[Volkom]

Hey all, to preface i've already solved this issue so no need to read with extreme scrutiny in order to help.

To skip the story just scroll to the end

Last year I replaced my N20 with a newer N20 after the timing chain failed. The new engine did not come with any accessories, so I swapped on my old alternator. At the time I had also replaced the then 7 year old ~1050Ah? AGM original BMW battery with a new 1000 Ah AGM (non BMW) battery.

I had registered the battery, though if i remember correctly selecting anything other than the original capacity was not possible through ISTA, so I defaulted to selecting that it was the same. I knew I'd have to go back and code it through E-sys or some other means to get the right capacity, but I never got around to it.

Months later I encountered my first 'charging malfunction - battery not charging, consult service center' or something like that.

I thought nothing of it, simply that it must have been the IBS (intelligent battery sensor) picking up that it was attempting to charge the assumed 1050 Ah battery and the 1000Ah actual capacity was giving it issues with expected readings. I continued driving until now, a year later. To be honest I had put so much work into the car I sort of didn't even feel like popping the hood- it was just mentally exhausting to open pandoras box again.

Every once in a while I'd get another battery not charging issue, this time coupled with a low battery warning. Most of the time it would go away after driving a few blocks, except this week when I took it on a longer drive.

On a two hour drive I got a charging malfunction notification maybe 5 times.

I got back home and brought my laptop in to start the coding process, thinking it was a software issue. I started the car a few times, engine ran great, no issues.
I start the car one more time and go over to pop the hood to test the battery voltage from the front positive terminal since the battery is a pain in the ass to get to in the trunk. I hadn't yet done the 'secret menu' via the odometer reset which shows you the voltage on the dash, which is very useful.

I noticed extreme engine shake this time around, and thought for sure my air-bag engine mount had gone bad, but it seems awfully coincidental that it happened right now. Oh well, it wouldn't be the first time two random things broke at once but whatever.
I get inside, drivetrain malfunction. I was about to shit my pants thinking that my 1 year old (to me) low mileage engine that I spent so much time and effort replacing had massive issues this quickly.

I checked the system voltage and it was ~11.8V - very low. The engine was misfiring with some sort of B2AAA body issue, a P0300, P0301 and a P0302- random, 1 and 2 misfires. I was so frustrated I didn't even feel like loading up ISTA to check the details.

I check my alternator post voltage and notice it's corroded like crazy. It certainly wasn't like this a year ago, nor was it like this throughout all the years it ran on the original engine.



I probed the voltage at the actual post and it's ~14.7 V.
I then probe the flat connector that runs all the way back to the battery and I'm only getting ~11.9V.
You can also see some of the plastic has melted, presumably due to the high resistance causing overheating.

I cleaned it up today the best I could with limited tools since I'm away from home just to get me by. I have to see if it's even possible to replace that lower washer since it seems to have corrosion too heavy for me to handle with a small steel brush. I'd like a crush washer in there but I don't have that on hand yet.
Below is the best I could clean it up with some electronics cleaner spray and a brush. Disappointing, I know.



TLDR: Alternator post to battery connection corroded somehow, wasn't charging the battery but the alternator was good. Battery got low, alternator did not output sufficiently high voltage due to high resistance to power the vehicle, resulted in misfires. Cleaning contacts worked.

No more misfire, system voltage back to 14.1V when running, ~12V when on battery since it'll take a while to recharge. I still have to clean it up properly but I hope this helps someone with a similar issue. Hopefully it didn't mess up the AGM battery due to the high discharge but i've got a 3 year (2 years left) warranty on it so whatever.

[pungo]

Originally Posted by Volkom

At the time I had also replaced the then 7 year old ~1050Ah? AGM original BMW battery with a new 1000 Ah AGM (non BMW) battery.

I had registered the battery, though if i remember correctly selecting anything other than the original capacity was not possible through ISTA, so I defaulted to selecting that it was the same. I knew I'd have to go back and code it through E-sys or some other means to get the right capacity, but I never got around to it.

I thought nothing of it, simply that it must have been the IBS (intelligent battery sensor) picking up that it was attempting to charge the assumed 1050 Ah battery and the 1000Ah actual capacity was giving it issues with expected readings.

Good you got it figured out

I was looking at that connection on mine a few weeks ago and it look new with zero corrosion. Do you live in a salt belt or near the ocean?

You're overstated the battery capacity by an extra digit

AFAIK, e-sys doesn't have a 100ah value. Can it be edited? I don't know, never tried to. Not sure what effect being off by 5ah will do, but I image it could slightly overcharge the batt.

[Volkom]

Yeah, good call. No tesla battery pack under my bmw yet hahahaha. The importance of units can't be overstated. Got used to dealing in mAh :-)

I do live near the ocean, but not right near the beach so I would expect that spread to be rather minimal. Other components of the same material (steel, no coating) under the hood are not nearly in the same condition. Being in the northeast, we do have a lot of salt, so maybe this is the right explanation. The rather sudden appearance of this problem over the past year versus the past 6 or so also puzzles me.

I guess I'll just keep it running the way it's been running and re-evaluate.

Thanks for the info about e-sys- I'm wondering if maybe the "incorrect" capacity, even if by 5Ah causes some sort of problem? I wouldn't expect that to be the root cause but who knows...

My initial inclination is that the corrosion found in most alternator to battery hookups is due to chemical reactions directly related to standard lead-acid marine batteries. In our case, the battery is completely separated from the alternator in terms of distance so it can't possibly be the correct explanation.

Interestingly I seem to be missing the cap for the post, after looking at old photos.

Perhaps it melted off due to high resistance because of corrosion or more likely:
the cap fell off randomly and this corrosion is a result of the missing cap

Below is a picture of the alternator last year, with the black cap still clearly on it, but before I mounted the flat cable that runs to the battery


EDIT:

Here is a photo after I assembled the entire engine back, with the cap still on it, so i'm inclined to say I put it back together properly and somehow it fell off....