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Electronic Ignition

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Hi Guys,

A friend and i are trying to put a 3.5 Rangie engine in a Disco: http://forums.lr4x4.com/index.php?showtopi...l=project+disco

the problem is we cannot get it started. it turns over fine, but there is no spark. we have done all the usual things (cleaned the dizzy cap etc) but there are two wires coming out of the distributer (not the cap) and i have no idea what to do with them...

So can anyone explain simply how electronic ignition works????!!!! Apologies for the stupidity of my question but who better to ask?! ;)

Thanks

Taka

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Hi Guys,

A friend and i are trying to put a 3.5 Rangie engine in a Disco: http://forums.lr4x4.com/index.php?showtopi...l=project+disco

the problem is we cannot get it started. it turns over fine, but there is no spark. we have done all the usual things (cleaned the dizzy cap etc) but there are two wires coming out of the distributer (not the cap) and i have no idea what to do with them...

So can anyone explain simply how electronic ignition works????!!!! Apologies for the stupidity of my question but who better to ask?! ;)

Thanks

Taka

They need to go to either side of the L.T. input (+ & -) on the coil.

edit.. now i think about it one wire should be 12v in and the other should go to the +ve on the coil, sorry about that!

HTH

Mick

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Hi Guys,

A friend and i are trying to put a 3.5 Rangie engine in a Disco: http://forums.lr4x4.com/index.php?showtopi...l=project+disco

the problem is we cannot get it started. it turns over fine, but there is no spark. we have done all the usual things (cleaned the dizzy cap etc) but there are two wires coming out of the distributer (not the cap) and i have no idea what to do with them...

So can anyone explain simply how electronic ignition works????!!!! Apologies for the stupidity of my question but who better to ask?! ;)

Assuming it's an electronic distributor (sounds that way) it will depend on the model. A number of designs have been used but the most common and latest version uses a small amplifier mounted on the side of the distributor which is where the 2 wires would originate.

If that is the case then one of them may well be connected to 12v inside the loom and you need to identify which one and connect it to the +ve terminal of the coil. The other wire than connects to the -ve of the coil. If the wires still have their plugs on the end then that makes life easier as they can only go on one way as one will be male and the other female to match the coil.

If you connect the wires up and turn the ignition on you should get 12v on the +ve of the coil, if you don't you will probably have to run a new feed, ensuring that it comes from a switched 12v that is also on during cranking. It's best to check it with the -ve of the coil disconnected, otherwise you can get 12v from the wrong side of the coil.

If the distributor is an earlier one it may have an internal amplifier or may require an external amplifier that is normally mounted under the coil. "All" the amplifier does is take the signal from the sensor inside the distributor and mimics the action of a set of points electronically, setting the dwell and triggering the coil at the correct moment based on the signal from the sensor inside the distributor. The advantages are a far more accurate dwell (better spark) and more consistent timing without all the problems inherent with a mechanical points/condensor system.

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If that is the case then one of them may well be connected to 12v inside the loom and you need to identify which one and connect it to the +ve terminal of the coil. The other wire than connects to the -ve of the coil. If the wires still have their plugs on the end then that makes life easier as they can only go on one way as one will be male and the other female to match the coil.

How do you identify which one is + ve and which one is -ve?

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How do you identify which one is + ve and which one is -ve?

+&- Moulded into the plastic coil top.

Steve

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Sorry :rolleyes:

I meant on the ign amp :)

Amp (type mounted on dizzy) has (hopefully) two blades, one in line with the amp body and the other across (also nearest the corner).

Inline should have a white wire which is ignition switched +12v also supplying the coil +ve.

Crosswise should be white/black going to coil negative.

The coil negative should also have a resistor coming off of it with the other end connecting to the ECU pin 1 with white/black wire.

Steve

Edit.......I'm not too far away from you and have most of the bits you may want to borrow to swap out with yours to find issues. Flapper, dizzy, ECU, coil. + a whole dead 3.5 engine recently removed from my Dakar.

