Ignition System L47

The 4.6L Northstar Ignition Control System consists of the following components:

In this ignition system, both ends of each of the four ignition coils are connected to a spark plug. Each coil is connected with spark plugs on companion cylinders, i.e. on top dead center at the same time (1-4, 2-5, 6-7, and 3-8). One cylinder is on its compression stroke when the other one is on its exhaust stroke.

When the coil discharges, both plugs fire at the same time by using the engine block to complete the electrical circuit. the cylinder on the compression stroke is called the event cylinder and the one on the exhaust stroke is the waste cylinder. The two cylinders share the energy available from the ignition coil to fire both spark plugs. This method of ignition is called waste spark ignition.

Since the polarity of the ignition coil primary and secondary windings does not change, one spark plug always fires with a forward current (center electrode to ground electrode) and its companion plug fires with a reverse current (ground electrode to center electrode).

It is possible for one spark plug to fire even though a plug wire from the same coil may be disconnected from its companion spark plug. The disconnected plug wire acts as one plate of a capacitor and the engine block acts as the other plate. These two capacitor plates are charged as a spark first jumps across the gap of the connected spark plug. The plates are then discharged as the energy is dissipated as the spark continues. Voltage requirements are very high with an open spark plug or wire. The ignition coil may have enough reserve energy to fire the connected plug at idle, but possibly not under some engine load conditions. A more noticeable misfire may be evident under load; both spark plugs may then not fire.

The reluctor ring is cast onto the crankshaft between the 3 and 4 main journals. The reluctor ring has 24 evenly spaced notches or air gaps and an additional 8 unevenly spaced notches for a total of 32.

As the crankshaft makes one complete revolution, both the A and B sensors will produce 32 ON-OFF pulses per revolution. In addition, the A sensor is positioned 27 degrees of crankshaft revolution before the B sensor. This creates a unique pattern of ON-OFF pulses sent to the ignition control module so that it can recognize crankshaft position.

The camshaft position sensor is located on the rear cylinder bank in front of the exhaust camshaft. The camshaft position sensor extends into the rear cylinder head and is sealed with an O-ring.

As the rear cylinder bank exhaust camshaft turns, a steel pin on its drive sprocket passes over the magnetic camshaft position sensor. This creates an ON-OFF signal sent to the ignition sensors. The camshaft position sensor produces an ON-OFF pulse for every one revolution of the camshaft or every two revolutions of the crankshaft. This allows the ignition control module to recognize camshaft position.

The camshaft position sensor is not adjustable. For on-vehicle service, refer to Camshaft Position (CMP) Sensor Replacement .

The knock sensor is located under the intake manifold, near the starter motor. The knock sensor detects abnormal vibration (spark knock or detonation) in the engine. The sensor produces an alternating current (AC) voltage which increases with the severity of the knock. The knock sensor is specifically tuned to the engine based on the frequency of vibration that the engine creates when it knocks. the knock sensor for the 4.6L Northstar is tuned to 7000 hertz. This signal is an input to the PCM, which then adjusts spark advance to reduce the spark knock. For on-vehicle service, refer to Knock Sensor (KS) Replacement .

The Powertrain Control Module (PCM) controls spark advance and fuel injection for all driving conditions. The PCM monitors input signals from the following components as part of its ignition control function to determine the required ignition timing: