Misfire driving me spare

[Julian B]

Help folks.

Still the same car here- 2005 V6 petrol D3.
Some time last year I replaced the engine for a major timing chain mishap and it was cheaper to replace than repair. Sourced a lowish km motor from a forum member in NSW.

Now I have a new misfire problem. At idle and with throttle. From cold and hot. It is driveable and intermittent misfiring but I don't like to tempt fate here and not pushing it. Under load it is much more prominrnt

OBD code only for cylinder 5 misfire and occasionally 'misfire in first 1000 revolutions'.

I have changed all plugs and leads, cleaned and checked connections, swapped coils around, and even spent good money on injector cleaning and testing (all 6).
Still the misfire persists.

I am operating on an assumption which I just realised, that the 5th cylinder is at driver side firewall. Can someone confirm this is the correct cylinder?

Alternator is a bit noisy and putting out 30V AC at idle but de-energising this before starting changes nothing and the misfire persists.

I am lost here. I am thinking one of:
- a higher level electrical issue, such as the AC ripple damaging the ECU/PCM
- spark issue with wiring
- incorrect cylinder getting my attention as I have not changed all the coils- need confirmation re layout of cylinders as above
- sticking valve (based on the intermittent misfire) but you'd think this would change as it warmed up
- another mechanical issue, but it runs very quiet

Any help here would be very gratefully received. I have made this a really nice car and it has been treated nicely in my hands and this is making me crazy.

Julian

[loanrangie]

What about crank angle sensor and or cam sensor if fitted ?

[Julian B]

Would that throw just a single cylinder off?
Is it a matter of changing for spares and seeing?

[justinc]

Alternator needs to be changed out first if noisy, can't believe that wasn't the first thing done, may have saved some money and time...
These crank and cam sensors are VERY sensitive to electrical noise, not saying it's a 100% fix in this case but electrical noises are first port of call.

[Julian B]

Isolating the alternator (as in functionally removing it) lead to exactly the same misfire so it seems as a cause it is not likely. A new alternator is $6-700 for a Denso unit [bawl].

[josh.huber]

Isolating the alternator (as in functionally removing it) lead to exactly the same misfire so it seems as a cause it is not likely. A new alternator is $6-700 for a Denso unit [bawl].

Functional removal? Belt off? Reg unplugged, battery cable unplugged? My alternator was noisy, but not for long before it died. It's always cheaper and easier to completely rule out known problems when diagnosing. they won't always cause the issue to resolve but they will stop other problems during the search.
Mechanical faults such as a valve are unlikely for a misfire. Can be easily and cheaply tested with a compression test.
Test the ohms of each injector. You can also check the ohms of the coil but I think it'll only show the primary winding from memory.
With it running go through and shake the wiring "tug test" lightly pull the wires .
Have you confirmed that it is number five? Disconnect either the plug or injector on that cylinder, if the engine doesn't change note. Then it's the culprit. If does then move on to the next cylinder. When you get to the cylinder that doesn't respond to the injector or plug being disconnected. Swap one component at a time till the cylinder next to it becomes the problem. If nothing makes the cylinder number change. You need to test wiring using a multimeter and diagram for continuity. Unlikely though. Will usually through an open circuit code.
Coil over plug type coils don't live forever.

[justinc]

Just replace the alternator, regardless....🙄

[Julian B]

Just replace the alternator, regardless....🙄
I intend on doing so. I need to defer the cost for a week at this point.



Functional removal? Belt off? Reg unplugged, battery cable unplugged? My alternator was noisy, but not for long before it died. It's always cheaper and easier to completely rule out known problems when diagnosing. they won't always cause the issue to resolve but they will stop other problems during the search.
Mechanical faults such as a valve are unlikely for a misfire. Can be easily and cheaply tested with a compression test.
Test the ohms of each injector. You can also check the ohms of the coil but I think it'll only show the primary winding from memory.
With it running go through and shake the wiring "tug test" lightly pull the wires .
Have you confirmed that it is number five? Disconnect either the plug or injector on that cylinder, if the engine doesn't change note. Then it's the culprit. If does then move on to the next cylinder. When you get to the cylinder that doesn't respond to the injector or plug being disconnected. Swap one component at a time till the cylinder next to it becomes the problem. If nothing makes the cylinder number change. You need to test wiring using a multimeter and diagram for continuity. Unlikely though. Will usually through an open circuit code.
Coil over plug type coils don't live forever.