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So can anyone explain simply how electronic ignition works
Hello Taka,

This may not be simple enough for you, however, here is a generic circuit diagram of a typical (mid '80's period) Rover V8 electronic ignition where the amplifier can be either on the side of the distributor or in an aluminium unit mounted adjacent to the ignition coil.

Ignition02.png

What follows is an extract from my upcoming ignition system manual describing each component function. Hopefully it will answer the above question satisfactorily.

The Basic Electronic Ignition Components and their Functions

From battery through to spark plug and beyond, these are the key components involved in generating the bright blue spark that ignites the awaiting air/fuel mixture and they must all work flawlessly for maximum engine efficiency.

A Battery in good condition, capable of lighting the blue touch paper even whilst churning a reluctant lump on a freezing cold day.

An Ignition Switch with four key positions: 1, Off, 2, Accessories, 3, Ignition On and 4, Cranking. The latter two positions both supply 12 volts to make the ignition circuit come alive.

A Distributor with three tasks. 1, Determine the exact moment during the cycle to generate a signal pulse to ignite the touch paper, 2, Route the resulting spark to the right firework, and 3, Advance the ignition timing according to either inlet manifold vacuum or engine speed.

A Vacuum Advance Module that senses manifold depression as soon as the throttle plate moves away from the idle position and advances the timing to capture maximum efficiency from the upcoming explosions at low engine speed, then passing over ignition advance responsibility to -

The Mechanical (Centrifugal) Advance Mechanism that uses bob weights and springs to control the amount of ignition advance according the engine speed and rate of acceleration.

A Magnetic Rotor with eight peaks produces a pulsing magnetic field adjacent to -

A Pick-up Coil that generates its own output (like an alternator, so not needing a voltage supply) to send a synchronised sine wave signal through its two electrical connections to -

An Amplifier Module already connected between Coil negative and earth that responds instantly to the incoming signal, switching a path to earth for the negative side of -

The Coil, actually not unlike a transformer which converts the switched current from the battery into (typ) 30,000 volts capable of bridging gaps of up to 15mm with a bright blue lightening strike.

A Condenser (or Capacitor) connected into the low voltage circuit across the coil/amplifier combo to suppress Radio Frequency signals otherwise destined to upset in-car entertainment systems and offend un-Neighbourly soap addicts watching their TV’s down the Eastend. It is also perceived to assist in rapidly collapsing the coil primary voltage for a sharper high voltage discharge.

A King Lead connects the high voltage terminal of the coil to the centre turret terminal of -

The Distributer Cap that receives and transfers the high voltage discharges to the -

The Rotor Arm which allocates the lethal sparks to one of eight turrets connected to -

The High Tension Leads with a particular internal impedance, resistance or other RF suppression characteristic, terminating at the prickly -

Spark Plugs where a flash of highly charged electrons ignite the expectant air/fuel mixture inside the combustion chambers, such that, under all the various engine conditions, its exact occurrence is determined by -

The Ignition Timing, not in itself a component, yet in conjuction with the vacuum and mechanical advance components, the most critical of all the functions, often maladjusted.

A Trigger Resistor connects signals generated at coil negative, to Pin 1 of the ECU to notify it the engine is running and please keep injecting fuel until these pulses cease.

The same signals from coil negative also go off to the Tachometer to indicate engine rpm and to the Cruise Control over-speed relay for engine protection if the Cruise ECU tries to accelerate the engine when the transmission or gearbox is disengaged.

Because the above is a "work in progress", errors and omissions gratefully received.

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This is a Brill Thread.

How do you get it put in the Technical Section??

Marc.

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Thanks Marc,

By asking :lol: .............being looked as almost as I type :)

Some tech archive stuff is spotted sometimes we need members to point to things when they feel its worthy

May be if this does a title change may be better ?

Nige

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