[Barneyhyphen]

hey guys,
I was having some problems with my 1999 323i's battery yesterday. I tested the alternator with a voltmeter and it was putting out about 9.3V. I had the battery tested and was told that a diode was blown in the alternator. So I bought and installed a new alternator. Immediately after fitting it, I ran the voltmeter across it and found it to be putting out about 13.5V. I then drove it around the block and after ten minutes all my electronics started going haywire. I tested the volts on the back of the alternator again but now its only putting out about 8.9-9.3V.:hmm: It appears the new alternator has already blown a diode. Please advise, anybody who knows what happening.

Thanks,
BH

 

[wdeerfield]

did you replace the better as well? always a good idea to do the battery when you change the alternator.

 

[Barneyhyphen]

No, battery not changed as it appeared to test out well. New alternator seemed to be putting out a good charge for 5+ minutes but then obviously popped another diode??

What could cause a diode to fail so quickly?

assume the heavy red wire from the back of the alternator eventually ends up at the battery in the boot/trunk as we are getting continuity between the red wire in the engine bay that attaches to back of the alternator and the other end (?) of that same wire at the + battery clamp.

Any thoughts on the diode problem?

Thanks.

BH

 

[330ciandr6]

u can test the voltage at the battery to see if the alternator is charging. but...sounds like u bought a bad alternator. i've seen it before

 

[Barneyhyphen]

So, if I hook up a new (good) alternator, to an undercharged battery, say one holding only 9v, and jump the car, from another car, to start it, the new alternator may have to work too hard, in an effort to "recharge" the poor battery and, in it's efforts, blow a diode?

Is this a possible scenario?

BH

 

[330ciandr6]

well...u can possibly also have a bad battery. even if you had a bad battery the alternator should still be putting out about 13v even if the battery is bad. if you have a bad battery the alternator isn't gonna have to work harder, its gonna do the same thing as it would with a good battery, just try to charge it

 

[hummer]

So, if I hook up a new (good) alternator, to an undercharged battery, say one holding only 9v, and jump the car, from another car, to start it, the new alternator may have to work too hard, in an effort to "recharge" the poor battery and, in it's efforts, blow a diode?

Is this a possible scenario?

BH

There was a caution tag on my new Bosch alternator that said: "Do not operate a new alternator with a discharged battery. Fully charge the battery first."

 

[MachRc]

when my alternator crapped out, i got a "rebuilt one" , that failed in less then a day...

the dealers sell two types of alternators.. one 9 and the other 12v for accessories.. i went with a 12volt and a new battery.. and stopped carrying the battery charger in the trunk..

once your battery dies and goes to the point of no return, you cant jump start it or recharge it becasue it is dead.

 

[Barneyhyphen]

PROBLEM RESOLVED.

Having had the original alternator tested three times (good first time, bad diode second time & good third time), now believed to be good and back in the car.

Battery tested four times (ALL FOUR told to be GOOD).

Last night, replaced the battery with a Duralast 94R-DLG from Autozone and the car drives like new!

Symptoms were continued CEL's, random misfires, cam position sensors, etc, etc.

Replaced two coil packs and plug boots, both cam position sensors and both intake bellows. Have now refitted all old parts, except for one coil pack/boot and will save all newly purchased parts for when they actually fail!

BAD BATTERY. Thanks for all the help here from everyone.

BH