possible failing alternator advice

[E9Wayne]

Hey folks, getting my e9 ready for Sharkfest and decided to pro-actively replace my 7 year old battery with a new one. The local auto parts store also tested my alternator which I've had since around 2009 which also got a new (externally mounted) voltage regulator courtesy of my friend Chris Macha who bailed me out of 2016 Monterey car week misery. Since day 1 the alternator has worked fine and I've only put about 25,000 miles on that alternator.

The auto parts store said their tester showed that I have an "open diode", whatever that means, and I should consider replacing the alternator or looking into fixing that part. The screen shot is attached here.. I've damn near replaced everthing mechanical and electric attached to my engine since the famous electronic gremlin meltdown my car had after the movie shooting in 2022 and I guess I should be comfortable replacing my alternator with a rebuilt alternative - Bosch AL45X? Or should I do more testing and verification first?

Don and others, what are your thoughts?

Wayne

 

[deQuincey]

Hey folks, getting my e9 ready for Sharkfest and decided to pro-actively replace my 7 year old battery with a new one. The local auto parts store also tested my alternator which I've had since around 2009 which also got a new (externally mounted) voltage regulator courtesy of my friend Chris Macha who bailed me out of 2016 Monterey car week misery. Since day 1 the alternator has worked fine and I've only put about 25,000 miles on that alternator.

The auto parts store said their tester showed that I have an "open diode", whatever that means, and I should consider replacing the alternator or looking into fixing that part. The screen shot is attached here.. I've damn near replaced everthing mechanical and electric attached to my engine since the famous electronic gremlin meltdown my car had after the movie shooting in 2022 and I guess I should be comfortable replacing my alternator with a rebuilt alternative - Bosch AL45X? Or should I do more testing and verification first?

Don and others, what are your thoughts?

Wayne

Wayne
replace the diode plate to meet the correct output voltage

i do not think the alternator needs replacement, just try to replace diode plate

 

[skk]

Perhaps that tester assumes a modern, highly computerized car and perhaps the latter imposes more stringent requirements on alternator output and voltage stability. 13.8V is plenty to keep a 12V system happy and a lead acid battery topped up. One dead diode out of the 4 in the bridge rectifier would take out an entire side of the alt's sine wave output. That would cause a huge measured ripple. I think you're ok, but a modern 1-wire, higher output alternator would be a healthy upgrade. The radio and lights would thank you.

 

[Arde]

Yes, an open diode situation would still work as a half-wave rectifier. The voltage regulator would compensate for the half wave lost by using a higher rotor current. It would be fun to put an oscilloscope to confirm that the bridge has one open diode, I would look at the waveform and then disconnect the battery while measuring, as I suspect the battery is a huge capacitor that may make the ripple much smaller...
The other option is to measure the diode bridge with an ohmmeter.

 

[E9Wayne]

Thanks folks and this is clearly above my amateur electrical knowledge. I also attached my current alternator which, if I'm not mistaken, looks like an 85 amp unit? Other than might lights, I don't need lots of amps as my only stereo/amp since getting this car in 2007 has been the inline six...I'm not going to bother with fixing an open diode if that's the case, but it's interesting to note skk's thoughts as the autoparts store guy could not calibrate my car to what his tester was asking for and he did remark that this could be an issue in and of itself. Maybe I'll visit my local mechanic who knows my car and ask them if they can check further or simply swap in a whole new alternator...what are the good options to the Bosch AL45X which doesn't seem to be available anywhere?

 

[skk]

The "midtronix" screen shot shows 13.85V under load, only 85mv ripple. That sounds like a healthy alternator and regulator. Get a 2nd opinion from an expert.

 

[jmackro]

a modern 1-wire, higher output alternator would be a healthy upgrade

If you do need to replace your alternator, an alternator out of an 80's era BMW will bolt in, eliminate the need for an external regulator and provide cleaner output. I have one in my coupe.

Another alternative is an expensive Delco alternator as discussed in this thread: https://e9coupe.com/forum/threads/ac-delco-alternator.44271/

 

[Stevehose]

Do you have an old school alternator shop that could test it and rebuild if necessary? I certainly wouldn’t get on the road with a dubious alternator.

