Tining advance, retard question

[Danza V]

Got a query really guys.

When the cars idling obviously the ignition timing is at a certain point at idle for for the spark fires and the timing will advance and make the spark happen earlier, but my question is; how does it do this? I mean, correct me if I'm wrong but does ecu communicates to the ignition through the king lead to the dizzy and adjusts the spark. How does it do this? Cause in my mind I see the dizzy on the end of the cam spinning around hitting all the contact points, so how does the ecu adjust the ignition timing? I know it communicates through all other sensors like the air/fuel etc.

Cheers for the help

[AdamB]

Take a read through these

http://auto.howstuffworks.com/ignition-system.htm

http://auto.howstuffworks.com/ignition-system4.htm

http://auto.howstuffworks.com/ignition-system3.htm

It is a very long winded process to explain as there are so many variables which effect the engines operation.

If it still doesn't answer your question let me know and I'll write it up

[Danza V]

Hoping you would reply I had a read through that to find the one thus I wanted but couldn't find it. I know how the system works but I just wonder " how " it advances the timing, obviously through ecu but exactly how I know it depends on the crank angle etc, fuel, air and all that jazz, just how it communicates to the ecu to do it and how it changes after

[AdamB]

Well basically the long and short of it is.

The ecu is programmed by a user for set characteristics, ie power, fuel consumption etc. The program or values are remembered by the ecu in the memory. When the ecu see's say a MAP load (used for forced inducted motors, TPS is used as load for N/A) 0.5 bar at 3000rpm, it will look up that cell in the map and it may say something like 15 degrees ignition advance.

Using a crank trigger the ecu is able to know where the engine is at, well No1 cylinder at TDC is what it looks for.

With a dizzy setup the ecu controls the ignition coil, the charging and collapsing of the magnetic field, well basically it just turns it on and off. When the field is collapsed is when the voltage is induced into the coils secondary windings which then is sent down the plug lead, to the rotor arm, to the contact point, down the corresponding cylinder lead to the spark plug.

After ignition has happened, or during if the engine knocks/pings the knock sensor picks up on this and will then reduce the ignition advance for the next cylinder.

Basically it just uses its predefined user programmed values, but then uses the various sensors to keep it running at its optimum. Open and closed loom control is another topic lol.

[Danza V]

Well, thanks for that intimation, helped greatly so the kinda inertia movement down the dizzy shaft moves the insides so to speak of the dizzy and then moves it back and forth to advance it?

[mech5107]

No, there is no movement in the dizzy, except for the rotor arm.

The ecu collapses the magnetic field in the coil just some degrees before or after TDC.

The rotor arm is in touch with each post for a range of degrees, so while ignition advanced or retarded, it is still able to deliver the spark.

Inertial or vacuum induced movement was something that oldschool carbed cars used.

[morgey]

basically the ecu can send signal to the ignitor which sends a signal to the king lead.

its when the ecu sends the signal that determines how advanced or retarded the spark will be.

it has to do that for every cylinder all through the rev range, so you can imagine how quick that ecu is having to work

[Danza V]

So the rotor arm in a carb engine when timing gets advanced moves by the inertia or vacuum?

In modern engines its stored on the ecu under a multitude of settings for certain stages the engine reaches right? So after the knock sensor picks up pinging/knock etc how does the rotor in the dizzy move?

Cheers for being patient

Edited August 18, 2013 by Danza V

[Danza V]

I get it now lol :-) cheers all. I studied it all st college about 4 years ago and I'm now refreshing memory

[Danza V]

Just found that out aswel lads through one if my old school books. Cheers for the explanations earlier though

Edited August 18, 2013 by Danza V