OK, here goes.

The height of the tall, thin line is the firing voltage. The sorta straight line after the big peak is the spark voltage. The length of this line is the duration of the spark.

When the spark stops, the voltage will oscillate up and down, eventually dropping to zero. It should go negative during these osccilations.

What I see is OK firing voltage, but low spark voltage with some spikes in the spark line. According to the book, spikes are from fouled plugs, low spark voltage is from excess resistance in the secondary circuit (wires, cap, rotor, plugs).

My guess would be a bad coil, coil to cap, or using high resistance wire ends with platinum plugs.

Also, if it runs very rich due to a bad o2 sensor, the plugs will carbon foul pretty fast.

If it were my car, this is what I would do: Verify the condition of the plug and coil wires. You must check the resistance to do this, eyeball won't work. All the leads must be very similar. Make sure the contact button on the cap to the rotor is good, they can get broken.

Check the resistance of the coil. I don't know exactly what it should be, but I seem to remember 1.5 ohm. This is between the ground terminal and the switchbox terminal, and between the ground terminal and the high voltage (coil wire) terminal.

While you have the coil to cap wire off, chech for burn marks or carbon tracks under the wire end. If you find any, the coil is toast, get a new one.

I'd also check the condition of the connectors on the coil -- corroded wire connections will limit the current and hence the spark, so the spark blows out under load, producing all your symptoms.

What brand of plugs are you using, and what is the gap?

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!