1988 735i electrical problems

[djgap]

While driving on a 150 mile trip this weekend, after about 50 miles, I noticed the "Anti Lock" light on the dash coming on. Not too long after that, the power was obviously disappearing quickly - my cd player shut down, then the OBC display disappeared and the headlights became very dim. I pulled over, shut down everything that might be a drain on the battery and let the car idle while I tried to figure out what was going on... Ater a few minutes, the anti lock light went out and the OBC display lights came back on again and a few minutes later I tried the headlights and everything seemed fine again. I started on my trip again and all was well for about 10 miles then the same thing happened again... this scenario repeated it a few more times, then after the 3rd or 4th occurrence it ran fine for the remaining 60 miles of my trip.

On my return the next day, it continued to run fine until after about 90 miles when the problem started all over again. This time, it never rectified itself and I managed to nurse the car home with very dim headlights for the last 45 miles.

Any idea what the likely cause of this is before I start shelling out big bucks to a mechanic to go troubleshooting?

Gary

[txhousedog]

i would start with the battery first. have it checked out,

[Bear]

Yes, battery but more importantly the alternator voltage as well, at idle the alternator should produce 13.5 VDC to about 14.1 VDC. There are hidden OBC tests that you can use in flight (I believe hitting 1000 and 10 at the same time while engine is running should give you the test prompt, use 1-10 key to get to test 9 and then hit S/R and you should see the alternator voltage (I used this all of the time in my 1988 750).

[Bear]

Yes, battery but more importantly the alternator voltage as well, at idle the alternator should produce 13.5 VDC to about 14.1 VDC. There are hidden OBC tests that you can use in flight (I believe hitting 1000 and 10 at the same time while engine is running should give you the test prompt, use 1-10 key to get to test 9 and then hit S/R and you should see the alternator voltage (I used this all of the time in my 1988 750). This is a good test to catch the alternator voltage when driving as it can be used when you get the power drop.