M84 injector wiring & AT functions

[fordpop]

Hi guys,

I'm new to motec and currently in the latter stages of fitting the M84 into my drag car. I have a few basic questions I'd like help with if possible.

1- Do you see any problems if I use just 2 of the switched lives (a26) to run to my injector harness as the harness then splices theses two wires to take power to all 8 injectors. This is a factory harness from my previous ecu supplier.

2 - are DIG1 - DIG4 configurable within the software? The manual implies they are, but I can't see how.

3 - what function input do I need to allow em to use AT channels as temp inputs (engine oil temp)

Thanks in advance,

Dave

[mstech]

The DIG 1-4 inputs are only able to be used as speed inputs, they are under the Speed page in the Inputs config (The three red stacked arrows on the menu bar) the only configuration available to these inputs is their calibrations, not their usage.

Engine oil temp is done using AT3 and configuring it as one of the user channels.

[fordpop]

Thanks:)

do you foresee any issues wiring the injectors that way?

[AdamW]

1- Do you see any problems if I use just 2 of the switched lives (a26) to run to my injector harness as the harness then splices theses two wires to take power to all 8 injectors. This is a factory harness from my previous ecu supplier.

It is not clear what you are asking here - A26 is the 12v supply to the ECU, it only requires low current and would normally only be a light gauge wire. Normally you would have a "main relay" that is switched by the ignition switch. The output of this main relay is then split into two or more supplies - 1 light gauge to power the ECU (A26) and 1 or more heavier wires to supply the injectors. The injectors need to be powered from the same source (relay) as the ECU so that the ECU can sense battery voltage and apply the correct deadtime comp.

[fordpop]

Yeap, I'm suitably confused now...

OK I have the large red cable to an switched ignition relay. The ECU powers up fine.

There are a number (8no) white whites contained within the ECU loom which I read (mis read??) on the wiring diagram WD0006 as coming from A26, to the injectors at the top right hand corner of the diagram.

So, I understood the white wires to be switched 12v from the ECU...........is this not correct?

If not - what a the white wires? And do I need to add the injector power wires myself?

Hope that makes sense...? Kind of difficult to explain.

Dave

[AdamW]

Oh sorry I probably confused you there. I just took a look at the M800 loom drawing here: http://www.motec.com.au/filedownload.ph ... docid=1222 and now understand what you are trying to do.
Although the drawing does suggest those whites come from A26, they are not directly connected to A26 - they just all splice into the same main 12V power feed.

So now to answer your original question - can you use just two of these white wire to power 8 injectors...
Well that will depend on your injector impedance and the size of these wires. You will need to measure the resistance of the injectors so that you can then work out how much total current they will draw, then check that the wire gauge can handle the current required. I'm guessing the original Motec loom would use 16 or 18AWG for the injectors but I havent seen one for a long time so you will need to measure.

I would hazard a guess that provided your injectors are modern low Z type of say 10ohms or more then you should be ok but please measure to be sure. Post back here if you dont know how to calculate the required current etc...

[fordpop]

Phew...thats OK then.

Thanks for your help & clearing that up.