318ti.org forum - View Single Post

**cooljess76** · 08-04-2010, 10:23 PM

Mine did the same thing. Had me confused for months. I kept killing batteries, it would take about 3 months for one to die. After three dead Diehards and 3 rebuilt alternators that all bench tested good, I was at my wits end. Basically I was in the same boat as you. I was ready to start grounding everything to everything. I was getting a fluctuation between 10-11v at the back of the alternator and across the battery terminals. I knew I should have been getting around 14v. Then one day, I was replacing my radiator when I decided to go ahead and degrease the front of the motor since I had the fan and radiator removed. I decided to remove the belts for better access at which time I accidentally snapped the A/C compressor bracket. Upon removing the A/C compressor bracket, I noticed the main engine ground. It attaches to the passenger side frame rail(chassis) and the passenger side motor mount arm. There wasn't much corrosion, but I noticed a lot of pitting on the cable end where it connected to the chassis. My only explanation was that it had a poor contact and would build up enough energy to create an arc and jump across the cable end to the chassis. This explained why I was getting a fluctuation in voltage and charging system failure. As soon as i got the car back together, I cleaned the mating surfaces on the motor mount arm and the chassis frame rail, and replaced the cable. Fired it up and checked the alternator with a multimeter. BINGO 14v!!!

If jumping the engine to the chassis corrects the problem, then your main engine ground is certainly the culprit. I recommend scrubbing the sh!t out of the cable and both mating surfaces with a stainless steel wire brush or lightly hitting them with a grinder(just make sure to leave the mating surface as flush as possible to maximize contact). You should also check continuity through the cable itself. It may have a corroded or broken segment under the insulation that you can't see. They sell heavy gauge grounding cables in the battery section at your local auto parts store, you don't need to special order the BMW part.

08-04-2010, 10:23 PM	#8
cooljess76 NOBODY F's with the Jesus Join Date: Oct 2006 Location: Ventura California Posts: 7,824 iTrader: (6) Photo Gallery	Mine did the same thing. Had me confused for months. I kept killing batteries, it would take about 3 months for one to die. After three dead Diehards and 3 rebuilt alternators that all bench tested good, I was at my wits end. Basically I was in the same boat as you. I was ready to start grounding everything to everything. I was getting a fluctuation between 10-11v at the back of the alternator and across the battery terminals. I knew I should have been getting around 14v. Then one day, I was replacing my radiator when I decided to go ahead and degrease the front of the motor since I had the fan and radiator removed. I decided to remove the belts for better access at which time I accidentally snapped the A/C compressor bracket. Upon removing the A/C compressor bracket, I noticed the main engine ground. It attaches to the passenger side frame rail(chassis) and the passenger side motor mount arm. There wasn't much corrosion, but I noticed a lot of pitting on the cable end where it connected to the chassis. My only explanation was that it had a poor contact and would build up enough energy to create an arc and jump across the cable end to the chassis. This explained why I was getting a fluctuation in voltage and charging system failure. As soon as i got the car back together, I cleaned the mating surfaces on the motor mount arm and the chassis frame rail, and replaced the cable. Fired it up and checked the alternator with a multimeter. BINGO 14v!!! If jumping the engine to the chassis corrects the problem, then your main engine ground is certainly the culprit. I recommend scrubbing the sh!t out of the cable and both mating surfaces with a stainless steel wire brush or lightly hitting them with a grinder(just make sure to leave the mating surface as flush as possible to maximize contact). You should also check continuity through the cable itself. It may have a corroded or broken segment under the insulation that you can't see. They sell heavy gauge grounding cables in the battery section at your local auto parts store, you don't need to special order the BMW part.