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Discussion Starter #1
hi everybody,

another 4 cylinder Mazda6 with charging problem here :(

The problem started last October. Battery light came on, along with check engine light, dsc and asc lights. I have a tablet installed in my dash and and OBD scanner, so using Torque app I was able to check voltage at PCM...it started dropping out of nowhere, momentarily, under 12V (11.5-11.7) and triggered all the warning lights.
I went to a local specialist shop (ex Mazda dealer), and decided we should change the alternator (we talked about repairing my current one, but there are many cases that with the aftermarket parts used in the repairs, the PCM no longer communicates with the reman alt properly). Due to cost of a new alt here (about 750 euros), we went ahead and installed a used one from a low milleage donor. Everyhting was ok until last week. The dreaded battery light lit again.
We tried again another 2 used alternators but nothing improved...undercharging again...I remanufactured my old alt after I was reassured by the mechanic that this particular alt part no. was ok for remanufacturing (I even got a 1 year warranty) but again battery came on after installation.

I then, tried to monitor what was going on with voltage, using the app and I found out the following:

In the morning when everything is cool, and no ac is used, it works fine..no voltage drop...charging V is constant at 13.7-13.8V...as engine starts to warm up, the charging voltage starts to drop a little gradually down to 13.4-13.5V but no problem at all....I even turn on headlights, rear defroster etc but again everything ok...just 0.2-0.3 drop of voltage for a split sec and back to normal as expected.

When I use a/c it is totally different...the drop in voltage when ac fan turns on, is significant (more than 1.5 volt). So that leads the charging voltage to fell below the 12V mark and the dash to lit up like a christmas tree. When that happens car also stumbles for a second btw.

I think the possibility that 3 different alternators are all bad is very slim...something else must be going on..maybe faulty PCM or cracked cables somewhere between pcm and alt??

The fact that charging voltage drops when engine gets warm is a clue...as is, the excessive, I believe, draw of power from ac fan (I don't know if it normal or not)..

The belt is less than a year old with no slack at all, and the battery is a few months old (the most expensive of the Boch line of batteries)..

I took some measurements with a voltmeter

Alt (+) --> bat(-) 14.13V
bat(+) --> bat(-) 13.96V
Alt(+) --> ground point near alt 14.08V
bat(+) --> ground point near bat 13.99V

these all seems normal and were taken with car engine being cool...

One final fact that might, or might not, be a clue, is that very often latelly, when I get out of car and touch the metal part of the door, I feel a small instant discharge shock on my hand...maybe some kind of voltage leak somewhere??

Any ideas could be very helpfull...I already booked an appointment with official Mazda dealer for next Monday, but I would appreciate and use any reccomendations until then...

Thanx everybody in advance

PS: I visually checked all ground points I could find, and cleaned them, but no change at all...I went out and bought a few meters of 2.5AWG cable to improve grounding and maybe connect directly the battery to the alternator to see if anything happens....
 
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