Drautotech

hello
i have 1990 corvette L98 motor
just finished doing a engine rebuild on it ( new piston, comp cam, crankshaft and bears.) the engine bored out a 355.(30 thousandths over)
speedometer has never worked in the car, but before engine rebuild it never did this.

Im having an issues where when i come to a complete stop or cruising the battery voltage will drop to 10 to 11 volts shown on battery voltage gauge on dash. most of the time it will drop idle very low about 400 to 500 rpm then jump back up or stall out
if it does not stall, i start driving and voltage will increase.

Things I've done so far:
load tested battery and got 655 CCA spec is 650CCA
battery voltage and alternator with car off and KOEO is 12.6volts
In park and running its around 14.2volts
once i put it in drive voltage starts to drop
Found some corrosion on both battery terminal leaks. cleaned them and still have the issue
red wire to alternator gets very hot.
seems to be dropping voting when engine is hot
voltage was at 12.64volts engine running in park when i got home
Got a new alternator.

Is there anything else i should check. Did some testing today and not really sure where to go to next.

Thank,
Danny C

WVZR-1

I'd maybe after doing what you've done do a dedicated ground from the alternator to engine block. You've done all of the reasonable checks for sure!!

Drautotech

how exactly do you do a dedicated ground? Ive never heard of that.

WVZR-1

A braided strap with serrated ring terminals on each end. Mounting bolt of alternator top or bottom to cylinder head or block. What gauge is the wire to the alternator? Is it a cut splice of sorts or you believe to be original? Is there any unusual stereo or accessory adds?

You said "GOT NEW ALTERNATOR" - is that now and NOT installed or you've already mounted it?

Joe C

- probably wouldn't hurt to add a secondary ground from the block the car's chassis.

Drautotech

okay ill look into that and the wire to the alternator is the original 10 gauge wire. i put in a aftermarket radio awhile ago not recently. wasn't doing this after i installed the aftermarket radio.

Drautotech

will look more into this

WVZR-1

You didn't answer THE NEW ALTERNATOR question! Is the 12.64 with the new or is the NEW still in the box waiting. You certainly could have internal alternator problems or maybe even the through terminal. You checked way more than most before posting. You did CCA, KOEO etc so ...

The braided strap may NOT fix but it ain't going to hurt a thing.

oldspeedr

Without the back story on this: Check the alternator to battery connection at the alternator. Mine had resistance also causing that wire to get very hot and impact voltage. Replaced connector and no more issues.

Benny42

Reset the base idle speed, 450~ rpms in drive is kind of low. You mentioned a cam but no specs. Any cam other than a stock replacement means you need to at least check it.

Drautotech

new alternator is installed. Sorry im in college havent been able to answer. The cca is at 655 i check it at school. Batter is fine and alternator seems to be fine. I got the alternator from autozone and it is a reman. One. I was gonna bring it back and have the test it. I gwve the old one back as a core. Battery and red wire going to alternator are reading 12.6v but in drive the idle drops and bring it down to close 10v. Voltage with the car running in park is 13.9v and in drive it drops to 12.6v.

Drautotech

i tested the connector and red wire to the alternator today at school and they are all getting around 12.3 volts with KOEO

Drautotech

the base idle is around 700 to 1000rpms but when i come to a stop it drops very lose and usually stalls ( 450 rpms or less)

Drautotech

ddahlgren

#10 wire seems kind of small GM or not. When voltage drops the wire is just that much more light duty as all devices in a car use watts volts X amps. Volts go down amps go up and wire is sized by amps and length of run.

By some chance do you have an under drive crank pulley?