Battery - Alternator HELP

[profundus-sanus 10+ year member]

Mike is telling me its the pulley aswell I got one just short of an inch and I'm going to try that tonight with the small pulley. Hopefully all goes well. My idle should be atleast 14 right? Pretty sûre that's what it was with stock altOk I'm using factory plug aswell no harness nothing

correct. your voltage shouldn't vary more than .1-.2 between cruising rpm and idle.

 

[cbuts 10+ year member]

correct. your voltage shouldn't vary more than .1-.2 between cruising rpm and idle.

thanks, ill be putting the belt in today, in a couple hours. hope the batt light goes out lol

 

[profundus-sanus 10+ year member]

thanks, ill be putting the belt in today, in a couple hours. hope the batt light goes out lol

indeed. that likely means that the pcm is commanding voltage and the alternator isn't producing it, so it thinks there is a problem with the alternator. By chance do you know what size pulleys he sent you? Do you know what the lowest rpm was that the alt would turn back on at? I can do the ratio calc for you really quick.

 

[cbuts 10+ year member]

indeed. that likely means that the pcm is commanding voltage and the alternator isn't producing it, so it thinks there is a problem with the alternator. By chance do you know what size pulleys he sent you? Do you know what the lowest rpm was that the alt would turn back on at? I can do the ratio calc for you really quick.

im really not sure, so your still saying the pulley will fix it right? and the battery light? lol its got 6 ribs on the best, and we got just short of an inch shorter then oem belt

i was sent the small one (attached) and a bigger one, i took small off and used bigger one for stock belt

my belt doesnt even seem to be slipping atm

 

[09civic 5,000+ posts]

I use a stock length belt in mine with no belt slip. It depends on the car though, I suppose some tensioners won't hold the belt as tight as others. Make sure to get a good belt like a Gates or a Gatorback.

Was the pulley size difference relatively small or big?

And the 04 Taurus's had auto tensioners so that's probably why.

 

[09civic 5,000+ posts]

The PCM in my car will not use the alternator unless a power source other than a stereo system is in use.

For example, my stinger voltmeter will read 12.7-12.8 until I turn on my lights, use the windshield wipers, roll down the windows, etc. Once I turn any of those items on, it will then read 14.4+.

PCM's will not compensate for your system's draw.

 

[profundus-sanus 10+ year member]

The PCM in my car will not use the alternator unless a power source other than a stereo system is in use.
For example, my stinger voltmeter will read 12.7-12.8 until I turn on my lights, use the windshield wipers, roll down the windows, etc. Once I turn any of those items on, it will then read 14.4+.

PCM's will not compensate for your system's draw.

a lot of gm's have a current measuring ring on the ground wires running to batt to determine draw on the batt.

my gp for example. if i take it right off the charge and go drive it it'll be at 13.0v in 5 minutes if i leave the head lights off. but if its been sitting for a couple days and it might stay above 14v for 20+ minutes.

 

[profundus-sanus 10+ year member]

im really not sure, so your still saying the pulley will fix it right? and the battery light? lol its got 6 ribs on the best, and we got just short of an inch shorter then oem belt
i was sent the small one (attached) and a bigger one, i took small off and used bigger one for stock belt

my belt doesnt even seem to be slipping atm

well i can't say one way or another. if your smaller pulley is .1" smaller then it might not. if it's 1" smaller then i'm sure it will.

 

[cbuts 10+ year member]

Well on my way to fix it.. hope no light after this

 

[NASTY08IMPALA 5,000+ posts]

We know its not the PCM since he by passed the harness,so yes it could be the pulley but since your gonna do a smaller pulley make sure you get a smaller belt to prevent slip

ok since no one will listen here i go again...hes using.the stock plug ..not bypassed ...yes he needs to change the pulley ..but the 05+up chevys are pcm controlled for fuel econ..period..when i bought my mechman i had to externally regulate it so that i could charge at 15.3 ..or else it would drop down to 12.9-13v ...anyone else??

 

[NASTY08IMPALA 5,000+ posts]

The PCM in my car will not use the alternator unless a power source other than a stereo system is in use.
For example, my stinger voltmeter will read 12.7-12.8 until I turn on my lights, use the windshield wipers, roll down the windows, etc. Once I turn any of those items on, it will then read 14.4+.

PCM's will not compensate for your system's draw.

exatly the same on the chevys ..honda u can do a eld bypass ...but the chevys will go from 13.9-14.5 then drop down to 12.9-13 .as controlled by the pcm ...no size puley will change that ..only way is a external reg.

 

[09civic 5,000+ posts]

ok since no one will listen here i go again...hes using.the stock plug ..not bypassed ...yes he needs to change the pulley ..but the 05+up chevys are pcm controlled for fuel econ..period..when i bought my mechman i had to externally regulate it so that i could charge at 15.3 ..or else it would drop down to 12.9-13v ...anyone else??

My Honda uses the PCM for fuel economy and I didn't have to bypass anything. Just plug n play. Yes, my alt is internally regulated.

It's not charging it at 12.9-13.0, it's not using your alt at all.

It's not just a GM thing.

 

[09civic 5,000+ posts]

exatly the same on the chevys ..honda u can do a eld bypass ...but the chevys will go from 13.9-14.5 then drop down to 12.9-13 .as controlled by the pcm ...no size puley will change that ..only way is a external reg.

Does using an accessory make the voltage jump back up?

The way I bypass my PCM is to turn on the fogs during the day to keep the alternator running.

 

[profundus-sanus 10+ year member]

ok since no one will listen here i go again...hes using.the stock plug ..not bypassed ...yes he needs to change the pulley ..but the 05+up chevys are pcm controlled for fuel econ..period..when i bought my mechman i had to externally regulate it so that i could charge at 15.3 ..or else it would drop down to 12.9-13v ...anyone else??

pcm regulation will not cause your battery light to come on when your using a stock plug. It will not cause your voltage to die at idle but be fine at cruising speed.

Your on the right track but your missing some key symptoms.

On several gm vehicles if you just trick the light sensor to keep the lights on all the time it'll keep you above 14.0v and wont throw a charging system error code, which some vehicles do if you bypass pcm regulation.

 

[NASTY08IMPALA 5,000+ posts]

Does using an accessory make the voltage jump back up?
The way I bypass my PCM is to turn on the fogs during the day to keep the alternator running.

when i had my stock alt i did.things like turn the air/heat on headlights anythig.to gwt the alts attention ..my car also kicks into 3cyl mode when cruising ..so if.i kept it.in 6 it wouldnt drop