Josh, yes I pulled the regulator cable so windings couldn't energise, and got a suitably grumpy chime and warning re no charging state and the AC voltage disappeared.

I agree that it seems unlikely mechanical.

Injectors were a completely different set professionally cleaned and flow tested accurately, all very close resistance. Fault remained following change. Manifold gaskets renewed with genuine at the time.

Coils each have 4 wires so not sure what values across what pins I am searching for. Also I swapped around coils and fault persisted.

Your check re isolating misfire by pulling components from cylinders sequentially is a familiar routine before I had vehicles with computers. Can I not trust the computer to tell me it is this cylinder?

Given that the misfire is not continuous, pulling spark to locate which one may not yield certain results as this is subtle at idle and making one cylinder dead will make it buck like a horse irrespective of the cylinder.

Any ideas about cause from someone who can read my process so far and advise next step. I am aware that the alternator is in need of replacement, as I listed the AC ripple voltage for this reason, but when this stray AC voltage is removed the problem is unchanged. Any further ideas from an electronics expert on these motors?

[FisherX]

What type of scan tool are you using?

If it is a decent one you should be able to access the generic OBDII modes. You'll find misfire data in Mode$06. Have the unit plugged in and monitor it while you drive. Also check your long and short fuel trims and 02 sensor performance.

It could just be a vacuum leak. I've seen quite a few misfires caused by a dodgy hose or PCV.

[josh.huber]

I'm not family with these engines, you mentioned leads earlier ? An Auto electrician with an oscilloscope should be able to look at the current in each one and tell you about spark condition. I've done it to a Falcon a long long time ago. Pull number 5 plug again and look at it. Compare to another. Component change on cars with computers is the same as before. Move the part. Move the problem. Yes you generally can rely on them to be right with which cylinder. But. There is always external variables that add to the misery

[Julian B]

So mechanical problem excluded, compression excluded, spark excluded.
Injectors and rails good.
Manifold gaskets new genuine.

There are some serious factors looking like fuel delivery, and the EFI expert recons this is the root cause.
Spraying some ether (start ya bastard) into the air intake clearly improves the random misfire sound.
When cold and in open loop the car runs normally so presumably the enrichment that occurs due to cold coolant temp is enough to avoid a lean misfire.
At operating temp the coolant sensor read correctly per the OBD.

Here is the odd bit- when the car is running and the fuel tank cap is removed, rough running worsens, and there is an audible fluttering noise from the opening.

I am wondering if there is a purging system or a fuel pump system issue causing reduced fuel delivery. I am yet to check fuel pressure but it seems logically the next step.

Has anyone had experience with the tank/pump side of fuel delivery that can raise some ideas for me?

[fredd63]

You may be on to something with the petrol cap/ fluttering noise. The American EPA makes manufacturers incorporate complicated petrol vapour controls on all vehicles as part of their emission regulations. When your motor was changed, a couple of the pipes may have been connected the wrong way around, perhaps giving the motor a lean mixture, ( because the system works by vacuum). You could check the fuel trims for lean mix. A member with a similar car might allow you to compare the arrangement of vacuum pipes on the motor.

good luck
Pete

[Eric SDV6SE]

Not that familiar with the petrol engines in these either. Just an idea, have all the injectors been correctly coded to the ECU when replaced? Might be an idea to check, but this needs you to check/ verify the injector serial numbers against whats in the ECU.

Pretty sure they run a closed loop fuel pump system to dump fuel back to the tank after the rail reaches pressure. Seeing as youve said injector and rail pressure is all good, i dont see (yet) how the in tank pump would affect cylinder firing/misfiring if fuel pressure behind the injector is fine.

If not correctly coded, the injector is not firing at the correct time or rate, causing misfiring (just thinking out loud here)

Perhaps you need to log rail pressures from cold, could be a pressure control valve in the system sticking that starves one of the injectors (first one on the rail?)

