Weird idle at 12.8 volts with DFI genVI

[turbo6man]

Ok I am getting ready for the drags and I installed a battery disconnect in the trunk, and when I first disengaged the battery disconnect, the car kept running due to how I had the alternator output wire connected. This is where I noticed the issue and it is: If the alternator is hooked up the system is at 14.8 volts and everything runs fine. If I disconnect the alternator so it is not charging (is at 12.8 volts) the car will not idle and hunts if you let the RPM's go below 2K. When I plug in the alternator back in, the volts go back up to 14.8 everything is fine again. This is very repeatable, has anyone ever noticed this? Thanks, James

 

[Craig Smith]

This is actually a normal response. Newer systems have battery voltage compensation strategies that lessen the impact of voltage fluctuation, but electronic fuel injectors work very differently at 12 volts than at 14 volts. The time they require to physically open once a signal is sent is a lot longer when the voltage drops, and it screws up your fueling.

 

[turbo6man]

Hey thanks for the reply, I am having the local rebuilder make me a GM "CS130" style alternater for me. He is making it a 140 amp model, and boy is that thing much smaller and lighter.