Voltage drop after warming up, not the alternator

[killerkali]

Trying to diagnose an issue that has developed over the last year. On a cold start I get a good output from the alternator(~14.3), but once the car has fully warmed up the voltage drops to around 13.5v. Initially I replaced my Alt with a used on, and had the same issue. Finally put a new OEM bosch in and although it seemed to help(voltage only will go down to 13.7) I still have this issue. Battery is relocated to the trunk with large 0 or 2 welding cable. Never had issues for the past 5 years or so until recently.
Are these Alternators controlled by our ECU at all? What is the single small wire that connects to the alt for? (The 2 pin connector that only has 1 wire)

[DieselElectric]

13.5v is acceptable charging voltage.

The single wire excites the alternator.

Charging voltage between 13.5v and 14.5v is considered good. If you are getting 13.7, there's no problem.

[Bordom]

What Diesel said. If your voltage was hovering around the 12.6-13v range, then you have a problem

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[MacDaddy]

Yeah its in the range of acceptable but it sounds like there is something going on that is worth looking into incase it turns into a bigger problem.

I would check the voltage comming out of the reference wire, if its not the same as whats at the battery then theres a possible issue there, not sure if it comes off the ECU but its likeley it does.

Fwiw i had a land rover that low charging, turned out it was the front window defrost was shorting out and drawing a huge amount of amerage and for some reason the fuse didnt pop, pulled the fuse and charging went back to 14.4

[DieselElectric]

A bad battery can also draw enough to make charging voltage appear low.

[killerkali]

Yeah its in the range of acceptable but it sounds like there is something going on that is worth looking into incase it turns into a bigger problem.

I would check the voltage comming out of the reference wire, if its not the same as whats at the battery then theres a possible issue there, not sure if it comes off the ECU but its likeley it does.

Fwiw i had a land rover that low charging, turned out it was the front window defrost was shorting out and drawing a huge amount of amerage and for some reason the fuse didnt pop, pulled the fuse and charging went back to 14.4

Interesting, from my experience almost every charging system should be in the 14v range, but seems that always isnt the case. I will check the reference wire.

Not sure if this could indicate anything, but when I activate all the windows "up"(or load the system quickly via other electronics) I get a quick spike to ~12v then it returns. Battery is brand new, have tried my previous battery with same results.

[DieselElectric]

I work on locomotives now, but I spent 10 years as a line tech for a few name brands. Everywhere was the same standard. 13.5-14.5.

[Timtheguru]

Worn out battery

[MacDaddy]

Interesting, from my experience almost every charging system should be in the 14v range, but seems that always isnt the case. I will check the reference wire.

Not sure if this could indicate anything, but when I activate all the windows "up"(or load the system quickly via other electronics) I get a quick spike to ~12v then it returns. Battery is brand new, have tried my previous battery with same results.

Yeah thats weird, try pulling he fuse for the windows and see if it changes (also could try other non essential circuits, id probably pull them with the car off to avoid possibility of frying anything) also is it possible to relocate the battery to the stock location temporarily?

My s4 has always shown just above 14v as long as ive owned it which is almost 10 years now.

Im not disagreeing with diesel, but with a new alternator and battery things should be higher than .2v above minimum spec.

[insomniacxp1]

^ I thought about the relocation increasing impedance and effecting the charging voltage but resistance at 10 feet of 0awg is .001 ohm so ....

[b5329]

A bit off topic but is it normal to see any voltage drop after the AC or is turned on?
For me, sitting in traffic and then turning on the AC, the voltage drop off is noticeable. Nothing to the point of the car dying, just wondering. Thanks

[Mille Bornes]

Have you verified charging voltage with a multimeter? I've seen inaccurate factory gauges.

My car's gauge has shown around 13.5 volts since I've owned it, so 5-6 years now.

[killerkali]

Wanted to bump this, today was showing 14v at the alternator, 14v at battery(in the trunk). Yet my cluster and wideband voltage gauge(on the 75x post) were at 13.4v. Is that a potential issue? Not sure how the cluster gets it reading, but the difference seems a little high.

Still have this issue, although a new alt/battery seem to hide it. I feel my a/c system or fan is drawing way too much current, but I've yet to figure out how to test that ...

[Silverex]

Did you try pulling fuses to see if any were the culprit?

If it was me and I’ve been fighting it this long I’d rewire the battery with some quality products just to eliminate that possibility.

[christianb5s4]

The AC fans should be easy to test, does the voltage drop turning on the AC? If it's hot out the fans draw more power running at higher speeds so it's normal to see voltage drop due to that under high load circumstances (which our CA heat wave certainly qualifies as).