Hope this helps ?

[Julian B]

You may be on to something with the petrol cap/ fluttering noise. The American EPA makes manufacturers incorporate complicated petrol vapour controls on all vehicles as part of their emission regulations. When your motor was changed, a couple of the pipes may have been connected the wrong way around, perhaps giving the motor a lean mixture, ( because the system works by vacuum). You could check the fuel trims for lean mix. A member with a similar car might allow you to compare the arrangement of vacuum pipes on the motor.

good luck
Pete

Thanks Peter. Luck is needed.
The car has been running brilliantly for the past 10,000km since engine change, so hard to think it would be only beginning to be problematic now.


Not that familiar with the petrol engines in these either. Just an idea, have all the injectors been correctly coded to the ECU when replaced? Might be an idea to check, but this needs you to check/ verify the injector serial numbers against whats in the ECU.

Pretty sure they run a closed loop fuel pump system to dump fuel back to the tank after the rail reaches pressure. Seeing as youve said injector and rail pressure is all good, i dont see (yet) how the in tank pump would affect cylinder firing/misfiring if fuel pressure behind the injector is fine.

If not correctly coded, the injector is not firing at the correct time or rate, causing misfiring (just thinking out loud here)

Perhaps you need to log rail pressures from cold, could be a pressure control valve in the system sticking that starves one of the injectors (first one on the rail?)

Hope this helps ?

Hi Eric.

The injectors on this petrol motor are just a resistor as far as engine management is concerned, opening for a pulse that varies in timing/width according to how long they receive voltage.

I have not yet excluded a fuel pressure regulator problem which might be allowing fuel back to the tank.

I have not yet tested fuel pressure at the rail, my mistake if that was something I mentioned.



I'm poring over the workshop manual to see if there is a vapour relief or purge system that might be leading to tank/pump vaccuum on the inlet side leading to suboptimal fuelling.

[Julian B]

So the pulsing noise is the purge valve opening and closing against manifold vacuum- drawing air presumably through the charcoal canister from the filler neck and into the motor. Blocking off the port at the manifold makes zero difference to running condition so this seems unlikely.

Taking close notice to the stuttering/misfire it is present at idle, and when driving in high engine loads, but not when revving in neutral. This to me feels very much like unmetered air leak.
There is no stalling or bogging down under load which to me points away from a fuel deficit.

Blanking off the EGR makes no difference to the condition when driving or idling, so seems not likely to be a fault, and the purpose of the EGR is to allow essentially inert exhaust gas to flow to the motor to reduce NOx emissions (as I understand it).

[discorevy]

Replace faulty coilpack

[discorevy]

Number 5 cyl is middle of left hand bank ( passengers side ) iirc

[Julian B]

Number 5 cyl is middle of left hand bank ( passengers side ) iirc

Cylinder layout from a manual I read stated driver's side closest to firewall was cylinder 5.

If you are correct I owe you a beer.

[Julian B]

Mate the layout you quoted is correct, but changing the coil on this cylinder lead to no improvement on misfiring condition.

[BradC]

Mate the layout you quoted is correct, but changing the coil on this cylinder lead to no improvement on misfiring condition.

For unmetered air leaks I've sprayed carby cleaner progressively over and around gaskets and seals. You'll hear the change if you hit the leak. I've also used ATF, butane and kero at various times depending on what I had available. All flammable of course.

I've not done it on a disco, but most common leaks I've encountered have been hardened injector seals. Since you've done the injectors I suppose that is unlikely.

If it is an unmetered air leak a smoke test should show it up pretty quickly also.

[Eric SDV6SE]

Taking close notice to the stuttering/misfire it is present at idle, and when driving in high engine loads, but not when revving in neutral. This to me feels very much like unmetered air leak.

Weird that when revving in neutral the issue goes away. Engine is still under load, but not the transmission. Does it have issue at idle in neutral?

Assuming you have thr 6spd auto, it may well be an issue in the valve body in the transmission as in one of the line valves not closing properly, due to contamination or a dodgy solenoid, more pronounced at high loads due to increased fluid pressures....

