Put a new alternator on my car about 800 miles ago. Battery is 2.5ish years old. Oem. Bosch alternator from fcp. Not a scratch on the box when it arrived. So when I first put in for about the first 500 miles voltage driving and idling with or without accessories on was showing a consistent 13.7-14.1V. Then sometimes it started showing 13.2-13.4V driving and idling again accessories on or off. And it stays then. Then sometimes it goes back up 13.7-13.9V while driving and idling. Wtf is going on? Bad battery maybe? Seems to start perfect. No discharge warning unless I leave car locked in jb4 map 1-6. Map 0 no draw. Keeps the cluster awake so I’ve jsut been switching it off when I park it. And no, having jb4 active or not doesn’t effect these weird voltage drops and rises.

 

So you're saying you're having voltage drops but not getting any errors.

I would say it has something to do with the battery. Have you checked the alternator voltage

 

Yes. Bigger drops into 12V as I slow down for lights etc. but some days it run 13.4 some days 13.9. Sometimes it changes mid drive. Alternator voltage was showing same as my radar. I’ve confirmed it with a multimeter. 13.4V idle sometimes 13.9 others. It’s a brand new alternator I don’t get it. I guess I’ll get the battery tested at an auto store when I can. Reads 12.4 Off with the car awake. 75% life left according to what I’ve read.

 

Before you condemn the voltage regulator as faulty, one experiment that you could run is to disconnect the IBS.

Others who have done this claim the voltage regulator should put out a constant 14.4v with the IBS disconnected.

 

Yeah that sounds like the IBS doing its job.

If you had any problems, you'd definitely be throwing codes.

 

The IBS will vary the voltage/current that the alternator puts out. Are you experiencing any problems? It appears that the voltage levels that you are seeing are normal.

 

No no issues I’m aware of. Pulls hard. All accessories work fine. I just wasn’t sure if that kind of fluctuation was normal.