ok i have a problem with my voltage. i can't seem to find the problem so i was wonding if anyone could help. I have a 250 amp alt with 2 runs of 0 gauge 3 batteries one is 100ah and the other is 139ah. Plus the blue top under the hood. The amps are a sundown 2500 on 4 12 skars and a sundown 1000 on 2 skar 8s and a old school Rockford 1500 on the highs. But at full tilt I drop to 11.8v and driving 12.2v idk what the problem could be. all grounds are to the frame and i did the big 3 all 0 gauge. all batteries tested fine. If u have any suggestions please let me know. Thanks!

Hm.. Well if your driving and your only at 12.2v, Id say it might be a bad alternator.

What is your voltage at idle with the system off?

i thought that the alt might be the problem as well but it did the same thing with my stock one. and my voltage at idle is 14.1

Could be one of a few things. Possibly a bad voltage regulator or a bad connection between the alternator and PCM. Maybe even a bad battery.

Could be one of a few things. Possibly a bad voltage regulator or a bad connection between the alternator and PCM. Maybe even a bad battery.

ok, would there be a way to test to see if that might be the problem?

unhook your runs to the rear.. take it to autozone and have them load test the alternator

i had autozone test it and they said it did 240 amp at 2000 rpm... but autozone also told me 2 of my old batteries were bad and there were fine when i had a mechanic test them lol. i don't really trust autozone people they really dont know what their doing. im going to take my car to a real alt guy next to where i live and see what his machines read.

You would need to test your batteries individually. Not just for voltage but a load test.

Make sure you have continuity from one end of your plug that goes to your alt to wherever the wires go to. Probably two or three wires. Your connection is probably a S-L-F type. One wires senses battery voltage, on 5v turn on for the alt and another is a field voltage wire that goes to the pcm. This is a common hook up yours could be different.

Well if autozone says you have 2 bad batteries.. That could really be messing with your voltage. Why trust mechanics at one shop compared to another? Unless they have done something to prove that they are wrong.

Well if autozone says you have 2 bad batteries.. That could really be messing with your voltage. Why trust mechanics at one shop compared to another? Unless they have done something to prove that they are wrong.

no i was saying 2 of my batterys that are not in my car anymore i sold them, autozone said they were bad but they were fine.

and edouble i belive that is most likley the problem beacuse i seen my stinger voltage meter go to 16v something once for 10 sec and was blinkning and over the weekend my car wouldent get higher voltage then 13.5 driving with system off. just a whole bunch of different issues.

OH alright, understood.

I have seen high voltage spikes with two different aftermarket alternators but not with the factory alt. In my instance the voltage regulators in bith of the aftermarket alts were not compatible with my vehicle for whatever reason.

16v to factory electronics is not good.

Excessive amperage is working on one of my alts now. He said that best thing to do is to use an external regulator that bypasses the PCM. I am anxious to see if that helps.

You may not need an external regulator. Just saying what I am doing.

Edited March 30, 201213 yr by edouble101

You would need to test your batteries individually. Not just for voltage but a load test.

Make sure you have continuity from one end of your plug that goes to your alt to wherever the wires go to. Probably two or three wires. Your connection is probably a S-L-F type. One wires senses battery voltage, on 5v turn on for the alt and another is a field voltage wire that goes to the pcm. This is a common hook up yours could be different.

This. Even if the voltage is say 12.6v doesn't mean it's "good." Put it on a load three times the battery's AH rating or half of it's cold cranking amp rating. Do it for 5-10seconds, if the battery drops below 9.5v then it's likely bad. Also if it's really cold out when you do the test, that will reduce the voltage. 70degree+ for 9.5v. 9.4 for 50degree, 9.3v for 40degree.

Hope that helps.

Edited March 30, 201213 yr by stefanhinote

I have seen high voltage spikes with two different aftermarket alternators but not with the factory alt. In my instance the voltage regulators in bith of the aftermarket alts were not compatible with my vehicle for whatever reason.

16v to factory electronics is not good.

Excessive amperage is working on one of my alts now. He said that best thing to do is to use an external regulator that bypasses the PCM. I am anxious to see if that helps.

You may not need an external regulator. Just saying what I am doing.

i was looking into doing that, getting the xs power one that you can set the voltage yourself. the seems to be the logical answer that the voltage regulator isnt woking with my h/o alt.

the tools they use at auto zone are designed to be used by tools... its all computerized.

your local mechanic probable used a analog load tester.. that are not very reliable

2ndly i have worked at autozone.. and there load tester for the alternators only goes up to 130 amps. im skeptical of them saying it was putting out 240 amps... i doubt they have a 300 amp load in there machine

i have had voltage spike issues before... it seem to be caused by bad batteries.. i replaced them and no more spiking...

but also can be caused by a weak ground to the alternator case.

Where can i add or upgrade the ground for the alt? And how would i do that?

Where can i add or upgrade the ground for the alt? And how would i do that?

your alternator should look a bit like mine.. this is a 6G .. yours maybe a 4G.. its just a little smaller.....

if you look at this pic.. there is a red wire that is on the mounting bracket... on the side of the alternator.. its a 0 gauge that runs to my front battery that also ties in with the other big three grounds.

let me know if the pic does not explain it well enough and ill try again

Yes i have the 6g and i have the 0 gauge wire to the battery from the alt but didnt know i should upgrade the ground off the mounting bracket. Should i use a 0 gauge there also and ground it to the frame where the grounds are for my battery and engine ground.

you can do that... i run mine to the battery... all my grounds tie into my front battery.

i have 2 0 gauge from battery to frame, battery to motor, battery to alt. all - so a total of 6 runs of 0 gauge for all my ground up front.

but i run a little more power.

you can do that... i run mine to the battery... all my grounds tie into my front battery.

i have 2 0 gauge from battery to frame, battery to motor, battery to alt. all - so a total of 6 runs of 0 gauge for all my ground up front.

but i run a little more power.

Sounds like a waste of wire bro. 1/0t used in lengths that short are good for +600a at 14v.

Ok yeah i understand that, ill try that tomorrow and see if i get somebetter voltage. Also i was researching a little bit right now and saw that if a car is a uni body u should run ground wires from front to back batterys so they all share the same ground. Have u ever heard that? I always thought a ground should never be longer then 3 feet.

you can do that... i run mine to the battery... all my grounds tie into my front battery.

i have 2 0 gauge from battery to frame, battery to motor, battery to alt. all - so a total of 6 runs of 0 gauge for all my ground up front.

but i run a little more power.

Sounds like a waste of wire bro. 1/0t used in lengths that short are good for +600a at 14v.

well my problem will never be not enough current then

im in no way saying he should follow me and do just as i do.... only sharing what i have done..

Ok yeah i understand that, ill try that tomorrow and see if i get somebetter voltage. Also i was researching a little bit right now and saw that if a car is a uni body u should run ground wires from front to back batterys so they all share the same ground. Have u ever heard that? I always thought a ground should never be longer then 3 feet.

your car has a full frame tho... so it really does not pertain to you .

Ok I'll try the alt ground tomorrow and post if anythings better