I've wired up a manual switch for datalogging on my S300, and its working... but the car runs different once I switch on the B5 (ground).

I tapped into B5 at the ECU... maybe I should just cut the original wire and have my switch the only wire coming into B5?

The car actually leans out a bit (not dramatic) when I hit the switch now... as if computer is trying to accomodate for the AC running or something.

Any ideas? I can share a datalog that I started manually (with my laptop)... then I hit the B5 switch.

 

screenshot of the datalog.... I started this on my laptop... then flipped the B5 switch I wired up (simple groud switch)

As you see, the timing goes from 16-17 immediately to 19

The A/F also temporarily leans fattens up, then leans back out to the proper range.

Bizarre, i'm sure its something simple, looking for some input

 

Does battery voltage change when you flip the switch? And does the idle return to normal of you flip off the switch?

 

Damn your fast Brian, haha. The voltage remains solid/consistent at 13.87-13.96

Yes, once I turn the switch off the car returns to normal

 

Guys , you are switching the A/C manually. If you have A/C then change your pinout. If you don't then disable all A/C controls in SManager and you can leave the wire as is. I personally just have tons of extra pin outs on hand so I can just pull the wire from the factory harness and solder my input to my spare pigtail. Not as clean, but I am a huge stickler for factory uncut wiring.