ECU Voltage lower than battery

[BigBoiMR2]

Hello,

I am still in the early stages of my tuning and trying to make sure everything is functioning properly before I fully tune my fuel map. I currently have the car idle and cruise areas safely tuned.

I am running a Gen2 3SGTE in an AW11 with the ST205 PNP G4+ ECU.

I was having inconsistent voltage issues that I attributed to ground issues. I added a second ground to the battery in the trunk and the voltage is holding fairly stable now but I am getting a few different readings depending on where I check,

Ecu voltage in pc link 14.10
Alternator to chassis 14.58
Battery positive to negative 14.58
B+ backprobing to each of the 5 grounds on the ecu connectors 14.48

Is this somewhat normal? I have checked the grounds in the engine bay and they all seem secure. 

I am mostly concerned about the ecu reading lower than what I'm getting at the ECU pins with a multimeter.

Hopefully someone has some experience with this. Thank you.
 

[Adamw]

Can you backprobe accross pins 1 & 71, these are the main 12V & ground.

[BigBoiMR2]

I had been using pin 61 as the main power for my tests and probed 1, 14, 23, 26 and 46 as the grounds.

I will test again using 71 as the main 12v power.

I have attached the numbered pinouts I am referencing.

Thanks for your reply

[Adamw]

61 is not even connected in our ecu, that is just the constant 12V wire that would normally be used to keep the original ECU volatile memory powered up.

Pin 71 & 72 are the main power supplies from the EFI relay.

[BigBoiMR2]

Thanks for clearing that up. I'll update once I've repeated the test properly

[BigBoiMR2]

Alright I just tested pin 71 and 1 and got 14.20 which is matching the ECU voltage in the pclink software. The battery at the time tested at 14.7

[BigBoiMR2]

Ok, pin 71 receives power from the Circut Opening Relay, which gets power from the EFI relay so I will check the voltage along the path and find where it is dropping. 

Thanks for the quick replies and helpful information, I'll update once I've found the cause.

[Adamw]

I wouldnt be too concerned about a 0.5 volt drop over the main supply, Im pretty sure in those cars the fuel pump, boost valve, idle valve etc all feeds from that same relay supply so that is probably quite normal.