Ignition wire question...

On one of the wires coming from the distributor, there is a coil of some sort. Anyone know for sure what this is for???

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Umm... you're referring to the spark coil, maybe? Or maybe an electrical advance solenoid? Or maybe something else? Since you don't mention what model and year the car is, or where the wire is coming from.... --scott
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wrote:

"the wires coming from the distributor"
Old HT wiring all wires are thicj and will give you a belt if you touch them when the engine is running
coil<---->distributor | | | | | | VVVVVV spark plugs
newer wiring
D------> Coil -----> spark plugI S------> Coil -----> spark plugT R------> Coil -----> spark plugI B------> Coil -----> spark plugU T------> Coil -----> spark plugO R------> Coil -----> spark plug except sometimes it is called something other than the distributor.
The key point is that the high voltage is only transformed at the coil that sits on top of each spark plug.

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Ok, I guess I didn't give near enough information... The car is an 89 325i and on the number 6 cylinder plug wire there is a choke coil looking piece with a cable that runs to a plug on the other side of the engine. I thought it might be a tach pickup but the tach functions without it.
On 1 Dec 2007 11:45:08 -0500, snipped-for-privacy@panix.com (Scott Dorsey) wrote:

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wrote:

It's for the Motronic 1.1 ECU. Looks like an extra plug wire coming off the loom, eh? It tells the ECU when that spark fires and uses it as a reference point. I can find more info iff required. Anyone with that flavor Bentley care to chime in? I sold off my 325s a few years back. The straight Motronic in my '86 535i doesn't use that set of wires, since it started on the Motronic 1.1.
Bill in Omaha '86 535i
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I'm going to take it that it does something important then. Reason I ask is that the wire is broke om my son's car and it's running a little rough and I'm trying to figure out exactly why. This doesn't seem like a part you can get without buying an entire set of plug wires either and it seems some performance wires don't come with it. This made me wonder what it was for. Another problem I'm having is the number 2 post (top one next to the hold down bolt) keeps arcing to the bolt. Going to try rubber caulk inside the plastic cover to stop this. This is the second brand new cap that is doing this...

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I do not think your car requires the pickup. You need to get the electrical manual and verify this.
But when you order wire sets, you can order them with or without the pickup, but a lot of folks just stock the ones with the pickup and use them on all the cars. If someone has done this, you will have a pickup in place which is not connected to anything but doesn't need to be connected to anything.
If you have replaced the cap and it's arcing, I'd replace the wires, and I would put silicone dielectric compound (NOT RTV CAULK) on the ends. A number of aftermarket dealers have wire sets that are reasonably priced and reliable; the BMW sets cost a fortune. --scott
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"C'est un Nagra. C'est suisse, et tres, tres precis."

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Thinking back to my E30, I remember the wire. As I recall it actually is a tach signal or timing signal, but it goes to the diagnostic connector. It isn't used by the car, but when hooked up to the BMW service computer. Someone will hopefully correct me if my memory is bad.
Bob
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That makes more sense. Most EFI systems which aren't integrated with the ignition take a sniff of the LT via a resistor. No reason to inductively couple.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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wrote:

I have a few PDFs of the Motronic units and some other info on the plug wires. Who wants a copy?
Bill in Omaha '86 535i
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http://www.autohausaz.com/search/group.aspx?sid=vgyil2qrnzt4s5qzqtjba0aq&mak eid0003@BMW&modelid11698@325I&year89&cid%@Ignition%20Parts
great pics of the wire set and ignition parts -----
wrote:

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Michael Yeager wrote:

Michael - I assume you're talking one of the old 2.5 or 2.8L engines.
It's an inductive pulse coil - that reads when the ignition pulse takes place and feeds it to something.. it's been so long I've forgotten exactly what - might be the tach, might be the Motronic.
In any case - you DO need this coil on the ignition wire (it's on #1 I believe?)
You can ignore most of the posters telling you you're not seeing what you see.. they just don't have a long enough BMW history.
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Michael Yeager wrote:

Michael - I assume you're talking one of the old 2.5 or 2.8L engines.
It's an inductive pulse coil - that reads when the ignition pulse takes place and feeds it to something.. it's been so long I've forgotten exactly what - might be the tach, might be the Motronic.
In any case - you DO need this coil on the ignition wire (it's on #1 I believe?)
You can ignore most of the posters telling you you're not seeing what you see.. they just don't have a long enough BMW history. -----
With the exception of the O.P., is anyone reading what I've posted??? I've explained what the trigger wire was and where it goes. I even sent a web page link and offered to send a diagram pdf file. I guess what they say is true...
Bill in Omaha '86 535i
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I appreciate the replies Bill. Sorry so many other people don't seem to read all of them. One other person replied that it was used by the motronic system but I don't remember who it was.

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It is for cylinder recognition.
It tells the Motronic control module when #6 cylinder fires. This allows the control unit to set up the semi-sequential fuel injection timing. If the sensor is not present, or not operational, you may get a rough idle as the control unit defaults to firing all injectors at the same time for 1/3rd of the required opening time. Each injector then opens 3 times before the valve opens. It's less precise, hence the move to semi-sequential (fires 3 injectors at a time instead of all 6) and then on to fully sequential where each injector is fired as needed.
FYI
Brett Anderson

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