[Bordom]

When is the last time you changed your accessory tensioner?

I fought a voltage issue for a while and replaced the alternator and battery twice before I realized my tensioner was too weak to keep force on the belt.



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[killerkali]

The AC fans should be easy to test, does the voltage drop turning on the AC? If it's hot out the fans draw more power running at higher speeds so it's normal to see voltage drop due to that under high load circumstances (which our CA heat wave certainly qualifies as).

Yeah only when it is on, which also makes my 2 electric fans run(factory and replaced the clutch fan). It draws .~6v , but that pulls my voltage down into the 13-13.2v range once warmed.

When is the last time you changed your accessory tensioner?

I fought a voltage issue for a while and replaced the alternator and battery twice before I realized my tensioner was too weak to keep force on the belt.

Not even sure how to tell if the belt is slipping...but may be worth replacing it. My tensioner is at least 7 years old, been through 2 timing belts

Did you try pulling fuses to see if any were the culprit?

If it was me and I’ve been fighting it this long I’d rewire the battery with some quality products just to eliminate that possibility.

Pulled them all, nothing was suspect except for my a/c system drawing a lot of power when running. Thats my next step, going to build a alternator/starter harness with welding cable, and rewire the battery as well..

[christianb5s4]

I just don't think that 13-13.2v at idle with high load on the system is all that bad. But for what it's worth, I've seen mine dip down to that at times under high load circumstances but always eventually stabilizes around 14-14.5v when driving.

[killerkali]

I just don't think that 13-13.2v at idle with high load on the system is all that bad. But for what it's worth, I've seen mine dip down to that at times under high load circumstances but always eventually stabilizes around 14-14.5v when driving.

I agree, but only if the system would recover back into the 14v range there would be no issue, unfortunately thats my issue.

Will update this when I get it rewired.. If anyone has pictures/info on the alternator+starter harness Id appreciate that! Want to build one out of the car

[christianb5s4]

Here are the best pictures I could find, ECS always is a step above with cataloging parts:

Positive side of the harness: https://www.ecstuning.com/b-genuine-...BoCYC0QAvD_BwE

Negative/ground side: https://www.ecstuning.com/b-genuine-...xoC6d8QAvD_BwE

[PoVolks]

Are there any other aftermarket, or modded electrical components on the vehicle? Radio, HID, amp/sub, and is the new battery rated the same as oem?

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[killerkali]

Bumping, where the exciter wire lead to from the alternator? I see in the picture below it goes to the purple connector after the firewall,but I can't find that on my car. Does it connecto to the ecu? Trying to rebuild the exciter wire as well, wondering if i can just tie it into the battery...?
https://www.ecstuning.com/b-genuine-...BoCYC0QAvD_BwE

Are there any other aftermarket, or modded electrical components on the vehicle? Radio, HID, amp/sub, and is the new battery rated the same as oem?
Sent from my lg g8 using Audizine mobile app

I have quite a few(Hids,fans,WB02,aux input to stock radio), but I've tested everything for abnormal draw and it checks out. I'm actually using a larger battery than the stock looks like, group 95 770cca.
I still suspect my Walbro 450, waiting on a clamp meter to see if it starts to draw excessive amps after its "warm". I read that happened in another car forum

[christianb5s4]

Do you run aftermarket wiring to the fuel pump? If not, I recommend getting a fuel pump harness which bypasses all stock fuel pump wiring.

[killerkali]

Do you run aftermarket wiring to the fuel pump? If not, I recommend getting a fuel pump harness which bypasses all stock fuel pump wiring.

With the 450, I initially ran a dedicated relay setup. Had issues with melting the stock fuel tank lid, went back to stock wiring with a custom pass through on the lid. On gas now so its adequate. Need to get the amp draw tested to make sure that pump isn't suspect.....

[Silverex]

Bumping, where the exciter wire lead to from the alternator? I see in the picture below it goes to the purple connector after the firewall,but I can't find that on my car. Does it connecto to the ecu? Trying to rebuild the exciter wire as well, wondering if i can just tie it into the battery...?
https://www.ecstuning.com/b-genuine-...BoCYC0QAvD_BwE

Pretty sure that connector your talking about is for the starter and the harnesses are different depending on year, like my car doesn’t have any of the circular connectors.

For the alternator it’s just the plug IIRC

[killerkali]

Pretty sure that connector your talking about is for the starter and the harnesses are different depending on year, like my car doesn’t have any of the circular connectors.

For the alternator it’s just the plug IIRC

I think you're right. But i see a blue and black wire on that connector, so seems both the exciter and starter trigger go to that. I'm pretty sure the exciter gets 12v once you key on, but I'm still trying to verify that so I can rewire it .