1985 Buick Century Alternator

MSH9663

MEMBER
1985 BUICK CENTURY
4 CYL
FWD
AUTOMATIC
99,000 MILES

I have been through two alternators. Each one I disconnect the positive cable while the car was running to see if the alternator would keep the car running. The alternator is putting out 11.96 volts. If I charge up the battery the car will start and run for three days. I let the car run for 30 minutes and got the check engine light soon light to stop coming on in the daytime, but when I drive at night with the light on the Check engine soon light come on. I have to keep charging the car in order to use it. This doesn't give me the opportunity to go to Walmart 25 miles away. If I bought another alternator and put in in would this make the car run the way it used to? What else would I have to do? Thanks.

6 Replies

RASMATAZ

MECHANIC
75,992 POSTS

There's a D-hole on back of the alternator ground the tap by inserting an object into it -this will bypass the regulator and make the alternator throw out everything its got-Now what's the running voltage?

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Thursday, September 25th, 2008 AT 2:29 AM

MSH9663

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I was told by my machanic that if I did this, it would overcharge my battery and make it boil. Because it would put out more than it is suppose to.

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Sunday, February 22nd, 2009 AT 2:29 AM

DOCHAGERTY

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I think what Ras is asking is that you test the alternator output and yes it will overcharge the battery IF you just left it that way. Please follow his request and report. The voltage should go to 14+ volts when you BRIEFLY bypass the regulator. What he is trying to do is to get if the regulator or the alternator is the fault here. Does this request seem reasonable?

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Sunday, February 22nd, 2009 AT 9:59 AM

RASMATAZ

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Thank You Doc-thats the whole idea behind it-Now 11.96 is not even enough to tickle the starter to crank the engine. However if the engine fires up and you bypass the regulator and that voltage zip sky high then you have found the culprit the IVR went southbound and needs replacement

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Sunday, February 22nd, 2009 AT 1:52 PM

MSH9663

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Would this ruin my alternator by shorting out the regulator this way? I have already bought three alternators, two were tested by Napa and they said they were good. The one in the car was tested good. Your request seems reasonalbe, but I have very little knowledge of fixing cars. I dont' know what IVR is.

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Tuesday, February 24th, 2009 AT 8:38 AM

ZACKMAN

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4,202 POSTS

IVR is the Internal Voltage Regulator. This is what controls the voltage coming out of the alternator. Now alternator can put out as much as 18 volts all day long, but obviously it will ruin your electrical if YOU LEFT IT at that voltage for a long period of time.

Ras was asking you to BRIEFLY bypass the IVR to make sure that the alternator is putting out the voltage, 14 plus volts. The IVR is responsible to limit the voltage output to usable level (between 13.1 to 14.5, roughly). You will be testing the alternator output with a DVOM (digital volt-ohm meter) only to make sure that the alternator is putting out the voltage. If you have more than 14 volts, than the alternator is good, but the IVR is bad.