Hi,
I've got a VL with a s1 rb25 with rb20 ecu (FP). I'm nearly ready to start a tune. My afrs are't holding steady at all on idle and nistune shows battery voltage fluctuating all over the place, 12v to 16v in spikes from 14 causing a miss (I assume from this). I checked my voltage at the battery and it's holding a steady 14.2 on idle and 12.4 engine off. Battery is good, exedy HP 1 yr old. I'm wondering, how does nistune detect the battery voltage? I might have an earth issue in my loom somewhere in that circuit?
exciter and dash light are wired correctly.
Battery voltage fluctuates
Moderator: Matt
Re: Battery voltage fluctuates
Yeah this is pretty common. I see it more and more in logs from RB's these days. I suspect it's an age related thing - from old alternators. New RB's (most R34's) seem to be pretty solid. But older ones (particularly track cars) with RB20's or 25's from R33 often have large fluctuations/noise. You won't see it at the battery because the battery is a giant capacitor so it'll smooth things out. And you'd need to use a scope anyway.
The other thing is that the voltage will drop (and often get noisier) across a dyno pull. It's not unusual to see voltage drop by over a volt from low rpm to high rpm.
I'm yet to do logs on a car before/after alternator replacement so this is purely speculation. But I take a log at the end of each tune and it's definitely something that I'm seeing more of as these cars age.
PL
The other thing is that the voltage will drop (and often get noisier) across a dyno pull. It's not unusual to see voltage drop by over a volt from low rpm to high rpm.
I'm yet to do logs on a car before/after alternator replacement so this is purely speculation. But I take a log at the end of each tune and it's definitely something that I'm seeing more of as these cars age.
PL