E30 Zone

I'm just preparing to do this swap and am wondering whether or not I'd need to remove the whole wiring loom to the ECU or whether I'd just be able to unplug the loom from the plug in the engine bay and swap ECUs?

The car is a H reg 316 completely standard and it's getting the M42 from a 318is of I believe exactly the same age.

I've got the entire engine, gearbox, ancillaries, radiator, loom, propshaft and a diff. m42 engine mounts from revshift Will I need to change the brackets? i think that's everything no?

First swap and would like to be able to get it done without having to wait on parts.. Cheers

You need to keep the looms with the engine. The 316i loom will be no good with the M42 engine.
You unplug the C101 plug (round plug by fuse box) to separate the engine loom from the body loom. Unplug the ECU and the plug pops back through the bulkhead and goes with the engine loom.

So I dont have to do anything crazy like take the dash out to change the loom?just disconnect the ECU and push the plug and connector through and take it out?
When I pop the plug through the bulkhead, where does that go? just a socket near the fuse box? and i guess this doesn't interfere with anything else to do with how the car runs?

I've had a good search around but can't find much info regarding the swapping of wiring looms. This leads me to believe its very simple and I jsut haven't done it yet :p

No, it really is that simple. The only bit you need to do under the dash is unplug the ECU (and swap it for the M42 ECU) and push the ECU plug back through the bulkhead - you may need someone to help guide it through.

If you remove the wiring cover on the bulkhead you will see the loom, on the passenger side you will see these two plugs...



The larger one is the diagnostic plug, the smaller is the engine loom to body loom plug (C101 connector).
Remove the cap of the diagnostic plug and unscrew the securing collar so the socket can be pushed down through the bracket.
Unclip the C101 and unscrew the connection...



Going to the drivers side, you will see the loom heads through the bulkhead - you will see this big rubber grommet...


This is where the loom goes to the ECU and where the ECU plug will pop out through.


Undo the two earth wires from the earth point on the strut tower. There is also the wire to the coil pack and you should find a wire thats clipped to the underside of the battery tray - these come out with the loom (not pictured)...


With that lot free (you may need to cut some zip ties to separate some bits), the loom will pull out of the wiring box (rubber grommet in the middle). The relays come out with it...



Just make sure you have disconnected everything and the loom will come out with the engine.
The M42 loom will come in fitted to the new engine and basically be refitted as a reversal of the above.

The only thing you must check is PIN 20 of the C101 connection on both the car side and M42 loom side. Pull the rubber back and check the wire colour to PIN 20 and if you find a brown (earth) wire, it needs to be removed.