[Roverdog]

Hi All
Some ideas on this issue would be appreciated.
I am running a 0.4.4b board on an old Rover SD1,originally L-Jetronic,using speedy with original hardware.
Anyway i now have fuel and spark, speedy is driving a BIP373 to the OE coil and locked distributor.
Tuning is going well apart from this voltage variation issue. If you check the attached log, with the engine idling the voltage moves approx 0.3 v at random, in synch with this the pulse width, coolant etc moves, causing a very slight stumble.
I have checked the supply voltage at the board with a scope, it is not changing.have also taken speeding power supply and earth direct from the battery via a relay switched by the oe system.
Could this be a faulty component in the battery reference circuit?

[theonewithin]

Check the actual input at the Arduino pin and all along the circuit.

[PSIG]

I would suggest diagnostic analysis, e.g., VIN versus VOUT of the reference circuit. If the issue on on the board-side, then 'scope for where the variation comes-from. If necessary, temporarily pull a component from the circuit and check again, in order to trace the source of the variation (load, component failure, noise, etc). Hopefully, it's something simple like a bad ground or ground-loop. Stuff like that. Good luck!