Question about Ford F-350

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2002 F350 7.3L, repalced the alt bad diodes 3 weeks ago and it is happening agian. what is causing this

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  • pvgomer Nov 15, 2010

    What is the issue with truck? also what Diodes did you replace?



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Did you fit new ones and not scrapyards pieces

Posted on Nov 15, 2010


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Why is battery draining ford 2002 Taurus SES

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Oct 01, 2015 | 2002 Ford Taurus

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Alternator bad diode

is this a question,?
1: is mine bad, how to test it or find it, in the global sense?
2: where to buy one.
3: which brands are best.
4: how to do a basic diode test , front to back ratio testing.
5: what are the symptoms of a bad diode.

ill throw the ice 2+3 = 5.
the Modern ALT has many diodes. (and more{in dah reg})
the 2 main, sets are , the 3 phase set.
and the keep alive pack.
ill not cover the keep alive pack or the regulator diodes..
the 3 phase pack take the 3 AC phases and converts them to Pulsating DC. (in effect simulating a DC generator)
if 1 diode opens , you lose, 1/3 of the total power.
so 50 amp alt is now a 33 amp alt. (weak as a cat)

if the diode shorts, it becomes this huge noise generator.
(turn on the AM radio , here it sing and raise pitch as you gun the throttle (i use a scope to see bad diodes) bingo.
the noise can in fact cause any electronics on the car to go nuts.

the diodes also have one other feature, ill skip here, (zener actions)

Nov 19, 2013 | Suzuki Cars & Trucks

1 Answer

The voltage jumps up and down

Have a shop put a scope on the alternator & look at the pattern

You may have bad diodes & a/c ripple on the circuits

A bad battery or some other cause of variable resitance

You may go thru 3 rebuilt alt to get a good one

Feb 08, 2013 | 2006 Chevrolet Tahoe

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Replaced alt twice in two weeks

I had the same issue a month ago. i'm not a mechanic. i took it to the local garage, and they replaced the alternator. when we picked it up, hte light came back on. he said it was the control module and asked us to go the dealer. the dealer replaced the alternator with an OEM altenator and it has worked since. was the first replacement bad or is the OEM different. not sure...but it has worked since

Sep 03, 2012 | 2002 Buick Rendezvous

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I recently replaced the alternator and battery in

maybe something shorting out drawing power did u have alt tested before switching out to make sure it was bad- sum auto stores such as auto zone/advanced auto can do a load test on vehicle for free will show if their is an excess draw on elect or if new alt is faulty (does happen) check serpentine belt and pulleys belt may be slipping then check ground strap , starter for draw or some other accessory

Oct 24, 2009 | 2002 Chevrolet S-10

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