Sudden voltage drop when warm ... help diagnosing please

A

AlbertaBeef

Member +
In my 4E-FTE Tercel I suddenly started having a weird alternator/charging issue which I'm looking form some help with...

When the engine is warm, my voltmeter suddenly drops from 14-ish volts down to 12-ish volts. FYI, the meter is currently hooked up to an ignition-controlled source in the cabin.

When it first happened, it was the common 'both brake/charge warning lights' issue we often see in Toyotas (at-least in N.America, anyway). I drove it home (only a mile or so) and shut it down. It was reading 12.1v when I turned it off. A few hours later I went out to start looking at it, put the key in and turned it on and ... it was reading 14.4v again. After driving about 6 or 7 minutes, it dropped down to 12.3 ...

So I get home, park it, shut it off ... Wait about 10 minutes and turn it on and it was still 12.2-12.3v.

A few hours later, go out to check it ... and surprise, surprise ... it's back to 14.4v when started. I've tested this a few times now, and the voltage drop ONLY occurs when the engine is warmed up to operating temps.

I've checked the battery ground to the chassis - added a second JUST in case. I checked the wiring from the alternator to the hot side of the battery ... seems intact and I've cleaned the contacts, but haven't been able to replace the wiring as I'm currently out of decent-gauge wire/cable.

Note: I don't currently have a multimeter ... not sure I can easily obtain one today as it's a stat holiday here in Alberta, but I will if I need one ...

Regarding more ground wires ... I'm not 100% sure where the engine block to ground in a 4E-FTE is supposed to be, I don't immediately see it ... so was wondering if anyone with one can tell me where it normally runs from/to? I haven't been able to look underneath yet as I've not gotten the car in the air ... as my garage is currently unavailable due to a sons' project ...

Wondering if anyone's experienced this and if it's maybe just a ground issue rather than an alternator issue ... I'd prefer to trace/replace wiring rather than get the car in the air to R&R the alternator ... which is a little more costly ... But looking for some input.

Any help/suggestions are appreciated, thanks!
 
A

AlbertaBeef

Member +
OK, so I borrowed a buddy's multimeter and here's the results.

with the car not started and no key in the ignition, battery reads 12.59v. Good.
with the car started/running warm, battery reads 12.34 - 12.35v
with the car started/running warm, alternator B+ post reads 12.34 - 12.35v

Measuring the voltage drop across the negative (Black wire to battery negative/ground, red wire on alternator case) resulted in a positive reading ... depending on where contact is, varies between 0.00 and +0.03. Both on outside case and the bracket.

Moving the red wire to the engine block, changes to +0.05 - +0.07

Later, I turned on the headlights, A/C, blower fan on full and cranked the stereo ...

Measuring the voltage drop across the negative ... again a POSITIVE reading from +0.04 to +0.07 at the alternator case. +0.06 to +0.11 at the engine block.

Measuring the voltage drop across the positive (red cable to positive battery terminal, black to B+ post on alt) showed a positive of +0.21 to +0.23 and measured to the nut secured on the B+ post was +.17 to +.21 - both readings with a little fluctuation up/down depending on if the A/C compressor was kicking in or not ...

Not knowing much about this, I'm somewhat confused as the the positive readings while measuring voltage 'drop' ...

Anybody that understands care to enlighten me? Now that I see the alternator is putting out a fairly-steady 12.35v or so from the B+ connection once warm, I'm confused as to what the issue is ... If it were a faulty alternator, wouldn't it put out considerably less (or at-least considerably less consistent) voltage??
 
SKINY

SKINY

Lifer
Should read about 14v when running/charging bud. Alternator ay be on its way out, rectifiers in them go and are a good bit cheaper to replace than full refurb. A good auto spark will be able to test it with a load on it.
 
Jay

Jay

Admin
I'd tend to agree, I've had a few faulty alternatives which have only flagged an issue on an intermittent basis. Would only see a warning lamp after a few miles driving.

Because parts supply here is decent it was a case of popping a new alternator in but you may find a local auto spark could sort your current unit.
 
A

AlbertaBeef

Member +
I was lucky enough to find a local shop that rebuilds alternators and starters. They'll test it for me and can rebuild it if need be. They offer a one year warranty on rebuilt Denso alternators and have very good reputation locally . Taking it to them tomorrow ...
 
A

AlbertaBeef

Member +
Well, it was the alternator. One of the brushes and a slip ring. Had the shop do a full rebuild (brushes, bearings, regulator, etc., etc.) which cost me a whopping $105 Canadian including tax, and gets me a 1yr warranty.

It did take me about an hour total to get it installed. I put it on ramps instead of jacking it ... which is a mistake in hindsight. If you jack it you have some suspension drop and it's easier to get past the CV Axle... On ramps I had to twist, turn, cajole, etc. to get it into position ... then I had the alternator belt too loose. So it didn't charge up fully. Then when I tightened it, it squealed upon revving it up... turns out I had it too loose again - Twice. LOL. But now it's all setup and runs and works EXACTLY as it's supposed to. NICE.

Thanks!

Thanks for the confirmation on what it was, always nice to save shop charges on diagnostics!
 
Jay

Jay

Admin
Happy days man, glad you got it sorted.

As for the installation fun and games you had that's the way most of my jobs go too!
 
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