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onboard voltmeter shows ~11.4v - what now??

Oct 30, 2001
Glen Burnie, MD, USA
1986 Bright Red Coupe
Changed the plugs this weekend in the 86 to Bosch +4's. First real drive out today (January in Maryland and the top off!!!!) and the voltmeter starts red-lighting me and reading between 11.1 and 11.5 volts. Reading didn't really change at idle or at speed.

Along with the plugs, I found a cracked vacuum line and check valve; the voltmeter light was on before and after replacing the valve.

Is there a chance that the plugs are drawing too much power? I'm not sure where the voltmeter does its readings - at the alternator, at the battery, somewhere else?

I checked the voltage at a couple locations. 11.5 at the battery at idle, which seems low, was the highest reading.

My alternator seems to be the non-user-reparable one :(

Should I just get a rebuilt alternator, look for the voltage regulator, or what? Or ignore the issue and hope it goes away as suddenly as it appeared?

I put the +4s in my92. It did not drag my voltage down. My digital gauge reads 14.x all the time. Before and after swapping out the ACs for the +4s. So I seriously doubt it is the plugs unless there is something seriously wrong with them.
Did you back and double check everything you touched to make sure you didn't loosen a wire, or move one so it's touching ground or bleeding over somewhere?

I just got back from taking my 95 for a spin around the neighborhood. I put the Bosch +4 plugs in tonight, No voltage problem here though still reads 14.7 volts on the dash. What did happen though was I removed the battery to replace a worn cruise control vacuum line. When I put the battery back in & buttoned everything up the Vette' wouldn't start. I checked the large fuses they were OK. I next got the voltmeter out & checked the battery with the terminals off & only had 9 volts. I had the hood open all night & those (2) lights were on & I had the passenger door open so the interior lights were on, so who knows. I charged it up for an hour & it fired right off.
Measure Voltage

The onboard volt meter in fairly accurate.

The regulator for the Alt is onboard.

Check for broken wires, loose/ corroded connections.
Measure voltage on back of ALT stud.

If under 13.5 @ idle...new Alt time.

The plugs will have nothing to do with the charging system. Unless of course when installing the plugs you leaned on the alt & broke something ( VERY UNLIKELY).



I hear that Mike. And I'll add one. Don't buy a STARTER from them either. Go with a DELCO there too!

Ok, I took the rubber cap off the "Battery" terminal on the alternator and measured the voltage between that and "ground" (one of the alternator fastening bolts). Got 11.29 steady.

Guess it's time for replacement.

No "Pep Boys" specials for me on parts like this. Starter was reman Delco and alternator will most likely be as well.

Thanks for the help, guys. I'm assuming the alternator replacement is a simple off-and-on job. Looks like a couple wires and a couple bolts and maybe moving an arm out of the way.

Ok. Got an AC Delco alternator off eBay (seller claimed it was low mileage, alternator looks brand new except for the pulley, which appears to be replaceable and is mildly rusted). This has to rank as one of the quickest car repairs I've ever done - 15 minutes start to finish, excluding time to jumpstart the car. Would that all accessory belts loosened as easily as this one...

Voltage read 14.7 after I fired it up, but dropped to 13.8 after a while and stayed there. Guess that's good enough for now. The alternator was cheap enough that I won't mind getting another one in a couple months if need be (when finances are a bit better - my *large* Vette repair bill is due next week :( )

Thanks for the help, guys.

Next job, TPIS custom-valved shocks, courtesy of my loving and very tolerant wife...
Correct O mundo

13.5 to 13.8 is right in the pocket.. when your driving a while and idleing it might drop to 12.5.


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