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mad_pete

How to earth MS like a pro?

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Currently I think my MS earths to the bulkhead in the engine bay. But I think the real pro way to go is earth to engine or battery and bring the os sensor to the same place. I think my pi may need earthing there too as it’s resetting ms when connected to the serial.

i have a marine fuse box with a chunky earth to the battery could go there or should I go out to one of the engine studs to get close to the sensors. 

It all works fine (apart from pi resets) so as long as it’s good earths does it matter too much or am I at risk from sensor inaccuracies ?

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The installation notes I have, says to earth to a common point on the engine; the object being to prevent various earth-loops creating very low voltages, which can interfere with sensitive electronics. Note that most earth wires go the common-earth; don't use one cable.

They also say that the noise created by say a high-tension lead, reduces as a square-of-the-distance, away from the sensitive component. So moving a component even a short distance from noisy components, may solve the problem.

Examples of noisy components; injector wires; coil; alternator; idle valve,

Cheers Charlie

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Thanks. The serial cable runs only the cab so should be pretty clean I think.

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I'd probably pick up earths on the body side of the earth strap. If you are fitting a wideband o2 sensor make sure that the grounds for that go back to the same place as the MS ground can cause major issues...

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One thing to bear in mind is that you do not want the MS wiring to act as the earth for the engine. That's why you normally try to use a point on the engine for all earths. If you consider the, not uncommon, situation where the earth strap between the engine and body fails, you don't want the MS or it's wiring to try and take it's place. All the earths in the MS are joined together so if, for example, you have one earth connected to the battery and one earth connected to the engine then the MS can try and provide a path for the starter motor if the earth strap fails or goes high resistance.

Picking up earths on the body side of the strap and then having another earth (TPS, coolant temp etc...) going to the engine means you risk bridging the earth strap. Anyone who's ever had their handbrake cable try to do that job will probably know why that's a bad idea.

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11 hours ago, Dave W said:

One thing to bear in mind is that you do not want the MS wiring to act as the earth for the engine. ...

Excellent advice Dave!

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I tend to earth all sensor grounds back into the MS connector and then earth the MS to a good solid ground using all available ground pins. Power-grounds (like lambda heater) I'd earth to the solid ground too.

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