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2001 f350 7.3, alternator quit charging, changed alternator…

2001 f350 7.3, alternator quit...
2001 f350 7.3, alternator quit charging, changed alternator and now charges for short time and voltage gradually drops, I’ve been a semi mechanic for 12 years and own my own shop, saying that.... I don’t think it’s the alternator, I think it may have something to do with the glow plugs in which I don’t have any knowledge about because the bigger diesel motor doesn’t have any, can someone help me out with this, btw, I do know where the solenoid is just no sure what wires do what. Thanks
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Answered in 18 minutes by:
1/6/2018
A. Penland
A. Penland, Ford Senior Master Technician, ASE
Category: Ford
Satisfied Customers: 6,921
Experience: ASE Master Certified, ASE Advanced Gasoline Engine Performance
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What does the charging voltage go up to and how long, minutes wise, does it take to drop and how low does it go down to?
Does the charging system warning light come on in the instrument cluster?

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Customer reply replied 5 months ago
Voltage goes to 14, after about a good 15 min or so it starts dropping and depending on what I’m running depends on how fast it drops down (with heater fan and headlights on) it’s within 20 mins it’ll go down to 8 volts

Ok. Are you sure the alternator you installed is good? The glow plugs will not effect the charging system. Sounds like the alternator is heating up and the internal voltage regulator is failing causing the drop in voltage down to below battery voltage after running little while.

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Customer reply replied 5 months ago
I thought that too and it might be the regulator but if the pcm is messed up and send signal to heat glow plugs, they’ll draw more current than the alternator can put out right?
Customer reply replied 5 months ago
It all started when it took about 20 minuets to start three days ago because I didn’t plug the block heater in, after cycling the glow plugs on and off the whole time it finally started and by the time I got to my shop the voltage dropped, so I put another alternator on and still same problem. That’s why I’m thinking I effected something to do with the glow plugs.

Not really. The alternator will compensate for the electrical load and raise the alternator output.

So you had the exact same problem with the alternator you took off and the one you installed?

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Customer reply replied 5 months ago
Ok, I checked the voltage on the plug wires and with it unplugged and running I have 12 volts on both, and when I plug it in my orange wire has 12 and the green has 3, charge wire only has 3 at high idle
Customer reply replied 5 months ago
This is with another new alternator installed

Is the charging/battery light on in the instrument cluster when the engine is running?

Does the charging/battery light come on when the key is turned to on, but not start?

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Customer reply replied 5 months ago
the light is on
Customer reply replied 5 months ago
I’ve put two new alternators on it and one good one off my service truck that works on that truck even now because I put it back on that truck after it made no difference on my problem truck

Look this pin point test over. It is from the Ford Factory Shop manual.

A. Penland
A. Penland, Ford Senior Master Technician, ASE
Category: Ford
Satisfied Customers: 6,921
Experience: ASE Master Certified, ASE Advanced Gasoline Engine Performance
Verified
A. Penland and 87 other Ford Specialists are ready to help you
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Customer reply replied 5 months ago
K, I did, with the plug unplugged, the pins test good but when truck is running, the ignition switch wire is only 3 volts and charging wire ( Big wire) is only at 3 as well
Customer reply replied 5 months ago
Which fuse ( is there a fuseable link for the alternator), I don’t have factory book to tell which fuse is which?
Customer reply replied 5 months ago
Just so you know, there are 2 fuseable links going to the solenoid on fender pass side, they were burnt.
Customer reply replied 5 months ago
Thanks for your attempt to help me with this issue, I have it repaired now, thanks again!

Ok.

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