Bad alternator= surging/dying/rough idle?

Mines an 08 4Runner but it’s got the same 1GR-FE 4.0 so I thought I’d get some more opinions.

Hey all, my battery died a couple times in the last month, tested the batt, it was ok, alternator showed only 13v output so decision was made to replace alternator (Denso reman)

After replacement, at the batt it showed 13.7v charging, OBDii showed 13.3-13.4

However about a week after I did the alternator, I got a horrible rough idle, the thing barely runs, dies at stop lights, pretty bad black smoke from tailpipe (ecu going full rich). It surges and chokes when driving and even the transmission shift points are messed ok. Battery still shows 12.4-12.6 at rest, however the alternator voltage at idle fluctuates between 12.4-13.9.

I have checked all the grounds and positive leads. Used a multimeter on the main cables to the fuse box and to/from battery to alternator, there’s no voltage drop and no obvious corrosion.

Could this be symptoms of a bad voltage regulator? I imagine the fuel pump/ecu/injectors would have a difficult time managing the wildly fluctuating voltage from the alternator to keep the rig running. Did I get a bad Denso reman?

 

The drive belt tight it does not need to squeal to be loose that could cause the output to fluctuate

Your charge light is tripping when the output drops off??

You ruled out any loose connections ??Alternator bracket tight as the alternator grounds by the bracket

Strange to see things fluctuating a loose connection could cause that a bad voltage regulator tends to go wide open or no output at all.

During assembly the inner nut for the B Terminal may be loose.

The 3 pin plug is good for getting corroded and causing all manner of fun issues because of where it is a pain to look at it gets over looked.

 

Thanks for the reply!
Drive belt was plenty tight and I watched it as it ran, no slipping evident, it’s only got about 30k on it. I replaced the idlers anyway as they were getting loose.

No battery dash light ever came on, surprisingly! Never tripped a code.

Alternator ground was good, the bolts all torqued in fine, all the connections were wire brushed and tight. I was also wondering about the alternator plug, the wires seem pretty flimsy, I might just replace it and see if it helps. I talked RA into a replacement alternator anyway, so at least the new one will confirm/eliminate the alternator as the problem.

 

Checked all the grounds and wiring again today, everything looks great.

Replaced the battery, no change, 2nd alternator went in, same issues.

Now I'm thinking this is a misfire issue separate from the charge issue.

Cleaned MAF, checked vacuum lines, changed plugs, checked all connections, filled up with premium fuel.

Still having the issue. It will idle perfectly, maybe a little high like it's in warmup mode, and then within a minute or two, RPMs drop to 400 and it starts running super super rich, black smoke out the exhaust. Still not throwing any codes.

At this point, I'm stumped. I did all the general maintenance stuff I know how, it's going to the dealership.

 

@F34Rnnr Any closure?

 

Not scene since this issue

 

I know, just going for a TW necromancer badge by pinging any interesting dead threads for a pulse. ‍♂️