M42 into '85 318i

[TheNewGuy]

What all does it require as far as wiring to swap an M42 from a 91 318i into an 85 318??

[DesktopDave]

I'd guess there's a good many differences, but it's do-able.  I'd get the big round chassis connector from the M42 donor car.  It's called the C101 connector.  In a pinch I'll bet any late model e30 (>8/87?) would do.  You'll need to open up the firewall hole for the Motronic harness too - it's much thicker and more integrated than your current Bosch L-Jetronic system.

You'll might also need the single fuel pump setup from an M20 or M42 donor, though the L-Jet s pretty similar IIRC.

I did a late-model M20 swap into an early chassis and also had to clip the ABS power off the chassis harness.  I think it was pin 19 (red/yellow) on C101...the late model engine harness runs ABS power off the main relay.  The early chassis harness grounds that connector.  It smoked the red/yellow wire when I switched the key on.:eek:  Luckily, no permanent damage!

Get the two wiring diagrams side-by-side and compare the chassis connector wiring.  Write it all down in a chart, post it here, then do some surgery!  BMW engines are a joy to swap...the whole motor harness is separate from the chassis harness and comes out very easily.  You might want to try the rear-mounted battery too...definitely helps with handling.

[TheNewGuy]

That connector is on the motor side of the fuse box, right? I don't have a car in front of me to look at right now. Thanks for your help!!

[Koen Bongers]

Dunno if still necessary, but I'm running almost the same setup.

318iS engine in a '84 318i. Both European. I don't know if that makes any difference but ok.

The wiring to connect the engine wiring harness to the car is as follows:
I used a round C101 plug from a 316i M40 car wiring harness and the C101 rectangluar plug from the original 318i engine harnass to make the cable to connect the two.

318i C101 rectangle - 318iS C101 round

brown/green - brown/black
blue/white - blue/white
green/yellow - green/yellow
green - green
black/yellow - black/yellow
blue - blue
purple/brown - purple/brown
green/purple - purple/red

Further, you need to enlarge the hole that you feed the motronic connector through a bit (iirc I used a 50mm holesaw for that), you need to connect a wire comming from the ECU of the iS engine to a wire underneath the dashboard to make the revcounter work (dunno which wire anymore tbh) and you need to build mounts for the ignition and radiator. Also you need to enlarge the holes on your subframe a tinybit (about a milimeter to the inside) to make the engine mounts fit. Also you need to find the correct propshaft. I'm running a M40 gearbox, so I'm using a M40 propshaft. Fuelpump didn't need any changing. Original 318i external fuelpump works just fine.

Been running this setup for over a year without any problems

[DesktopDave]

Nice post!  Great to have solid info.

BTW, on the chassis side of the M10 cars (NA cars at least), you'll have smaller struts in front and smaller bearings & drum brakes in back.  There are other wiring changes as well.