Should have suggested these checks for you earlier in this thread, jaydee. One has a life case of the perception and cognition myopia. The vision is fine, however. No need for glasses, yet.

http://www.volvowiringdiagrams.com/volvo/960%20Wiring%20Diagrams/Volvo%20960%201997.pdf

Have you pulled spark plugs and checked their condition?

Have you check the condition of each coil pack, or moved coil packs around?

You could be able to test the coil pack condition using a multimeter with a healthy battery set to test both continuity and resistance (ohms).



Using continuity check, first, check across the two (low tension) connector pins of the coil pack. If yes to continuity, then check for resistance (ohms). You should have continuity, yet the correct resistance on across the two pins I do not know. The consistent resistance value you get most may be a guide.

Next, check continuity, and then resistance, between each of the low tension pins and the haute tension side that secures to the sparkplug. Again, I do not know the value should be, so, let the most consistent value be your guide.

You may be getting spark through the harness conductor between each coil pack connector and the:
- Ignition coil relay - serves up 12 VDC B+ through the red / green wire to each of the six coil pack.
- The two Motronic power stages, front and rear, for assigned each three coil packs. Turns ground -0 VDC (negative 12 volts) on and off to power the coil.

You say you switch the ignition control modules from back to front using the two ignition control modules that came on your 1997 Volvo 960.

You surmised a failed Motronic ignition control module. Yet have you swapped the three around with any change in operation. I'll guess no?

Have you pulled the spark plugs in order? Which spark plug does not fire? If you have found that:
- The six ignition spark plug coils check out okay? (Have you swapped these around in an ordered way to trouble shoot a faulty coil? Continuity / Resistance checks.)
- Conductor continuity between each ignition spark plug coil connector and the Motronic ignition control module wire harness connector pinout.

If you don't find fault here, then there may be issue with the wire harness connectors / conductors between the two Motronic ignition power stages and the Motronic ECU. (Disconnect battery, wait, access ECU connector. Back probe connector as assign ECU pin / conductor color and at assign ignition power stage pin / conductor color.

Close inspection of engine bay wire harness connectors and conductor (wire) may help.

So, to put this in an ascending procedure (Well, sort of debatable problem solving order. If I lived in Surrey, I'd be glad to stop in and help, tool boxes and all. You can pint and laugh at the Volvo 240 I never have a garage to park it in.)
1. Check OBD for fault codes.

Any fault codes may help ...

2. Pull coil packs in order. Use a spark plug socket and identify the non-firing sparkplug.

4. NOTE and Interim step procedure: Check spark plug condition. From you written here in this thread, one of the six spark plugs do not fire? Correct? And the same spark plug position? Check gap? What make and model sparkplug do you have? Any indication of sparkplug failure such as bad seal, lost electrode, lost continuity? Perhaps insert a spare known good like sparkplug and fire it up? (You can test a sparkplug for both continuity and resistance.)

If no faults .... yet at a concurrent level in the trouble shoot

5. Swap the ignition coils. (Why I suggest you grab a small handful from a salvage yard.) If the faulty ignition coil may remain faulty on a different spark plug. Yet

If no faults .... yet at a concurrent level in the trouble shoot ... (I'd rather you test the ignition coils before swapping them. Either test can prove an outcome, yet testing the ignition coils is a more proven way to qualify for a failed coil.

5. Resistance / continuity check of ignition coils. When testing between the ignition pack wire harness connector, use tester + VDC probe for the low tension wire harness connector and the the negative at the park plug connector. (New batteries in the tester helps. One with at least a nine volt battery.) Start with the coil connected to the non firing sparkplug.

If no faults ....

6. Check Conductor continuity between each ignition spark plug coil connector and the Motronic ignition control module wire harness connector pinout. Start with the conductors connected to the non firing sparkplug.

If no faults ....

7. Check the wire harness connector / conductor continuity between the two Motronic ignition power stages and the Motronic ECU.

If no faults, the ECU may be in question.

There mere act of disconnecting and reconnecting wire harness connectors can help. Dressing with dielectric DeoxIT helps.

Disconnect the battery before each step. You may opt to reassemble that which you have tested, reconnect the battery, and fire it up.

I hope that helps to further you along.

The line art wiring diagram at the Volvo Wiring Diagrams use essentially useful enough to help you.

http://www.volvowiringdiagrams.com/volvo/960%20Wiring%20Diagrams/Volvo%20960%201997.pdf

PDF page 5. Between and to the right of the two Motronic power stage modules is an illustration of a field coil pickup on the wires near the power stage modules coming from the ECU. I believe this is part of the ignition control sensor that inductively picks up the signal from the ECU to the power stages.

Also, in the diagram, on ignition coil one is a red and whit wire that terminates in a connector to a SERVICE SOCKET CLAMP.

I think that does it.

Questions?

Hope that helps.

What Do I Do Today with Sat-Your-Day MacDuffy's Tavern?
--
Give your brickboard.com a big thumbs up! Way up! - Roger Ebert.