What is this bit and what does it do???

[AndyMack]

http://homepage.ntlworld.com/mackintosh ... 260(1).jpg
http://homepage.ntlworld.com/mackintosh ... 261(1).jpg

I was changing the HT leads and there is this cable attached to the #1 HT lead from the old ones. I dont know what it is or what it does so just left it attached. anyone help me?

[smithy318i]

Pulse sensor for ECU

[AndyMack]

so will bad things happen if i take it off? cause i cant get it on the new HT Leads.

[smithy318i]

TBH i have seen lots of people who just "left it off" and it doesn't seem to make a difference.

[AndyMack]

so should i snip the ht lead so it is still connected and flopping around the engine bay? or just unplug it?

if unplug it where does it plug in? I couldnt follow it with my fingers

[smithy318i]

erm. mine is pluged in below the inlet manifold.

can you remove the rubber boot from the end of the HT lead and feed the sensor on? (without breaking the lead)

[AndyMack]

i couldnt really like to try case i break it.

i'll give it a go.

does it matter what lead it goes on?

[smithy318i]

yes it does matter what lead it goes on (must be #1)

If it doesnt come off easy, dont force it off.

[smithy318i]

I need sleep. CU

[Brianmoooore]

On earlier versions of Motronic the sensor just connects to the diagnostic socket, but on later versions it's used by the ECU as a cam position sensor, and is required.

[drewjak]

i have a 1990 20i i left mine off when i changed the leads 2 months a go, i just left it coiled up by my air box, it dont seem to have caused any problems for me

[DelaneyG]

better off putting it on, its there for a reason, the rubber sleeve on the lead should slide off then you can carfully remove the connector for the plug with a pair of pliers

[Brianmoooore]

better off putting it on, its there for a reason, the rubber sleeve on the lead should slide off then you can carfully remove the connector for the plug with a pair of pliers

As I said above, on some versions of Motronic it does absolutely nothing except provide an input to a dealers diagnostic computer, which most of our cars are never going to see.
On other versions of Motronic it gives cam position info to the ECU and if this info is missing, it will affect running.

[Simon]

better off putting it on, its there for a reason, the rubber sleeve on the lead should slide off then you can carfully remove the connector for the plug with a pair of pliers

As I said above, on some versions of Motronic it does absolutely nothing except provide an input to a dealers diagnostic computer, which most of our cars are never going to see.
On other versions of Motronic it gives cam position info to the ECU and if this info is missing, it will affect running.

All previous posts about this lead have pointed to this lead doing totally nothing, and I've always argued that it has sorted a running fault I had on a previous car of mine, and nobody ever believed me!

[stuartgallafant]

Yes this lead IS important, and yes it DOES need to be refitted!!

[Brianmoooore]

Not necessarily. Depends on the Motronic version fitted.

[tickle]

brianmooore is right there, he really knows what he's on about.
best thing to do would be see if it runs without it, if it does your lucky + you have an early model.
if it chugs like a sick fat lady with tb it's a later model, the sensor is what it uses to set the ignition timing.

on early models it simply tells you when it's at top dead centre, so i don't see how this could improve performance unless the wiring was dodgy in the first place. im sure that i will be corrected if im wrong though

[AndyMack]

well its a 1988 325i so yeah its an old one. i'll see if i can get it on the new ht lead though.

[tickle]

you do the right thing there really, for the effort it is you may aswell try, you do after all have the origional lead to have a practice on and it's good to get into the habit of not missing bit's out cos they may not be needed, this is how most of my major boobs have happened

i remember doing a dash at a ford dealership and there was a connector that didn't fit anywhere, so i left it as there seemed to be no problem. a couple of days later back came the customer with a deployed passenger airbag, woops.
would never have happend if id have not been under pressure to get it done while running another 2 jobs at once, (damn efficiency ratings)

if a job is worth doing it's worth doing properly or not at all

[jog5000]

I have the same lead on an 89 325i, problem is, its on the number 3 lead - so should I move it to number 1 asap?!

[Brianmoooore]

Just noticed the mistake running right through this thread, including the OP.
Pickup is on lead SIX not one!!
OP says No 1, but in the pic it looks like a lead going to the far end of the engine.

[DelaneyG]

Just noticed the mistake running right through this thread, including the OP.
Pickup is on lead SIX not one!!
OP says No 1, but in the pic it looks like a lead going to the far end of the engine.

Well spotted!