Grounding ECU harness and sensors?

[rcx132]

I'm getting on with the design of the Engine/ECU wiring loom for my buggy. The ECU has multiple ground pins and I'm wondering if I need to do something special with them?

The dizzy also has two ground pins each one going to a different "web" of wires on the physical harness that I took from the donor car. The dizzy is a combined item and contains the coil, camshaft sensor, and ignitor. The ECU also has a pin labelled "Sensor ground" which goes only to the Throttle Position Sensor, Coolant temp sensor, and Oxygen sensor and doesn't seem to have continuity with the chassis ground, so I assume I keep this isolated from the chassis ground on my new harness.

Unfortunately there is only a conceptual wiring diagram available for my model of ECU which I'm attaching.

I have the original loom on my work bench, I'll brave the cold later tonight and see if I can reverse engineer the ECU ground circuits, but if anyone knows if there's something special I need to watch for with sensor/ECU grounding, would you let me know?

Ah, also the noise suppressor has a wire that goes to the clocks console on the original loom and I can't figure out what that does or what to do with it.

 

[sako243]

The ECU has multiple ground pins and I'm wondering if I need to do something special with them?

Just connect them all - without pulling it apart and reverse engineering it there's no real way of determining why there are multiple grounds. Most likely in an ECU it's because the connector pins and/or wiring harness cables are not capable of supplying the full current via one pin / cable. In different circumstances you might have an analogue and digital ground (for example) which ideally need treating differently but they'd most likely be labelled as such and it's extremely unlikely on an system like a vehicle ECU.

 

[ajlelectronics]

All of the ECU earths need to go to a common ground point. This is to prevent Potential Differences between grounds. It would be nice if that common earth could also be the battery negative termination point, but it is more important that all the signal grounds terminate at the same place.

 

[jsf55]

Is the noise suppresor something to with the radio power ? As above ground everything too one point or you will have ground offset issues

 

[rcx132]

I've followed all the ground wires on the original harness and will connect them the same way on the new harness.

The wire from the noise suppressor to the clocks turns out to be for the RPM meter. I'm guessing I can just ignore it? Would it work with an aftermarket RPM meter ?

 

[ajlelectronics]

Adaptable tachometers...

 

[Keithmac]

Some ECU'S have a dedicated "sensor ground", just make sure yours isn't one.

When I'm building a loom I supply all grounds from within the loom itself (not from frame/ body).

Car manufacturers go the other way (local grounds on chassis) but they also run sensor grounds in loom itself.

As said above, last thing you want is a ground offset at the sensors.

It's common to ground inlet manifolds if not plastic.

 

[rcx132]

Some ECU'S have a dedicated "sensor ground", just make sure yours isn't one.

Hi Keithmac, my ECU does have a sensor ground which is isolated from the chassis and which is used on a few of the sensors only, not all.

When I'm building a loom I supply all grounds from within the loom itself (not from frame/ body).

Do you mean that the loom should contain a distribution of ground wires that serve all the sensors? But this should still go to chassis at some points right?

It's common to ground inlet manifolds if not plastic.

The donor car did ground the manifold. I'll be sure to do that also.

 

[ajlelectronics]

Do you mean that the loom should contain a distribution of ground wires that serve all the sensors? But this should still go to chassis at some points right?

Yes, they should all go to ground at the same point. Otherwise is it possible to get mV of PD between them, which can give the ECU a confusing signal.

 

[Cato]

Yes, they should all go to ground at the same point. Otherwise is it possible to get mV of PD between them, which can give the ECU a confusing signal.

One of those bodges you always look for after the first time you find it "it's an earth so I'll just connect it here instead". Usually onto the nearest bolt on an engine.

 

[rcx132]

Yes, they should all go to ground at the same point. Otherwise is it possible to get mV of PD between them, which can give the ECU a confusing signal.

Ok thanks, the penny has dropped the original loom had three ECU grounds, two each served a few sensors, one only grounded the ECU and all three came together at the manifold I think. Plus a signal ground which served another few sensors and didn't go to chassis.

Attaching diagram with the recreated original grounds for posterity, never know if someone Googles "Vitara ECU wiring diagram".

 

[Keithmac]

Looks good, all the grounds to one point is what you want.

 

[rcx132]

Thanks. I'm sill a bit worried that if I wire something wrong it will blow the ECU, but at least they are not too expensive. I have a selection of 12 wire colours which also isn't going to cut it, just the loom from the ECU to the engine is 27 wires. Looks like I need to do some shopping first.

 

[rcx132]

I noticed that Vehicle Wiring Products sell wire by the metre. I bought 3m of each of their 115 colours and it came to a very reasonable £125. That should do me for the whole loom, not just the engine/ECU loom.

 

[Robotstar5]

I noticed that Vehicle Wiring Products sell wire by the metre. I bought 3m of each of their 115 colours and it came to a very reasonable £125. That should do me for the whole loom, not just the engine/ECU loom.

I bet the person filling your order loved that

 

[rcx132]

No problem identifying the connectors for the sensors using the connectorexperts.com website, but the prices are just silly. Here's the connector for the dizzy, $90 plus taxes.

 

[ajlelectronics]

Craziness isn't it? That is why I used the old ones and spliced right up close to the pins.

 

[Scalarocco]

Try Kojaycat. The one below looks similar and the price is easier to swallow!

7 Way HX 040 Series Female Wiring Loom Connector

kojaycat.co.uk

 

[rcx132]

It seems like connectors are available at low cost, but searching for them is difficult.

 

[Scalarocco]

The other option is to see if you can strip the original connector and just buy the correct terminals. I've done this before when I was unable to find the correct connector but the pins were fairly common.