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Old 08-06-2013, 04:30 PM
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batteries or alternator?

the old 'stoke has been giving me fits as of late.

but, i think i have it narrowed down to an electrical issue. problem is, batteries or alternator?

charged both batteries individually. both took charge to 12.7 volts. load tested. both were marginally weak, not bad, but still showing weak on my meter. Put them in the truck, it fired up like new. with the truck running though, i am only showing 13 volts at each battery. is this normal? i know most vehicles i work on usually show closer to 14 while running.

amp probe shows a pull of 22 amps out of the alternator. i have had to jump the truck multiple times in past weeks. once out driving however, it always seems to re-start, usually weak start, but it has never failed to start while driving.

i would just hate to drop $300 on a pair of batteries only to find out i really needed a $200 alternator to fix it. I plan on batteries before winter no matter what, but if the alternator is bad now i'd rather fix it and wait a bit on the batteries.
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Old 08-06-2013, 05:20 PM
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Quote:
Originally Posted by Underpowered View Post
the old 'stoke has been giving me fits as of late.

but, i think i have it narrowed down to an electrical issue. problem is, batteries or alternator?

charged both batteries individually. both took charge to 12.7 volts. load tested. both were marginally weak, not bad, but still showing weak on my meter. Put them in the truck, it fired up like new. with the truck running though, i am only showing 13 volts at each battery. is this normal? i know most vehicles i work on usually show closer to 14 while running.

amp probe shows a pull of 22 amps out of the alternator. i have had to jump the truck multiple times in past weeks. once out driving however, it always seems to re-start, usually weak start, but it has never failed to start while driving.

i would just hate to drop $300 on a pair of batteries only to find out i really needed a $200 alternator to fix it. I plan on batteries before winter no matter what, but if the alternator is bad now i'd rather fix it and wait a bit on the batteries.
so start, run, shut off, start, shut off start, its fine
shut off, sit for a couple days, hard to restart?
Only batteries affect starting, if the alt was bad electrical use would gradually draw the batts til the truck dies.
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Old 08-06-2013, 05:27 PM
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Provided the glow plugs are off, you should be measuring at least 14 volts at the batteries when the engine is running. With my headlights and AC on, I get 14.6 volts at idle, but I have also upgraded my alternator.

Try checking the output voltage at the terminal on the back side of the alternator with one probe on the terminal and one on a good ground to get an idea of what your alternator output is; however, make sure that you wait long enough for the glow plugs to shut off, as they draw a lot of current.
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Old 08-06-2013, 06:26 PM
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so start, run, shut off, start, shut off start, its fine
shut off, sit for a couple days, hard to restart?
Only batteries affect starting, if the alt was bad electrical use would gradually draw the batts til the truck dies.
true, but in the past i have had an the internal diode in an alterernator go bad, causing a voltage drain on the truck.


after manuall charging both batteries, it starts great, but even after longish trips ( a couple hours straight driving) re-starts were slow, nothing like today with the fresh charge.

but yes, after a couple days sitting it usually fails to start. I started it friday, drove two short 15 minute trips, then sunday morning it failed to start. charged one battery sunday, the other yesterday, installed today and it fired right up, cranking faster than i am used to. i plan on driving it tomorrow, and will see if it seems crank slower as the day goes on and will check voltage after it has ran for a bit to be sure glow plugs are off.
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Old 08-07-2013, 05:24 PM
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going thru that now.my alt output was 50.13 was going back to batteries for recharge.however my voltage was close to normal.over the course of a couple of short trips my truck was getting slow at cranking.take a long trip and good for a while.dont get alt tested at advanced.mine passed there.the garage my brother uses checked mine and loaded to the max and only got 50 amps output.cost me 10 bucks.i actually went to exchange batteries until he tested everything and checked my cables.22 amps way to low.
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Old 08-08-2013, 07:11 AM
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I've had the same issue with my truck, starts fine if I am just running around town but if it sits for a day or two starting is slow and sometimes takes two trys. Took it to the shop and all they found was a crack in the positive clamp on the passenger side battery. I still have the same issue if it sits, interested to see what the fix is for yours.
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Old 08-08-2013, 12:50 PM
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When I had my 7.3 I had similar problems. Cranked slow every morning but would pretty much be dead after it sat a weekend. I replaced the batteries and still had the same problem, which then lead me to the alternator. I went to Autozone and brought my first alt and had the same problem after a couple weeks turns out the alt was bad, tried another it was also bad then third one worked fine. Solved all my problems. Moral of the story buy a quality alt not one from the parts store.
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Old 08-08-2013, 04:57 PM
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Originally Posted by NCDeerHunter View Post
When I had my 7.3 I had similar problems. Cranked slow every morning but would pretty much be dead after it sat a weekend. I replaced the batteries and still had the same problem, which then lead me to the alternator. I went to Autozone and brought my first alt and had the same problem after a couple weeks turns out the alt was bad, tried another it was also bad then third one worked fine. Solved all my problems. Moral of the story buy a quality alt not one from the parts store.
i thought about taking it off and having a local place rebuild it. They usually can rebuild one for less than half the cost of new. and they stand behind their work.
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Old 08-08-2013, 05:42 PM
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I don't know why Ford didn't put a battery gauge or 2 or even an Ammeter in these trucks instead of the idiot light. Is there a way to monitor both batteries separately?
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Old 08-08-2013, 05:47 PM
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easily, no as they are connected in parallel. you would have to add some diodes into the system or some sore of isolator to individually monitor them.

the voltmeter is very vague in them. mine still shows well into the good range every time it will not start.
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