808 ECU earths

[shifty6]

Hey.
Finishing up converting a VR auto loom to VN manual.
Now the VR auto look seems to have less direct ecu earths than the VN 808. I have two wires from the VR loom which went to pins C2 and C3, but need to earth pins D1, D3 and D10 and A12 according to the VN diagram.
These two earth wires are already connected within the loom from the factory, will it be ok to splice in These two extra ecu earth pins as mentioned above? I don't know if these pins serve different functions and I want to avoid intermixing noisy and quiet earths.
Cheers

[Circlotron]

I want to avoid intermixing noisy and quiet earths.
Cheers

Relatively few people understand electrical stuff and/or electronics.
Of them, stuff all appreciate the significance of noisy and quiet earths.
Give yourself a medal.

[immortality]

Vl400 will have a definitive answer but I would just connect the extra earths as intended on the block. Better safe than sorry.

Holden fell for this trap with the earth wiring of one of the VS V6 O2 sensors causing no amount of grief.

[shifty6]

Well even from the factory the VR harness had all the ecu earths joined together in the loom, except for the o2 sensor earth, which was only joined to the others by being crimped to another earth wire where it bolts to the block. But the VN ecu has extra earth pins so I would need to run new earth wires for these to earth at the block, or just join them into the other ecu earths, with the exception of the o2 earth, which I have kept separate.
I would rather just join them near the ECU tho as I have already loom taped and fibreglass sleeved the loom.

[Charlescrown]

I would like to know what is a noisy and a quiet earth? I would think that an earth is an earth. I have always connected all the earths together and have had no problem that I know about.

[delcowizzid]

noisey earth is all the high draw stuff injector earths etc quiet is all the sensor earths so as not to interfer with signals

[shifty6]

I pulled apart my VR loom to see what the factory earthing was like. I was expecting the earth from the ignition module to be separate but it was joined to the ecu earths in the middle of the loom. There were only two earthing points as well, one lug to the back of the head and another to the front of the motor near the water pump. These two points were interconnected within the loom.

[VL400]

When sorting out grounding, you need to consider everything has resistance. This causes volt drops along the length of cable, so for simplicity if the block is considered absolute 0V the ground wire that runs from the block back to the PCM for say the injectors will end up at something above ground every time the injectors are switched on and draw current. You could measure a square wave signal that is exactly the same as the PW.

When the PCM is measuring a sensor voltage its the difference between the ground at the PCM (end of the wire) and the signal, so if your ground connection at the PCM has a square wave on it because the same earth wire is also carrying switched current your sensor voltage reading will too. Normally the analog sensor voltage readings are filtered, so what you get is an average DC voltage of this square wave which becomes the ground offset. As this changes with load its pretty hard to null out (say its injectors causing this, vary injector PW and so does your ground offset).

The solution is to run ground wires that carry only the heavy switching currents and do not care for any small offsets. The sensitive voltage signals use a different wire, the oxy sensors being 0-1V and even more critical usually have a dedicated ground connection. You can then have a couple of points on the engine block for connection of the various grounds. Just need to be careful of ground loops.

[shifty6]

So can you tell me which pcm pins are used for things like injector switching and heavy current applications and which are not?
Cheers for your responses.

[VL400]

For an '808 style ECU...
D6 - O2 sensor signal ground
A12 - General engine earth. Links to A11 internally to the ECU
A11 - MAP, MAT ground
D1 - \
D2 - / TPS, CTS ground
D3 - Injector Ground
D10 - Injector Ground