Not too long ago I submitted an assignment on the theory and operation of the distributor-less ignitions that our A-body cars came with; specifically, the 3300. I used a lot of information from my 1990 Oldsmobile Cutlass Ciera Service Manual. I'll copy/paste it here. Hope it helps you out.
Engine Ignition System Assignment
AT615 Engine Performance
October 12, 2013
Waste Spark Ignition Theory:
In 1990, General Motors equipped their A-body vehicles with a Computer Controlled Coil Ignition System. My personal Oldsmobile Cutlass Ciera with a 3.3 liter V6 received such a setup. To be specific, the system is of the waste spark variety. Waste spark systems fire two plugs simultaneously, one cylinder on the compression stroke, the other on the exhaust stroke. Since the cylinder on the exhaust stroke is under little to no pressure, minimal voltage is required to fire the plug. As a result, one coil can fire two cylinders. This decreases emissions by burning off excess fuel that would otherwise exit via the tailpipe. The spark plug on the compression stroke receives the initial voltage and the electrical charge carries through the engine block to the opposite plug on the exhaust stroke. This plug fires, then electrical energy carries back to the coil, reaching electrical equilibrium. Each cylinder is paired together with the opposite cylinder in the firing order. The 3300 engine firing order is 1-6-5-4-3-2. The cylinders paired together in the ignition system are 1/4, 2/5, and 3/6.
Computer Controlled Coil Ignition Synopsis:
GM’s CCC Ignition System utilizes three coils, an ignition module, reluctor rings, and a crankshaft position sensor. The ignition module is located underneath all three coils and serves as a mounting plate for each coil. It serves to time the ignition of the fuel/air mixture based on inputs when the engine is under 400 RPM. Above 400 RPM, the ECM applies 5 volts to a bypass circuit which causes the ICM to defer to the ECM and timing is controlled by the ECM. Reluctor rings which signal the crank position sensor are mounted on the harmonic balancer and the crankshaft position sensor is mounted at the three-o=clock position of the harmonic balancer, bolted to the engine block. Two reluctor rings are used and the crank position sensor is made up of two hall-effect switches. The crankshaft position sensor is adjustable for precise placement according to OEM gap (0.025 of an inch). Secondary ignition wires transfer current from the coils to the six spark plugs mounted in the two cylinder heads of the engine.
Of the ignition system, the following are outputs: ECM, Ignition Control Module, coils, secondary ignition wires, and spark plugs. The ignition control module receives input from the crankshaft position sensor, coolant temperature sensor, tachometer, and mass air flow sensor to calculate proper ignition timing under 400 RPM. Above 400 RPM, the ECM controls ignition timing based on input from the crank position sensor, tachometer, engine coolant sensor, mass air flow sensor, throttle position sensor, knock sensor, vehicle speed sensor, and park/neutral state switch.
No Start Diagnosis Procedure:
Begin diagnosis by checking for spark on cylinders 1, 3, and 5. Crank engine to command ICM to trigger spark. If no spark is found on all cylinders, the fault is a loose/intermittent connection at the ICM or a faulty ICM. If no spark is only on one or two cylinders, check resistance of spark plug wires. Resistance should be less than 30,000 ohms. If not, secondary wire is at fault. Assuming the secondary wire’s resistance is acceptable, remove suspect coil and connect a test light at the two exposed terminals. If the test light does not blink during cranking, the ICM is faulty. If ICM is OK, check the suspect coil’s primary resistance (0.5 – 0.9 ohms). If within specification, install a back-probe on Pin M of the ICM connector. Connect the positive lead of the voltmeter to the back-probe and the negative lead to a chassis ground. With Ignition “ON,” voltmeter should read battery voltage. If battery voltage is not found, a short to ground has occurred in wire #839 (Pink w/Black tracer). At this point, the crank sensor is the next thing to check. Back-probe the crankshaft sensor connector at pins “C” & “D.” Measure voltage between terminals “C” & “D” of the crank sensor with Ignition “ON.” Voltmeter should read between 10 to 12 volts. If not, an open or short to ground has occurred in Connector #644 or #645. If the harness is OK, the ICM is at fault. If voltage is within specification, the crankshaft position sensor has improper gap or the crankshaft position sensor is faulty. Check the sensor for signs of the reluctor rings hitting it.
General Motors engineers specified a particular spark plug to this system; multiple aftermarket equivalents will also be listed. AC Delco #R44LTS6 is a resistor spark plug with a long tapered shell calling for a gap of 0.60 thousands of an inch. Thread size is 14 millimeters with a heat range rating of “4.” Accel Ignition, a performance aftermarket supplier, offers an alternative spark plug with a silver core for increased conductivity and lowered voltage requirements. Part number is 526S. NGK, another spark plug manufacturer offers an OEM plug equivalent: Part number is TR55. NGK specifies a gap of 0.59 thousands of an inch for their TR55 plug. Factory tightening specification is 20 lbs. ft. due to the spark plug having a tapered seat. Spark plugs with gaskets included would require a higher tightening specification. NGK recommends 10.8 lbs. ft. – 18.0 lbs. ft. for tapered seat spark plugs installed in cast iron engines. However, NGK specifies to defer to OEM torque specifications when available.
When testing or diagnosing ignition system, never crank the engine with the coil towers not connected to spark plug wires. Irreparable damage to the ignition control module or coil may occur. In addition, crank position sensor to reluctor ring gap is critical! Factory specification is 0.025 of an inch.