HELP! I am currently experiencing a horrendous charging fault which is now into its 4th week of investigation! I was driving to work and the interior lights started flickering suggesting bad battery or connection, or alternator charging fault. All the normal checks were done, ie clean connections, check battery, check alternator belt and the car ran for approximately 30 km's beforethe problemstarted again. The battery was changed and the car ran for approx 60 km's before it started again. I then checked the voltage at the battery and found it to be only 12 Volts, suggesting alternator. All connections were thoroughly checked along with belt and tension. At this point i also noticed extreme overheating on the pulley end of the alternator. The alternator was changed with a new one and the symptoms remained. After much digging around from mazda and the internet, i found out that this charging system uses a 'P-D' or 'Half-Monty' system where voltage regulation happens within the PCM and alternator. Again, after much investigation, the 'D' or driver signal should be between 1 to2 Volts at idle and i found it to be at 12Volts. Great i thought, the PCM is kicking out an incorrect Voltage to 'Drive' the base of the power transistor, i will replace that and problem solved! Not. I managed to get a PCM from an Auto Wreckers in Calgary, where i was assured it was working. I fitted it and the problems remained! I checked the harness from the PCM for various shorts, open circuits and it all checked out. After many more checks, ie replacing the main POS from the alternator output to battery and ensuring the whole engine,chassis and PCM were grounded properley, the fault still remains,ie alternator getting really hot and still not charging. Other tests i did included taking off the main POS cable from alternator output to battery, to simulate an 'unloaded condition.' Mechanically the car ran great with no overheatig of the alternator pulley and the 'unloded' alternator output got upto 17.5 Volts???? I am therfore at a stage where there looks like a major current draw 'loaded' and no major current draw 'unloaded.' Hope this makes sense to some of you out there. None of the codes match these symtoms. I am now wating for some divine inervention to help me out, thankx Mick Mc.

 

Have you had any of the amperage reading checked to see if the alternator is maxing out with amperage which would drive that output voltage down when max alt output has been reached? It does sound like you may have a tremendous draw on the charging system from your description mickmc.The question is what??
I think I would start by removing the fuses in the underdash fuse/relay box one at a time while watching that alternator output and see if removing one of the fuses brings output back up to near the unloaded condition where you were getting 17.5 volts. That is extremely high and should be closer to 14.5 volts. You should be able to remove all of the fuses with exception of 100A main, 30A INJ, and 50A IG KEY and still be able to have engine running for testing. Hopefully removing one of these fuses will give you a direction to search in.

 

Thanks for your suggestion. I will get hold of a current clamp and put it around the main POS cable from Alternator to Battery, the alternator is 70 amps rated so that will give me a major clue to see what is drawing 'loaded.' I will let you know in due course if this helps. Someome also mentioned the main battery POS Start cable, however the car starts great and doesn't sound like the second stage is sticking, although there is also the solenoid to consider. Any suggestions on this course. Note, the starter is in a real crappy position to be disconecting after the car is started and running! Thanx Mickmc

 

If the fuse pulling part in the fuse/relay box does not work out then we might just be looking at a short to ground in the main cable. Would not worry about pulling the starter cable just yet untill we have a little more information about what is causing the problem .

 

Put a current clamp on the main POS charge cable and it showed approximately 15 Amps 'loaded.' The pulley end of the alternaotor still getting red hot within 15 seconds or so of running car. !5 Amps a little high??? What seemed strange however is switched in some ancilliries such as heater, A/C etc and the amperage didn't change!!! Pulled all fuses except obvious ones you suggested and amperage didn't budge, still 15 Amps!! Also managed to get clamp around main POS Start cable at battery end, which showed approx 15 amps with IGN switch to On and approx 27 Amps when car idling! Ha Ha i thoght, i've found it! So what i did was manage to alter the POS Start cable at the battery end to start the car and then remove the cable so it was isolated from the vehicle. Before i removed the cable i put the clamp on again and there was no obvious current draw with IGN On and at idle. Marvellous i thought, this has got to be it, NOT. I put the clamp again on the main POS charging cable and the current dropped to approx 10.5 Amps but the Alternator is still getting red hot within 15 seconds or so. By removing the POS Start cable right at the battery i'm pretty sure i have isolated that circuit!! I noticed you mentioned in your last e-mail about a short to chassis of the main cable. Is thsis connected to the MAIN 100 Amp fuse and if so, how do i isolate it? Any more suggestions from these weird and wonderful results above? Thanks again MickMc

 

Anybody got anymore ideas before i burn the car! Thanx Mickmc

 

15 amps at the alternator output cable is peanuts. Was expecting to see maxed out at 70 amps or so?? Are you sure the amp gauge is accurate? Not making any sense the numbers you noted. Looks you could also isolate the battery/starter circuit out by removing the 100A main fuse after engine was running. Power to the EGI system should still be getting voltage from battery side. Are the alternator voltage readings changing as well when these checks are being made? That voltage reading you noted in first post of alternator volts changing from12 volt to 17.5 volts when alternator cable was removed is a good indication of alternator ouput being maxxed out.

[IMG]local://upfiles/1377/6A8B2F1652C746F0A737DE47A07D2E6A.jpg[/IMG]
The alternator output cable highlighted in green. Main cable to battery in blue.

 

Dont worry Mick, I'll fix it. Im great.

 

Hi everyone,
I am having exactly the same trouble, the only difference is that a service guy fused the regulator and installed the alternator = it was not spontaneous and accidental.
The story is HERE, together with some photos.

Needless to say how interested am I in finding out about the solution.

On Tuesday I have to drive to the only Mazda service in the country BUT I'm afraid they won't be able to solve the issue because 99% of their cliens are 'oil-change' folks.

Thanks for listening!

 

How did it end, if it did?
Was the second ECU blown?
[:-]