Battery Light

[Tj Krawler]

I've got an issue that started a few days after I got my truck home. First time it acted up was when I had the socket for a fender light out while running to the Ford dealer. Figured it was from having it out. Went out shortly after I put it back in (When I turned onto the road). Figured that was the cause of the battery light. It wasn't. Came on a few days later right after I told my Dad I HAD a problem but it didn't seem like anything. Started the truck, light came on. Hit the skinny pedal (1,400 RPM at most, motor was warm) light flicked and went off. Truck sat 5 days at ~40*. Today go out started right up, no battery light. Drive ~10 miles. Turned off, run in a store maybe 5 minutes. Start it, battery light comes on. Again, rev to 1,200 (again, warm), light flickers twice, goes off. Go to parts store, maybe 10 mins. (regretting not just getting the repair book they had) Start truck, battery light comes on. Won't go off this time. Pull out on a little side street, little aggressive (2k shift) let off, light flickers but stays on. I think the light went off as I pulled onto the street. Drive a few mins. Go into Wegmans for a sub. Come out, start it, light is on again (no surprise at this point) Take the long way back to the house ~3 miles. Running @40-45 with 3 red lights, OD off @2200 RPM. (Been thinking it's the alternator at this point, seeing if the higher RPM helps) Get home light still on. Turn it off, eat. 30 mins later I leave for work, which is ~2 miles away. Light still on. Getting a little worried about it. Look down sitting at the light to turn into the parking lot at work, light is off. Come out 4 hours later ~40* out, starts up, no battery light.

Truck has ~97k on what I assume to be the original alternator. Batteries look new (750 CCA Motorcraft). The battery connections are tight, but a little corroded, but I can see metal all around. No engine light. No difference in starting. Haven't had the battery light come on with the motor cold yet, only warm. Belt has some play in it, I can push it in maybe 1/4-3/8" or so, with 1 finger. (truck OFF) I had my Mom run to the parts store (Pep Boys) and wanted her to just get me one, but they said there was a 90% chance it was the belt tensioner. (For the record a new "Ford" alt is $200, rebuilt is $169 from them) They said to watch the belt with the truck running and see if it has any "flop" to check if the belt is tight enough. Didn't end up getting one...

Tomorrow I have to drive ~100 miles. I have roadside assistance, but really hoping I don't have to use it. Is there any warning sign before it uses the rest of the battery power? (Volt gauge on the dash?)

Any ideas of what it could be? In the Morning I will try to clean the battery posts. Any special way to pull the cables off? (never done it with 2 batteries, I assume pull both negative wires first?) I may tighten the belt too, depending on if I think it's loose. Is it possible to test the alternator without taking it off and going to the parts store? (No volt meter Parts stores are closed tomorrow, I work Friday and Saturday. Friday if we still have one where I work I'm buying a volt meter)

On a side note, I'm pretty sure they overfilled the oil. Not by much. Getting oil this week, and it's already made almost 700 miles as it.

Thanks.

[coot1]

Sounds like brushes getting bad in alternator. I suppose it could be the belt tensioner but I would think you would hear the belt squeaing some or find it hard to turn if you try and jerk the wheel quick.

[justinmix]

Yeah, I would bet on alternator. You should be able to verify this with a voltmeter. With the truck off check battery voltage at the batteries, then check it at the large terminal of the alternator. The readings should be very close, within a half volt at most. If this checks out then the wiring and fusible link going to the alternator is ok.

Then start the truck and measure battery voltage. It should go up to at least 13 volts. Normally it will be around 13.5-14.5 volts when running with a good alternator. If it's not getting to 13 volts then the alternator is toast. If it's ok and the light is off, drive it around and try and get the battery light to come on. When the light is on take your voltmeter and retest. If the voltages still look good then you might have something else going on with the "dummy" lights. I've seen the little 2 wire connector at the alternator messed up before which will cause a battery light.

Normally it's the alternator though. If you have to drive 100 miles and the alternator quits charging then it will most likely die on you. Since the injectors are controlled electrically it will use up the batteries rather quick.

[Tj Krawler]

Originally Posted by coot1

Sounds like brushes getting bad in alternator. I suppose it could be the belt tensioner but I would think you would hear the belt squeaing some or find it hard to turn if you try and jerk the wheel quick.

Belt tensioner could be it... its never been real easy to turn while stopped. Rolling slowly is easy.

Originally Posted by justinmix

Yeah, I would bet on alternator. You should be able to verify this with a voltmeter. With the truck off check battery voltage at the batteries, then check it at the large terminal of the alternator. The readings should be very close, within a half volt at most. If this checks out then the wiring and fusible link going to the alternator is ok.

Then start the truck and measure battery voltage. It should go up to at least 13 volts. Normally it will be around 13.5-14.5 volts when running with a good alternator. If it's not getting to 13 volts then the alternator is toast. If it's ok and the light is off, drive it around and try and get the battery light to come on. When the light is on take your voltmeter and retest. If the voltages still look good then you might have something else going on with the "dummy" lights. I've seen the little 2 wire connector at the alternator messed up before which will cause a battery light.

Normally it's the alternator though. If you have to drive 100 miles and the alternator quits charging then it will most likely die on you. Since the injectors are controlled electrically it will use up the batteries rather quick.

Should have access to a volt meter today.

[Tj Krawler]

Main battery cable was really loose. If I pulled on it, it would have came off the battery post. Cleaned the connections and made sure everything was tight going back on. Hopefully that was it.

[Tj Krawler]

Made it just under 25 miles when the battery light came on which was only a few miles to where we were going. Left my Grandma's house for my other Grandma's house. Battery light stayed on. 50 miles more, battery light never turned off. Stayed there 5 hours. Started pretty slow. Lights on, radio and heat on the 25 miles home. (65 mph, giving it the best chance from just under charging until the truck died) Battery gauge seemed much lower. (could see the "-" sign under the needle before, before I got home it was visible OVER the needle) Made it home though. took it to work today, I was a little surprised it started, especially with how slow it was cranking. Volt gauge is just over the "acceptable range" line No battery light. 10 mins at idle, gauge is right up where it should be. 2 miles to work. 2 hours later start it, gauge is a little low again, cranks a little slow. Take it right to Pep Boys. Alt is charging at 12.1 volts. Batteries at 660 CCA, tested good, just not fully charged. Tensioner is bad for sure. Getting a new one tonight and hopefully that will be it.

[justinmix]

Umm, 12.1 volts is not charging. That is battery voltage. It should be over 13 volts when running. Sounds like the internal voltage regulator is crapping out, which means you need to replace the alternator. If the tensioner was really that bad the power steering pump wouldn't work, and the belt would be squealing all the time.

[Tj Krawler]

Originally Posted by justinmix

Umm, 12.1 volts is not charging. That is battery voltage. It should be over 13 volts when running. Sounds like the internal voltage regulator is crapping out, which means you need to replace the alternator. If the tensioner was really that bad the power steering pump wouldn't work, and the belt would be squealing all the time.

Steering at idle is really hard. You can push the belt in probably 2" or so. I said much less before, but I was hardly pushing on it for that.

[justinmix]

Well I guess it's worth a shot, but if the belt was slipping on the alternator that much it should be squealing pretty good. Guess it can't hurt to replace it.

[Tj Krawler]

I really don't know. Trying to replace the least about possible. I would be doing the belt too, but I don't want to pull the coolant hose if I don't have to. (Belt looks good, but I'll replace it in spring when I do the coolant)