Ill see if i can find a way of wording this so people understand....

So if you have a distruibutor thats locked in and all its doing is distributing the spark, there no mechanical advance or anything else in it, and using aftermarket, or even stock style managment, how is timing actualy advanced? I deal with hondas and base timing is set at 16* btdc. And advances up to 48* in some maps. So with nothing moving except the rotor inside if the distributor, how is timing actualy being advanced or retarded? I know the rotor looks like it covers what looks like about 20*. Is the spark sent somewhere when the duration of the rotor is passing by the post inside the distributor? Can someone make sense of what im asking?

 

more liking the timing is locked at 48*, and retarded back to where you want it..

 

Im assuming there is some form of ignition control from the factory. The mustangs use a tfi module, but in any case, the computer or mechanical advance distributor just changes when the spark fires in relation to the piston on the power stroke. Advanced timing is before top dead center, around 30-40 degrees at wot n/a seems to be the sweet spot.

 

Well I indexed my dist. I run locked timing and was worried about what you said, I drilled a hole in a old dist cap and watched where it as sparking, It was all the way beyond the rotor tip, So I changed the correlation of pickup to the dist housing till the spark was in the middle of rotor finger. Now there is less chance of firing the next cylinder and causing misfire.

 

I understand the way mechanical advance works. But im asking about distributors that do nothing but distribute the spark. I have this same question posted in other forums and what im figuring out is that the rotor itself can cover 55-60* of sweep. So from the post in the distributor as the rotor is sweeping past it has the 55*-60* of or rotation for the ecu to tell the coil when to fire based on where crank trigger or cam angle sensor show the motor is at.

 

The distributor is just a mechanical means of getting the spark from one cylinder to the next; it's designed to be able to fire within a certain range if degrees. The ecu and or ignition module is responsible for telling the coil when in relation to crank angle to fire. You will see a difference in rotor tip size for a "fixed" position rotor electrode (wider) and a mechanically advancing style distributor (narrower tip).

 

Spark will jump from the rotor to whatever terminal in the cap is closest when the coil fires, even if the contacts aren't directly aligned.

 

I'll try...ignition timing advance/retard is done through the ecm/ecu based on inputs from the various sensors that feed back info telling the ecm/ecu what the engine rpm is,what the load is, how wide open the throttle is,etc. Not exacting info here but I think this gets the point across.

 

Typically when an ignition coil is grounded it begins to charge, building a field. This charging time is known as dwell. When this ground is lifted, the field begins to collapse, and spark is initiated.

On old points style ignitions, the points and cams/eccentrics governed this. Timing was mechanically advanced because they were attached to the same shaft as the rotor. With modern ignition systems, the control device controls the grounding of the ignition coil, this allows for full control of timing (within the limits the rotor physically lines up acceptably well with the coil post).

 

Wantabe got it right.

 

I don't know of any OEM stuff that works that way. Aftermarket stuff, yes. But not in the example the OP asked about.

 

From what I gather, here is the question

And it looks like this is the answer

 

If the magnetic trigger tells the computer to fire the coil, then how can the coil fire that cylinder before its triggered?

 

Because an ECU/PCM/aftermarket timing control sits between the pickup/trigger device and the coil primary side, and based on various inputs alters the point when the coil is fired.

 

Your correct you cannot make something happen before it happens, its that what is happening is actually retarded 45*(or whatever is designed into system) so when it advances it just comes closer to the actual trigger.

 

Again, no... OEM systems actually do make it happen before the trigger for that particular cylinder occurs, if the desired timing is earlier BTDC than the base setting at the distributor (or crank sensor, whatever). MSD timing controls do it the way you describe, pulling timing back from the base (max possible advance) setting.

 

How does this happen?

 

Duh, magic! oke:

LOL, kidding, but it's microprocessors and software. The [whatever timing device] knows how fast the crankshaft is turning, it knows how many cylinders there are, it knows how long it's been since the trigger pulsed for the previous cylinder, so from there it's just simple math to figure out when to fire the coil to make spark X degrees before the next trigger pulse occurs.

 

yeah,

the processor looks at the speed the engine is turning by how often the triggers go past, the triggers are usually set to somthing like 60deg BTDC the processor then does an equation to work out whow long to wait after the trigger to deliver the spark.

on my engine for example (4 cilinder) the Ecu is controlled by a 36-1 wheel, there is a tooth every 10 degree's, but one is missing so the ecu can caluclate from a starting point, my missing tooth is 90 deg BTDC.

 

^^ Those two posts explain it well for me, thanks!