Good Afternoon, as I've noticed and seen many times in this thread, C5's are awful for having electrical gremlins and other problems. I have been having a problem with my car for a little while now and have been searching countless forums and YouTube videos for an answer, to no avail. I figured my last shot before taking it to a professional was to post on this forum with all the steps/tests I've done to see if there are any other ideas. I recently replaced the starter, and have a brand new battery in the car so those I ruled out. I also took the starter that's in the car and bench tested it, and it works fine. Here is a write-up of what happened to start the issue, and what I've tried doing so far:

The car ran perfectly fine, and did not have a draw issue unless I left it without driving for a few days which I just fixed by putting it on a battery tender. I decided I wanted to put longtube headers on the car, and did them myself. Everything went as planned following the steps given by LS1HowTo's guide to installing the headers. On my first start-up, it ran great for a few minutes but started to run very rough. Come to find out, the grounding strap on the rear driver's side head was loose causing the driver's side to not fire. I fixed that issue tightening the bolt up, and it started up and ran beautifully. I turned it off and tried to start it again five minutes later, and *click click click*. Sounds like a dead battery and the starter is clicking and trying to start. I put the battery on charge and charged it up to full and tried again, same issue.

This is where I started to run tests and tried multiple things to solve the issue, listed below:

• Me and my dad started to do a draw test on the battery with the multimeter set at 10A, and noticed that the draw once the circuit is complete reads 1.38, drops down to 0.58 after a few seconds, then drops down to 0.24 after a few more seconds. I believe that the 0.24 reading is still too high as the GM normal draw is at max 28 MilliAmps. Someone please correct me if I'm wrong on this.
  
• After we found that, we started to pull every fuse in the engine compartment fuse box. None of these fuses changed anything, so we separated the fuse boxes and sure enough it's the interior fuse box that's drawing.
  
• We then pulled every fuse in the interior fuse box, and the draw did not change.
  

This is when things got weird. We noticed that when either door is opened, the draw reading on the multimeter read 4.6 Amps! This also caused the battery to instantly drop down to 9.8 volts, even when it was fully charged prior to opening the door. When you close the door, the battery voltage slowly climbs back up to around 11.8 volts. While the door was open, we tried pulling fuses to see what would cause the draw to go away. The only fuse that changed the draw was the #25 fuse for the BCM. This dropped the draw down to 1.4 Amps, which is still too high. Even pulling the fuses for the doors didn't change anything.

I am now going to try to disconnect and clean all the grounding locations on the car. I am hoping that my mistake with the grounding strap did not fry my BCM or my PCM. Any help at all would be greatly appreciated, as I am at a loss with this and have never seen anything like it before.

 

C5s have problems with wiring in the "accordian" boot that carrys wiring from the door to the interior. Just a suggestion, but check the wiring harness that is running thru the boot. Those wires flex every time the door opens, and then closes. So, probably thousands of times thru the cars life. Many have found issues there. Bad BCM and seat control modules can also be an issue....

 

"Grounding strap" is not registering with me. There is a ground terminal G107 at the rear of the left head, is that what you mean? It does not make any sense that this was disturbed for a header install.

There IS a "Ground strap" at G105, which is located on the left/lower/rear part of the block. It DOES make sense that this was disturbed during a header install. There should be a ground strap and ground terminal at this location.

So wait. You said you charged the battery fully, and got the same result....car would not crank. Why would you start chasing a parasitic draw in the battery if you had not solved why the engine will not crank with a fully charged battery?


Boy, are you going to get chastised by C5Diag for pulling fuses, with a double violation for opening the doors and waking the BCM.

First thing you need to do is start with a fully charged battery, and troubleshoot why the engine will not crank. I encourage you to read through this section. Very long, but will explain how the BCM sleep works, and prevent you from chasing a ghost.
https://www.corvetteforum.com/forums...tion-long.html

 

Lucky,

Sorry in advance as I am not familiar with posting in forums and quoting peoples replies to organize a response, but thank you for the reply nonetheless! You are correct as I was referring to the "engine ground strap" and accidentally said it was on the back of the head. I disconnected that bolt with the two wires and so on with my original post.

As for your second question, we found that the battery was charged and by the time I got into the car to turn the key, the battery was dropping down to 9.8 volts so I couldn't get the starter to do but one click. That is why we instantly assumed that something major is wrong, because it is losing voltage so quick just by opening the door.

Thank you again for your response, and I know someone out there has some idea of what is going on lol. I also figured maybe there's something we're doing wrong, and I could get some pointers. Corvettes and their weird problems are new to me and it's fun finding them all haha. I will have to read the linked forum and see if there's answers in there!

 

Thank you I will have to try that. Hopefully it is something simple I am missing!

 

OK, just because you can fully charge your battery doesn’t mean it’s good…if you have a 240 milliamp draw for a while your new battery will be nuked after a few discharges depending on how low it gets…you should see around a 20 milliamp (.020) after all the modules go to sleep…either get another new battery or have it load tested at an auto parts store…watch the video and since you need to access the passenger side door to check the IP Fuseblock latch the passenger side door with a screwdriver….everything else should closed and if you have your hood light working disable that….when you get the draw diagnosed…with your new battery if the car doesn’t start connect one end of your voltmeter to battery negative and the other lead to the engine block…read the voltmeter while cranking…you shouldn’t see more than .5 volts…if you see a value like 4 volts that means only 8 volts getting back to the battery through battery ground…it should be 0 but seeing 0.2-0.3 is normal…you can do the same with a 12 volt test light connected to battery negative…when cranking the test light should NOT light…if it is you probably have a bad block ground which is above the starter…remove the battery negative cable and clean the cable terminal end and the block with a wire brush or emery cloth and reinstall…I will include a video below on how to perform starting system voltage drop testing.

 

 

 

Thank you for the suggestions! I will watch the videos and give it another try tonight and tomorrow, and let you know what my results are!