99 & up 7.3L Power Stroke Engine and DrivetrainDiscussion of the 99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.
I had a dead truck the other day and picked up a new alternator thinking that was the problem since my batteries are new. Installed the new alternator and it still doesn't want to charge the batteries. Took the new alternator back to the parts store and they tested it on their test bench; it checks out fine. Question is: with a new alternator and good batteries why am I not getting 14.5 volts showing up on my voltmeter when the engine is running. Do I have a blown fuse somewhere?
Have you checked the output at the alternator with a multimeter with the motor running, checked the batteries seperately, battery cables etc? A weak tensioner will cause the alternator not to charge properly, it can seem fine but, not be doing the job. I don't know if there is a fusible link on a 99.
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I recall some others talking about a few fuses associated with the charging system like you describe. I believe they were in the engine compartment box. Easy enough to just check all of them.
I recall some others talking about a few fuses associated with the charging system like you describe. I believe they were in the engine compartment box. Easy enough to just check all of them.
There's one fuse to the alternator in the under hood fuse box. Check Fuse #6, 10A, which supplies power to the sensing and switching circuits inside the alternator via the orange/lt blue wire on the alternator connector. If you don't have voltage there, the alt either won't work at all or won't know what to do.
Another fuse under the inst panel (#29, 5 A) powers the battery side of the charge indicator circuit for comparison between the battery voltage and alternator output. That fuse is hot in Start or Run and actually turns on the alternator.
To paraphrase the service manual:
With voltage applied to I circuit (powered by fuse #29) regulator is activated, allowing current to flow from B+ circuit (the big wire on the alt) to the generator field coil.
I was having the same problem a while back. My mechanic worked on it for a day and a half trying to figure it out. He finally cut the wire coming off the alternator that goes back thru the instrument cluster to the idiot light and ran it straight to the fuse in the fuse box under the dash and I haven't had any trouble since. Before that I was going thru an alternator about every 30 days.
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Early 99 (4/98) F250 X-CAB 4x4,automatic tranny,DP Tuner 40HP tow PCM,Sonnax tranny kit,C-Betr mirrors, XM radio, Cobra CB,gooseneck hitch. 315,000 miles and counting!!!!!
What is your temperature gauge showing, is it getting up to normal temperature, or is it staying barely off cold?
If the thermostat is stuck open, the engine stays cold, the glow rail controller keeps the glow plugs turned on due to the low engine temperature, especially during winter, with lower air temperature, more use of lights, defrost, etc, the alternater can't keep up with the draw off, due to the glow rail staying on. Altinater is charging, but battery still goes flat occasionally.
Wasted money on battery and altinater replacements, before I cottoned on to this, I initially found the glow rail stayed live (volt meter) and thought the relay was at fault, but the engine was not getting above 50 deg C. It would charge, after parking (at idle) due to heat soak increasing the engine temperature after a trip.
So this can easily be a non electrical fault, which presents as a very electrical symptom!
I had a dead truck the other day and picked up a new alternator thinking that was the problem since my batteries are new. Installed the new alternator and it still doesn't want to charge the batteries. Took the new alternator back to the parts store and they tested it on their test bench; it checks out fine. Question is: with a new alternator and good batteries why am I not getting 14.5 volts showing up on my voltmeter when the engine is running. Do I have a blown fuse somewhere?
Is it a Autozone alternator ? Those things are junk. I get those in work all the time and some test 'fine' on Autozone's test bench yet we put in a Motorcraft and....Presto!!! Fixed.
Same thing with starters....
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With your truck running you should have about 14 volts measured at the batteries. If not, the alternator is not charging. There is a fusable link (fuse inside the wire) that would feed the battery for charging. It is the bigger wire that comes off the alternator and I think is connected at the glow plug relay. Check that also. If you blew that fuse you need the new fusable link/wire.
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Good alternator, still not charging system
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before I cottoned on to this, I initially found the glow rail stayed live (volt meter) and thought the relay was at fault, but the engine was not getting above 50 deg C. It would charge, after parking (at idle) due to heat soak increasing the engine temperature after a trip.
Linear Mode
