[paul]

Little long ..

Car is my '97 328i - mileage is approx. 220K - hard to read w/ dead pixels.
Alternator replaced last July. Battery is approx 3.5 years old.

Last drove the car last Friday and sat all weekend on the driveway. I remembered some additional cranks to start but thought nothing of it. Yesterday morning - started but weak (instrument lights dimmed a bit). Drove to the office (around 7:30) and left it thinking - need to check that battery later. Around 1 PM - checked the voltage and it was less that 12V (11.7). Got a jump and drove to Advance Auto and they checked out the battery and he said battery looks good. Must be the charging system or some short. The guy insists I should be reading 14+ V at the battery when running. Is this true?

Got home - did some measurements.
With engine running - voltage at battery is approx 13.4/13.5V (same as the terminal in engine bay). Got the wife to rev the engine to 2K/3K and voltage drops to 13 and less (12.9ish). Is this normal? Don't know.

So - it seems to me there are 3 possibilities
1 - Battery
2 - Short
3 - Alternator/charging circuit

In order to remove the battery as a problem vs. short.

Charged the battery w/ external charger for a couple of hours. Once charger disconnected, battery was at 12.9. Left it disconnected overnight until this morning (7-ish). Voltage at 12.45V. Re-connected ground and started the car no hesitation. Got to work (approx 30 minutes) and checked voltage w/ engine running - 13.3V. Disconnected ground - voltage at 12.47V. Left it disconnected.

Do the numbers look right? If all is right w/ the world - shouldn't the battery at the end of my commute be more than 12.47?

I plan on checking the voltage in a couple of hours to see if dropped any.

Appreciate any insight/suggestions

Paul

[Vicegrip]

Reving the motor should not produce a voltage drop if the charging system is working properly. Based on the details you presented I would go over the charging system. Start simple and check all the wires, connections belt and anything you can see, feel and smell.

[cmartin]

I'm pretty impressed so far with the voltage tester I recently picked up. Nothing fancy but feel free to stop over if you want to check it out. Assuming good connections/cables I like to put a load on the system and check voltage.

[paul]

sent you pm

[LPM911]

grounding strap?

[paul]

I checked the battery about 30 minutes ago - approx. 12.4 and started normally. I borrowed a clamp-on ammeter and placed it on the ground. Turned off the engine and it's showing a 2.7A draw. Looks like I have a short.

[Vicegrip]

Originally Posted by paul

I checked the battery about 30 minutes ago - approx. 12.4 and started normally. I borrowed a clamp-on ammeter and placed it on the ground. Turned off the engine and it's showing a 2.7A draw. Looks like I have a short.

Most clamp on amp meters are for AC unless they are self powered or made for automotive. Another way to find a short is to disconnect one battery lead and read amps between the terminal and the lead. If there is a draw you go fuse by fuse pulling and replacing until the draw drops off. A real poor mans/side of the road way to find a draw is to take some stranded wire and part the strands until there is only one strand. Use the wire from post to lead looking for a little spark when to brush the strand to the post. A 2.7 amp draw will make a notable spark and drain a battery in short order.

[paul]

I used a DC/AC clamp on - battery powered. It's looking more like there is some short somewhere. I will check the current draw using a meter and start pulling fuses.
Thanks for all the suggestions

[Vicegrip]

Originally Posted by paul

I used a DC/AC clamp on - battery powered. It's looking more like there is some short somewhere. I will check the current draw using a meter and start pulling fuses.
Thanks for all the suggestions

good^ Some ammeters will give an odd reading with DC and it sucks to be faked out by a bad test.

Good idea to test the DC output voltage from the alt for AC too. This can let you know when things are going bad but not all the way bad just yet.

[paul]

Update

I believe I have found/fixed the issues. Started fine this morning

The wire bundle from the trunk lid to the lights - cracked insulation and exposed wires touching. Also the trunk light wiring was causing a "short" condition - drawing approx 670 mA with ignition off. Left it disconnected for now.