Modifying a BMW M52 engine loom, advice, suggestions please!

[andyborris]

As the title says, I'm trying to modify the BMW M52 engine loom that's in my Triumph.

The loom as it stands has lots of redundant wires and lots of huge plastic boxes, into which BMW have stuffed wires, (literately stuffed), it looks like badly cooked spaghetti!

This bundle is impossible to de-tangle, It's made this way!

So, I'll have to cut and rejoin the wires, the power and earth wires aren't a problem, the sensor wires may be (a problem!).

2 real questions please, will cutting, shortening and using a connector to rejoin the wires affect the reading from the sensor?
I'm thinking of the more complicated sensors, crank, O2 and camshaft.

And can you suggest a neat and 1960's looking way of doing this please? I'm trying to get a bit more of an uncluttered under bonnet look!

Thanks

[sb]

For style you could try some of this?:




Comes in loads of colours, I just stuffed a bunch of audio cable into one and love the result. Its only standard 3 core inside though so dependant on the cable you might not get a lot in. Still looks better than plastic covers though.

Amazon Link

[benjy_b]

You have to be careful with some of the more sensitive sensors (the ones you mention), any additional resistance or "noise" can interfere with their readings.

A lot of modern cars run earthed shielded cable to prevent this. I couldn't tell you if this is the case on your BMW loom, but if it is, they require one continuous run with no interruptions.

My Honda S2000 loom had seven shielded cables.


If I were you, I'd methodically remove one redundant wire at a time by disconnecting the terminal from the plug.

[benjy_b]

Also, a mechanical connection is far superior to a soldered connection.

Something like this is ideal:

www.easternbeaver.com/Main/Elec__Products/Terminals/Open_Barrel/splice-terminals_1779.jpg

[andyborris]

From memory, the O2 and knock sensors are shielded, the rest aren't...

Not quite sure what I;m doing yet, have removed all the redundant bits, right back to the ECU plug, still got a tangled bundle in the middle of loom though! I think BMW make it this way to reduce stress on any one wire?

I want to have a normal 60's looking loom, not one that's in a small suitcase size box, which I don't really have the space for.

I'm going to try an experiment, cutting and rejoining an old loom and see how this affects the voltage drop...I'm also toying with the idea of just using adhesive lined heatshrink to make the joints, in the hope this keeps the loom slim.

[benjy_b]

The box you mention is probably a junction box. Grouping a number of earths, 12v or 5v wires together. If you're wanting to neaten the loom, there are a couple of options you could do.

You could either run independent wires to each component and join them at the ECU connector. Like this:




Or you could link the components in parallel at source with one wire going to the ECU. Sometimes this is done to make "sub looms" for things like injectors or coil packs.



Then, if you want to neaten the loom further, you could look at concentric wiring.

Here are a couple of decent websites:

www.rbracing-rsr.com/wiring_ecu.html

www.rbracing-rsr.com/sq6wiringloom.html


I'd limit the use of adhesive lined heat shrink to transitions and end plugs. It cures very hard and really doesn't allow any movement which is desirable on an engine loom. The go to product for Motorsport looms is Rachem DR-25, it's incredibly flexible and heat resistant.

[Hillmanjames]

String!

I've done this before, but not got any pictures. Its time consuming but makes a neat nice job of it in the end.

Take the loom off your motor and run in string instead of the wires to each sensor, and back to the ecu. Label them all up and route them however you wanted them to be. Next, get yourself a big sheet of cardboard (local bike shop can help you out as all pushbikes come in a big box and they just chuck them out) and tape the string loom down onto it.

next, cut off all the covering on your old loom, and either cut the wires and solder up new ones so it matches the template on the board or just shorten the existing ones.

Essentially, you ll end up with something looking like this, with all the wire the correct length and all the rubbish removed *lab coat optional*

[andyborris]

Thanks everybody, have now done it.

It's not to F1 standard, I haven't got F1 money and considering I didn't cut any sensor wires, it doesn't look too bad.

I removed all the unused wires from the ECU plug and loom and then wrapped it in this Loom wrap.

It looks quite factory, was easy to use, attaining a finish that's as good as on a BMW.

I decided against shortening any wires in use, all the ways I've got of reconnecting them would make the loom bulkier and (I think) more prone to failure!

I know the pins that fit into the various connectors can be purchased for at a reasonable price (for BMW!) from BMW and although this would let me shorten wires by removing connectors, it's very time consuming and the cars been of the road too long now!

And the crimp tool is very expensive!

Will post pictures when it's finished and here's a picture of the plastic box, they used to live in.