Voltage question - is this odd?
Voltage question - is this odd? I have a 2005 CTS-V LS6 that's got H/C/I and has been tuned by 2 good/known tuners. Before the tunes and after, I've had a weird, intermittent RPM drop and bounce when I let off the throttle. I haven't ruled out something tune related but doubt it at this point.
I've replaced things like the TB and can't find any vacuum leaks.
I've done the "big" three as I relocated my 1 year old Optima Red Top to the trunk (0/1ga to the starter then to the fuse box, 2ga to the alternator, 0/2ga ground to the frame, redundant 4ga ground from battery to the block).
It seems like the RPM dip is electrical related - my volts drop from 14.4 to like 12 when the drop happens (chicken and egg, I know). I found I had a bad alternator diode and expected replacing the ALT to fix my problem. It's better but not solved.
Here's what's odd, I think. Even though, while running, I get 14.4-14.6 across the battery posts, I can't get my battery to stay above 12.47-12.5V when the car is off. I can charge the battery and it will stay at 12.6V while off the car. When I connect it to the car (after an initial, small "system on" dip) it reads 12.47-.50V I've tested for voltage leak and am only pulling 30 milliamps. I've tested my grounds and they're showing very little resistance. Is it odd that I don't have any voltage leaks, my battery will keep 12.6V off the car but doesn't get above 12.47 on the car?
I've replaced things like the TB and can't find any vacuum leaks.
I've done the "big" three as I relocated my 1 year old Optima Red Top to the trunk (0/1ga to the starter then to the fuse box, 2ga to the alternator, 0/2ga ground to the frame, redundant 4ga ground from battery to the block).
It seems like the RPM dip is electrical related - my volts drop from 14.4 to like 12 when the drop happens (chicken and egg, I know). I found I had a bad alternator diode and expected replacing the ALT to fix my problem. It's better but not solved.
Here's what's odd, I think. Even though, while running, I get 14.4-14.6 across the battery posts, I can't get my battery to stay above 12.47-12.5V when the car is off. I can charge the battery and it will stay at 12.6V while off the car. When I connect it to the car (after an initial, small "system on" dip) it reads 12.47-.50V I've tested for voltage leak and am only pulling 30 milliamps. I've tested my grounds and they're showing very little resistance. Is it odd that I don't have any voltage leaks, my battery will keep 12.6V off the car but doesn't get above 12.47 on the car?
Last edited by jclayc; Apr 17, 2015 at 02:55 PM.
Thanks for the reply. I'm not familiar with a battery sense circuit. Are you talking about the smaller wires to the alternator? I've replaced that pigtail and verified I'm getting 10.5V to the hot wire when the ignition is on. I can't really find what that number is supposed to be, though.
BTW, I've also replaced the VSS, MAF and MAP trying to pin down this issue.
BTW, I've also replaced the VSS, MAF and MAP trying to pin down this issue.
Staging Lane
Joined: Aug 2014
Posts: 50
Likes: 0
From: Detroit, MI
You'd have to pull up the wiring diagram and look how the system is set up, but usually there is a circuit that tells the BCM or the alternator what the battery charge and load is, that's the circuit I'd be looking at. You should disconnect the circuit completely, from end to end, to check resistance in that circuit. If its more than 5 Ohms, you have a problem somewhere.
