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1979-2004 V6 Mustang Tech Discussions

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Unread 04-22-2010   #1 (permalink)
1965stang is offline PONY Member

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Default 2003 Mustang V6 intermittent battery light issue

Ok guys I've got a strange thing I need a little help figuring out. I usually hang out over on the classic side with my '65 build, but it's time to put an end to this problem on my 2003 mustang. Here's the facts:

- I have an intermittent battery light
- I have a stereo system
- I have upgraded to both an optima yellow top and a pa performance 130 amp alternator to compensate for the stereo system.
- I have changed the terminals on the wiring for the battery because when I swapped batteries the terminals were too corroded to use again. I have all clean terminals now.

Here's where it gets strange. For a year or so, this setup worked perfectly, no problems, no battery light. Then one night driving home, the battery light kinda flickered on, stayed for a bit, and flickered back off. Very inconsistent, this happened again about a week later. No effect on performance at all, just temporary dim lights, then back to normal.

Then the problem disappeared entirely for a couple months. I decided if it came back, I'd look into diagnosing it.

Well, it came back a couple months ago. My car started having real problems staying on when it was running, and would practically almost die if I put it into drive and tried to accelerate. If I stopped with it in drive, the engine hesitation would stop with the lower rpms back. Then before I had a chance to start getting stuff tested, one day while it was doing this behavior, the car just completely died at a stoplight. Completely dead, no lights, dash needles stuck pegged over, nothing. Jumped it, car went back to acting normal again. It also died on me going 70 on the highway one night (that was fun).

After this, I had the battery tested, it was fine (a little low on charge, but passed the load test). Tested the alternator on the car, measured correct voltages. Found that one of the terminal wires was a little loose. Tightened everything up, seemed like I solved the problem to a bad ground. Problems, battery light, everything went back to normal.

Couple weeks later, battery light came back. This time I ordered and upgraded the power lead wire from the alternator. This made a huge difference on overall power output, headlights were brighter than they'd ever been (a nice change).

Here's where I'm stumped (sorry for the long explanation but now you have the story of what I've done and how I got here). After I upgraded that alternator wiring, the battery light went away again. I don't have any more of the issues of the car wanting to die anymore, but this battery light just keeps coming and going on a whim now. When it's not on, the car runs and acts perfectly. When it comes on, I can affect the light by running on the highway at 70, clicking off the overdrive, and shooting up cruising speed to 3200 rpms or higher. Click it back on, drop the rpms, light goes away. Sometimes it stays off, sometimes it comes back on. Sometimes this rpm thing doesn't do anything to it at all. Again, very inconsistent.

Last odd thing - when the light is on cruising the highway daytime, the car acts perfectly normal. Slow down for a light and drop the rpms to idle, and sometimes the light stays on. Other times, the car seems to get a really rough idle for a couple seconds (like the drivetrain is shuddering), then when that quits, it returns to a normal idle and the light disappears. At night with the added headlight load, it does the same thing, only my lights are really dim until I slow at a light and it does this shudder thing, then all of a sudden the lights are bright again and everythings normal. This shuddering thing is an every once in a while thing.


So, any suggestions on things I should look at? I just want this battery light to go off for good.
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2003 V-6 - the usual bolt-ons. Traded for 2012 V-6
2012 V-6 - premium "Pony Package" edition. Leased, so no mods. Traded up for 2013 5.0
2013 5.0 - premium package, visual mods for now.
1965 coupe - Born - straight six standard issue
Now - 5.0 motor, T5 tranny, R&P, full length subframe connectors, Caltracs draglink bars, hedman headers, disc brakes, MSD 6, paxton supercharger, and probably a bunch of other stuff I forgot to mention. It's loud as hell, and my new toy
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Unread 04-23-2010   #2 (permalink)
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1965stang, It's a funny thing you asked because just yesterday, my light started to turn on as well. On mine, it would turn on when ever I accelerate and off when my foot is off the pedal. I am about to investigate to problem today and hope it is something tiny. The only thing i added were hids! I hope that is not the problem.

My first suggestion is to maybe recheck your terminals again. maybe the corrosion followed further down the wire? I had changed one terminal end, just the end and not the whole wire.

I will let you know what happens with my prognosis!
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Unread 04-23-2010   #3 (permalink)
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Terminals don't have an issue with corrosion anymore...I cut all that stuff off to clean copper wire.

Any other thoughts out there?
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2003 V-6 - the usual bolt-ons. Traded for 2012 V-6
2012 V-6 - premium "Pony Package" edition. Leased, so no mods. Traded up for 2013 5.0
2013 5.0 - premium package, visual mods for now.
1965 coupe - Born - straight six standard issue
Now - 5.0 motor, T5 tranny, R&P, full length subframe connectors, Caltracs draglink bars, hedman headers, disc brakes, MSD 6, paxton supercharger, and probably a bunch of other stuff I forgot to mention. It's loud as hell, and my new toy
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Unread 04-23-2010   #4 (permalink)
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im no electronics expert.. how about your grounds?
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2003 3.8L V6 4R70W
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Best 1/4 time: 15.036 @90.92mph, 2.148 60'
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Unread 04-23-2010   #5 (permalink)
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Grounds don't seem to be the issue anymore...after i tightened everything up that one day, everything went back to normal with no more running issues and the car quit wanting to die. Gave it a week, and the battery light issue returned. I'm trying to figure out why the rpms can affect the light sometimes, but not always, and after the drivetrain shudders a second or two sometimes that affects it too.

