Tom,

If it's the pickup or the module the tach should drop to zero when there is a problem.

The tach senses the voltage on the negative side of the coil.

To create a a spark the module grounds the negitive side of the coil through a transistor. When a spark is needed the module stops the current flow through the coil. This causes the magnetic field in the coil to colapse, generating about 20,000 volts onthe coil wire side and a 200 to 400 volt pulse on the negitive side of the coil.

Putting a scope on the negative side under load will show what is happening on the high voltage side. The tach is also connected to the negative side of the coil and will show complete failures by dropping if the coil stops working.

It wont show a high voltage leak to ground. Thats a bit harder to test under load.

The basics of keeping an engine running are compression, fuel and spark.

The fuel can be monitored by looking at the O2 sensor while you drive. You can also look for an over rich condition by having somone follow you as you drive. You should see a large amount of black smoke when it happens.

The carbs go rich if the bowl vent valve leaks and the motor will die out with RPM and load.

a lean out would be most likely caused by a fuel delivery problem. I would suggest using a temporary fuel pressure gauge to make sure you have fuel pressure under load.

In summary:

I would test for the basics, fuel pressure, and spark. Since you cant easily test the high voltage side of the coil under load it makes sense to try another coil.

The rest of the ignition system can be figured out by watching the tach.

A low cost gauge connected to the O2 sensor can tell you if the fuel system is a problem. The other solution is to put a scope on the sensor lead where it enters the fuel computer by the passengers feet.

You can also use a good digital voltmeter to measure the sensor. A scope probe is better but a voltmeter should work.

Kevin