1995 Ford E150 5.0L No/very weak spark

I've got the weirdest issue I think I've ever come across. I'm working on a 1995 E150 van with a 5.0L. No spark at plugs, but get an indication of spark from the coil wire at the distributor cap. Further testing found that while there is ignition, it is very weak,  see attached shot of my scope. Top (red) is PIP (CMP) signal. Green is primary ignition coil trigger and blue is secondary ignition voltage. All is good, primary circuit closes and starts to charge and then starts to oscillate between 0 and system voltage. Secondary voltage can be seen to follow this oscillation. When we finally get to the point of ignition there is a tiny amount of energy stored in the coil and we get about 2kv ignition. Seems like the ignition module is turning on and turning off as it's supposed to, but I don't understand what is causing the oscillation within the dwell period when it should be charging the coil. Tried replacing the ignition module, as well as the condenser just on the off chance.... 

Anybody every come across something like this? Any input would be helpful. Joe

 

How strong is the sark from the coil wire? Sounds like a bad cap and rotor. If you have spark from coil but not the plugs