Wiring warning for anyone swapping E30 engines!

[Brianmoooore]

Spent the last two days building up what was little more than a late 87 2 door saloon rolling shell into a complete car. Engine/box I fitted was a 1990 318i M40.
Dropped the engine/box in, connected up the loom, and fired up the engine. All OK.
Fitted a dashboard and instruments, and connected up all the wiring there, and fired up the engine again.
This time there was clods of smoke from under the dash, out of the fuse box and from the engine loom!!!!
Switched off quickly, disconnected the battery and started the investigation as to what and why, and how much damage had been done.
Started with the engine loom. I found that the (unfused) red/yellow wire from the DME relay to pin 20 of the C101 plug had melted all its insulation off.
Strange, I thought, as this is the feed for ABS, and this car doesn't have ABS!! Wouldn't have expected to find any connection to pin 20 on the car body side!
However, there is a wire connected to pin 20 of the socket, a badly melted one! Went back through the fusebox and down through the trunking into the cabin.
Cut as much of the remains away as possible and checked under the glovebox area, where, strangely, I couldn't find any damage at all!
Next step was to check out some spare looms.
A engine loom the same age as the car had no connection at all to pin 20. A newer one had the red/yellow wire. All as expected.
I then found a body loom from an early '88 4 pot, and found something very surprising. A brown wire connected to pin 20, going through the fusebox, down through the trunking, and then joining a host of other brown wires at a soldered joint, with a short thick brown wire going to the earth point above the glovebox.
The first time I started the engine, this earth hadn't been connected, but the second time it had.
Switching on the ignition had closed the DME relay and applied a dead, unfused short circuit directly across the battery.
Why these early facelift looms have an earth at pin 20 on the body side of the C101, I don't know, but it's there, so, BEFORE CONNECTING ANY FRESH ENGINE LOOM INTO AN E30, CHECK PIN 20 ON BOTH SIDES OF THE C101.
Engine looms aren't quite so interchangeable as I'd always assumed!!

[eko]

Well isnt that interesting
I too have never noticed anything like this and have changed more than my fair share of E30 engines,obviously ive been lucky!
Feeling a bit guilty about bothering you with my wiring issues now,sounds like youve had your fair share of fun and head scratching

[Gunni]

I´ve had that happen,

there are NOT supposed to be any grounds in the C101 but on those oocasions they can be at pin 20
and are brown, so do check them,

my car was a ´88 318i, and I was fitting a 318is engine,
fitted the same engine to a same year 316i without issues,

[Laimis]

Heh, we had same problem in the past too ..

[frankiej]

Bad ass Brian. Thanks a lot for the heads up brother. That would have made me want to

[gareth]

that's very un-BMW like!

good call on the heads-up though. that's another issue that could affect sooooo many engine swaps

unlike you to get caught out though brian! you feeling ok?

[Brianmoooore]

It was an interesting experience to see just what does happen when you short circuit the battery through the loom.
The amount of acrid smoke produced was unbelievable!

[billgatese30]

This might come in handy Brian

[gareth]

i've only ever done it on a mini and that had a lot of cable between the teeeeeny battery and the butchered loom at the front. that was messy / smelly enough! happened at 60mph too, i had to stick my head out of the window to see where i was going to stop

i suspect a fully charged and meaty E30 battery will turn must gauges of wire into a 'fuse' in very little little time!

i have short circuited a (luckily old and tired) bmw battery with a screwdriver before... that got very hot and angry very quickly! a very close call

[gareth]

This might come in handy Brian

classic!!!! that's the exact same grade that was fitted to the aforementioned mini!

[dicko]

Thanks Brian i am starting a m50 conversion soon and if that happened to me i would cry
Its a bit scary the amount of unfused wires in auto wiring and when they are fused it is very close to what the cable can accually take

[dicko]

This might come in handy Brian [/quote]

I wonder how they got all that smoke into the loom when they made it ,they must use the same machine that puts the figs into fig roll

[ian332isport]

Brian,

I have seen this connection a few times when doing wiring charts for people. The brown wire on pin 20 is used to provide an earth connection to the coolant temp sender. I know this is not required, as the sender gets its earth direct from the body of the sender, and it only has a single connection anyway.

