Voltage bouncing at idle
Thread Starter
4th Gear
Joined: Dec 2022
Posts: 4
Likes: 1
Voltage bouncing at idle
Hi everyone,
I'm having a strange issue with my 1996 C4 (Auto). Anytime I'm below ≈1k RPMs, my voltage jumps up and down between 12v-15v, almost as if its charging and then not charging. The engine also stumbles each time it bounces. Additionally, I've had greatly reduced MPG, around 4 MPG lower. I've replaced the alternator, battery, and belt. The belt is tight so there doesn't to see to be any slipping. I also had the alternator tested before putting it in and it passed. If I'm over 1k RPMs, the variation is still present, but extremely small, only bouncing between 14.4v-14.7v. Something worth noting, it doesn't happen immediately after a cold start. Only after I put it in gear and drive it a little bit does it begin. I'm really scratching my head on this one. hopefully you guys will have some ideas for me. I've attached a video of the problem so you can get a little bit of a better idea.
Thank you all!
I'm having a strange issue with my 1996 C4 (Auto). Anytime I'm below ≈1k RPMs, my voltage jumps up and down between 12v-15v, almost as if its charging and then not charging. The engine also stumbles each time it bounces. Additionally, I've had greatly reduced MPG, around 4 MPG lower. I've replaced the alternator, battery, and belt. The belt is tight so there doesn't to see to be any slipping. I also had the alternator tested before putting it in and it passed. If I'm over 1k RPMs, the variation is still present, but extremely small, only bouncing between 14.4v-14.7v. Something worth noting, it doesn't happen immediately after a cold start. Only after I put it in gear and drive it a little bit does it begin. I'm really scratching my head on this one. hopefully you guys will have some ideas for me. I've attached a video of the problem so you can get a little bit of a better idea.
Thank you all!
Thread Starter
4th Gear
Joined: Dec 2022
Posts: 4
Likes: 1
I finally was able to dig into the vette the other day. Pulled the AC compressor connection to no avail. I checked every input and output of the charging circuit, with everything in operating range. I checked the continuity on every single fuse, under the hood and in the passenger compartment. The fusible links behind the battery both looked and felt intact. I even cleaned the battery terminal connections just in case. After all that, I reconnected the battery and took it for a drive. It worked perfectly that night, no fluctuation at all. The next morning it worked great as well. When I started the car to head home after a day of work, the issue returned. Since then it has stuck around in the same exact fashion as before. I feel that since the sense circuit tested all good, including the grounds to the block, the problem has to be with some electronic piece somewhere else. Does anyone have any other ideas?
Safety Car
Joined: Sep 2001
Posts: 4,157
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From: Glenbeulah Wi
What your video did not show was rpm, is the engine dropping down low in RPM due to a stumble causing the alternator to stop charging? This could be an engine issue (Like miss firing plugs) that causes the charging issue.
Thread Starter
4th Gear
Joined: Dec 2022
Posts: 4
Likes: 1
Hi everyone, I believe I fixed the issue. There was a bad ground strap from G107 to the frame rail. After replacing it and cleaning up the contact area, I haven't had any bouncing for the last couple of days. I'm keeping my fingers crossed that it will stay that way.
