Mk1 golf DTA ECU wiring

Hi there, I've just received my DTA ECU and I'm currently going over the wiring diagram to get my head around what needs doing.
The ECU requires a direct fused feed from the battery , switched via the ignition switch. I'm keen to give it a good clean supply. The rail that is marked 30 on the mk1 golf wiring diagrams is supposed to be a direct feed from the battery. Where is this physically located on the fuse box and will this provide a good supply for my ECU? By the looks of it other devices share this direct feed from the battery which makes me wonder is it worth running a separate power cable specifically for the ECU?.
The fuel pump relay needs to be triggered by the ECU.*
I see that relay J17 is responsible for this on a mk1 GTI. The fuel pump also receives 12V from terminal 30 once the relay is energised. Is this going to be a good enough supply or is to again worth running a dedicated supply and grounds?
Thanks in advance.

 

If it were me, direct feed every time (controls engineer)
Jon

 

Always get a good power supply for your Ecu esp. good clean earth

Permanent feed of Battery via fuse 1.5mm sq min

Main earth(s) from engine block, also 1.5mm sq min

Make sure engine/box has big juicy earth cable to it via clean contacts

As for fuel pump also make sure that it gets solid voltage at all times. Good earth via 2.5mm sq min and +12v via relay fed straight from battery via fuse in 2.5mm sq min but i have also used 4mm sq in past as you really can't over do it

Also your coil pack(s) and injectors will require good +12v feed in 1.5mm sq min, obviously fused

 

Thanks for the input! I thought I'd be best running dedicated power lines like that but didn't want to create more work for myself if unecessary. So dedicated fused feeds for the fuel pump and ECU it is.
The ECU diagram is shows a direct feed to the ECU switched by the ignition with a 40 amp fuse. The power feeds for the coil, injectors, and fuel pump relay switching are spliced together from the 40 amp fused line.
As far as actually rewiring the relays can the same type of relay be used for both the fuel pump and ecu?
Is there a straightforward way of incorporating them into my fuse box as they will obviously need somewhere to plug into. I'm guessing ill also need to buy a couple of recepticles and wire them accordingly?. Thanks.

 

Fuses are there to protect the wiring, not the electronics. 40A is a biggy. I only have one 40A in my whole rally car and that is for my lamp pod (240W). If the ECU is just doing calculations then a much smaller separate one will be better. Avoid anything less than 5A, as it will act like a resistor and drop voltage.
A relay is a switch, you can use a common one (say a 40A one) if the load on that circuit is 40A or less
Hope this helps
Jon

 

Thanks jon, I think the fuse will also protect the electronics should a 12 V supply be connected to a sensor ground inadvertently.
It is a beefy fuse as I'm only running 4 injectors and a coil pack. I think it's for multi coil 8 cylinder engines.

 

Common misconception. Electronics 'blow' in microseconds (usually) and fuses blow in milliseconds
Jon

 

So in reality it's not going to.protect the ECU at all?

 

Sorry, no. But don't worry, if you wire it up properly it wont need protecting
Jon

 

That's what I'm worried about I'd rather it was idiot proof . It's fairly straightforward really I'm just seeking reassurance that I'm heading in the right direction with it.

 

I would always try to wire up and ECU using the feeds and relays the OE would have used for their controller.

If the vehicle has the OE fuse box, the ecu can be wired in and you would have the fuses for protection already in place.

If not then as suggested.

 

There is a relay for a fuel pump but I'm not sure if there is anything for the ECU, I think the mk1 GTI had some kind of ignition module though.
The plan so far then is to run a direct feed from the battery to the fuel pump relay with a suitable fuse. I'll also connect the ECU fuel pump trigger and run a new earth cable.
I need to work out if there is another relay already in place that I can use for powering up the ECU. This would make life easier and then I'll run a new feed and earth for that. Hopefully this all sounds okay to those of you that have done this a lot more than me? Appreciate the help .

 

You don't need to feed your Ecu via relay, it is just something else to go wrong if you know what i mean

Only thing you should always use relay for is your fuel pump triggered by ecu for safety reason. If you have an accident damaging engine or engine blow up ecu will turn fuel pump off

And yes fuses are in place to protect wires from overload and short circuits both of which may lead to fire, that is it

 

According to the DTA wiring diagram the ECU needs to be powered via a direct feed from the battery switched via a relay and fused.

 

Ah i see, sorry i misread your first post, just read it again, i thought you wrote that your ecu requires 2x positive feeds, permanent and ignition live as well

Reason why it says to go via relay may be is if that same supply goes to your injectors and coil pack(s) as well, to prevent them staying powered on without ignition

 

Great thanks for that. I've been looking into the fuel pump wiring further and noticed the pump relay relies on a feed from the coil to energise it. I've done away with the coil meaning there will be no signal to switch it. Saying that it seems there is a switching circuit there already without the coil feed so I'm not sure why it wouldn't work without it?
The DTA wiring diagram shows the power feeds for the coil pack, injectors and the switch for the fuel pump all coming direct from the battery spliced together via a fuse. Would this not be simpler to do? Or am I best trying to utilise what's already there in the fuse box?

 

I need to go back to school on this one, I'm not sure what you mean by the rev limiter or what the DTA rev limiter is. I knew this was going to be a bit of a learning curve :/.
The DTA harness I've got has a fused 12 V supply line which is spliced to connect to the ECU and also supply the injectors, coil and fuel pump relay switching circuit. My diagram shows a fused supply direct from the battery going into a relay and then out of that is my spliced power cable. It was made up for me and the fuse would be after the relay if this matters?
I'm just looking for the most straightforward was of doing everything without compromising on the overall effectiveness. Appreciate your help.