New alternator, still not enough voltage

[colo525i]

Hah, I'm about at that point myself!

[colo525i]

Well after all this it is fixed. a $4 4gauge battery cable that has the same size post openings as the ground strap fixed it. I checked the resistance and connections on the ground, without taking it out and flexing it. When i did that it made a sickening crunching noise, not enough wire to move the current needed. Takes a while for the OBC to show 14.1 after you go from a stop, but driving down the road it never dips below 13.7. Problem solved.. finally! Thanks to Bill G for reminding me about the "just because there is no resistance doesn't man the cable is good" principle.

[bsell]

Well after all this it is fixed. a $4 4gauge battery cable that has the same size post openings as the ground strap fixed it. I checked the resistance and connections on the ground, without taking it out and flexing it. When i did that it made a sickening crunching noise, not enough wire to move the current needed. Takes a while for the OBC to show 14.1 after you go from a stop, but driving down the road it never dips below 13.7. Problem solved.. finally! Thanks to Bill G for reminding me about the "just because there is no resistance doesn't man the cable is good" principle.

Glad you found the nasty bugger!

Did you think about redoing the voltage drop test to see if that got all of your problem? The reason I ask is the positive cable is just as old (but doesn't see the same flex) as the ground cable and could be corroded internally causing high resistance to massive current flow...

Brian

[colo525i]

Well i spoke too soon. While the car will run the first time you go with 14.1 volts with full load, (headlights/ac/radio) As soon as you slow down into city traffic with that amount of load, the voltage dips and never recovers. If i charge the battery externally it will run up to 14.1 again, but will fall as soon as you get off the highway. Could there be something wrong with the battery as well?

[bsell]

Well i spoke too soon. While the car will run the first time you go with 14.1 volts with full load, (headlights/ac/radio) As soon as you slow down into city traffic with that amount of load, the voltage dips and never recovers. If i charge the battery externally it will run up to 14.1 again, but will fall as soon as you get off the highway. Could there be something wrong with the battery as well?

Sounds heat related...did you check all of the other connections/wires back to the battery to include cleaning all of the grounding points?

I wonder if you have a rotten cable running along the floorboard from the engine to the battery that gets hot and resistive over time. I swear I've seen this kind of mess before and finally found it by flexing a positive cable and hearing the crunching noise from the corrosion under the insulation. To look at the wire, you wouldn't have suspected it was garbage but once I cut the insulation off of it, what a mess!

You can find the culprit, you just have to hang in there and be thorough in your search.

[colo525i]

Ok figured out the common thread to all my "low voltage times" It had either rained earlier or was raining meaning high humidity. I am thinking something in the engine bay as it would be most affected by outside humidity changes. I am going to try to patch between the b+ post and the alternator output to see if that helps.

[bsell]

Ok figured out the common thread to all my "low voltage times" It had either rained earlier or was raining meaning high humidity. I am thinking something in the engine bay as it would be most affected by outside humidity changes. I am going to try to patch between the b+ post and the alternator output to see if that helps.

High humidity created electrical problems makes me think crusty grounds are at fault, as in a connection or wire somewhere (outside more than likely) has an air gap (due to corrosion) that gets more resistive with increased humidity.

I had an older Skyline that stumbled coming off-idle when it was hot out. Chased it for a year before finding it. The internal connection from the circuit board in the MAF to the external connector had broken the solder on all six-eight pins. When it got hot or humid out, the resistance would pop up due to engine movement and cause the stumble. A quick re-solder and away she went for the next four years (sold the car).

Seek and ye' shall find...

Brian

[colo525i]

Had the same problems this morning with low voltage. Decided to pull the grounds near the front turn signals. Sanded down all the connectors even though they were fairly clean. Voltages came up and have stayed up since. It shows 14.17 while running on the OBC where it only would peak at 14.10. Fingers crossed they were just resisting a bit..

[colo525i]

Hate to revive an old thread but my problems have not gone away. I have bypassed every bit of wire from the alternator to the battery to see if i could find a bad piece of cable, but to no avail. I am on my second replacement alternator with the same results, low voltage when loaded. Here's my list of replaced stuff. Alternator x2, ground strap, battery (new duralast). I have even tried to bypass the front cable from the alternator to the B+ post but with no change. Is there any other part of the charge system at all? 2 shops have been unable to figure out what is going on, the bmw dealer charges $100/hour labor, at which point i'd be better off scrapping the car.

[colo525i]

Well after all this, it turns out i am a moron. The belt was on wrong, going over the idler pulley next to the alternator instead of under it. The belt was loose, but not squealing. It is also much easier to get the belt on this way If anyone has a random problem like this, make sure to check the belt routing, it is far too easy to overlook!