Can an alternator charge some times and not other times ?


Asked by Sep 18, 2015 at 11:31 AM about the 1994 Mazda MX-5 Miata M-Edition

Question type: Maintenance & Repair

First time the battery was checked, Advance Auto Parts did not find any
problems with the alternator. Second time, they told me that the alternator
was not charging. Is that possible ? Do I need to check also for the
regulator or should I change both ? When the engine is about to die, I
have noticed that the ABS light starts to light on until is stays on, then the
engine dies. Another mechanic told us that the problem could be a sensor
? Thanks for your advice.

5 Answers


Would you advice to take it to the dealer's to have this job done or any other mechanic shop will be able to do this job ?

Michael Kane

The Miatas small battery is usually good only for a few years before it needs replacement. What is the symptoms of the car is it dying when it comes to a stop? is the battery sometimes dead? It could be a bad ground or IAC idle air control which could cause the cars idle to fluctuate or even die when coming to a stop. The ABS senses the car about to shut down triggering the ABS light / engine light/ ect.

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Michael Kane

The altenators rarely go bad in the first gen miatas.

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Hi Michael , below please find a detail log of the events where the car has failed . Please let me know if you need more info or if the log is confusing Thanks for all your help Manuel ELECTRICAL PROBLEMS WITH MIATA 1994 Background Bryan - previous owner for 20 years ) told me that he had some issues with the battery. That the battery was being discharged with no apparent reason and the engine shuts off. He took the car for inspection on 07/15 – Diagnostic – Battery was low, was recharged, everything seems to be working fine. If more problems appear, bring it back for further testing. A year back (09/14) Bryan bought a new battery in Advance Auto Parts (AAP). 1st Event Morning: Greenbelt to UMBC (23 miles) UMBC to GB (23 miles) OK Night: Greenbelt to Columbia MD, (20 miles) I had lights on, charging my Mobile and listening to music. When waiting for my son, I turned the engine off and let the switch on to continue charging the mobile for about 15 min. When my son came out, the engine did not start. We pushed it in reverse and was able to start it (manual shifts). However, it died again few minutes later. We were still in the parking lot. Then I drove and started it by letting it go downhill. I started in 2nd gear and after that, the engine worked perfect. We were able to return home with lights, no radio. Next day, the engine started without any problems. I Took the car to AAP for testing. Diagnosis: Battery seems new, is holding the charge, and the alternator is loading fine. 2nd Event Afternoon: GB to UMBC (23 miles) OK Night: UMBC to GB. (23 miles) Started raining, had lights on, radio and wipers after 15 miles, where there is a big bump in the bridge. The ABS light started to light on and off. The headlights started to fail and one of the lamps even retracted. Still the engine was running, but did not have power. At NASA employee’s entrance(. 20 miles), I had to pull since the engine was about to die. I turned all lights off and was able to continue my trip (NO lights). When I got to the last intersection to my house, I had the courtesy lights on, and the engine did not have any power. I switched them off and engine recovered power. I was able to make it to home (last mile) Next day, the car started without any problems. 3rd Event Night: home to shopping mall (5 miles) Returning home: I don’t remember if I had the music on, most probably NO since I knew about the problem. Half way back home,, the ABS started to light on and the engine died. I was not able to start the car until one person agreed to give us a jump and we let the connection for about ten minutes to charge my battery. The car started fine after that and we made it home safely. Next day, the car started without any problems. 4rd Event Afternoon: GB to Beltsville (10 miles) OK Returning home: My son stopped in the Mall and was not able to start the engine until he got a jump he moved for one block and the car died again. We were able to get 3 jumps, however the engine continue dying. The last jump was for about 10 minutes. After that, we were able to go back home safely. Once we were at home, my son tested the car and turned the AC, Lights, Radio and : The engine never died. Next day, the engine started without any problems. I Took the car for testing again to AAP, the Battery is OK, however the Alternator is NOT charging. APP cannot replace the battery. Ithey told me that I have to take it to an specialist to check for other electrical problems such as the alternator/regulator , or others ?


I have done further testing and noticed that the Alternator chargers (14. x Volts measured at the battery terminals) when the Battery bulb lights (deem) in the dashboard at the moment of starting the engine. If the Battery bulb does not light, my readings indicate the alternator is not charging. I was sure that the battery was fully charged. I also noticed that at the beginning, the reading was going above 15 V while I heard a squeaking noise. Few seconds later, the reading went back to 14.x Volts.

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