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Replaced batteries and alternator, voltage still lower than it should be!

3K views 33 replies 14 participants last post by  Kmay 
#1 ·
I just replaced the batteries and after driving around on weak batteries for about a week and a half i replaced them but it was way too late as it was beginning to kill my alternator. I replaced with 2 EverStart MAXX 850CCA. With the truck doing nothing, the SGII indicated about 12.5-12.7 volts which is normal. Right after i cranked, the alternator wouldnt really kick in much unless i started driving the truck gut it never got above 13.8 volts. I got it load tested and determined what i suspected, it was weak so i bought a rebuilt one from Advance auto parts with a lifetime warranty and the guy replaced it in the parking lot actually lol. I cranked it up and within seconds it went to 14.2v. I went in to the restaurant next door to have lunch and when i came out 20 min later i cranked the truck but the voltage never went above 13.8 the ride home and dropped down as low as 12.9. Well just a few min. ago i decided to go test it out. I check my SGII and it said 12.5 and i turned to KOEO 11.2, cranking 10.9, and i let it run for a few minutes and the highest it got was 13.0. It took it a few seconds to kick in but from what ive been told it should be in the high 13s while idling.

What could be going on.
 
#2 · (Edited)
Just a quick guess but you may want to check all of your cable ends (positive and negative) for corrosion and if you find any, clean it up good.

You might also check to see if your serpentine belt is slipping (tensioner pulley is weak) and etc.

Just for voltage reference I installed an AC Delco 140amp alt with the smaller Ebay pulley and a new Gates greenback serp belt and see 14.0 - 14.2 volts at idle. And with all accessories on it will fluctuate between 13.7 and 14.2 volts. And that's reading from my SGII. I replaced the OEM alt because it was fluctuating between 13.0 - 13.8 with no accessories on.

And, I am starting to see some corrosion inside the passenger side positive battery cable so I'll be fixing that in the near future.
 
#3 ·
The tensioner was noticed to have not caught on to the tool so the belt had to be manually stretched back on and there doesn't seem to be a slip and it's nice and tight. I really don't know what the issue could be but I'm NOT happy. I'm driving to FL tomorrow and I have NO time for screwing around!!
 
#4 ·
Check it with a regular volt meter, could be the SG or a bad connection to it. That would also allow you to narrow it down if your seeing the correct voltage at the alternator but not at the battery, etc. On the other hand you could just have a bad rebuilt alternator, it happens a lot.
 
#5 ·
The past year or so, many 7.3 and especially 6.0 owners are having new Alt issues. This is due to reman companies using junk regulators. I've seen many owners go through 2-4 different ones to finally get a good one. DC Power alts are top notch and I haven't seen anyone have any issues except just taking awhile to get theirs. But that's not that common.

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#8 ·
Put my name down on this list as well. My "lifetime warranty" autozone alternator that is 1 year old is now starting to clank and clunk when I first start the truck. For about the firsst 15-20 seconds then it goes away. So Im afraid something is going/gone away in the inside. And when your dealing with the weather and the area's that I take my truck and the throw in a pack of kids I cant just figure it will die in a nice easy place at a good time. (like town) So I think Im back to lookin into the DC as well. I just hate doing/paying for repairs/parts twice.
 
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#6 ·
^ +1 to above post. Not just us getting crappy parts, my wife's car, I had to swap out THREE different starter's before I got a good one, and went through 2 alternator's before I found a good one. Absolute rubbish.
 
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#7 ·
That's about normal unless you put a high volt alt on it. Also check your ground from the alt. Sometimes alt to body is not a good enough ground, might want to try to ground the alt to the frame not the body
 
#9 ·
We installed 3 on my son's 05 till we found a good one. Hard to find good parts any more, seems to be a crap shoot, especially electrical parts.


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#11 ·
#12 ·
UPDATE! Acting weird now like some days its bad and some days its good. Even with accessories running. As for the alternator it has a lifetime warranty from Advance Auto!! And i was thinking tensioner too, the guy who changed out my alternator stated he couldnt use the tensioner tool because he couldnt fit it in the hole so he had to put the belt on by pulling with all of his strength until he got it on. Of course right there the alternator worked perfectly lol.
 
#19 ·
OP the fact that the guy that changed your alternator could not get the tool on the tensioner is his problem. Most of those tools will not work because you cant get the thing inserted due to the angle of the insertion point. I carry in my truck a 1/2 inch ratchet and a 3 foot pipe that I slip over the handle of the ratchet; works every time.
 
#20 ·
your lifetime warrantee on the alt is good as long as you want to keep changing the alt. thats my plan until i get tired of them. my voltage never sees above 13.5 but it hasn't gone below so i'm still confident in its ability to keep the truck running. when it dips down, i'll take it back to o'reilley and get another bowl of lucky charms.
 
#21 ·
I just had my alternator rebuil at a local shop. I had it rebuild to 170 amps but it's still hangs around 13.5 to13.9. I'm on my second set of crappy walmart batteries(replaced under warranty) so I'm pretty sure that's the problem. I'll be dropping in some new motorcraft ones when these crap out but they are only 6 months old and can't justify buying new ones at the moment.

I would have never bought walmart batteries but they were in the truck when I got them and they replaced them no questions asked.

My voltage drops to 13.2 when I turn my lights on at night. Should I be worried?


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#28 ·
There are only so many battery manufacturers (the ones who actually make the battery) and walmart is not one of them. Certain batteries you can get there are just as good as anywhere else. Granted I hate walmart personally.
 
#25 ·
Ok so we have tested batteries and alternator again. Alternator is bad. We also did a little digging in terms of the serpentine belt and tensioner. Belt does stretch slightly and the tensioner appears to wiggle a little bit and we were sure that was the cause until we fired it up and heard NO squeaks and it appeared to be operating normal. We are gonna try just replacing the alternator first as it will be free cuz it has a lifetime warranty. the first one I got could have just been a bad one in general. I will have them test the new one before I swap just to be sure.
 
#27 ·
well when we were testing mine last night I moved to another parking spot in my complex a few feet away. truck literally ran for a minute tops and engine was cold. however I touched the alternator, it was VERY hot while rest of engine was cold. problem is intermittent
 
#32 ·
Well I did a little testing this am. I recently installed a prodigy p3 brake controller and it has a troubleshooting feature that shows what kind of voltage the controller is getting.

I set it up to troubleshoot on my way to work this am and learned that my sg2 reads .3 to .5 volts lower than the brake controller.

Would the brake controller be more accurate or would it just be best to go by what the scan gauge is seeing a as that's what the accessories are seeing coming out of the PCM?

On my way to work it was 13.9 to 14.1 volts on the controller and 13.5 to 13.8 on the sg2.


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#34 ·
I'm not so worried about the difference cause if I know the sg2 reads a little lower I will compensate in my head.

My main concern is that I don't want to fry my BPD ficm.


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