Help with parasitic draw?

[StevieC]

The diodes can be bad but not show up in AC ripple but show up when the car is no longer running. That's why disconnecting the alternator over night would for sure rule it out.

I've seen diodes do weird things based on temperature. They operate fine when say room temperature to warm, but when they get cold or overly hot they start passing current the other way. It's like they are on the edge of failing and just need that nudge to push them over the edge. That being temperature.

Keep in mind they spend their life being beat up by continuous heat cycles.

 

[vwmaniaman]

It may be a hidden lamp like under hood or glove box or console, Don'y forget alarm systems.

 

[WyrTwister]

I agree , if it was me , I would try disconnecting poth the power and control wires on the alternator first . If that does not work , then start pulling fuses .

 

[LazyDog]

I had to use this procedure to find a problem with a bad module.
https://www.youtube.com/watch?v=lRcj1fQcWwU&t=333s

 

[buck91]

Alright so it looks like (and I never knew this) you can test for a bad diode by looking for AC current while the engine is running. Normal should be 0-1vac. I am seeing 31vac with a well charged battery testing out at over 1000cca on the parts shop monkey's handheld tester. Does this add up?

 

[StevieC]

Originally Posted by buck91
Alright so it looks like (and I never knew this) you can test for a bad diode by looking for AC current while the engine is running. Normal should be 0-1vac. I am seeing 31vac with a well charged battery testing out at over 1000cca on the parts shop monkey's handheld tester. Does this add up?


If you have 31vac showing up there is definitely something wrong with the alternator.

 

[buck91]

Originally Posted by StevieC
Originally Posted by buck91
Alright so it looks like (and I never knew this) you can test for a bad diode by looking for AC current while the engine is running. Normal should be 0-1vac. I am seeing 31vac with a well charged battery testing out at over 1000cca on the parts shop monkey's handheld tester. Does this add up?


If you have 31vac showing up there is definitely something wrong with the alternator.



One would think but I compared it to two other similar generation Fords which also were showing similar AC voltage... And neither of those vehicles have any issues iwth batteries dieing. One actually gets minimal use, maybe every other week!

 

[buck91]

clamped the multimeter probes on and left it hooked up for two hours this morning. Was reading 40ma every time I checked. Have it hooked back up, hoping to leave it sit until tonight.

 

[StevieC]

Originally Posted by buck91
Originally Posted by StevieC
Originally Posted by buck91
Alright so it looks like (and I never knew this) you can test for a bad diode by looking for AC current while the engine is running. Normal should be 0-1vac. I am seeing 31vac with a well charged battery testing out at over 1000cca on the parts shop monkey's handheld tester. Does this add up?


If you have 31vac showing up there is definitely something wrong with the alternator.



One would think but I compared it to two other similar generation Fords which also were showing similar AC voltage... And neither of those vehicles have any issues iwth batteries dieing. One actually gets minimal use, maybe every other week!


You might have non true-RMS type meter that isn't measuring properly. https://www.youtube.com/watch?v=7ZzwlklBbKc

 

[buck91]

Problem located and sort-of solved.

The CAN-BUS interface (Metra XSVI-5520-NAV) which I used to wire in my Alpine radio a couple years ago is the source. Tried re-flashing the firmware without change. Replaced with a new can-bus interface, no change. Re-flashed the firmware and reset the BCM and slight improvement. Went from 0.96A to 0.83A drain. Reinstall factory headunit, under 40ma drain. Now why would this become an issue two years after install and why would it continue with a completely new interface unit?

Crutchfield has a different brand interface (Crux). Has a 60 day money back guarantee, so I guess I'll order one and see if it works correctly...