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1999 350 Mag MPI Timing Question

H

highflight2k2

Contributing Member
"This question is just for my

"This question is just for my edification. How exactly does the computer adjust the timing. The distributor has the standard looking cap and rotor but seems to have nothing but a sensor inside? I understand how the computer determines to change the timing under the different conditions, but how does it actually affect the change? The coil isn't a capacitor right? My only theory is that the rotor has a wider pickup and the computer tells the coil when to fire...but I thought coils generated constant current.

I'll stop blabbering and hope someone can enlighten me! :)

Thanks very much.

Jon"
 
"That would be a t-bolt V dist

"That would be a t-bolt V distributor with, as you said, just an ignition sensor. The ECM receives a reference signal from the igntion sensor and, based on the input it is getting from the other engine sensors (RPM, throttle position, manifold pressure, ect.) it calculates the timing advance and uses it's internal coil driver circuit to fire the coil.

FYI, the timing advance value you see on a scan tool is the total advance including base timing (it assumes you have the base timing adjusted correctly)."
 
"So the coil is more like a ca

"So the coil is more like a capacitor in this case? Or does it have switching circuitry? And I guess since there is no mechanical advance/retard at the rotor, the computer can only advance or retard relative to the size of the contact on the tip of the rotor?

Thanks for the info!

Jon"
 
"The coil functions the same a

"The coil functions the same as they always have. They are powered up at 12 volts constant and the ground is pulsated by the control module (formerly points on older ignition). Due to the dynamics of the windings, removing power from the coil causes a discharge of high voltage to the distributor and on to the plugs.

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

The electronic advance essentially has a base ignition curve (programmed into the ECM) and the ability to advance and retard within prescribed parameters based on input from other sensors that indicate collectively where the engine is in speed/load and transient throttle conditions."
 
"Jon,
The coil functions just

"Jon,
The coil functions just like it does on a points and condenser ignition where the coil is charged by a 12 volt current and then the ground is removed to collapse the magnetic field and induce a high voltage into the secondary winding, but in this case a transisitor is used to do the switching instead of points."
 
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