[discorevy]

Is it possible you have moved cyl 5 coilpack to a different spot while initially diagnosing ?, if so a rescan may show which cyl it is now at.
Did you use a new or known good one ?

I would expect if a vacuum leak was big enough to cause a misfire it would usually throw lean mixture related codes.

You can rule out transmission faults with an engine misfire

[Julian B]

For unmetered air leaks I've sprayed carby cleaner progressively over and around gaskets and seals. You'll hear the change if you hit the leak. I've also used ATF, butane and kero at various times depending on what I had available. All flammable of course.

I've not done it on a disco, but most common leaks I've encountered have been hardened injector seals. Since you've done the injectors I suppose that is unlikely.

If it is an unmetered air leak a smoke test should show it up pretty quickly also.

Haven't the gear fr smoke, but cannot trace a leak with carby cleaner.


Weird that when revving in neutral the issue goes away. Engine is still under load, but not the transmission. Does it have issue at idle in neutral?

Assuming you have thr 6spd auto, it may well be an issue in the valve body in the transmission as in one of the line valves not closing properly, due to contamination or a dodgy solenoid, more pronounced at high loads due to increased fluid pressures....

Transmission was replaced and service 2 years ago- butter smooth shifting. I doubt this is the issue.


Is it possible you have moved cyl 5 coilpack to a different spot while initially diagnosing ?, if so a rescan may show which cyl it is now at.
Did you use a new or known good one ?

I would expect if a vacuum leak was big enough to cause a misfire it would usually throw lean mixture related codes.

You can rule out transmission faults with an engine misfire

Scan with every change I make. Misfire persists at number 5. I'm beginning to wonder about a computer signal issue as I can't see a leak here.

Tried replacing numerous sensors and blocking off EGR- no change.

[FisherX]

Just a quick input here. When using a scanner Cylinder 5 is the fifth cylinder in the firing order not necessarily cylinder 5 on the engine.

The fifth cylinder in the firing order as per the manual is cylinder 3. So driver's side rear on a RHD.

[Julian B]

Just a quick input here. When using a scanner Cylinder 5 is the fifth cylinder in the firing order not necessarily cylinder 5 on the engine.

The fifth cylinder in the firing order as per the manual is cylinder 3. So driver's side rear on a RHD.

I changed this coil also with no change, but good thought.
I might try to be a little systematic and swap out all of them and see what happens.

This is crushing me.

[Julian B]

So changed all coils no difference.
Just got a crankshaft sensor pending error, though not illuminating CEL. Interesting. I wonder if this is the cause, or a symptom of a wider error.
Looks like parts shopping again.

[DiscoJeffster]

So changed all coils no difference.
Just got a crankshaft sensor pending error, though not illuminating CEL. Interesting. I wonder if this is the cause, or a symptom of a wider error.
Looks like parts shopping again.

As mentioned way back in post #4. Check crank/cam sensors. I hope the crank sensor isn’t gearbox side on that engine [emoji21]

[Julian B]

As mentioned way back in post #4. Check crank/cam sensors. I hope the crank sensor isn’t gearbox side on that engine [emoji21]

It is. Ha, at least the manual says it can be accessed without removing the engine.
Life wasn't meant to be easy.
Then daddy bought a discovery.

[Julian B]

So, new crank position sensor installed. No change to the misfire/stuttering at idle and under load such as driving up hills.
This was a good thought but so far this and the cam sensors seem now excluded from contribution to the running condition.

Overall the only thing thus far that has made an improvement is artificially enriching the mixture with some ether sprayed down the throat when running. This implies a lean condition being corrected which would lean towards an air leak.

I am lost unless there are any further brainwaves.

Anyone?

[DiscoJeffster]

Smoke test. You can DIY one as I did using something that makes smoke clean smoke in a tin and an air compressor to pump up the inlet, and watch for a leak. I’ve used it a few times now and makes leak identification simple.

[Julian B]

Smoke test. You can DIY one as I did using something that makes smoke clean smoke in a tin and an air compressor to pump up the inlet, and watch for a leak. I’ve used it a few times now and makes leak identification simple.

