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Have a 2001 Ford Mustang with a 3.8 engine, automatic transmission. For starters the battery light is usually ON, and along with that is a misfire. No codes are being thrown.. Brand new battery, and a brand new alt, along with new battery cables and terminals. Checked, and triple checked all my grounds and connections. There is no issue with battery dying on me, it all seems fine, but the light will come on, stay on all week, then go off, back on.. I can feel the car misfire while driving, and i can almost hear it in the exhaust, faster I go worse it gets. No engine codes, new plugs, wires, has a new fuel pump and filter. Not sure if my misfire and battery light on are related, but its driving me nuts now. Any ideas, suggestions, or comments would be great!
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You need to diagnose both your issue as 2 different problem at this moment.
Battery light: You may have a defective alternator when it comes to the battery light. The LG/RD wire is the ground supply from the alternator that turn the battery light’s on. If you disconnect that wire the light should go off. You can have a perfectly good alternator that would only fail on the light being on. The alternator would need to test.
For your misfire. Are you sure to have the proper spark plug and being gap properly. I doubt you can reverse the way the fuel filter goes on your model but I would check on that …. if it is in the wrong flow side the material can go clog the injector. Check where you replace part before being brain lock if possibilities
Check to see what your battery is charging at…. Could be a bad voltage regulator (most are now in the alternators)…..
If it is not charging consistently, it could be causing other electrical issues… Computer controlled cars need a clean, consistent supply of electrical power….
I would fix the battery light problem first and see if the second problem remains…
-Karl
Thank You both for your input. I checked over everything again, found nothing, had the alternator tested over and over and its charging fine. The battery light will come on and stay on for however long it feels like, then it goes off, had the alternator tested when light was on, and off, same result with good working alternator. Doesn’t matter if the battery light is on or off, the car still has this misfire, with no engine codes. I’m not saying to two issues are related, i just thought maybe there was a chance they were, and someone might know something.. If i do ever get this figured out i will update.. Also i have recently installed a new fuel pump, fuel filter, and not long after that had new plugs and wires. Misfire issue, and battery light was already ongoing when I did all this work…
You may want to check your ripple voltage (for bad diodes)…
Here is a write up on how to do it..
Ripple voltage or (AC voltage) can be measured by switching your DMM to AC and connecting the black lead to a good ground and the red lead to the “BAT” terminal on the back of the alternator, (not at the battery). A good alternator should measure less than .5 VAC with the engine running. A higher reading indicates damaged alternator diodes.
Mmmmmm Ripple…
I had a 04 mustang with the 3.8l, and it had the same issue when i got it! Ended up being a bad coil pack, and a plug wire…it would run good at idle, and once you try to take off it would miss.
Well its been like two months now since i posted my issue. Still having the same problem, but I am certain now the battery light and misfire seem to be connected. I had discovered a cracked manifold, so that is now fixed. I swapped out the alternator again and triple checked all my connections, cables, grounds etc. When the battery light is ON i can feel a misfire but when the battery light is OFF the misfire leaves. It’s driving me crazy now, I think it is playing games with me i swear!! I start the car, battery light ON, I put the car in gear and start driving you can feel the misfire, if I open the throttle up and get her rolling to around 80 mph the battery light usually goes off and then no more misfire, sometimes it just stays on… Hoping someone in Eric The Car Guy Land can help me out before I goes nuts!!
Well, if that light is on, there are only a few possibilities, the alternator has an issue, line, fusible links, fuse(s), wiring itself, or a ground. Possibly the battery itself with a weak/shorted cell, might want to swap in another just to see, assuming you have a friend that will let you use theirs to test..
http://www.paladinmicro.com/documents/ChargingSystem.pdfThat light is a direct feed from the alternator to the display cluster without any ECU interpretation as I understand it; only triggering when there is <13v with the engine running.
I'd check the fuses first, the line that goes to the display cluster is actually what triggers the alternator to actually charge. Some have had issues with wiring coming loose there, or that 15amp fuse could simply be blown. I check that and the other simpler reasons first.
You're likely going to wish to check out that guy's site, as he's put up a plethora of information on that generation to that website. http://www.paladinmicro.com Including wiring diagrams and FSMs.
Well I suppose you’ve eliminated an alternator issue based on the fact you’ve replaced it twice at this point. That may leave a problem with the wiring or a connector somewhere. I suppose you need to check the alternator output when the light is on. This way you’ll know for sure if the light is a result of the alternator output, or a problem with the circuit that turns on the light. That circuit is usually contained inside the voltage regulator in the alternator BTW. You have something effecting alternator output somewhere. I would forget about the misfire problem until you’re able to track down the charging system problem. I suspect they’re related. Low system voltage can effect every electrical system on the vehicle and also cause performance issues. I suspect once you solve the charing system issue, you’ll also solve the performance issue. More info on solving electrical issues here.
http://www.ericthecarguy.com/faq/solving-automotive-electrical-problems
Good luck and keep us posted.
Thank You Eric and everyone else that gave me input on this issue! I really believe the misfire and battery light just seem to be connected, when light goes off the car runs sweet. So I have kinda solved my cars issue today… I was at the gas station, some guy really liked it and wanted to buy it really bad. I was not looking to sell it, and I told him about the issue, told him it was driving me nuts, then he made a cash offer I could not turn down! Thanks again for everybody who took the minute to reply to my topic, and stay dirty!
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