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Discussion Starter #1
Can anyone be bothered to snap a couple of pictures of the connection to the throttle body? Mine is missing and it's a real wonder how the thing managed to work so far.
 

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Discussion Starter #3
I know the ECU gets its earth from the plenum. How is the plenum grounded though? I thought there is an earth wire connection to the throttle body which also grounds the plenum. There also seems to be an indication of a wire going there but it's been ripped off in my case.
 

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Brera TBi
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The plenum has it's own earth strap which runs from the main loom behind the engine right where the two connectors to the ECU split out. But failing that the plenum is bolted to the main block which will no doubt be earthed too.

This is the best example I can find: https://lh3.googleusercontent.com/-S-zwLxyV2BYy1-fSndWoQlvG9STrAj-9lU2K8TAaYn_VnL0z6Lp5ajnaQ-CBruWAcPvhE9nZLY5jHbx2R_OI1n7yHov60TN6Vy4ehb8UHxq0QbXCWgbTw85fVXKOYN9L3mDgkk124tULeo31qPd9GaMZ-oL3lVGjGZyy6ECCwoiY1qfa4QrQIZuz5Ki4nZvF630p5DhpE4TgeOOeqxa5ZAXaxr7DG_wALui1N7V8hzcUAiUz8blEsrS4QpBuurmc2Ad2C6pXCv0cXmL7LfsTQECOwvO5jE1-mf_89-QY4bXLqFSpGHwkInDtUt0wISMaBEqPq32qySbnkhF8KHGWMAf-0Zzi_v_y08yCunX3kauzK7xu0ZO3xubHCRp3UmqkgNiGDIcSaO6V2duoOPcQX-h0jGH_X-2FQjNBohFVNkMHd0rluzPMeTisCWWBLVmpQb2v2qtDyKe_eUYfheNAca5eMQd98FDGTAGEWLTHU5CNrzYjyQz4dcpwvZmuEwGmHnZ14EakDHrAmPWiu3fggYAUQmlwnxgDdmZqBaI8eE5ArYaIQWlBXNDDUXmUuHFgZBMTA=w582-h775-no



It's the little black cable which is looping around under the two upper breather hoses on the plenum, it then bolts onto the back of the plenum just below the 4 ECU studs.
 

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Discussion Starter #5
I see. Thank you!

It should be enough but if anyone has a more detailed photo feel free to post it :)
 

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This was the cause of fault code P1688 on mine...

The differences between a 156 and a 147 appear to extend beyond the (to quote Gus) "internal strategies" within the ECU. For instance, it would appear that the throttle pedal connection shown in this pic;



Is 147/GT only, the 156 lacks it. So you may wish to consider these wiring diagrams as being for the 147/GT only;

M10 - Engine ECU
K55 - Throttle pedal pots
K41 - MAF
D49 - Connection on bulkhead (?)
C10 - Earth

Note the link highlighted in green between the MAF and the throttle pot - I think this is the earth that's common to the two and ends up at C10.



Untitled by chris147gta, on Flickr

Untitled by chris147gta, on Flickr

Untitled by chris147gta, on Flickr

Untitled by chris147gta, on Flickr

Untitled by chris147gta, on Flickr
 

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Discussion Starter #10
Chris, thanks for that.
I'm studying these diagrams now and I'm guessing the C40 and C10 earths join on the plenum since on one diagram for the ECU there is only a C10 earth and on another there is only a C40 earth.
I'm also attaching a photo of my mystery connector which I'm guessing is a C40 earth. So if I'm reading this correctly there should be another wire from it also going to the ECU and joining the C10 earth since according to the diagrams C10 is definitely on the ECU?

I guess I really like to complicate things :biglaugh:
 

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Brera TBi
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That's definitely a broken earth there! I would get a replacement cable on that asap, you might find there is just enough copper remaining to keep the ecu happy. If that breaks completely while you're driving though everything will go down!

Edit: What's that cable that (in the second picture) appears to have a light purple line running down it. From the camera angle it appears to bolt onto the same place of the rocker cover as the "broken" earth, and then loop back up to the plenum / ecu ? It looks like a non-factory cable to me and it could be this that is earthing your ecu and throttle body?
 

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Agreed, that earth is all but broken and the black wires with the purple tracers are almost certainly non standard.

The OE earth in your pic (C40) also looks like it's bolted down in the wrong place which may be why it's broken.

C10 goes through the MAF and earths on the chassis leg under the battery as shown in the drawings if I recall correctly.
 

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Discussion Starter #13
Ok so just to clarify, that earth on the picture should only be for the engine and should not have a split? Where should it be bolted to?
 

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Ok so just to clarify, that earth on the picture should only be for the engine and should not have a split? Where should it be bolted to?
To the back of the plenum as per Rob's piccy.

There may be other pics of it in my 147GTA progress thread - see sig. I can't go looking as I'm in work and the firewall filters out images.

There should also be a heavy earth to the gearbox. There's one to the plenum as it's very nearly isolated from the cam cover by the rubber feet it should sit on.
 

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Discussion Starter #16
Yes, mechanic bolted it there at the end, together with an extra wire directly to the ECU I think. So whatever the next problem will be, I'm guessing it won't be that earth :biglaugh:

Thanks for your help!
 

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are they wire from the gas pedal mixed with brake wire going through the footwell under the bonnet seen four wires broke having same problem
 
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