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Alternator failure - a strange story

9 October 2012
Riverside, California
Hello fellow NSX owners,

I recently had a strange electrical experience that I pass along - maybe it will help someone in the future.

I have stored my NSX in a garage with a battery tender (a CTEK model) since I didn't drive it often (5000 miles in nine years - yes, a crime!). Some time ago the battery must have given out. The tender tried to keep up but obviously couldn't. I replaced the battery but noticed the cable clamps were destroyed so I had those replaced too. I did not replace cables - man those things are expensive, and the positive cable looks like a real challenge to replace.

After all this some really strange things happened. One a few occasions the engine would cut for an instant; my only indication was that all of the warning lights would indicate. After a week I noticed it was really hard starting - I had to leave the throttle open cranking and hold it there. I never had to do that as in the past only turning the key would allow the engine to crank and start.

I checked this site as well as a general search of the internet. The general conclusion was that either the main (ignition) switch had poor contacts, or there was a really poor cable connection somewhere. I ordered a new switch and checked ground and positive connections - all of the connections were tight with absolutely no evidence of corrosion.

While waiting for the switch to arrive I noticed a new symptom - a strange moan from the alternator but only at speed. I didn't sense it at idle. Voltage appeared good - 14 plus generally with maybe a small dip to about 13.5 when really warm with the air conditioner running full tilt. At this time I did not see the electrical indicator light come on. Based on more research I also ordered an alternator. I did not get a new one - another very expensive so called "Honda" part, but was able to source a rebuild.

When it came I was between disappointed and hopping mad as the box was no more than a colored ball of tape. Removing the alternator confirmed everything as the pully would not turn - the unit had been dropped so hard that the frame was bent!

Based on curiosity and my anger I removed the moaning alternator from the car and tore it apart, removing the regulator and diodes (note to any users who are tempted to do the same - go for it; its extremely easy!) I swapped the regulator, diodes and brushes from the purchased unit and installed in my unit. After bolting everything back I tested and found the following:
- My car now starts at the first twist of the key again.
- No more strange moaning.
- I still see a small voltage dip when hot but nothing that interferes.

I don't know how the bad alternator caused all this; maybe there is an expert out there that can explain it. But like I stated in the beginning, I did not see anything like this in our archives so I present it as a learning experience that may help one of us.


Rebuilding alternators is easy, finding quality replacement parts is not... where did you get the parts?

I nearly always recommend rebuilding the factory alternator. If you must buy a rebuild and pay the core charge (if any), always keep your original core as a backup and rebuild when the opportunity arises. The quality JP bearings get replaced with low grade ones that do not stand the test of time.

Sounds like your diodes were bad. They tend to fail as a result of age. They dry out. Mine sounded like a bad bearing as the alt howled at low speed. A local shop rebuilt it including bearings, brushes and diodes. Jerry
I purchased a rebuilt Denso unit, but like I noted, was completely thrashed by the time I received it.

I swapped everything over to the original unit. I am a fan of the Nachii bearings normally used in such applications - I used to specify them in my old life as a brake engineer (think off road cranes and platform lifts).

So far I have kept everything.....I will eventually check the components out for curiosity's sake.

Its just strange to me that an alternator issue could mimic a switch/connectivity issue. I never had this with any old Chrysler product I had!