Strong spark on 2 but even after swapping coils around still no spark on 1 and 4

 

The power to the two coils comes directly from the ignition switch and that circuit appears to be OK. The control for the coils/spark is provided by the ignition module by pulsing the coil grounds. As you know, each coil provides spark for a pair of spark plugs. Has anything been done to the ignition module? Also check all the wiring and connectors in and out of the ignition module and the spark plug wires and plugs on the bad pair. If everything checks out then you have either a bad ignition module or a problem with the control of or input to the module.

George

 

Some more information on how your system works:

You have a wasted spark ignition system. Each coil generates spark for 2 cylinders simultaneously. The cylinders are paired so that on a given coil, one cylinder is at TDC on the compression stroke and the other cylinder is at TDC on the exhaust stroke. The cylinder on the exhaust stroke just "wastes" its spark. Each coil pack has power supplied by the ignition switch which is on during run or start. The timing of the coil firing is supplied by the crank position sensor. The selection of the coil to fire and the ignition timing is supplied by the PCM. I've never worked on this ignition system but I believe that during start the coil firing may be controlled by the crank sensor alone. If you disable the fuel pump and crank the engine do all 4 cylinders have spark?

George

 

No nothing done to module, I changed plug wires. They are new. I have not disabled fuel system to try spark test. I need to locate ignition module and try that.

 

Here is some more information and clarification. Again, I don't know this ignition system in particular but I do understand these systems generally. We are handicapped because the most elegant diagnosis and confirmation would involve an automotive oscilloscope but I still want to guide you to avoid parts swapping if possible.

As I explained before you have a waste(d) spark ignition system. Those two cylinders get their spark from that one coil and they are both fired at the same time, every time. That means that the failure is the ground/control for that one ignition coil. You also have a bypass system which means that the ignition module supplies all of the control signals to the coils during cranking and the PCM does not take over coil timing and dwell control until after the truck starts. What this means is that during cranking, the PCM is not involved in spark, hence the crank/spark test. That said, in this system, coil firing selection may be handled entirely by the ICM in either mode but we should still see if crank has different behavior than run.

You also have a crank position sensor which is integral to this whole process, its an essential sensor input. I don't know if you you also have a camshaft position sensor, but if so it may also be a part of the essential sensor input.

So what does all of this mean? In order for proper spark you need proper function of sensors, ICM, coils, PCM, and all of the associated wiring and connectors. An automotive oscilloscope can make quick work of determining the fault but without one we have to do some trial and error to isolate the problem. You don't have a coil problem because you swapped them with no change. The crank test will tell us if the system provides spark at both coils during crank/bypass (no PCM involvement). If you still don't have spark then its sensors, ICM, or wiring connectors. At that point, its free to inspect wiring and connectors and cheap to swap out the sensors. What would be left is the ICM which is expensive. A junkyard unit would be the cheapest swap test there. I don't know if any of the parts stores can test that ICM.

George

 

The problem was the ICM, I TOOK it in,had it tested and it failed. Bought a new one, installed it and truck is running really good.

Want to Thank George for helping me understand the system.

 

My pleasure, I’m glad that your back up and running.

George