Voltage drop @ idle

[rootusr]

I never know how to start a thread, so first, the back-story:
I got a 1995 Mazda B2300 from my dad last summer. I've known/driven the truck most of its life. It currently has 225K miles on it and back in december, it got put in the driveway. And it sat. I call it the doom truck (plate is DOOM TRK)
Around the end of may, I finally had a chance to figure out what broke, and start fixing it. The safety inspection had expired last december (2009) and registration had expired in April.
In a month, visiting my parent's house after work (full-time software developer), I managed to fix:

• Rear leaf spring mount (drivers side)
• Blend door (the hybrid-hard way)
• fuel filler neck
• seafoamed the intake (NOT the oil)

And now the truck drives juuust fine.

This brings me to my current predicament. When idling, with the air set to 'off' the truck is fine, no problems to really complain about. When I turn the air/ac/max ac on (any temp any fan speed) the voltage starts fluctuating and the idle gets slightly rough, and then about 2-3 times a minute, the voltage will drop a LOT and you'll basically hear a missfire (as if the timing was dropped significantly, or the spark never happened) and the voltage needle will drop and all of the needles on the dash will begin to drop due to lack of voltage. if I just tap the gas pedal however, everything is fine; the needles go back to the correct position, voltage goes back up, truck sounds happy. When I'm driving, there is no issue with voltage.
I've done a bit of research and I've already decided I'm going to redo the +/- wires from the battery since they're the original ones that came on the truck. The battery is good (it had damn well better be, I just replaced it because I left it connected for 6 months and destroyed it).
I'm wondering if anyone can offer any suggestions of other things to check, I just found it weird that it only seemed to happen when the blower was running.

Things remaining to be fixed on my truck:

• Voltage-drop@idle ONLY w/ blower running
• Washer-fluid squirter doesn't work
• Alignment (not looking forward to this)
• Fix steering (might be related to pitman arm or alignment)
• Repaint the bed / cut fender rust

Thanks!!

 

[gwaii]

see if you can find a smaller pulley for the alternator....it's not turning fast enough at idle to feed the draw on the system.a smaller pulley will make it spin faster.there is a chance that the alt was changed in the past to one that had a bigger pulley or the alt could just be getting weaker,but a voltage drop at idle is pretty normal-but annoying when it has that much effect on running.there might also be an issue with the ecm,as if i recall correctly,max a/c should kick the idle speed up a bit.

 

[rootusr]

see if you can find a smaller pulley for the alternator....it's not turning fast enough at idle to feed the draw on the system.a smaller pulley will make it spin faster.there is a chance that the alt was changed in the past to one that had a bigger pulley or the alt could just be getting weaker,but a voltage drop at idle is pretty normal-but annoying when it has that much effect on running.there might also be an issue with the ecm,as if i recall correctly,max a/c should kick the idle speed up a bit.

Hmm. interesting. I know that the serpentine belt is worn (significantly) and so it might not be 'gripping' the alternator as well anymore...

I'll try changing the wires and belt and see if that fixes it. Thanks for the suggestions.

 

[martin]

Check that the a/c compressor is not seized. Also might want to check that the crankshaft damper pulley outer has not become unglued from the inner. these suggestions might seem bizare but I have seen it happen.

 

[rootusr]

Check that the a/c compressor is not seized. Also might want to check that the crankshaft damper pulley outer has not become unglued from the inner. these suggestions might seem bizare but I have seen it happen.

Ok, would I still get cold (really cold) air from the ac if the compressor was seized? The damper pulley would be under the front casing of the engine I assume?

 

[kemo]

If your ac compressor is seized, you will not be getting any cold air. Our ac compressor was seized on our 94 suburban, and you KNEW it was soon as you tried to turn on the ac. The belt would fry.

 

[rootusr]

Ahh, I am getting lovely crisp cold air (though every once in a while the blower cuts out when on max a/c...)

 

[trader007]

so it does it just with the blower motor on and not the a/c as well? in any case, it sounds like a new alternator is in line for you. blower motor sucks a good amount of electricity and alternators commonly do what you describe. try putting a load tester on the battery while the car is running (scratch that, i meant put a different 30a load on it. most load testers are only to test batteries while not running). it should do the same thing. it probably idles rough because its not getting enough voltage to spark/work properly.

 

[martin]

If the a/c is working then the compressor is obviously working ,you did imply that the belt was quite worn. The damper pulley is the one on the front of the motor that the serpentine belt goes round and drives all the accessories. It has a steel inner and a steel outer that is joined together by a moulded rubber piece. If the rubber part becomes seperated the inner part can rotate without the outer and is usually only a problem at lower rpm until it becomes really loose. you can check it by making a chalk mark across the front of the pulley and running the motor for a few minutes, if the chalk marks do not stay aligned then it's rotating. I've seen this a few times over the last couple of years but never on a ford.

 

[rootusr]

Thanks for all your suggestions!
I think I'll start with redoing the main wires off the battery, then move on to the alternator (I think autozone does free testing?) then I'll check the damper pulley. I've had one of those fall off an engine while driving, it was definitely an "oh sh**!" moment

I'll keep this thread updated as I go, and I really should start a 'repair thread' somewhere as I really have done quite a bit to this truck in the past month... tonight I wire the right back-up lamp to the left one in order to pass inspection