LC-1 when hooked up scanner is showing 1/2 a point richer than when not hooked up

I hooked up the LC1 to PIN 1 and ground PIN 5 on the MPVI. Hooked up with ignition on it reads 21.4 as well as the LC1 gauge. However, when unhooked, it reads 21.9 on the gauge. Is the ground not suitable or something I'm over looking?

Thanks!

Bump for any suggestions or help?

I'm not exactly sure what you are saying.

So you hook up the LC1 to be logged through the MPVI, and are grounding it through the OBD-2 port, correct? And it appears to be working okay like this?

What exactly are you unhooking when you say unhooked? I guess I don't understand exactly how you have everything installed.

When I had my LC1 in my old Camaro, I had a connector under the dash I could pull out depending on what I was doing. The LC1 was permanently installed, so when I was not logging data through the MPVI, I had it grounded to the engine block. When I was logging data, I disconnected that ground and grounded it through the interface (and thus the OBD-2 port) instead.

Maybe I can clarify.

The LC1 is ran to a gauge and the MPVI interface. Using the instructions here, tap into the brown wire and run it to PIN 1 on the MPVI. Then, I ran a wire from PIN 5 on the MPVI to a ground.

When the gauge is on and running and I hook up PIN 1 and PIN 5 to the MPVI, I can physically watch the gauge go from 21.9 to 21.4 with ignition on. When I unhook PIN 1 and 5, the gauge reads back at 21.9.

Does that help clarify? If not, I can take a video.

What are you doing with the ground wires on the LC1?

Ground wires on the LC1 if I remember correctly are going to a ground under the dash. I think I might have used the same ground bolt for the MPVI interface wire as well.