Volt Gauge reading low - Page 2 - Diesel Forum - TheDieselStop.com
Power Strokes 1994-1997 General Technical discussion of topics related to vehicles powered by the Power Stroke engine in 1994 through 1997 models.

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post #16 of 20 (permalink) Old 01-14-2013, 02:54 PM
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Originally Posted by bugman View Post
That is low. What is the voltage on your batteries with the cables disconnected? You may need to put a full charge on them with a battery charger and then check the alternator again.
I will check the batteries in the morning with them disconnected, but both batteries had a fresh charge when I installed the new alternator. I called NAPA and told them the new alternator was only putting out 11.9V and they said it was low and ordered a replacement. I'll pick up the new one tomorrow and see if it fixes the issue. Hopefully the new one is stronger and takes care of the issue.
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post #17 of 20 (permalink) Old 01-14-2013, 03:56 PM
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FWIW... Everybody that walks out of my local auto electrical rebuilder's shop with a new or rebuilt alternator has about three pieces of paper saying the battery/batteries have to be up to 12.8 or 12.85V before the engine is first started with the new alternator. It's hard on the new alternator to charge at high amps right off the bat.

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298,500 mi & NO Problems, LUK Clutch
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post #18 of 20 (permalink) Old 01-16-2013, 08:04 AM
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Well, changed the Alternator and charged the batts individually to 100%. Start the truck and the same thing is happening. So where to next? I cleaned the cables and terminals, so I know its not a corrosion issue w/ the batt cable. New Alternator made 12.68V last night, and gauge was on the N in Normal. I took it for a drive, and then checked the GPR Voltage when I got back and truck was at operating temp. One large terminal read same as Alternator, and the other read 0.01V. What are the small terminals supposed to read? If I remember correctly they were reading over 11V each, and I seem to remember something about they should only read 8V.

This morning I start it back up and gauge is reading the same as the old Alternator. I think its pretty unlikely that 2 NEW alternators would have the exact same issue. Any ideas?
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post #19 of 20 (permalink) Old 01-16-2013, 12:46 PM
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What are your batteries reading with the cables disconnected? On the glow plug relay you will have battery voltage on one large lug all the time. With the key on you should see battery voltage on one of the small lugs while the relay is energized and then on both of them once it turns off when the ground signal is removed.

Just for kicks I would take the truck to Auto Zone and have them do a battery load test and alternator test with everything still on the truck and see what they say.

96 F250 PS XLT 4X4 long box, 5sp,4.10, manual hubs,pyro+boost guages, Dark Toumaline, add a leaf, Dale's TYMAR, and HX hose, downpipe, coolant filter, Luk clutch
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post #20 of 20 (permalink) Old 01-16-2013, 08:40 PM
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It may be you simply have one or both battery bad. I noticed my volt guage was low a few weeks ago and the truck barely started, then the next day did not start. I knew my batteries were bad though and didn't even consider the alternator and new batteries and all is well, but my truck never has ever read any higher than the N in normal. I believe there is an alternator charge idiot light that should light if the alternator is not working.

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