When do you use signal ground vs power ground

Discuss which Sensors work best with these ECUs and share how you are using inputs and outputs
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alevien
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When do you use signal ground vs power ground

Post by alevien »

I am having some drift between AFR readings from my gage (AEM) vs what I am reading on my analogue input. Iam concerned about grounding and which ground I should be using, Power ground vs signal ground. Shouldn't they be common to car chassis? When I check resistance between pwer ground and signal ground on the box is is 0ohms when the ignition is off, what I would expect. But when I power up the resistance between the two grounds as around 22ohms
stevieturbo
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Re: When do you use signal ground vs power ground

Post by stevieturbo »

Wiring diagrams are very clear.

NO sensor should ever connect/reference to chassis ground.

And no power wiring, ie that which carries any significant current or powers any device should ever be connected to ecu sensor ground.

Eventually after the ecu yes all grounds will return to battery/chassis ground, but the sensors after the ecu MUST be kept isolated from this and kept clean to ensure reliable signals.
Rob Stevens
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Re: When do you use signal ground vs power ground

Post by Rob Stevens »

However some widebands for example come with their own signal ground i.e. Inovate, this is good, I connect this to the ecu sensor ground. I also have a 'plx' this has no sensor ground and I suspect the 0-5v signal is much more erratic as a result.
What you must not do as Stevie says is use the ecu sensor ground for the power ground from the WB
stevieturbo
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Re: When do you use signal ground vs power ground

Post by stevieturbo »

This is why external widebands that feed an analogue voltage are never the best solution.

There's no logical reason they shouldnt give good reliable signals, but for some reason a lot just dont.

but yes if the wideband offers you a sensor ground, then pairing that with the ecu sensor ground should be fine.

I guess the next best thing if they do not, is to connect the wideband ground directly to the ecu grounding point at the battery
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