Voltage on my 357 '88 IROC drops a little after I drive the car for a bit. At first start up the volt gauge reads way above 13 (normal). But once I drive the car for a bit, the voltage slowly drops to a hair above 13 and sometimes right on 13. What gives? I replaced my Alternator couple weeks ago along with my starter. I also got new Positive and Negative cables as mine burnt to a crisp after one of them touched the header. I just don't understand. It never drops below 13 so maybe it's a small issue? Oh, I got a new battery as well. What voltage should the alternator be at with the engine running?

 

As a general rule of thumb, the system voltage should be at least 0.5 volt with all electrical loads on (lights, blower, fans, etc.) and the engine running above steady-state battery voltage off. Your voltage is high after starting because the system is recovering from the starter load.

 

Well as that may be true, it drops alot. My old GTA never went that low and I'm using the same stereo that car had. Right now the stereo isn't hooked up because of this voltage drop. If I was to run the stereo, I know the gauge would read below 13.

 

Dropped a tad passed 13 tonight so something is defiantly up. I'm going to get my alternator checked out but maybe it has to do with the new negative cable. It's grounded to my fuel pump block off plate which is chrome. The old cable was connected to the same spot and never had a problem so maybe it's the cable? The system is not recharging so I don't know what to do...

 

Check with a multimeter. You cannot trust the stock gauges.

Also, with full load, 13 is fine.

 

That's what I was thinking x2.


I believe the ground strap goes to the chassis, not the fuel pump block off plate.

 

So I can remove the ground that goes to the battery and attach it to the chassis? I figured it had to be ground to the motor.

It's at 13 now with just lights on, car running etc but that's after driving around. At start up, it's in between 13 and 18. I'm not even running my stereo right now which I know will drop it below 13. I'll try switching the negative cable to the chassis.

 

The block is a good place to have the ground as long as the engine is grounded to the chassis with good ground straps. If you move the ground to the chassis, MAKE sure the engine has ground straps to the chassis, or else its gonna have problems. I had a car once that had no ground straps from engine to chassis, so I simply left the battery to chassis ground wire and put another battery to engine ground wire. It doesnt hurt anything to have both the chassis and engine grounded.

 

Not to hijack this thread, but this seems to be sounding exactly like what i am fighting right now. I have an 89 GTA. When i first start up, it's running about 13.7volts at the battery, not trusting the gauge, but after it runs for a while, the voltage drops especially at idle. With everything off, the voltage drops a little bit by the gauge, but when the lights are on and the fans kick on, the voltage at idle drops bad, sometimes as low as 9v according to the gauge. The only reason i'm believing the gauge then is the lights dim down as well.

One thing i noticed today was the battery lead from the alternator is getting real hot. I change the butt splice out and started the engine and let it run and it's still getting hot. Any ideas on what i can check on? Both battery cables are new. The ground goes to the engine block, i cleaned it when i replaced the cable.

If i need to make a new thread, let me know and i will. I didn't mean to hijack this one, but it sounds like the same problem i am having. Thanks

 

I noticed that when I upgraded the "big 3" it alleviated most of the idle voltage problems...

FYI my old alternator did the same before I rebuilt it and replaced the brushes,diodes and regulator. It would start nice and high, but as it heated up it would start to crap out.

An interesting test for a blown diode is to turn the multimeter to "ac volts" and read teh output voltage of the alternator. It should be in the millivolt range. This is the ac ripple voltage that makes it past the diodes. If it is any more, there is a weak or blown diode that is not performing its duty.

 

Ok, i probably sound a little dumb right now, but what is the "big 3" i hear alot about? lol. I try to search it, but no explanation of the big 3. lol.

 

Big 3 = Heads, Intake, Cam

My car still dies off after driving for about 20+minutes. Only thing left I can do is go back to where I got my "new" alternator and see if they can check that or give me another new one.

 

Oh ok, thanks. I wasn't even thinking about the heads, intake and cam. I was thinking electrical stuff. lmao.

At some point i'm going to be doing a rebuild so i'll see then what that helps. I was just trying to get it figured out before then.

I drove the car tonight after some work i've done this week and it still drops down. Guess i'll keep digging until i find something.

 

There is another electrical big 3 as well

Upgrade the following:

Battery to Chassis
Battery to Alternator
Engine to Chassis.

 

Oh ok, that makes more sense then. lmao.

I've replaced both battery cables. Replaced the lead from the battery - to the radiator core support. I've checked the ground strap, but haven't removed it and cleaned it up. It looks good, but i am going to get it out and clean up the connection points to make sure it's getting a good connection.

 

If you look at the alternator charge wire, it is pitifully small. Upgrading that really helped my car.

 

Yeah, i replaced it as well. I used a 10ga wire. I was going to drop it to a 8ga, but i didn't have any connectors for an 8ga.

 

Hey guys im in the same place right now. Need to know where each of the wires lead to... its for an 88 Carar 305TBI. Is there a way to jump the alternator to the battery to see if it changes the charge at all???-Rev

 

There should be a wire that goes from the back of the alternator straight to the battery.

 

How did you do that and keep the fusible link? I'm having issues with my car here too. I fried the fusible link and had TONS of issues so I replaced the wire with a standard fuse in the middle. The bummer is I kept frying the connector, not the fuse.

 

TTT for this?