Help: Big power draw on idle- bouncing voltage

[Krhee]

Hey team,

Changed the alternator couple times now.. at idle you can physically see the voltage drop on my meter (bouncing). Only non stock electrical item is led interior and rear lights which we replaced back to OEM and seems it wasn't it..

Has anyone had this issue come up? Reputable toyota mechanics are baffled and can't find the source either.

Help appreciated! (2013)

 

[KLF]

Start pulling fuses until it stops?

 

[NoClue]

Are you having an issue with your charging system? I'd like to know the history of your problem since you've stated that you've been through a few alternators... Most smart alternators can vary voltage even at idle.

Edit : just for giggles, whats the condition of your drive belt and the tensioner?

 

[CruiserFan88]

Assuming you are using at least an 180 amp alternator, correct?

 

[Sandroad]

How’s the battery? A failing battery could cause this with intermittent internal shorts. So could a bad connection to the battery. I’m not usually one to just throw parts at a problem, but unless you‘re certain the battery is good, my next move would be a new one (Toyota TrueStart) and a careful cleaning of + and - connections.

 

[TeCKis300]

Solid suggestions prior. I'd also consider the battery a likely suspect with an intermittent short causing this issue. Very few things in the system can cause this level of current changes enough to cause voltage fluctuations, and the battery is a prime suspect. It's also low hanging fruit.

Next item if not the battery, would be the major electrical grounds. Particularly the battery ground strap at both the battery and fender, and the engine block ground straps to the chassis (I think there's 2?).

Alternator pulley, drive belt, tensioner can potentially do this too, but I'd assume after swapping in 2, that this would have been examined?

 

[Krhee]

Thank you all for suggestions. Reputable mechanic guarantees work and we've changed alternator before, then got the dreaded cam tower leak, (and dropped oil all over alternator) and they replaced the alternator(on them) when this started happening. He's putting in another thinking it might be a bad alternator so adding in a second, I can check up with him on the other items but would assume they would check (battery/drive belt/tensioner) so they don't put a new alternator in on their own dime!

 

[grinchy]

voltage regulator?
Agree with above that a bad ground connection or bad battery connection also strong possibilities

 

[Krhee]

Okay... After two weeks we've figured it out. Mechanic gets alternators directly from denso (who supply toyota) and apparently they have either changed the serial numbers and have had some duds from the assembly. Mechanic decided to give it a go and buy an alternator from Toyota directly and we're clear. They are double checking serial numbers and with denso.. Really odd that they've had so much trouble with these from denso but no issue with this one supplied by Toyota themselves. Same problem with last three from denso.

Odd case hopefully just me but hoping this helps those who run into this. It could be 100rpm higher than idle and no issues, but starts dropping at idle.

Video below and glad I have my car back! And don't worry, honking wasn't at me!

New video · Friday, Dec 18, 2020 ð¬

Tap to view!

photos.app.goo.gl

Thank you all for chiming in!

 

[MikeVpdx503]

Really odd that they've had so much trouble with these from denso but no issue with this one supplied by Toyota themselves. Same problem with last three from denso.

Not sure where Denso alternators are manufactured, but I have ordered Denso branded air filters and found them to be made in China. I returned them and ordered the same part from Toyota/Lexus and found it was made in Japan. That could possibly explain the quality issue.

 

[Lou Gill]

Do have any phone chargers plugged into cigarette lighters? Take them out!