Voltage question?
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Junior User
Joined: Dec 2001
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From: Texas
Voltage question?
Please help me out with a quick question:
my truck (02 7.3L) has been cranking slowly for the last few days... Also noticed the AC blower seemed to be running slower than ususal.
Both batteries were replaced a few months ago. (factory batteries lasted over 4 years... better than i expected they would)
I put the charger on for a few hours and the truck cranked normally, so i'm guessing the alternator is going out. So i checked the voltage coming off the alternator while running (11.7) and the batteries while the truck is off (11.9). What should the voltage be? Any reason to suspect something other than the alternator?
many thanks
my truck (02 7.3L) has been cranking slowly for the last few days... Also noticed the AC blower seemed to be running slower than ususal.
Both batteries were replaced a few months ago. (factory batteries lasted over 4 years... better than i expected they would)
I put the charger on for a few hours and the truck cranked normally, so i'm guessing the alternator is going out. So i checked the voltage coming off the alternator while running (11.7) and the batteries while the truck is off (11.9). What should the voltage be? Any reason to suspect something other than the alternator?
many thanks
Logistics Pro
Joined: Jul 2001
Posts: 4,137
Likes: 41
From: Marble Falls, Texas
With the engine running, the alt should show 14.4 (I believe) I would definatly suspect the alt. Pull it off and have the parts store check it.
By the way, where you at in TX. I'm in Spicewood. Just outside of Austin.
By the way, where you at in TX. I'm in Spicewood. Just outside of Austin.
FTE Leadership Emeritus
Joined: May 2001
Posts: 13,653
Likes: 6
From: Cabot, Arkansas
Yep...that's a bad alternator, or voltage regulator. All part of the same assembly on these trucks.
You should see 13-15 volts output with it running, and a full battery will show nearly 13 volts static.
You should see 13-15 volts output with it running, and a full battery will show nearly 13 volts static.
Junior User
Joined: Nov 2003
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Only 4 years on your batteries? I'm surprized, my truck is a 96 and I still have the originals, however, i only have 147k miles on it. Although now that I have said that, I'm sure this weekend I will need to replace them! lol
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Junior User
Joined: Dec 2001
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From: Texas
Are you in Michigan Weldboy?
perhaps they last longer up there... i think the high heat really gets to 'em down here in texas :-)
perhaps they last longer up there... i think the high heat really gets to 'em down here in texas :-)
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Lead Driver
Joined: Jul 2005
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From: Eccles, WV
High heat along with extreme cold will destroy a battery. The high heat will do it faster as it causes the plates to swell and short out. The cold does it as it causes the engine to attempt to draw more amperage than the acid can transfer due to thickness of the engine oil
Postmaster
Joined: Apr 2005
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From: round rock, tx
Originally Posted by osb
Please help me out with a quick question:
my truck (02 7.3L) has been cranking slowly for the last few days... Also noticed the AC blower seemed to be running slower than ususal.
Both batteries were replaced a few months ago. (factory batteries lasted over 4 years... better than i expected they would)
I put the charger on for a few hours and the truck cranked normally, so i'm guessing the alternator is going out. So i checked the voltage coming off the alternator while running (11.7) and the batteries while the truck is off (11.9). What should the voltage be? Any reason to suspect something other than the alternator?
many thanks
my truck (02 7.3L) has been cranking slowly for the last few days... Also noticed the AC blower seemed to be running slower than ususal.
Both batteries were replaced a few months ago. (factory batteries lasted over 4 years... better than i expected they would)
I put the charger on for a few hours and the truck cranked normally, so i'm guessing the alternator is going out. So i checked the voltage coming off the alternator while running (11.7) and the batteries while the truck is off (11.9). What should the voltage be? Any reason to suspect something other than the alternator?
many thanks
I still have the CHECK GAUGE and Batt lights remaining ON just as I put the key into start, is that normal?
I may hae a bad alt, I experienced the same FAN problem with the A/C running and then cutting out the other day
New User
Joined: May 2006
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Alternator problems
Just replaced mine with a 200 amp. Same symptoms, and a buddy of mine told me about a problem with the alternator diodes, that if they go out the voltage from the batteries can back feed and run the batteries down almost like a short. My alternator was putting out 12.4 volts at idle and 12.7 at 2000 rpm. Also check your battery cables and see if there is any corrosion in the wire itself. This can cause charging problems also.
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