Why do engines need grounding, exactly?

[Mangudai]

I know it can be beneficial to add more ground points from the chassis to the engine, but why? Breaking it down, what does it do exactly?

[r3v_v3ng3]

instead of running various ground wires all the way to the battery, all you have to do is ground it on the frame since the battery is grounded to the frame. it also lowers electrical noise and stabalize it.

[r3v_v3ng3]

the stock ground wires are very thin wires. so adding a bigger wires would be beneficial. there are claims of better idle, better throttle response and others.

[hellboy006]

i have 2 ground wires running from the battery to different spots on the motor, i used to have a pretty irregular idle... it MAY have helped.. or it might have been some of the other things i was doing to the car around the same time (cleaning MAF, etc) that helped, cant say.

[bruinbear714]

I know it can be beneficial to add more ground points from the chassis to the engine, but why? Breaking it down, what does it do exactly?

Everything has resistance, so grounding the motor can help prevent ground loops due to the electrical resistance in metal. Engineers design the chassis and engine harness to account for this resistance and although the OEM setup may not ground the engine to the chassis via a wire like you see in grounding kits, the setup works perfectly until the OEM wire harness gets hacked or aftermarket products are installed with an improper grounding point.

[twistedsymphony]

technically you're not grounding the engine so much as you're providing better grounds for all of the engine SENSORS.

the battery attaches ground to the chassis and the engine block the sensors don't have a ground wire they simply use the block as their ground signal.

Ground is important for the sensors because it's the reference point ground =0

a generic example:so lets say you have a sensor that SHOULD be sending a signal of "5" to the ECU the ground is good so the sensor measures 5 over ground and sends "5" to the ECU.

now lets say you have a bad ground on that sensor and it's causing ground to equal 1... the sensor only measures 4 over ground and sens "4" to the ECU. the ECU is now using the wrong information and is instructing the engine to do the wrong things and as a result it runs poorly.

typically a bad ground will actually move about... if the ground was always 1 off the ecu is actually smart enough to compensate, unfortunately a bad ground will be at 1 then at 0 then -2 then -1, then whatever...

improving the grounds on the engine, making sure you put the cables close to where sensors attach to the engine and chassis will ensure that your sensors are working as well as they possibly can and it ensures that your ECU is making the right decisions as a result.

[Mangudai]

Awesome explanations, thanks a lot guys.

[lovespeed]

Twisted you left out the advantages to the injectors and ignition systems better grounding helps these systems work better and faster by giving the currant a more direct path back to the battery this is a small increase but it is better nonetheless. Great explanation of the reason for proper grounding to.