Hi guys. I am having a few issues with my 1991 coupe. I did do some research on the forums before writing this thread, but all of the threads I found are too old and don't show pictures of the ground locations or issues with the distributor.

Issues:

(1) There is a buzzing sound from the radio - not sure where it's coming from and I have already sent all the speaker and amps in to be rebuilt but it still does it. It gets louder as I give the car more gas.

(2) When I hit the brakes my dash LCD will dim down for a second.

(3) Occasionally my dash LCD will have impartial numbers that are dim, it appears to stop when I slow down or come to an idle. It does not change when hitting bums, just does it randomly on occasion.

(4) Randomly my voltage reader will bounce around, it is the analog gauge (I don't think I have a digital in the car). It doesn't bounce all over, stays a quarter of the way below 18 and probably bounces around 1 volt.

(5) Randomly my oil pressure gauge will bounce around, still stays half way and bounces slightly

I was wondering if this could all be do to a ground issue, wire interference with the distributor, or possibly the voltage regulator in the alternator. I had the alternator tested at auto zone while still in the car, they said it's fine.

Any help would be appreciated.

 

Just to let everyone know, the current alternator in the car is a ACDelco 10463007, which the product number shows it's a remanufactured 105 amp stock alternator. It has been in the car since I got it 2/3 years ago. Maybe I should just replace it with a higher amp alternator since this car has the miniram, aftermarket cam, a MSD box, shift light, DUI distributor and a radar detector; therefore it probably uses more amps.

Maybe a 140 amp alternator, what do you all think?

 

Bump.

Any guesses or advice would help greatly!

 

The "whine" I'd think is maybe typical of a GM alternator with a failing diode - a typical alternator test done by an auto parts store or others doesn't typically find that. An alternator/starter shop in the area could likely do the test "on the car" particularly if you mention the whine. It needs to be someone that "understands". Other than this check, the check is usually done when disassembled.

Coupled with the "floppy" volt-meter on the dash maybe you've actually just got very poor battery connections, alternator connections etc. Maybe do a separate ground from the alternator to the engine block and check all of those grounds at the block, frame rail etc.

The oil pressure isn't related.

I'd solve the "whine" and connection issues with what you've got before you consider maybe the upgrade to a larger unit. Your current is a CS130 - some say fine BUT others will insist a CS144 would be an appropriate upgrade for you.

 

Remove the serpentine belt.

Test the radio with the engine not running.
Does it still buzz?
If it does the CDM is probably bad. The CDM is the tuner and pre amp for the radio. It's located under the glove box area and mounted on a plastic tray. Very hard to get to. You remove the passenger side foot well panel lay on your back, disconnect around 4 wiring harness plugs that cross underneath the module to gain access to the module.

If no buzz start the engine. Does it buzz? Could be the ignition creating interference. (Not a common problem).

Does the dash behave normal with the engine running with no serpentine belt. (Alternator disabled).

If it appears normal, reinstall the serpentine belt.
Start the engine
If the voltage gauge is bouncing use a volt meter across the battery is the voltage stable? if the voltage is stable that would point to a dash or ground problem. If the voltage is bouncing around it could be a bad alternator.

The ground for the dash cluster is G201.
Location beneath left hand side of instrument panel at kick panel.

Here's a picture of a Bose CDM. If you have a Delco radio it also uses a CDM but it's different than the Bose.

 

Alright guys, so I moved some of the distributor wiring away from the firewall to see if it would affect the noise from the speakers. After doing that I took the vette for a 6hrs drive the other day for an interview, the buzzing from the speakers seams to have gone away!

Below is a picture of the other issue I addressed; the LCD display sometimes going on the fritz. While on the long drive I had noticed it happens only while driving, it stops when i come to an idle. Hitting bumps in the road does not effect it at all, so I doubt it's a ground issue. While on the drive and going 65-75mph I had tried turning off the radar detector and radio, it did not change anything; but when I turned the radio back on the LCD went normal for a few seconds. So at this point I think it may be the regulator in the alternator.

What do you guys think?

 

Has the alternator been replaced before? How old is the battery? Those are the 2 culprits that I would suspect.

 

I replaced the alternator yesterday. Then when I took it for a drive the LCD was going nuts. I had the new alternator bench tested before I put it in to make sure it was good since I hear a new alternator may be bad upon delivery, it tested fine, I also had it checked again today while on the car and it passed. I did notice the battery was at 12.3v after replacing the alternator, but I believe it may have been due to starting the car while forgetting to plug in the alternator harness the 1st time I started it. The battery is a diehard gold and is at east 2yrs old, since it was in the car when I bought it. I put it on a trickle charger to 12.6v and the LCD still goes crazy above 2,000rpm.