I was hoping someone could help educate me or point to a good resource that explains how the advance on my distributor works. The truck is a 96 F250 with a 460efi.

Im interested in better understanding how the electronic advance works. I understand mechanical (centrifugal springs) and vacuum advance but I have not found a good source to explain how the electronic advance functions.

thanks for any leads!

 

Distributor Ignition (DI) System

The ICM in the distributor ignition system is not mounted on the distributor but in another location within the engine compartment. The ICM module is represented pictorially in Figure 22.

The components consist of the ICM, sealed distributor, CMP (hall effect PIP) sensor and E-core ignition coil. The CMP (hall effect PIP) sensor is located inside the distributor. Note also that there are no mechanisms for centrifugal or vacuum advance.

The CMP (hall effect PIP) sensor inside the distributor responds to a rotating metallic shutter on the distributor shaft and produces a digital PIP signal. This signal provides base timing information and is an indication of engine speed (rpm) and position. Note that since the shutter is mounted on the distributor shaft, two revolutions of the engine crankshaft are required to fire each spark plug once. This is because the distributor rotates at half the crankshaft speed.

The ICM determines when to turn the coil ON based upon engine rpm information. The coil is then fired, or turned OFF, whenever a rising edge of a SPOUT signal is encountered. The SPOUT signal, short for Spark Output, is a digital signal generated by the PCM providing spark angle information to the ICM. The rising edge of the SPOUT signal controls the firing of the coil. The falling edge of the SPOUT signal controls the time the coil is turned ON (Figure 23). The coil ON time, or dwell, for this system is thus entirely controlled by the SPOUT signal. The ICM does not internally determine when to turn the coil ON as it does on the push start system. It responds directly to the SPOUT signal it receives.



The CMP (hall effect PIP) sensor is a digital output device located within the distributor. A rotary vane cup, used to trigger the hall sensor, is mounted on the shaft of the distributor and is made of a ferrous metal. When the window of a cup is in the air gap between the hall device and the permanent magnet, a magnetic flux field is completed from the magnet through the hall device and back to the magnet. This condition results in a low (0 volts) output signal (Figure 24). As the distributor shaft turns, a tooth on the cup will move into the air gap. The magnetic field will be shunted by the tooth (Figure 25), preventing it from reaching the Hall device, and the output signal will change from a low to a high (B+).

On engines having sequential electronic fuel injection (SFI), one tooth on the vane cup is smaller than the rest to identify when cylinder No. 1 is at 10 degrees BTDC. The width of the PIP signal generated by this tooth is smaller than that of the other teeth and is called signature PIP (Figure 22). It is required by the PCM so that it can accurately control the sequential firing of the fuel injectors.

The DI systems have a Misfire Detection (MD) sensor that is similar to the EI system Crankshaft Position (CKP) sensor (refer to Figure 8). The MD sensor is a magnetic transducer mounted on the engine block adjacent to a 4 tooth trigger wheel located on the crankshaft. The four teeth are spaced 90 degrees apart. By monitoring the trigger wheel, the MD sensor indicates crankshaft position and speed information to the PCM. The PCM determines if a misfire has occurred by measuring rapid decelerations between teeth.





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That’s a lot of good info, thank you.

So one thing I’m still struggling to understand....

Is there a rotational “phasing” of the rotor within the cap?

If not, I guess I don’t understand how the timing of when the electrical signal from the distributor reaches the plugs would change.

I mostly follow how the system replaces breaker points to control when I the coil fires.

thanks

 

The timing advance/retarding is all controlled by the computer. By varying the input to the Ignition Control Module (ICM) the timing is advanced from base timing, factory is 10* BTDC, to a calculated value. The only moving part inside the distributor is the shaft that is connected to the camshaft. Just like a points distributor the rotor is attached to that shaft, but there is vacuum advance mechanism or weights that increase timing based on RPM. Both of those parts are replaced by the computer and ICM.

 

No there is not any rotational “phasing” of the rotor within the cap in either the point or PCM/ICM systems.
You say you understand the point Ignition system well this system works the same way.
In the points system the points mounted on a plate would open and close at different times depending on the movement of the plate. This would change the off and on signal to the coil.
In the H system that you have it works the same way except the PCM tells the coil when to fire by way of the ICM with the SPOUT signal.

 

Ok, yeah I get it now I was way over thinking it. Appreciate the replies