I don't recall what year/model I was looking at, but it is shown on some of my wiring diagrams.

Ian.

[Brianmoooore]

Not too clever of BMW to change what was an earthed pin to an unfused ignition controlled live, though! There are a couple of other unused pins that could have been used for the ABS feed.

[ian332isport]

Here you go Brian.



This was from an 88' wiring diagram.

[Brianmoooore]

That confirms what it was there for then, but I've never seen an E30 with a two pin brown temp sensor!
What's the C191? Injector plug under the manifold on a 6 pot?

[gareth]

E32/4 M30 donors have a 2 pin temp sensor which needs to be swapped for a single pin E30 one... still not seen a 2 pin on a E30 myself either!

[Brianmoooore]

E32/4 M30 donors have a 2 pin temp sensor which needs to be swapped for a single pin E30 one!

M50s as well.

[gareth]

would that be all E32's and E34's then? i've never tinkered with anything other than a M50 E34 (and i didn't touch that area as it never broke!) and a M30 E32.

or are E32/4 M20's fitted with 2 pin systems too?

i just thought it was down to a later design or something but using it for a while midway though the E30 is just downright wierd!

[ian332isport]

What's the C191? Injector plug under the manifold on a 6 pot?

Yep, it's the one under the manifold that often needs rewiring due to water damage.

[joe323]

my car has a 2 pin brown temp sensor!

[bigbhpwannabe]

i rlly wish i had read this a week ago , had the same problem with 88- 325 . fitted a 90-325 loom and now we have meltage

[magpie]

hi people i'm so glad i read this. after going to southern meet {27/07/08] i've decided my m40 318i is ok but i need 6 of everything instead of 4 ie pots plugs,soits time after 8 months the 2.5 conversion is on.oddly enough i have said potential meltdown material i think .88 face lift reg on 01 07 88 is this the model? if so what do ido to avoid this?

[witch]

Done the Same thing that pin 20s a bastard!!!

[no2lurch]

right then, i have a spare loom ready for my 325 and i have just checked the mentioned plug and they are different.

pin 20 on my exsiting loom (the side it goes off to the engine) is empty but on the replacement loom it has a connector.

am i now in big trouble if i use this repalcement loom? i do not plan to change the loom which is the other side of the connector...

please help.

[no2lurch]

i've just had a look at my loom again and the other side to the c101 connector is empty too...

where does the other side of the c101 lead to?

[Brianmoooore]

Check whether there is any wire connected to pin 20 on the car loom side of the connector. If there is, it will either be red/yellow or brown.
If it is brown, cut it away from the pin, and make sure the free end can't come into contact with anything.
If it is red/yellow, then leave it alone - it's the power feed for the ABS system. You will then have to check pin 20 of the engine loom side of the connector, to see if it has a red/yellow as well. If it has, all well and good, but if there is no red/yellow fitted, you will have to add one, between the pin and the terminal of the DME relay that has a red/blue on it.

[no2lurch]

please see here. i started a thread...

http://www.e30zone.net/modules.php?name ... 55#1291555

[Baurluvva]

I am fitting a m30 1990 3.5 into 1990 e30 316 baur......... will I experience any issues regarding pin 20?

[Brianmoooore]

I am fitting a m30 1990 3.5 into 1990 e30 316 baur......... will I experience any issues regarding pin 20?

Probably not, but check anyway.

[tinnaM42]

yt

[mt1104]

As my car doesn't have ABS can I safely assume if I find a brown wire from pin 20 on the car side of the loom I can just cut it, tape it off and forget about it?

[Brianmoooore]

As my car doesn't have ABS can I safely assume if I find a brown wire from pin 20 on the car side of the loom I can just cut it, tape it off and forget about it?

You can. The brown wire has no purpose on any but very early E30s.

[mt1104]

Awesome, thanks Brian

[e30topless]

would this make any difference to the conversion I am doing at the moment ?

I am changing a 1992 touring M40 1.6 (the car has ABS ) to a M20B2.5,

the donor loom for the M20 is from a 1989 which also had ABS ?

I hoped it may be a simple plug and play or should I disconnect pin20 ?