Like I said, this is a strange problem that I'd like to put an end to because quite frankly it's just really annoying and it's so intermittent that it's hard to diagnose.
__________________
2003 V-6 - the usual bolt-ons. Traded for 2012 V-6
2012 V-6 - premium "Pony Package" edition. Leased, so no mods. Traded up for 2013 5.0
2013 5.0 - premium package, visual mods for now.
1965 coupe - Born - straight six standard issue
Now - 5.0 motor, T5 tranny, R&P, full length subframe connectors, Caltracs draglink bars, hedman headers, disc brakes, MSD 6, paxton supercharger, and probably a bunch of other stuff I forgot to mention. It's loud as hell, and my new toy
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Unread 04-24-2010   #6 (permalink)
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1965 stang, I went to a mechanic today in regards to MY battery flickering. I ask them to do a full diagnostic test on the battery/ alternator and what have you....
Everything checked out fine! I was told that if anything that was ever recently installed may cause the flickering. The only thing new may be my hid ballasts for the headlights. Not sure if that's my problem, but i must start doing a process of elimination for this one. I know it's an annoying thing. Hope you had luck with yours....
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Unread 05-09-2010   #7 (permalink)
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So you've stated that u already changed the alternator. Question is, did u get a new one? I got the same problem a year ago with my 04 mustang. Battery lights were flashing especially during high rpms and there is rough idling like the car is gonna die. It ran for like 3 months like that but then one night my car totally stalled infront of a traffic light, no power at all not even hazard lights. So i got it towed next morning to the Shop and have the alternator changed. They put a new one and luckily it didn't show any symptoms. It's been a year now and it's still running smooth. In addition, I installed HID lights couple months ago and it didn't show any battery lights flashing. I don't think HIDs can cause that prob cause it uses less power than regular halogen. Most likely it is due to bad alternator. Hope this helps. Goodluck.
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Unread 05-10-2010   #8 (permalink)
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It was a brand new alternator that I ordered, built for the increased load a stereo system puts on it. The fact that you said your car was doing the same thing mine is kind of confirms for me that the alternator is still a suspect. I have a lifetime warranty on it, but since the problem is so intermittent and hard to pinpoint that it is the alternator, I talked to them about it a few months ago and they didn't really want me to send it in since we weren't sure it was the alternator. It reads right with a voltmeter though. I'm going to try to catch it with the light on and read it. I forgot to add in my original post that I changed out my spark plugs and wires - it was time for maintenance and that fixed the car wanting to die thing. I want to blame the alternator, I just can't prove it yet.
__________________
2003 V-6 - the usual bolt-ons. Traded for 2012 V-6
2012 V-6 - premium "Pony Package" edition. Leased, so no mods. Traded up for 2013 5.0
2013 5.0 - premium package, visual mods for now.
1965 coupe - Born - straight six standard issue
Now - 5.0 motor, T5 tranny, R&P, full length subframe connectors, Caltracs draglink bars, hedman headers, disc brakes, MSD 6, paxton supercharger, and probably a bunch of other stuff I forgot to mention. It's loud as hell, and my new toy
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Unread 05-18-2010   #9 (permalink)
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Question Alternator

Anything new happen?

A couple weeks ago my battery light flickered on for a few seconds when I accelerated fast. The light went off right away.

Then it has happened again on fast acceleration. The battery light turned on at about 3000 rpm.

I have noticed for a while that my alternator has a slight noise/whine coming from it for the past few months.

Today I tested the volts at the battery with the car running and it read a little below 12 volts. I also tested the volts directly at the alternator with the car running and it read about 13 volts. This is weird because in the past, it has read at least 13 at the battery with the car running. So it seems like the alt isn't working correctly.

It could be that the battery is trying to charge since the alt is not working right. I have a yellow top optima that is pretty new.

Is this the end of the alternator? It is the original that came with my car in '04.
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Unread 05-18-2010   #10 (permalink)
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Alright so I went to Pep Boys and they connected their tester to the car and it said the alternator was bad. There was no voltage/load or anything. It read at 11.38 v on the graph. Will be looking for a new alternator now!
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2004 3.9L/auto
-Mac CAI, 73mm Mass Air
-Dual Flowmaster 40s, H pipe, 2.25 in pipe
-42% Underdrive Pulleys
-SCT Tuned
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Unread 05-24-2010   #11 (permalink)
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Hey guitarstar - well I've got some good?? news. Last night I finally caught that stupid light on when I was at home in my driveway and could finally get a proper readout on my voltmeter while it was having its charging issues. Battery volts (keep in mind the car was on under full load of stereo, a/c, lights, etc and revving it to a higher rpm) were reading at just under 11.5 volts, matched by an alternator readout of the same 11.5 volts, measured from the alternator directly to the fuse box post and the alternator to the negative ground.

Sooo....to anyone reading this, does this intermittent battery charging issue appear to be an alternator that is just slowly bleeding to death, and sometimes just driving it around changing how fast the alternator spins affects the voltage output to where it acts normal most of the time? When the light isn't on, both battery and alternator read in the normal voltage ranges (13ish, depending on the load).

I figure if it weren't for my trusty optima and/or dropping below 11 volts, I'd be having catastrophic electrical problems again and that the upgraded wiring and maintenance I did just fixed some underlying problems.

What are your thoughts?
__________________
2003 V-6 - the usual bolt-ons. Traded for 2012 V-6
2012 V-6 - premium "Pony Package" edition. Leased, so no mods. Traded up for 2013 5.0
2013 5.0 - premium package, visual mods for now.
1965 coupe - Born - straight six standard issue
Now - 5.0 motor, T5 tranny, R&P, full length subframe connectors, Caltracs draglink bars, hedman headers, disc brakes, MSD 6, paxton supercharger, and probably a bunch of other stuff I forgot to mention. It's loud as hell, and my new toy
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