 

[Krzysztof]

Oh my... It is so sad mechanics/electrics having a lot of equipment are relying so much on the tester.

I agree that one diode out would cause e.g. light flickering visible at dash or driving at night with all lights on. Sometimes is can also cause charging indicator to be blinking or barely illuminating at all possible lights/devices being on.

I would use bolt-on option.

Is the alternator still under warranty? Probably alternator-repair shop can be better in the issue detection than standard shop with "smart" tester.

 

[sfdon]

Wayne- replace it with a rebuilt unit now.

 

[E9Wayne]

Thanks, again, all, I will definitely get my alternator checked out before doing anything. I do like the external regulator mount units as the wear and tear part is easily swapped out...but I don't see many AL45X units for sale and I'm not yet thinking towards the single wire internal regulator alternative. Does anyone have the Bosch 65 amp AL41X installed? There seem to be many more of those in the low $200 range for remanufactured?

Per Don's input just now - replacement will be forthcoming once I locate a decent replacement part - tips and suggestions on the Bosch replacement part...

 

[sfdon]

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www.buchananautoelectric.com

 

[E9Wayne]

And another thought, since my long block is from a Euro 1984 635CSi, the Bosch AL46X seems to be the direct replacementa and there are more of those available...

 

[sfdon]

It’s the bracket- not the block Wayne.

 

[E9Wayne]

thanks Don, I should know that by now . Do you recall what alternator I had installed? It pre-dates your engine swap so my guess it's AL45X but I can't locate any part numbers on it...Can I install a 41X, 44x or 46x?

 

[Stevehose]

I do like the external regulator mount units as the wear and tear part is easily swapped out

Except that external regulators are mechanical, a modern internally regulator is solid state, more accurate and reliable - and easily swapped out without even removing the alternator. I kept my external one for looks and a spare internal regulator in my road trip box.

 

[sfdon]

To be clear- there are 2 brackets that look the same.

They aren’t the same at all. One is slightly larger to accommodate the later alternator that has bushings.
And there are 2 different bolt hole sizes.

Get your alternator rebuilt and you won’t have a problem.

I haven’t seen many AL45x alternators available lately.

Thats why I have them rebuilt.

 

[Ohmess]

Wayne - As I recall from our Monterey trip, and Macha's emergency repair, you don't have an external voltage regulator, which means you don't have an AL45X alternator. An external voltage regulator would be mounted on the fender, whereas your voltage regulator is mounted outside the alternator. It looked like this: https://www.rockauto.com/en/moreinfo.php?pk=10430216&cc=1012543&pt=4884&jsn=10971. Yours is therefore considered to be integrated into the alternator itself.

I had the alternator on my coupe rebuilt when I lived in the DC area. There was nobody in Virginia near DC, you have to drive to MD. I'm pretty sure I used these guys: http://www.autoelectricinc.com/, and in any event I just called them and they do rebuild alternators.

By the way, I recommend getting yours rebuilt rather than buying a rebuilt unit, even though the cost is about the same. All the Bosch rebuilt alternators, even those sold by Bosch, are done in the same factory in China. If you have a local guy do your rebuild, he might still be in business the next time someone in the area needs this done.

 

[E9Wayne]

Thanks, Don, Chris, Steve, etc. Chris, you are right, I was assuming an external voltage regulator was simply attached outside the alternator housing - duh! I will try the local rebuild route...

 

[sfdon]

“By the way, I recommend getting yours rebuilt rather than buying a rebuilt unit, even though the cost is about the same. All the Bosch rebuilt alternators, even those sold by Bosch, are done in the same factory in China. If you have a local guy do your rebuild, he might still be in business the next time someone in the area needs this done.”



hahaha- so true!

For Wayne- you likely have the AL45x that has had an internal voltage regulator installed.
Also, that appears to be a lock washer being used and it shouldn’t be there.

Strongly urge you to follow Chris’s advice. Local rebuild is best.
If in dire need I have 7 fresh ones on the shelf now. You will need to remove yours, measure the gap and the bore.


Not cheap I’m afraid. Buchanan is very good but a bit pricey.