC voltmeter will tell you the output.

On the subject of quick/dirty alternator tests:

The rotor 'field' windings, when energized turn the alternators shaft into a fairly decent electro magnet.

With the engine running, and the alternator charging, the end of the shaft should attract a screwdriver or other ferrous object. One that isn't charging might still retain a very small amount of residual magnetism. You can even turn on something like turn signals, and 'feel' the magnetic strength fluctuate as the voltage regulator modulates the field current up and down. Try it!

Sometimes, you can also kinda hear the belts working a little harder on a working unit... you can have someone load & unload the alternator with lights, blower, R window defogger or whatever while you listen. This was never really conclusive, and worked better back in the 'V' belt days of yore.

As usual, a clear head, common sense, good judgment and situational awareness are paramount... especially working with and/or around running engines/machinery.

Erik

And the third one is a real long-shot.

---------------------------------------

No, the third one is not the problem. One open diode in the rectifier will give low voltage at any RPM. I've had this one twice. Once, I replaced the rectifier assy., as a local shop did alt. work and had the parts. 2nd time, just replaced the alt. Which is what I'd do with this one.

Garrett Fulton

That is quite true.

That Depends. Some AC voltmeters will read ~RMS ie AC+DC; so test the voltmeter first.

An easier test is a AM radio. Listen between stations, if you have lost a diode (or diodes) the whine under load will be FAR louder. A baseline help, give a listen before it fails.

When I am in doubt, I use a scope.,

And:

I find bad diodes to be the most common failure mode.