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I haveing a electrical problem with this mr2 na that i just bought. previous owner is one of my good friends but I havent talked to him in a few days to ask him if he has had this problem, but he did mention anything. I bought the car from him on thrusday after work. It started fine then and i took it for a test drive , he drove it to my house, no starting or alt lite problems. The next day after work. I came home, started it a couple times with no problems. Saturday morning, it wouldnt start. just click. Jumped it off, pulled it into the garage to fix another problem, wouldnt start back up at the end of the day. Went and bought a new battery Saturday afternoon, starts right up and the alt gauge is up into the 18v area and the alt lite is on, tach is not working. Check voltage at the battery and its about 18 or so volts. Sunday, I went to start it up and just click. Voltage at the battery was about .49volts. Jumped it off and started right up. No alt lite, no high voltage, battery voltage was about 13 14 volts, Just prefect. Let it run for about 15 minutes and shut it off and restarts no problem. I did a parasitic draw test and between the neg cable and the neg post was 12.2 volts. Pulled all the fuses and the only one that seemed to make a little difference was the alt senseing fuse and the ecu fuse in the frunk. Maybe half a volt. I couldnt get to the big fuses in the same box. The neg cable looked like crap so i put a new one on and didnt help the problem. Tach hasnt worked sense. Any comments? Im leaning towards voltage regulator has an internal short.

Thanks
Matt


Thanks
Matt
 

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when you do a parasitic draw test, you need to test using an Ammeter or a test light, not a volt meter. the battery will always put out the same amount of voltage.... you are testing for amperage, not voltage.
 

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ok I checked the amperage and this is what i found. with the ecu fuse in it read about 12m amps. Which to me is nothing. I take the dome light fuse out and it goes down to about half. around 7.2m amps. Is 5 or 6 milliamps enough to case a battery to go dead overnight? And it still doesnt explain why with a good battery the alt was putting out 20 volts. Any comments?

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Matt
 

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no, 5 or 6 mA is not enough to drain the battery overnight..

so after the NEW battery had drained down overnight, you had to jump start the car and the alternator began generating 18V at the battery?
 

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Saturday morning it wouldnt start up. Saturday afternoon I put a new battery in and it started like a champ. But the alternator light was on and the voltage was about 18. I let it run for about 30 minutes. Sunday morning the battery was dead. If i jump start it right now the alternator will put out about 14 volts where it should be. The only time I saw the high voltage is when the fresh battery was put in.

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Matt
 

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Check for the voltage at the S terminal (backprobe) at the alt with the key on engine off. It should read the battery voltage which indicates there is no resistance on the voltage sensing wire before the alt.
You could go ahead to replace the voltage regulator if it is still overcharging on a fully charged battery with no resistance on the voltage sensing wire.
 

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You could buy only the voltage regulator from dealership for this Nippon-denso model, however the cost for an oem voltage regulator would be more than a rebuilt aftermarket alternator.
 

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Discussion Starter #12
Well I have found the regulator but im afraid it wont fix my battery dieing problem. It maybe 2 different problems. I thought maybe an internal short in the alternator.

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Matt
 

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Ok so if you are pegging 18+ volts the Alternator is the culprit like I assumed. Great gotta order one up. Or is there a possible explanation other than the Alt going bad for 18-20 volts. It got so high today on my drive home from work it blew my EFI fuse in the engine bay.
 

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nonboostedmr2 said:
Well I have found the regulator but im afraid it wont fix my battery dieing problem. It maybe 2 different problems. I thought maybe an internal short in the alternator.

Thanks
Matt
Your battery is being overcharged, that's why it's dying. 18-20V is WAY too much voltage and the cells inside the battery are likely being damaged and it completely drains overnight as it cools. You should be seeing 14-16V. The new battery will eventually be damaged beyond use as well.

So there's definitely a voltage regulator issue or an alternator sensing issue (S pin as listed above).
 

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^^Agreed^^. Rarely this is the case with overcharging but it is possible if regulator is faulty. Need to pull the alternator out and get re-built (not a fun job). Make sure you get the correct amperage alt as there are several different types (70, 90 & 100) from memory.

I don't think that this is your problem but I'd check the ground connections from the ECU and engine/tranny to chassis. This is a common problem and can produce some strange results if the resistance is too high in this circuit. Main one which corrodes is on top of the tranny to the chassis and many owners neglect. Often a cause for engine fires as it will use the throttle cable for return if this cable has an open circuit.

Jim
 

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70amp - base, non-PS; 5SFE/3SGTE
80amp - automatic 5SFE, non-PS; Canada spec 3SGTE
90amp - 9201+ PS
100amp - 9001-9201 PS

So says the parts catalog. Automatics are always rated 10amp higher since they're power hogs too.
 

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My experience is that voltage regulators in automotive alternators (in general, not Toyota specific) are serious weak points. I've had overcharging, "won't start charging until driving for 2 minutes", and random dash lights flickering (with what appears to be good voltage), all be solved by swapping the alternator. I always struggle to find another cause, but ultimately give up, swap the alternator, and guess what, that was the problem... :)
 

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benckj said:
I don't think that this is your problem but I'd check the ground connections from the ECU and engine/tranny to chassis. This is a common problem and can produce some strange results if the resistance is too high in this circuit. Main one which corrodes is on top of the tranny to the chassis and many owners neglect. Often a cause for engine fires as it will use the throttle cable for return if this cable has an open circuit.
This also wise. I had the ground strap fall off the starter on my Mitsubishi. Trying to start the car was real rough. Eventually we found it and fixed it. However, apparently it had been sending it's current through the ignition cable as I suffered a power transistor and coil failure right after that. Those parts don't take kindly to carrying the kind of power that a starter draws! Grounding issues can be very serious fire hazards!
 

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Yes, but what is being said is not related to the alternator. Your alternator may need replacing but is only a symptom with the problem elsewhere.

Jim
 
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