Sensor Ground not isolated from power ground in R34 GTR Engine loom

[burn4005]

Hi All,

wiring in my Emtron KV8 at the moment and was checking the sensor ground in pin 30 of the stock engine harness was isolated from power ground (pin 50&60) I'm seeing about 26kohm. this is with the ecu disconnected, and the water temp, air temp and TPS disconnected which are the only devices shown to be wired to pin 30 in the nissan schematic.

any ideas where this would be coming from?

to clarify, I'm not looking for suggestions on how to fault find this, I'm asking if this is:

-a normal condition for the stock R34 GTR engine loom and where the impedance between sensor and power grounds comes from or

-I have an issue somewhere in the loom that i need to find

[burn4005]

I think I've worked out what the culprit is. the Atessa computer using the TPS signal from the ecu.

[GTSBoy]

Makes sense.  I've been sitting here wracking my brain trying to work out what would put a medium sized impedance on that line.  had already discounted AFMs, on the assumption that you'd likely removed them to suit the new ECU.  In input on another CU would be the right sort of impedance.

[burn4005]

yea, Pin 30 on the ECU (sensor ground for TPS,Water temp and Air temp) is connected to Atessa ECU pin 34 as the TPS signal ground reference, so I'm guessing there is a link between the Atessa ecu pin34 and chassis ground inside the Atessa ECU with a 26kohm impedance. looking at the MFD display wiring schematic, the sensor ground doesn't appear to be wired to it, so just the Atessa ECU responsible.

the AFMs have a 12v and chassis ground to them, the stock ECU has dedicated ground pins (in 26 and 34) for the AFM signals (in 27 and 35) they are not connected to sensor ground in the loom.

Edited January 9, 2018 by burn4005

[gtrnz]

Stumbled across this trying to resolve a fault on my r34 gtr. I wondered where that impedance was coming from. The diagram shows atessa pin 34 as sensor ground connected to pin 43 of ecm, except ecm pin out for pin 43 is ign switch start signal according to manual. However, something is giving me an unstable throttle position signal when driving causing the car to surge, when tps signal pin 23 is taken away from the atessa the car drives normal again. The Mfd still shows the thottle % fluttering +/- ~5% with steady throttle and at idle up to 2% flutter when the atessa has the tps signal removed. At this stage it’s seeming like an ecm or atessa computer fault. Anything else anyone could think of that might cause this?