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Old 01-25-2013, 06:24 PM   #1
camopaint0707
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Default Weird electrical issue

This is on a 2004 F150 fyi. So would this be a battery or alternator issue? Battery dies overnight and requires a jump start. When driving the volts are normal around 14.8. When I come to a stop the volts drop to like 12 and below and the lights dim and the rpms drop and I feel like it's going to stall. Battery was bought in october 2012 and alternator is less than a year old too.

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Old 01-25-2013, 09:49 PM   #2
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Internally regulated alternators is something Ford always had a problem with. I'd pull it off and get it tested. Also if its dead over night something is draining it overnight, underhood light isn't turning off, glove box light stays on but something is killing it over night. Try to disconnect the battery overnight and come morning hook it back up and see if it starts, if it does then you know somethings draining overnight.
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Old 01-25-2013, 11:13 PM   #3
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You'd say alternator before battery?
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Old 01-26-2013, 12:17 AM   #4
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Unplug the regulator connector from the alternator, this should put the alternator in full field and charge at max. If it stays at 14.50 or above while it running, then its a regulator issue, if not replace the alternator. Also, there is a wire in that regulator connector that is the battery sense wire. This wire detects battery state and charge, if there is excessive resistance in this circuit, it will not charge properly. The connector has 3 wire in it, one of them should have battery voltage at all times. Check resistance from that wire to the battery positive, the spec if 5 ohms or less. If its excessively higher than that, then clean your battery terminals and recheck it. If it's still excessive, use a jumper on that hot wire in the regulator connector, and jump it right to the battery lead on the alternator itself. 14.8V is overcharging, anything over 14.5V is overcharging and will cook the battery. This could be due to the battery needing to be replaced, need to charge the battery and load test it to be sure. The alternator should not drop below 12.5v at all while its running. Sounds to me you have a bad battery and faulty charging system that probably killed your battery. 14.8V overcharges that battery and kills cells inside of it, and anything under 12.5V is not charging. If it hits 14.8V that could be cause of a bad battery. Installing a new battery could change that, but would still need to have the charging system looked at as i described above.
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Old 01-26-2013, 03:55 AM   #5
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G8One2 - Can you shed any light on the G8 charging system? (Op sorry for the thread jack but we may have found an charging system expert)

I put a new fresh battery in and then drove it for a 100 miles. It stayed at 15.2 V the whole time. I was pretty concerned but then the next time I drove it a couple days later it was at a more reasonable 14.2 V.

Seems others have experienced this too but nobody mentioned anything bad beyond that.
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Old 01-26-2013, 01:29 PM   #6
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I am by no means an expert. I just have a unique job in the vehicle development field, and i am very familiar with Ford products. Im am not familiar with the G8 charging system because i have not a need to mess with it yet, but here's what i do know. Most of our newer vehicle's today have what we call a "Smart Charging System" or a "BMS - Battery Monitoring System". The BCM (Body Control Module or SJB - Smart Junction Box, the computerized fuse box inside the vehicle), continually monitors load and charging state of the battery, it adjusts it charging voltage in accordance to battery state and load on the system such as headlights on, blower, radio, etc. etc. If your battery is going bad, it will start to overcharge the system in attempts to charge it. I believe the reason your system was charging at 15v after the new battery install was because the BCM needed to relearn the charging state of the new battery. Once it relearns, it should charge the system accordingly to load and battery state. Of course im speaking in terms of how the Ford systems work, but im sure GM is generally the same but in its own way. Once the BMS system re-learns, charging voltage should never be above 14.5. But again, its a GM vehicle, so the specified regulating voltage for the system my vary a bit from a Ford.
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Old 01-26-2013, 01:44 PM   #7
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This video was taken on a Ford F150 you know that right.
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Old 01-26-2013, 01:50 PM   #8
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Yep, his truck is not equipped with a "Smart Charging System". Its strictly controlled by the 3 wire internal regulator.
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Old 01-26-2013, 04:41 PM   #9
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Thanks for the response.

Quote:
I believe the reason your system was charging at 15v after the new battery install was because the BCM needed to relearn the charging state of the new battery. Once it relearns, it should charge the system accordingly to load and battery state.
That's apparently what's it doing as mine and the others had the state of charge out of wack low with the new battery installed. Then after a day or two it figures it out and then behaves normally. But did the new battery get damaged getting 15.2 V for a long period?
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Old 01-26-2013, 05:31 PM   #10
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It would have to be at 15V for an extended period of time to do any real damage to the battery. At most, it may have shortened the life of the battery a tad bit, but nothing to worry about.
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