The Incredible Working/Not Working Alternator

[HPhillip]

On Nov. 6 my 97 Escort, with a battery only 6 mo old., goes dead while in progress. The dash battery light comes on but I have power; the motor just won't turn over. I have it towed to a Goodyear service place.

They tell me that I have to replace the crank position sensor and also what they call variously a "circuit fuse" or "breaker fuse." I let them do that and drive out on Nov. 8. I saw a brief flickering of the red battery light but it didn't stay on.

Nov 9 the light comes on constantly and my car dies again in progress, but this time because my power dies to almost nothing, so the engine's not even turning over. Another tow to Goodyear, and they say the alternator needs replacing. For the last two days, it seems like that may have fixed it.

But I thought it was fishy that the alternator was supposedly working OK one day and not working the next. They claimed that they tested it the first time. I believe they would've been more than willing to push a new alternator on me if they'd correctly diagnosed that I needed one early on, but I think I went through a lot of hassle because they sluffed off.

Has anyone here heard of an alternator that tested good one day and bad the next? And if I had some electrical surge that fried my sensor and fuse, why wouldn't the alternator have gone blooey at the same time? Why would it go blooey only AFTER the other blown parts were fixed?

[denisond3]

Yes it is possible for an alternator to be working okay one minute, not charging the next minute, and to work for another day or two after that. Its because the brushes or the commutator rings for the field coil are worn down and barely making contact. At this point 99.9% of the alternator's life is behind it, but a bump or something jarring the alternator might make the brushes work for another day or two. And there isnt any test that will show this condition up, other than removing the brush holder and having a look inside.
I would be suspicious that they replaced the CPS because they didnt find anything wrong with the alternator (which might have indeed let the battery get very much discharged), but had to replace something so they wouldnt come across as clueless. The 'fuse' they talked about would likely have been in the fuse box next to the battery, under the hood. (At least that is where it is on my 2nd gen. Escort).
I doubt any 'surge' of current the alternator provided would have damaged anything - in fact its the purpose of the battery to absorb those fluctuations - which come normally from the alternator.
Its a fallacy that you can test an alternator, have it indicate 'good', and have any assurance that it will work okay an hour later. They can fail (due to worn brushes) without any warning. They can also go 'partially' bad, whereby a 75 amp alternator may lose 1/3rd or 2/3rds of its current output capacity. If you did mostly daytime driving and made long drives, an alternator only producing 25 amps max instead of 75 amps, might work just fine.
Its also possible to have a battery cable end that is dirty, corroded, and not carrying current reliably. That situation can also come and go, but will get worse with time. I have replaced the ground cable and ground connections on all 3 of the 2nd gen. LX Escorts that I have.

[Intuit]

Just a few weeks ago I noticed my dash lights dim and the battery light eventually come on. By then I had made it to my destination, and didn't risk going anywhere (in that vehicle) for another 2 hours. When I came back and jumped it, low & behold the alternator was charging. So I quickly drove back home, periodically checking the voltage level via the dome light. Charged all the way home (~20 - 25 min) with no issue. Prior to that failure, I had heard a screeching coming from the serpentine belt area. I thought it was the belt (>60k Goodyear Gatorback) and left it be. Didn't occur to me what that noise was until the battery light came on. Brushes did need replacing; somehow I went through the BWD brand replacement brushes in ~10k. The OEM brushes lasted 240k. Brushes are about $10 and take less than five minutes (no exaggeration) to install into the alternator. So seconding Denisond3.

Frankly, I believe they took you for a ride on that crank sensor. They're pretty reliable and don't ordinarily fail, however have read several cases where DIY mechanics have broken them, removing the timing belt. As for the fuse, I wouldn't be surprised if they accidently blew that, themselves. Your first name wouldn't happen to be "Heather" would it ? News reports and studies conclude that women are far more likely to be taken advantage of at auto service centers. If possible or practical, register your car with the service center under you husband's, son's or boyfriend's name, then have them accompany you when you pick it up. May save a couple of hundred dollars that way. Grrrr....

[zzyzzx2]

You need new alternator brushes.