Lost #3 cylinder on my NA8

[lonesailor]

I wanted to check the tightness of the hose clip on the heater hose on the back of the engine in my NA8. I lost a head some time ago due to a blown heater hose, so I am a bit paranoid about it. To get at it I had to unbolt the coil packs on the back of the head, this is not fun. Anyway ,I managed it,after much swearing and missing skin only to have the engine running like a hairy goat, it appears that #3 is not firing. Everything was running well yesterday so obviously I have stuffed something up. I have a spark, although it looked a little weak,I changed to another plug which appeared to be a bit better. The plug wasn't wet. The injector sounds like it is firing. The wiring behind the engine is in a bit of a mess, but I can't see anything obviously wrong, I did find the temp gauge wire knocked off and reconnected it, the wiring to the exhaust sensor is OK. When I did the head I had a similar problem which turned out to be an improperly assembled lifter holding the inlet valve open, I fixed that and have had no trouble since,it has developed a slight lifter tick but I find it hard to believe that that could be the trouble.I am confident that the timing is OK its on full advance and is worse if I retard it at all. Has anybody got any suggestions?

[manga_blue]

It's fairly common for the wiring where it enters the connectors on the coilpacks to get a bit weak with age, so one of the coilpacks only gets an intermittent supply or signal or earth. Fiddling around with the coilpacks is often what starts it or makes it worse. Normally when this happens though you get 2 cylinders affected, 2 & 3 or 1 & 4. Are you sure it's only #3?

[lonesailor]

#3 with the plug lead off doesn't change the way it runs. #1 ,#2 or #4 lead off and it stalls. taking the HT lead from the coil and it sparks to the frame of the coil. Perhaps cracked bakelite on the coil? I hate doing anything around the back of the head, perhaps I need to bite the bullet and fit coils on each plug.

[manga_blue]

Might just be a HT lead with an internal crack then. If you convert to COPs it can take weeks to get coils and pigtails and fab it all up.

[bruce]

Spark plug leads!

[CrazyRacer]

Try swapping the coils around.

If the miss moves to a different cylinder, you've got a dud coil.
If the miss stays on #3 it will be one of spark plug, HT lead or wiring harness/plug (assuming the problem is spark related).

[lonesailor]

At this stage looks like you'r right, which annoys me because they are a new set, replaced when I did the head, the old ones were fine and I gave them away. I checked all the wiring this morning and it seems OK. The miss changes cylinders when I swap the leads, still could be a leak through the bakelite I'll go and find another lead this morning and see how I go.

[lonesailor]

When I pull the plug lead off either #1 or #2 nothing changes, a lead off #3 or #4 and it stalls, the coil which works #1 and #3 fires the a sparkplug when earthed on both and seems reasonably strong on idle. I cant compare the spark on #3 or #4 on it at idle because it stalls. My only guess is that the #1-3 coil is weak and only has the power to run one plug properly. Does this make any sense to anyone? I have tried another( new) HT lead on different cylinders and it makes no difference which seems to rule out leads. I don't want to spend around $500 on a new coil, specially as I dislike the mess behind the cylinder head intensely, nor am I keen to wait ages and spend still more more again to convert to COP. The car idles reasonably well but misses badly under any load. It doesn't use any coolant and was running perfectly until I moved the coil to check a hoseclip for tightness (I got a a bit on it but it wasn't unduly loose). Looking for suggestions.

[manga_blue]

One coil feeds 2 & 3 while the other feeds 1 & 4.

[lonesailor]

I realize that, I've got that right. my hypothesis - coil for cylinders 1&3 is weak- pull #1 off- #3 has enough power to run properly thereby engine idles reasonably OK on 3 cylinders.. pull #2 off Coil can run #1 properly. Pull #3 or #4 and engine tries to run on 2 cylinders and stalls. I admit this is unlikely but I can't come up with another logical explanation. I have been trying to check the coils to see if they meet the resistance specs which I have from a NA6 w'shop manual which I have in memory on my computer. So far the secondary coil winding checks out OK but I can't get a reading from the primary coil. It produces a spark so it must have continuity. I also haven't been able to confirm that I have 12V to the coil, but again, there is a spark so it must have power. Tomorrow, if I don't come up with another theory overnight I will sacrifice some more skin from my hands taking the coils out again, and try to borrow a Megger to check the coils properly. If that checks out I suppose I'll need to start stripping wiring looms, I'm not looking forward to that.

[lonesailor]

Apologies to all who has been reading this. Talk about overthinking things. I had the plug leads on wrong, all good now. I'm amazed that it would run at all and idle,almost smoothly, because it must have been running on 2 cylinders. There is the best part of 2 days I'll never get back (Or live down)

[manga_blue]

That's OK. I bought a Fiat once.

[Red_Bullet]

Don't they run wasted spark on the stock ECU? Sparks every time whether there is anything to burn or not?

Whoops, I answered my own question by reading this:https://en.wikipedia.org/wiki/Wasted_spark