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Three important events are needed for Spark and then Fuel:
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 to each pulse by "triggering" the coil's negative terminal #1 to generate the high voltage in the coil's center wire, to be "distributed" to the proper plug.
C) At the same time, the ICU must also send a timing pulse to the Fuel ECU to keep the Fuel relay energized, control the injectors, etc.
Either test below 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 above)
1) Pull coil HT wire from distributor cap, attach/adapt to spare (grounded) sparkplug.
2) Remove distributor cap.
3) Rotate engine till an open Vane "window" is centered in front of the Hall Switch "pickup".
4) Turn Key ON.
5) Pass a feeler gauge blade (or similar) through the Hall Switch (simulating a moving Vane segment).
•) If the Hall Switch and ICU are OK, you should get a spark at the test plug and fuel pumps should run for a second.
•) Repeat step 5 as needed to verify spark and pumps.
•) If no spark, test ICU operation below (bypassing the need for 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 Hall switch test).
2) Remove the 3-wire connector plug from distributor body.
3) Insert a jumper from plug socket B (Yellow wire) to socket C (Black wire). When jumper is REMOVED (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 operate now, suspect Hall Switch or wiring.
•) If no spark, suspect ICU or wiring.
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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