"Guess it's time to buy the factory manual"

Or at least the Bentley 240 Service manual, which addresses your Volvo/Chrysler Ignition ('82 thru '88 240's). In the meantime here is a "canned" response I can offer on the subject:

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A) To get sparks from the coil, the spinning distributor's "Hall Switch/sender" must send weak pulses (1 per cylinder/plug) to the Ignition Control Unit (ICU).

B) The ICU must then respond by "triggering" the coil's negative terminal #1 to generate the high voltage that leaves the coil to be "distributed" to the proper plug.

C) At the same time, the ICU must also send a timing pulse to the FI ECU to energize the Fuel relay (or keep it energized), and control the injectors, etc.

Below are 2 tests that should help isolate a "no spark" to either "A" or "B", and verify that "C" also occurs correctly. Either test can be done first, and both assume +12V at Coil terminal #15 with Key On.


Hall Switch Test (tests for A to initiate B and C)
1) Pull coil wire, attach/adapt to spare (grounded) sparkplug.
2) Remove distributor cap.
3) Rotate engine till a Vane "window" is centered in front of the Hall Switch.
4) Turn Key ON.
5) Pass a feeler gauge blade (or similar) through the Hall Switch (simulating the moving Vane).
•) If the Hall Switch and ICU are OK, you should get a spark and fuel pumps should run for a second (item "C" above).
•) Repeat step 5 as needed to verify spark and pumps.
•) If no spark, test ICU operation below (eliminating Hall Switch).

ICU Switching Test (bypasses A and tests only for B and C)
1) Key OFF. (Coil wire and spare plug still set up as in Step 1 above).
2) Remove the ICU 3-wire plug from distributor body.
3) Insert a jumper from plug socket B (Yellow wire) to socket C (Black wire). When jumper is REMOVED in step #4, the plug should spark and the fuel pumps should run briefly.
4) Key ON. Check for spark and pumps as jumper is removed.
•) If Spark & Pumps now, suspect Hall Switch or wiring.
•) If no spark, suspect ICU or wiring.
•) If no Fuel pumps, suspect wiring to FI ECU pin #1. Pulse source depends on car year: Coil #1 for '82-'84, ICU #8 for '85-'88.

<=================Hope this helps

--
Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.