new battery, new ALT, battery wont stay charged

[Silent_White]

The alternator outputs about 12.5 volts when the car is running. The alternator and battery are new, less than a week old... the old alternator and battery had the EXACT same symptoms.

If the car sits for a while it regains enough juice to start just fine. if i try to start it right after i turn it off, the battery is low enough that it barely turns the starter and often kills the battery. A jump will start the car every time, and the 12.5 volts output from the alternator are enough to keep the car running again until i shut it off.

I replaced the battery first, then the alternator.. what next??

Battery cables are very tight and not corroded at all.

 

[dsm'r sk1mp]

ok New battery, new alt, new fuse. still wont charge the battery. i did a load test at the battery and it was at eleven and a half. alt puts out thirteen and a half. I have bought brand new terminals and connections and it still wll not charge this battery.

 

[turbo98eclipse]

at the battery it was 11 and the alt was 13? this would tell you its SOMETHING in between the two-- you said you got new terminals or new CABLES? the wire between the alt/bat may have a short or an open-- try testing the resistance in that wire from end to end to see if its infinite or not (or just really high resistance)

 

[Silent_White]

Ok, I'm hi-jacking my own thread back. i have tried 3 different ECU's brand new battery, and new alt. I've checked all the fuses. I used my multimeter to check continuity on the 4-pin alternator plug. toned out the red one and traced 2 of the wires back to the ecu. This leaves the black/yellow wire (L terminal at the alt) going to the generator relay (not an actual relay).. not sure where to trace this wire back to? does it go from the alternator to the generator relay under the air filter, or to the charging light?

basically, the alternator hovers between 11 and 12.5 at the alternator during idle. at 2500rpms it will hold around 14.1. but the idle voltage is simply too low, lights flicker, radio turns on and off... very annoying.

I have that one wire (black/yellow at the L terminal on the alt) to trace back to its origin as soon as i can figure out its path. Other than that im stuck with replacing the alternator again. (it's a remanufactured alt from Oriley's)

 

[AndrewD5418]

Did you check the two white wires? They run from the alternator to the alternator fuse. Then the alternator fuse to the battery. I ran all new 4awg charging wire on mine because stock uses two 8awg and I just don't like that.

Sent from my DROIDX using Tapatalk

 

[Silent_White]

yes i did check them and they are good

 

[jmitch]

Run you some 4ga wire from alt to battery, and since it seem u checked everything under the hood have you tested anything inside the car to see what voltage its getting?

 

[Silent_White]

voltage at the alternator is roughly 12.5, running a larger wire to the battery wont raise the voltage at the ALT...
Ive measured voltage at the alt, the battery, with dsmlink @ the ECU... doesnt really matter though. if i had 14 at the alt and it wasnt charging, id start testing voltage in other areas of the car, connections and grounds.

SO... The big question still remains. where does the black/yellow wire on the L terminal at the alt go to? Does it just go to the generator relay?

 

[TSI_AWD_FTW]

sounds like a bad connection i had the same problems, and i went threw many alternators and batteries it stumpted me, then i checked all the wiring and found a bad ground.

 

[j_biggz]

Good information here. I am having a very similar issue with my gst. Starts with a jump and and is getting between 11.9-12.7 at the battery. I will have to test it at the alternator. I have already replaced the connection points at the battery but with no luck. Very glad I looked on here. Thank you everyone. I will report back.

So I did the test today with my multimeter and at the alternator with the ground on the battery I am getting 12.4 at idle and 13.0 -13.4 at 2500 rpm. Now at the battery I am only getting 11.5 at the battery. I have checked the fuse and it looks like its in good shape. I couldn't pull it out because its bolted on and didn't take it apart. From my understanding from calling parts stores the 100amp fuse is a dealer item, well at least in my area. I also have replace all the end connectors with copper and made sure they have a good connection. Any ideas or is it time for a high output alternator?

 

[andreikali9]

I have the same problem, trying to trouble shoot it right now, while the car is running the voltage drops really fast while the car is running, alt was tested at advance auto parts and it seems to be working fine, tried 2 different batteries its doing the same thing.

My engine harness was recently pieced back together and it was running fine after that hopefully there is no issues because of that.

fuse and relays look fine, my mechanic seems to think its the alternator. I just don't want to buy one and find out its not the problem.