Ford 3G Alternator Ripple Voltage High. Regulator?

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I have a 2008 Ford Ranger 3.0 and have been chasing down a frustrating intermittent P0340 error and I'm trying to narrow things down electrically. Apparently sometimes these can be caused by a bad alternator.

I have one of those handheld battery testers and there's a charging mode test. I'm getting about 150 mV ripple. My understanding is that it should be usually below 100 mV.

Before changing out the entire alternator, I wanted to see if swapping the regulator + brush would change things. So I swapped out a regulator assembly from the junkyard and my ripple is 120 mV now. Still seems a bit high.

So my question is, on a Ford alternator is it solely the regulator and brushes that may affect the ripple, or could the stator (or contacts) affect that as well? Wondering if I need to replace the entire alternator.

Thanks!
 
I read Ranger fora and continually add to a "handbook" for my own use. I've an '05 Ranger 4.0l.
Here's the Ripple test from my notes, taken from Ranger-Forums.com

AC Ripple Test:
Use a Volt meter with AC volt setting at higher RPM.
Locate B+ connection on the back of the alternator, the Stud with the larger wire connected
Start engine
Have someone raise RPMs to 3,000 and hold it there
Test AC volts by touching 1 meter probe to B+ and the other probe to Alternator's Case (ground), there is no +/- with AC Volts so color of meter probe doesn't matter
AC Ripple under 0.50 AC volts is passing, so 0.49 is passing but................

Your alternator passed.

Your code comes up as, "Camshaft Position Sensor "A" circuit malfunction. I'd check its wiring.

This sensor went out on a 4 cylinder car I had years ago. It had a magnet built in which was pathetically weak compared to that in the replacement.
I do not know if the Ranger's 3.0l sensor is magnetic but I'd look there. They're cheap to replace even as a guess.
Someone will tell you, "These sensors rarely go bad..." Sure, but mine did.

How many miles on your Ranger?
 
Thanks! I've already replaced the camshaft sensor and synchronizer with the Motorcraft OE. The code is intermittent and comes in/off randomly.

Where did you get the 0.5VAC limit? On most vehicles they shouldnt ripple more than 0.1VAC (100 mV)
 
I ended up replacing the alternator. I did intend on taking this apart myself and attempting to diagnose, but noticed the bearings were starting to make noise anyways and the stator contacts were getting worn in from the brushes. Got a remanufactured unit for only $120. Trying to get individual parts like the rectifier, new regulator/brushes...wouldn't have been really much of a savings.

Before, my ripple was 140 mV @ 14.0V (idle), now it's 30 mV @ 14.4V with the new unit. I definitely think there must have been a diode starting to go bad in there. Hope this gets rid of the P0340 for good, but I'll have to drive it around a few weeks and see.
 
I ended up replacing the alternator. I did intend on taking this apart myself and attempting to diagnose, but noticed the bearings were starting to make noise anyways and the stator contacts were getting worn in from the brushes. Got a remanufactured unit for only $120. Trying to get individual parts like the rectifier, new regulator/brushes...wouldn't have been really much of a savings.

Before, my ripple was 140 mV @ 14.0V (idle), now it's 30 mV @ 14.4V with the new unit. I definitely think there must have been a diode starting to go bad in there. Hope this gets rid of the P0340 for good, but I'll have to drive it around a few weeks and see.
You have given away your age by saying rectifier. Now people call them diodes.

$120 sounds like a good deal on a reman alternator if it's a good reman. Time will tell.
 
I have a 2008 Ford Ranger 3.0 and have been chasing down a frustrating intermittent P0340 error and I'm trying to narrow things down electrically. Apparently sometimes these can be caused by a bad alternator.

I have one of those handheld battery testers and there's a charging mode test. I'm getting about 150 mV ripple. My understanding is that it should be usually below 100 mV.

Before changing out the entire alternator, I wanted to see if swapping the regulator + brush would change things. So I swapped out a regulator assembly from the junkyard and my ripple is 120 mV now. Still seems a bit high....
As mentioned, an oscilloscope with the vertical amplifier in AC mode is the only way to properly observe and measure ripple voltage.
 
As mentioned, an oscilloscope with the vertical amplifier in AC mode is the only way to properly observe and measure ripple voltage.
Yes but not easy to get a hold of for the average DIYer. I have one of those cheapo electronic battery testers and there's a charging test mode which shows the ripple and a very simplified waveform. Not the best and the unit technically categorized the test as "pass" but the decrease in ripple with the new alternator was definitely noticeable. It seems the old alternator was straddling around the grey area in functionality, which possibly explains why my check engine light was intermittent.
 
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