Voltage issues

Wings65288

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Very cool you found it. I was also gonna mention the ground wire for the alternator. It's one of the two wires that's on the alternator connector. It usually gets disconnected cuz when people change out their alternator they yank on the wire to get that connector out. The ground is very small and can become very weak and will mess with the voltage exactly how you described.
 

Blown38

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Cool deal! I'll have to break out the EVTM and see what I got. I have removed a couple components from the car. Like the cruise control motor, the horn wire runs thru that. So if you remove cruise the horn no worky.
 

04torchred

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So after all my testing i have finally found the issue. So i was not getting good voltage to 2 out of the 3 B+ inputs to the pcm. After some testing i found the issue to be a bad ground to the body. The one good B+ input to the pcm must have been getting its ground from the engine and the other 2 from the body. Problem solved


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Do you have a picture of what ground you improved/fixed?
 

First-on-race-day

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Do you have a picture of what ground you improved/fixed?
My engine was grounded directly from the battery in the rear of the car with a 2gauge wire. I then found a spot near the original ground to body wire right by the oil filter and ran a 2gauge wire from engine to body

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testorossa1989

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So I had similar things going on that would drive me up the wall trying to figure out why my car's battery died after sitting for 2-3 weeks w/p parasitic draw. This is the conclusion...

The fan on low draws a f-ton of voltage when you're just sitting still in park testing it. If it kicks onto high, enjoy the worry feeling you get when you see that voltage number. Here's the reality, certain alternators function differently and with pulley setups people sometimes over/under spin the alternator. If you suspect a charging issue, you shouldn't be testing voltage since an alternator is a rectifier. You want to be testing for charging differences not DC voltage. The number changes all the time and only tested & true when a battery is removed and tested 24hr later. That being said, you'll see the numbers vary while idling. Remember your car is not really charging itself when it's idling as much as it's maintaining itself.

Finally, if you suspect power draw or other issues.... DO NOT Jump a fully dead battery & let the alt charge it up. All that does is put unnecessary excessive load on the alternator which will lead you to replacing the alternator before seasons over. It only takes 2-3 times of doing this practice before you start seeing a issue depending on modified your car is. The alternators have a difficult time as it is with the insane engine bay heat and load from the blower, don't add another thing to the list. Also, each battery charges differently!! I believe Red Top AGM type battery only have something like a 10v max static holding charge. Very each to kill a battery when you start playing with different type batteries. I suggest using a battery tender. Saves yourself the headache later

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