Irregular Leading Coil Spark
 

My car (series 4) is lacking power above 5000-5500
rpm, and there is a rapidly oscillating (1-2 Hz), irregular hesitation,
accompanied by small blips in my air-fuel ratio. I checked my grounds with
an ohm meter and all seems well. However, when I take the cap off the crank
angle sensor and trigger my timing light on the leading coil (either plug wire
gives the same results), I see the prongs on the top spindle jumping around
at higher rpm. They change position back and forth, 90 degrees, at random at
1-2 Hz. Sometimes two are visable, sometimes 4 (like a cross). I'm obviously missing some spark. Does this sound like a problem with the coil, the crank angle sensor, or the computer? How can I further diagnose this? If I trigger the timing light off of either trailing coil, all is rock solid.

Instead of trying to decipher optical illusions at the CAS, just put the pickup on a plug wire and stare at the timing pin & marks. You also have to remember the ECU is advancing or retarding spark throughout transients, which will give the appearance of the CAS magnets "jumping around"...How is the igniter/coil pack-to-chassis bonding?

Well, if I just point the timing light at the timing pin, I get transient, missing flashes (every other flash, I think) at high rpm. What I am seeing is different than spark advance, which ocurrs smoothly throughout the rev range. If I hold the idle above 4 or 5k, I see a cross at the crank angle sensor (just like I do at lower rpm), but then the cross disappears for like a second and I get either a verticle or horizontal line instead, because of a coil missfire pattern. It just switches around at random like that as long as I keep the idle above 4k or so. The coil ground checked out fine with the car off, I'll go retry with the car warmed up and running at high rpm.

All right, start at the top- read out your CAS coils (160 ohms apiece or so), get to your ECU and check your CAS input voltages (FSM, fuel section), make sure your plug threads are clean in the rotor housings, both igniter bodies are grounded well with the hardware (sometimes corrosion gets the best of 'em), close visual on the plug wires for insulation breakdown, you get the picture...