Technical > Wiring & Sensors

Good Grounding

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Volvo850r:

--- Quote from: rob@vems.co.uk on February 27, 2007, 02:25:10 pm ---Grounds are a much under estimated part of any ECU installation, just count the number of ground wires on your standard ECU if you don't believe me ;D
Because of the way we isolate the delicate sensor grounds from the noisey ignition and control grounds it is ESSENTIAL that the grounds are grouped correctly.  It's always best to explain using an example, and thanks to Damo we have the perfect example of a good grounding setup:



Wires are all joined securely 10 to 15cm outside of the unit.  It is possible to use a longer wire after the join (of >6mm2) if a suitable grounding point is not within reach.

--- End quote ---

Where would you connect the sensor grounds?

I say this as looking at phatbobs guide and the vems manual it shows the sensor grounds being wired pin 26 (either directly at pin 26 or 20mm from the common ground point along the branch to pin 26)

so looking at the above picture, would it be ok to wire your sensor grounds to that ring terminal? if so that would be good for me a my ecu is a solid metal case and i was going to put a screw\bolt through the case and then connect all the grounds with the use of ring terminals to it.

rob@vems.co.uk:
You connect the sensor ground to the common ground, the 20mm part has turned out to be not necessary.

Tony C:
Rob,
will it be ok to join the sensor ground wires at the ring terminal point?
im doing a loom for stuball's v8 capri (dnb doing ecu),
at the ring terminal point it will be where i go up to 6mm cable to run to the back of the head,

or do i need to run the sensor earths direct to the vems at pin 26? (as you say the 20mm up is not needed)

also i see on the wiki (your post) you show this,

where do i need to do this? or where i do the solder join to 6mm be ok?

Volvo850r:
Rob,

what would you consider to be the "best" method of wiring the sensor grounds (in an ideal world)? ie all directly at pin 26, all at the common ground point, or 20mm from the common ground point. I know you said the 20mm part wasnt necessary, but is that because you can "get by" by wiring at the common point or because it really makes no difference at all.

Thanks.

rob@vems.co.uk:
The 20mm point was one of those things that came about when someone who was not a native english speaker told me that the sensors should ground 'not more than 20mm from the common' - or words to that effect.  It turns out that anywhere between common ground and 20mm up the wire to the pin26 is acceptable.

But...

If you cut into the wire that leads to that ground pin you can add a stress riser that could potentially break - and that would cause the P259 chip to pop - pulling the VR chip voltage down and stopping your fuel pump, easy enough to fix, but not a fix you want to have to make.

So I go for the common grounding point, using an additional wire with its core exposed mid way which I wrap around the twisted wires then solder - this gives me two sensor ground wires to fix my sensors to.

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