84 QV rear misfire continues

A timing light on the coil might be revealing...I'd start there.
A scope on the Digiplex inputs would tell you the condition of the input signal.
And, if they look good...I'd swap the Digiplex boxes and see if the problem moves.

 

Not necessarily. This just confirms that you have a misfire. There are several approaches that will get you to the end here. Starting with the bank that has the misfire, clamp on to the coil wire and see if you see the same flicker. If yes, then we need to look further upstream such as the coil or more likely, the Digiplex box. But, before we going that route, let's check each wire (individually) on the suspected bank. If just one flashes erratically, you'll need to ohm test that specific lead. New doesn't mean good, new just means new...

 

Yes. Contrary to what you might think, the tach signal comes from the Digiplex box, not the crank triggers.

 

Sounds like your 1-4 sensor is at fault, rearmost bank.
This video of a my test may be revealing.
There are 3 sensors 1-4 and 5-8 and a TDC.
The engine will run with 1-4 and 5-8 disconnected as a simulated sensor failiure in a kind of primitive limp mode, the engine runs rough.
If TDC sensor fails the engine will stop, TDC is the critical one.
See here and you will get the idea.

https://www.youtube.com/watch?v=Tw2WV7FTSd0

https://www.youtube.com/watch?v=Ph3EOIKdLgI

 

Swap the Digiplex boxes. If the problem moves, you've got a bad Digiplex. If it doesn't move, then you're dealing with a crank trigger and/or harness issue. If you have a scope, you can confirm the quality of the signals at the Digiplex boxes.

It should be a simple problem to solve from this point forward. PM if you need additional assistance.

 

No, the 1-4 is the sensor at the top most nearest the firewall ie nearest cylindar head 5-8 ;-)

Quick, easy, cheap fault diagnosis, with engine running pull sensor wires 1-4 then reconnect and pull 5-8 as shown in the video.
If you pull wire and engine note changes all is well.
If you pull wire and engine note doesn't change, there is your fault.
Start with sensor it's cheap and work back to thw packs etc or as others have suggested swap wiring between the packs and test again.
The sensor is the most likely problem given that you are getting some kind of spark.
PS. My problem wasn'tthe sensor but the plug to the sensor...a wire had fractured inside the rubber gator.

 

I'm just checking here. What bank is front and rear as you see it...
Cheers
, Bell.

 

Ok I think we may get at cross purposes referring to them as front and rear banks.
May I suggest you refer to them as 'bank 1-4' and 'bank 5-8'
Based on that I'm assuming your fault is with Bank 1-4

 

The bank nearest the firewall (the front of the car) is 5-8 the one nearest the trunk (the rear of the car) is 1-4
Well anyway the first test is are getting a spark from both leads to each distributer, a quick and simple one.
If you are not getting a spark to one of the distributors then you work back from there...
Let us know, regards Bell.
Here's a diagram to help orientation, so we are both on the same page.
Regards Bell
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OK if you have spark to both distributers then you work forward to the sensors ie away from the coils and Digiplex boxes.
1. Pull both 1-4 and 5-8 sensor wires.
Even with 1-4 and 5-8 sensors disconnected both 1-4 and 5-8 banks will recieve a spark but the timing will be out on both banks but engine will run rough (limp mode)

2. Now connect 1-4 and timing on that bank will fall into line and be correct, engine will run better. (check with timing light)

3. Now connect 5-8 and timing on that bank will fall into line and be correct, engine will run better. (check with timing light)

4. If when you connect 1-4 there is no change in engine running then that sensor is suspect.
If when you connect 5-8 there is no change in engine running then that sensor is suspect.

Check also you haven't mixed wires and connectors on 1-4 and 5-8.
ie Make sure you havn't connected 1-4 wire with 5-8 sensor and 5-8 wire with 1-4 sensor.
Regards Bell

 

Have another look at my video, I will check too.

I'm assuming that this is a recent fault with your car and that it was running fine until recently. Therefore the wires cant be the wrong way round unless someone has been in there?
Anyway you can verify with a meter or just swap them one at a time and verify that way, if wrong the engine will pop and fart a bit, but if right engine will run smooth and you found your problem.