LC-2 only 1 ground - signal or power ground?

[turbogrill]

Hi,

I have a microsquirt and a LC-2 wideband. The LC-2 only has one ground, no sensor ground. My harness is 30 inches.
This leaves me with 3 options:

- Ground at MS engine ground. (Max 20A at 30 inches for 18awg gives = 0.64v voltage drop between MS and sensor)
- Ground at same sensor ground as MAP,IAT. (Max 3A at 30inches for 18awg = 0.1voltage drop between MAP,IAT and MS)
- Ground at own sensor ground (pin 18)

The first option is not great since the voltage drop over MS cable can mess up the AFR readings. 0.32v inaccuracy seems to be a lot for the AFR. MS manual says that 20A can flow in the ground cables (2 of them). This doesn't take into the account the additional voltage drop over LC-2s own ground cable.

The second option would be better but messes up the other sensor readings a little. LC-2 says that 3A can flow, I guess this is during heatup.

The third option is interesting but according to the manual this is not connected.

Why did they remove the sensor ground in LC-2!!!!!!!?!?!?!??!

[rickb794]

DO NOT run the O2 heater ground current through an MS. Noise will likely happen.

If your O2 setup does not have a separate sensor ground your only choice is to ground to the motor.
Well you could ground to the body, but that would be worse.

See section 3.2 of TFM

Contact your O2 Mfgr and ask them why they do not include a sensor return path?

[turbogrill]

DO NOT run the O2 heater ground current through an MS. Noise will likely happen.

Contact your O2 Mfgr and ask them why they do not include a sensor return path?

It's surprises me as well. They list it as a feature

Why is a wideband noisy? They seem to have a high current draw while heating up but is that the only thing?

[rickb794]

DO NOT run the O2 heater ground current through an MS. Noise will likely happen.

Contact your O2 Mfgr and ask them why they do not include a sensor return path?

It's surprises me as well. They list it as a feature

Why is a wideband noisy? They seem to have a high current draw while heating up but is that the only thing?

I think the O2 controller pulses the heater

[turbogrill]

Thanks!

I will create a ground point close to MS and ground everything from there. The ground point will be connected to engine/chassis using a beefy cable.

[Danbob]

Hello all, as LC-1 is discontinued now and LC-2 does not have a separate ground for sensor and heater I think more and more people are going to come across this problem (myself included).

What potential problems would be caused by:
A, grounding the LC2 heater and sensor to the same good engine ground as the megasquirt.
B,. Creating a separate engine ground for LC2 heater/signal away from ms ground
C, grounding LC2 heater and signal both to Megasquirt sensensor pin?

I'd like to understand what is the best way and what problems the other methods could cause and think this info will be useful for others in the future also.
Alternatively if there is no way of doing it that will work well maybe all LC2's will have to be binned and have to reinvest in a different controller!

Thanks
Dan

[Targa44]

I got a reply from Matt some time ago about my AEM single ground and he suggested to go directly to the battery.

kj

[racingmini_mtl]

Definitely not C: that will destroy all the other sensor signals. Option A has also the potential of creating noise in the MS supply. So that leaves B and the suggestion above of using the battery is a good one.

Having a single ground is not an ideal design choice in my opinion.

Jean

[Danbob]

Interesting, I was expecting option A to be the consensus.

Would grounding to battery not cause a potential error in your wideband reading at megasquirt? If the battery ground is not at the same voltage as the megasquirt ground? (I don't know, I am very much an amateur in this field)

My battery is in the front of the car and ECU in the back. Engine grounds to chassis as does battery. So would grounding my LC2 to the point the engine grounds to the chassis while keeping all MS grounds on the engine be the same as taking the LC2 to the battery?

[rickb794]

You have basically two choices ground to the battery or to the motor.
Grounding to the body is not a choice because of noise, it is similar to pulling power out of the dash harness.
I prefer the motor as the sensor is on the motor (sort of).
Grounding to the battery puts a certain amount of electrical resistance between the sensor and the ground.
The engine has more mass than the battery and is likely to be quieter that the battery connection.
Battery connections are "dirty" and there is a higher likelihood of corrosion.

[Blown88GT]

Follow Innovate's LC-2 Instructions.

[goodysgotacuda]

I just chassis grounded my LC2 as innovate defines and have no issues.


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[racingmini_mtl]

I just chassis grounded my LC2 as innovate defines and have no issues.

Their manual says to use the battery ground.

[goodysgotacuda]

I just chassis grounded my LC2 as innovate defines and have no issues.

Their manual says to use the battery ground.

By how they define I suppose I meant without adding any additional wiring/ground connections.

The ECU is also grounded to the chassis nearby. I have no issues with either.


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[Danbob]

Grounding to battery isn't really a good option for me as it's a mid engined car with all the electronics in the boot/trunk and the battery is at the opposite end of the car in the frunk.
The LC2 and gauge are currently running absolutely fine on their own at the moment both grounded at the engine, so not worried about the functionality of the LC2,. Much more concerned about ensuring the megasquirt gets an accurate wideband value from the lc2 and that the lc2 doesn't spoil my Megasquirt's other sensor readings

[turbogrill]

Follow Innovate's LC-2 Instructions.

They suggest signal ground.

"
grounding source as the device to which you are feeding the analog outputs,
the easiest wait to accomplish this is to run an aux ground wire from the
ground point of the LC-2 to the ground or signal ground of the device you are
interfacing with."

[racingmini_mtl]

This contradicts what the LC-2 manual says just a few paragraphs above which is what I posted before.

Do NOT use the sensor ground: this is a known problem and you will introduce noise into all the analog inputs into the Megasquirt.

Jean

[Blown88GT]

Mount the controller close enough to the sensor so the controller harness connector will mate with the sensor harness connector.

2018-03-10_080459.jpg (28.28 KiB) Viewed 1152 times

Add a relay as shown.

2018-03-10_080526.jpg (36.13 KiB) Viewed 1152 times

[rickb794]

Not covered here is the need to shut off the O2 heater when the motor is not running.

Most all O2 mfgrs recommend the O2 not be powered if the motor is not running.

Powering or triggering power off the fuel pump is a logical fix.

If you power of the fuel pump relay this will also have the effect of shunting any noise the O2 controller may generate thru the fuel pump.

[rickb794]

This contradicts what the LC-2 manual says just a few paragraphs above which is what I posted before.

Do NOT use the sensor ground: this is a known problem and you will introduce noise into all the analog inputs into the Megasquirt.

Jean

Exactly! Never ground any external device to the sensor ground, this will put current flow on the signal ground and have a negative impact on MS operation.

Sensor ground is not a ground path per say, it is a zero reference common to the processor and all sensors only.

Any noise introduced is directly connected to the processor < bad thing[tm]

The sensor ground circuit was created to provide a quiet noise free path for the sensors and the processor, not to ground outside devices.