intermittent charging system failure

[crashoverride7]

ok here goes. about three weeks ago, on my way back from a trip to the beach, my alternator went bad. limped the car home, and got a reman unit from advanced. installed it and everything was hunky dory, and drove the car since. but two nights ago, my lights started going dim again, and i wasnt able to restart the car the next morning without a jump, and when restarted, it still wasnt charging at first. after a few minutes though, i revved it one last time, and the lights all popped back to normal and everything started charging again. ive already pulled the cluster to check the idiot light. and it lit with direct voltage.

{odd thing though, normally when i turn the car off, for the moment when the engine is spinning down, the battery light used to light up, now it doesnt do that. is there any way to trip the light while the cluster is connected, ie fooling the car into seeing a failed alt and illuminating the dash warning light?}

also....car is an prod date 9 85 eta.

[jlevie]

The generic rebuilt alternators from Advance, AutoZone, etc., are an iffy prospect. I wouldn't be surprised if your rebuilt is not working properly. The factory rebuilt alternators that your dealer can supply are more expensive, but they they are of OE quality.

[crashoverride7]

{go go gadget flame suit} i understand that an oe replacment is less of a gamble, but the price just doesnt work for me. i got the rebuilt for 89 bucks. and it is a factory unit, just rebuilt. testing at the battery produced around 13v. ive changed batteries with another car, and it seems to have made the problem go away for now at least.

{i could afford a brand new alt, but thats a weeks pay. if i have to exchange this alt three times, big deal. i still save 200 bucks.}

[crashoverride7]

ok, back to this post instead of starting a new one. the charging system woes have gotten somewhat better, but they are definitly not gone. ive replaced the alternator three times. with the same symptom. everytime i start the car, the tester reads 12v at the battery all day untill i rev the engine to 3k rpms. anfter that it jumps to 13.5-14v. and will hold steady there. but if i dont rev the engine up, it will just discharge the battery untill the car dies. and like i siad before. the warning light on the dash is not lighting up with engine off key on position. the book says it should. anyone got a clue as to what gives?

[jlevie]

You need to find out why the battery warning light isn't illuminating when the key is turned to the ignition position. On this car that light is a crucial part of the charging system and is the means of applying exciter power to the alternator. There could be a fault in the exciter circuit, in the cluster, or in the alternator. A bit of detective work with the wiring diagrams and a multi-meter should reveal where the problem is.

[crashoverride7]

as far as the bulb goes, its been tested and changed to no end. and i took the chance to sharpie my gauge needles red while i was in there. i have a spare cluster ill try next and post here with my findings. whats funny is this problem has a 30+year a.s.e master technician stumped as much as me.

[jlevie]

The problem could be bad solder joints or damage to the PCB in the cluster, a problem with connections in the C101 connection, or problems in the wiring on either side of C101. As I said, a bit of work with a multi-meter will pretty quickly tell where the problem is.

[crashoverride7]

im gonna bust out the meter tomorrow during class and see if i can find it. im also gonna dig out my old cluster and give that a shot. ill post if i figure it out. thanks for the help. its just so strange that it will charge after ive reved the engine past 3000 rpm and continue charging after that. but not untill.

[crashoverride7]

alldata isnt helping me here. anyone know a good source for the pinouts for the blure white and yellow connectors for the gauge cluster?

[jlevie]

See http://wedophones.com/BMWManualsLead.htm

[mikeedler]

replace the guage/cluster assy. I had a touring 5 years ago, the soldering on the board were bad and sometimes it would do the same thing. replaced the cluster and all was great.