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Voltmeter readings jumping to 18

C

charley88

Guest
This problem started a few weeks ago. I figured the regulator was on it's was out. A couple of days ago the system stopped charging all together with battery idiot gauge lighting. Just put in a rebuilt AC Delco alternator and I'm still getting Voltmeter readings of 18 (sometimes), no battery light though. I recently changed the MAF relays (made a big difference), but the high volts started before that job. This is a stock 1988 coupe. Any thoughts out there?
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
What does a REAL voltmeter say?

Does it agree with the 18 volt reading?


Vig!
 
C

charley88

Guest
There is a 2-3 volt difference between the battery posts and the dash now. However, I checked this numerous times in the last three weeks and it matched the dash every time. How could this be?
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
That the regulator is toast

Inside of the ALT... and it's putting out FULL throttle!


Vig!
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Clarification

Internal of the ALT is a voltage regulator.

This limits the voltage output of the alternator.

When it shorts OUT the Alternator goes to FULL OUTPUT
(IE 18volts depending on revs of alt)

My magic internet 8 ball of automotive repair is indicating

REPLACE ALT NOW!


Vig!
 
E

Eagle85C4

Guest
Regardless of when it was replaced...you have a bad alternator. Mine just went through the same thing....red light...18.3 volts...SES light on...
Replaced it with NEW AC-Delco 124 amp alternator... problem solved.

You need to take that one back...
 

vigman

Motor head!!!!
Joined
Feb 13, 2001
Messages
3,471
Location
Valencia, CA,USA
Corvette
88 Convert ( SOLD ) /1973 coupe 4 speed/1964 Vert!
Just because it's rebuilt

doesn't mean it's perfect! There are ALWAYS chances that stuff fails!


Vig!
 
L

LarryBible

Guest
I'm assuming that you are getting this 18 volts from the voltmeter in the instrument cluster. Just for giggles, how about putting a voltmeter across the battery with the engine off, then again with the engine running. It should hang pretty close to 12 Volts with engine off and 13,4 to 14.1 with engine running. This would just be a good, quick cross check before messing with these guys to get the alternator replaced.

If the voltmeter across the battery confirms 18 volts, the regulator is shorted and your new alternator is a defect. It should be replaced under warranty.

Good luck,
 
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Eagle85C4

Guest
I may be a bit daft at times...but I swear...that is what Vig and I just said....
 
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LarryBible

Guest
Sorry,

I missed the question from vigman asking what a real voltmeter said. I had been assuming that the voltmeter being referred to was the instrument panel.

I'll back off and shut up.:duh
 
E

Eagle85C4

Guest
Well don't do that....in case we are wrong it's another person to share the blame...or acolades as the case may be....:beer
 

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