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Old 04-05-2021, 07:06 PM   #1
Board Member
Join Date: Nov 2018
Location: TLV, IL
Default Spartan2 Lambda controller wiring to MicroSquirt V3

My question is at the bottom, but I need to set the scene first, so that you could feel my pain.

Looking at the MicroSquirt V3 grounding and sensor grounding docs -

This is a dedicated sensor ground wire.

Pin22 and Pin23
The ground wires from pins 22 and 23 should be run to the same spot on the engine.

In this diagram -

We can see that the Wideband controller is shown to have 2 grounds. One goes to Pin20 (like other sensors do) and the other goes to "Power Ground".
We also see that the MS unit is grounded via Pin22-23 to a "Good Engine Ground".

Now, looking at the Spartan2 Lambda controller documentation (this one is a PDF, sorry) -

It also has 2 ground wires.


Black wire, Electronics Ground, Ground where interfacing device is grounded.

White wire, Heater Ground, Ground to chassis or engine block.

Also, some more detailed explanation is available here -


Grounding is very important, Spartan 2's black wire (electronics ground) should be grounded where the MegaSquirt ECU is grounded, Spartan 2's white wire (Wideband Sensor Heater Ground) should be grounded to the chassis far away from where the black wire is grounded. The white wire carries upto 3 Amps and if grounds are not properly chosen, it can cause very large ground offset errors.

Now, there are several contradictions here -

If I follow the Spartan docs, they specifically say one ground on engine, another ground where MS is grounded (which is on the engine as well via Pins 22-23) but they say that these grounds should be far away from each other. WTH?

If I follow the MS docs, I do not understand what is "Power Ground" as opposed to "Good Engine Ground" and is Pin20 far away enough from it. WTH?

I'm in pain...

Could some one please tell me how to wire the Spartan2 Lambda controller to MS? And the rational behind it? Cause I really want to understand.

Thanks in advance!!
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