Grounds, gauges, and sensors.

[Absit]

The short and sweet is how important, and why is it important, to have grounds for your, say, MAP sensor and boost gauge, in the same spot (or grounded on the same wire)? Since everything is common ground, shouldn't it not matter what grounds where?

I'm not an electrics guy, but I'm setting up my gauges, sensors, and feeds to the ECU and I want to do it right to achieve the best accuracy possible, but while running as few wires through the firewall as possible. According to the manuals I should basically ground everything together, on the same lug or via a grounding block. If I do it this way, should I run a ground from the ECU's sensor ground wire to the same block or lug (the ECU will be fed 0-1v NB sim, 0-5v WB, and 0-5b MAP inputs)?

Edit: Also, why are my temp and pressure sensors designed to ground via threads/interface rather than through a wire, or the gauge?

 

[97gst_spyder]

It is better to have fewer grounds. If you create to many you could cause a reverse loop and noise in the electrical system.

As for the map sensor, is it a 3 pin? If so you can use the factory MDP sensor input. No grounds/power/signal to worry about.

 

[brads]

It isn't always better to have fewer grounds. Ground, in many cases, is just a name for a circuit. It isn't always truly a 0V reference. And the more current/noise you have running through it, the bigger of a deal this is. If the sensors have a separate ground for them coming from the factory ECU, use that same ground wire when you modify the harness.

If you ground a sensor to the main ground, instead of the sensor ground, you might actually create ground loops and additional noise by eliminating grounds. Obviously this doesn't apply to sensors like the coolant temp where the circuit was designed to work with the sensor tied to the main ground.

In this case, the MAP sensor ground should go on the ECU sensor ground circuit. And depending on how the output of the wideband is, you may want to have it grounded on the sensor ground circuit too. You don't want to run any high current ground from the wideband through the ECU sensor ground. But if the wideband has a seperate wire for the ground reference on the output, that goes to the ECU sensor ground. A single wire from the ECU through the firewall, and then split that wire to the various sensors will be adequate.

 

[Absit]

So I should ground the wideband by itself, and I should ground the MAP sensor via the MDP harness (ECU sensor ground). In that case, should I ground my gauges to the same wire (ECU sensor ground) because the manufacturer is very specific to run the gauge's +5V wire to the MAP sensor, and ground them together. If I use the MDP harness I'm getting my +5V from the ECU and the ground is separate.

 

[brads]

So I should ground the wideband by itself, and I should ground the MAP sensor via the MDP harness (ECU sensor ground). In that case, should I ground my gauges to the same wire (ECU sensor ground) because the manufacturer is very specific to run the gauge's +5V wire to the MAP sensor, and ground them together. If I use the MDP harness I'm getting my +5V from the ECU and the ground is separate.

The wideband grounding would depend on the instructions of the wideband. If it has a ground reference that is just for the output, tie it to the ECU sensor ground. If it just has one ground for the whole box, it should be grounded by itself.

The MAP sensor gets the ground and 5V from MDP. Use both wires, or neither. And I would suggest the same for the gauges. If they are designed to work off the factory MAP sensor 5V signal, hopefully they do not draw much current.

 

[Absit]

The wideband grounding would depend on the instructions of the wideband. If it has a ground reference that is just for the output, tie it to the ECU sensor ground. If it just has one ground for the whole box, it should be grounded by itself.

The MAP sensor gets the ground and 5V from MDP. Use both wires, or neither. And I would suggest the same for the gauges. If they are designed to work off the factory MAP sensor 5V signal, hopefully they do not draw much current.

Only the MAP sensor requires a dedicated 5v in, the rest just run one wire (except the wideband). I've determined I'm going to plug the MAP into the MDP harness and then jump the MAP signal and MAP ground to the Wideband/Boost gauge.