Possible (probable?) charging system issue?

[Geilt]

First off I'd like to comment on the solid information I've seen come from the members of the forum. I've been looking for some answers and the information I've seen here is head and shoulders above most other web forums.

I have a '94 Legacy AWD Wagon that has been killing batteries for the better part of 18 months now (I know, nothing like a little procrastination huh?). The symptoms are as follows:

Everything is working beautifully for months on end and then out of nowhere I find that accessories are sluggish and lights are dim. I'm clearly running on battery and not alternator provided power. I can drive for about 12 miles and then we're done and the car won't start. I can jump start the car no problem and the battery will hold a minor charge but nothing like it should. I can drive about a half mile on this minor charge before we're dead again (which is typically long enough to get to a parking lot so I'm not blocking traffic). Clearly the alternator is not charging the battery even if at idle and over a span of 30-60 minutes. Admittedly I think the issue at that point may be a deep discharge on the battery so its not going to hold a charge period.

I've tested the voltage coming out of the alternator, based on the procedure outlined in the Haynes manual, and my readings are good at idle and 3000 RPM. I have not taken readings from the battery when the issue is not happening. Likewise I have not taken readings from the alternator immediately after jump starting the car when the issue happens.

I've checked the connector plug on the alternator and the terminals on the battery. Both sides were clean and tight. I will also recheck the physical wiring on the alternator connector to ensure I don't have worn wiring or a connection is loose.

I have not checked the grounding from the battery. I will do that when I get home from work tonight.

I have not replaced the alternator either and based on what I've read here, I may need to anyway if I have been driving around with low voltage for a while.

I have not checked the fusible link. Heck, I just learned I had one so that's on the "To Do" list for tonight as well.

Any help or suggestions would be greatly appreciated. I am almost to the point of ripping out the alternator, cabling and battery itself and replacing everything. That may be the best route to take but I want a second opinion before I start gutting the charging system.

Thanks!!

[Geilt]

Follow-up question... would a faulty fusible link cause the car to use battery power over that provided by the alternator?

I have also not looked at the belt driving the alternator. If its loose or slipping I assume it could be affecting the overall system. I'll add that to my list of things to check tonight.

[Legacy777]

Check the voltage at the battery at idle. If it's not around 14v your alternator needs to be replaced.

[Geilt]

Check the voltage at the battery at idle. If it's not around 14v your alternator needs to be replaced.

Got home last night and to my surprise the battery, which didn't have enough juice to start the car earlier that morning was back up to 12v. It ran for a couple minutes max and sputtered out. I couldn't get the car to turn over after that and the battery charge was between 8.5 and 9v.

I have pulled the alternator and will be taking it to Napa in the morning for a verdict (although I am almost positive I know what it will be). While I was at it I checked the belt and it was pretty cracked with some chunks missing along the inside circumfrence. Not two inch gaps but I will replace it anyway while I'm replacing the alternator itself.

While I have the alternator out, are there other maintenance tasks made easier to complete?

Second question, and this is a shot in the dark, but on the engine, covered by the alternator itself, is some sort of sensor with either a large gauge wire, or small gauge conduit, going in to the top. Based on the nearly useless description, any idea what could be?

[Legacy777]

No I don't beleive the car would continue to run without the battery. If it were a generator, then yes. An alternator just charges the battery. Typically it's not a good idea to do what you did as it may produce voltage spikes.

The sensor in question is likely the oil pressure sensor or the crank position sensor.

Oil pressure sensor
http://main.experiencetherave.com/subar ... P_2480.JPG

Crank sensor (near top left of pic)
http://main.experiencetherave.com/subar ... P_2728.JPG

[Geilt]

No I don't beleive the car would continue to run without the battery. If it were a generator, then yes. An alternator just charges the battery. Typically it's not a good idea to do what you did as it may produce voltage spikes.

The sensor in question is likely the oil pressure sensor or the crank position sensor.

Then I certainly WON'T be doing that again!

Thanks for the quick response!

[Geilt]

Well the new alternator and associated belt are in. Everything has been tested and is performing wonderfully.

I want to thank not only those that responded to my own post but the help offered to everyone else. The knowledge provided here was a tremendous help and made the job a piece of cake.

[evolutionmovement]

Due to the intermittent nature of some of the alternator failures, a test isn't always reliable. When the one in my wagon went, it was due to cracked solder joints on one of the diode packs which came and went. Previously, most of the alternator failures I'd seen were bad voltage regulators or bearings.

[Geilt]

Due to the intermittent nature of some of the alternator failures, a test isn't always reliable. When the one in my wagon went, it was due to cracked solder joints on one of the diode packs which came and went. Previously, most of the alternator failures I'd seen were bad voltage regulators or bearings.

Being the untrusting type I took the alternator to two parts stores (Napa and AutoZone) and had them test it. Both places came back with failures. My initial concern was that there was an intermittent issue, unrelated to the alternator, as normally everthing appeared okay.

Once I got the new alternator installed there was a noticable difference in the electrical power being provided to the vehicle. For example, when the original unit was supposedly working fine the dome light was still rather dim and other electrical accessories were not as I would have hoped but the car was new to be and I didn't know what to expect. With the new alternator installed everything is much improved. The car even seems to be idling smoother and I have better acceleration from a stop. The last observation may just be me reading too much in to things.