PWM narrow band output

Just got my Spartan 3 lite, and was planning on using the narrowband PWM output to the ECU, whilst logging WB signal. i.e. using the one bung for effectively 2 probes (brilliant idea).

The problem I’ve got however is that the stock NB lambda probe input to the ECU (2 wires - signal and earth), is not grounded to the chassis. Also checking the ECU side 2 wires, it also doesn’t seem to be grounded to chassis.

It seems to use the Spartan PWM output your return/ground is the electronics “ground”, as there is no dedicated return terminal. i.e. it doesn’t have an isolated PWM output? Is this the case?

The ECU I have is a Siemens/Continental EMS3110, from a Renault Megane RS250. It also has open/short cct testing on the lambda circuit. This is typical of most european cars.

I’m reluctant to connect the Spartan electronics ground to the ECU lambda input for fear of frying the ECU. If not upon connection, maybe at a later time when a unrelated short pushes some current down the lambda earth.

Any thoughts or experience on this issue?? Is it a potential problem? How to overcome?
To be safe is there a signal isolator that you know of that could be used?

Look forward to your comments

Speaking in general as I do not have experience with your particular ECU. You only need to connect the signal wire to the simulated NB output. The earth wire is most likely not required to be connected.