I have had my LT1 swap running for about a month now and the other night I noticed that the battery was draining all of a sudden (radio turned off). My first thought was the alternator because I just re-used the one that came with my engine. So I replaced the alternator the next day but I was having the same issue, so then I thought that the battery must be going dead. So I put in a new battery. The car is running now and isn't really draining anymore (it seems) but the volt gauge on the dash is reading lower than usual (about 3/4 of the way between 8 and 13). Before this issue started it was reading just after the 13. My electric fans also stopped working around the same time so I thought that perhaps there was a draw with the fans causing the problem. However unplugging the fan relays did nothing to solve the issue. Today I put a multimeter on the battery and it read 12.36 volts at the battery with the car off. With the car on, it's fluctuating back and forth between 12.09 and 12.11. It's almost exactly the same numbers at the alternator as well, and at my power distribution block. All of the power wires that had fusible links in them are now hooked up to a power distribution block with fuses.

For grounds I have 2 4 gauge ground straps from the engine to the car; one coming from the passenger head to the firewall and one from the lower driver's side block to one of the studs holding the k-member brace on. For the battery ground I have a 2 gauge ground to the k-member brace on the passenger's side.

So I think there is probably a draw somewhere that is causing the drain. Any suggestions on finding the issue? The next thing I'm thinking of trying is unplugging a bunch of fuses and see if the volts go up while the car is running, then plugging them back in one at a time to find a problem spot. I just don't get why the problem seemed to appear out of nowhere.

 

When you say with the 'car on', do you mean running or just ign on? If running, your alt isn't charging - should be 14-ish volts.

 

Yes 'car on' means running. I do believe that the alt is charging because I was able to drive 60+kms today without charging the battery and it still has power.

 

Checked the numbers again and this time it was reading 12.15 at the alternator with the car idling. That went down to 12.9 with the headlights up, and with the headlights up the battery was reading 12.4. Is it possible that the alternator is giving a partial charge? Just in case it's important, my main positive cables are the following: 4 gauge from battery to starter, 4 gauge from battery to power distribution block, 4 gauge from alternator post to power distribution block. When the problem began I originally had the 4 gauge from the alternator going directly to the battery but I read that this could cook a battery so I moved it before I installed the new battery but there was no difference.

Also if it's important the only alternator that was readily available locally was a 105 amp version so that's the new alternator that I installed. After that didn't make a difference though, I re-installed the original. Is a 105 amp alternator insufficient? They apparently did come with the 5.7 LT1 in some B-body cars.

 

Just drove the car another 60 kms at night this time. By the time I got to my destination the volt gauge in the car was reading about 11. So the battery is getting drained but I don't believe the alternator is completely gone. I think I'm going to take the alternator to a shop to get tested on Tuesday if I don't figure anything else out by then. The post on the alternator should be reading more than 12.15 while the car is running, right?