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99 F250 7.3l Chronic alternator(s) failing

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99 F250 7.3l Chronic alternator(s) failing

  #31  
Old 09-30-2018, 07:48 AM
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Both terminals of my plug tested with battery voltage, this was removed/tested/reinstalled while engine was already running.
I figured one was to turn alt on (either key on or ecu controled), and other an output for ecu/dash light. Didn't think both would show voltage.
​​​​​​​As soon as plug was put back in alt started charging, connections and plug looked good (no corrosion ect)
 
  #32  
Old 09-30-2018, 07:27 PM
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very interesting

Thanks for the heads up on the fixes you implemented...I'm still problem solving! I appreciate your time and effort.
 
  #33  
Old 10-01-2018, 04:32 AM
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Originally Posted by enormiss
I figured one was to turn alt on (either key on or ecu controled), and other an output for ecu/dash light. Didn't think both would show voltage.
According to the circuit diagram, both go back into the PCM. What goes on inide there is a mystery to me.
 
  #34  
Old 10-02-2018, 01:48 PM
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Originally Posted by enormiss View Post
I'm curious as to how all this works, As said by someone above you need to understand the problem to cure it...
1. What causes the in dash batt light to illuminate?
2. What are these two wires for?
Originally Posted by shadams3 View Post
I'm still trying to figure this all out myself!!!
Originally Posted by enormiss View Post
Both terminals of my plug tested with battery voltage, this was removed/tested/reinstalled while engine was already running.
I figured one was to turn alt on (either key on or ecu controled), and other an output for ecu/dash light. Didn't think both would show voltage.

In the test scenario you described ("engine was already running"), both wires should indeed show a voltage.

The expected voltage for both wires should be anywhere between 13-15 volts while the engine is running.

The voltage could be less than 13v if the glow plug relay is still energized (as it can be for up to 3 minutes after the wait to start light extinguishes, depending on engine oil temperature, and in such a case where the EOT was below 145 degrees, you just started the truck, and you immediately began your voltage testing, the voltage could be below 13v, but climbing until the relay timed out).

In a different testing scenario, with the key in RUN, but the engine NOT running, the voltage will be much less (between 1 to 3 volts) on the light green with red stripe wire (ignition circuit 904 that turns on the voltage regulator and powers the battery symbol light on the dash during self test and when there is a problem detected), while the voltage in the orange with light blue stripe wire (battery sense circuit 35 that does just that... senses battery voltage) will remain at 12.xx volts (if your batteries are decent). In this scenario, the red dash light will be illuminated, powered by the 1-3 volts measured on the light green with red stripe wire.

The only scenario where one of the two wires will show voltage, and the other wire will show zero voltage (like what you were originally expecting), is if the key is off. Then Circuit A, the battery sense circuit, which is the orange wire with the light blue stripe, will show whatever voltage your batteries are good for at rest... hopefully 12.50 volts like you previously found. Meanwhile, Circuit I, the ignition circuit, will obviously be off, since the key is off. Hence no voltage will be found on the light green with red stripe wire in that scenario.
 
  #35  
Old 10-09-2018, 05:49 PM
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Originally Posted by enormiss View Post
In my poking around I discovered simply unplugging and reconnecting the two wire connector got the alt charging again.
to update... The light came back on after 8days and couldn't get alt to resume charging, just finished installing new one
 
  #36  
Old 10-09-2018, 09:20 PM
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Have you checked the fusable links and the connection to the fuseable links ? A melted link or broken connection from the charge wire to the links is a know cause of repeated alternator failure.

follow the charge wire to solinoid on the inner fender well, unwrap the harness tape and inspect as well as put a ohm meter to the charge wire to test the links themself. Ford doesn’t sell new links so you will need to get a section of fusable link from Napa and rebuild it yourself.
 
  #37  
Old 10-09-2018, 09:24 PM
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Fwiw, The other wire Is the PCM power supply and also has 2 fusable links. Check them while you are in there.

removing the vacuum canister makes working in the area simpler to access. The 3 11mm nuts hold it in place are in the fender well on the tire side.
 
  #38  
Old 10-09-2018, 09:41 PM
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Thank you!

Many thanks, I haven't thought of this but will plan on checking them all this weekend, when the snow stops.. I appreciate it
 
  #39  
Old 10-09-2018, 09:52 PM
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Originally Posted by shadams3 View Post
Many thanks, I haven't thought of this but will plan on checking them all this weekend, when the snow stops.. I appreciate it
dont forget the grounds, the one by the starter solinoid and the fuseable links as well the engine to frame ground.... and while you are at it the PCM ground is on the driver side fenderwell right behind the airbox, it is tucked up under the fender lip.

after you clean up the ground wire and the body panel to get a solid ground be sure to coat The Whole thing with a spray protectant like battery terminal corrosion from CRC. This will help slow down future crossion.



 
  #40  
Old 10-09-2018, 10:48 PM
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Many thanks

Thanks so much for taking the time to reply with such a great reminder! Thanks
 


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