Yeah next step I think.
This is bizarre.

[Eric SDV6SE]

Injector issue (check for error codes P062B or similar) or an exhaust valve not seating properly? But you said mechanically all was ok...

[josh.huber]

So, new crank position sensor installed. No change to the misfire/stuttering at idle and under load such as driving up hills.
This was a good thought but so far this and the cam sensors seem now excluded from contribution to the running condition.

Overall the only thing thus far that has made an improvement is artificially enriching the mixture with some ether sprayed down the throat when running. This implies a lean condition being corrected which would lean towards an air leak.

I am lost unless there are any further brainwaves.

Anyone?

If you have a reader. Look at your MAF sensor. Run the thing at full throttle in say 3rd gear. The air flow should be 80% of HP. No KW rating of engine. In G/S .
100hp engine. Full throttle loaded not free revving. Should be approx 80 G/S air flow.

[josh.huber]

So, new crank position sensor installed. No change to the misfire/stuttering at idle and under load such as driving up hills.
This was a good thought but so far this and the cam sensors seem now excluded from contribution to the running condition.

Overall the only thing thus far that has made an improvement is artificially enriching the mixture with some ether sprayed down the throat when running. This implies a lean condition being corrected which would lean towards an air leak.

I am lost unless there are any further brainwaves.

Anyone?

The engine thinks it is rich. That is why it has leaned itself out. I don't think it would an air leak. Because that would show up on the O2 sensors as rich fault or lean fault. It's unusual that you don't have a fault for fuel trim or of range if you can sweeten it up on the can.
70% of all codes I deal with for people on petrol engines are MAF sensor. Should only be replaced with genuine too. I've learnt that before

[josh.huber]

Have you changed that alternator yet

[PhilipA]

IMHO, you cannot discount that one of the injectors , although cleaned and tested, is faulty.

Maybe change the injector to another cylinder and then see what the scantool says.
Regards Philip A
BTW in an injected engine , if you are testing plugs or injectors, you should make sure that the lead is grounded or you can damage the ECU.

[Julian B]

The engine thinks it is rich. That is why it has leaned itself out. I don't think it would an air leak. Because that would show up on the O2 sensors as rich fault or lean fault. It's unusual that you don't have a fault for fuel trim or of range if you can sweeten it up on the can.
70% of all codes I deal with for people on petrol engines are MAF sensor. Should only be replaced with genuine too. I've learnt that before


If you have a reader. Look at your MAF sensor. Run the thing at full throttle in say 3rd gear. The air flow should be 80% of HP. No KW rating of engine. In G/S .
100hp engine. Full throttle loaded not free revving. Should be approx 80 G/S air flow.

Thanks Josh, yeah I'm starting to think the ECU is compensating for some fault, but didn't quite extrapolate to the MAF. I did clean it with the proper spray cleaner early on but this made no difference.


Have you changed that alternator yet

Not yet, I'm saving for a Delphi and removing the AC voltage made zero difference to running condition.


IMHO, you cannot discount that one of the injectors , although cleaned and tested, is faulty.

Maybe change the injector to another cylinder and then see what the scantool says.
Regards Philip A
BTW in an injected engine , if you are testing plugs or injectors, you should make sure that the lead is grounded or you can damage the ECU.

I swapped out the whole set for a new set that were cleaned and flow tested. Same issue.


Injector issue (check for error codes P062B or similar) or an exhaust valve not seating properly? But you said mechanically all was ok...

I thought this but seems so unlikely after all the testing.


The only thing that can make a difference is spraying ether down the throat. Seems like Josh's direction is the next step in hunting down the cause for an incorrect mix. I've booked it in with the local land rover gurus.

[Eric SDV6SE]

Maybe an obvious one and i cant recall if youve already mentioned this, so sorry in advance, but I trust your mechanic has checked compression on all cylinders? Just seems weird if its a mixture / air leak issue that only one cylinder is misfiring. If mixture overall, then should affect all cylinders. If, as reported its only #5, then it can only be something specific to that pot, so either mechanical (valves or piston rings) or electrical (injector) plug or lead.

I'd be retesting compression on all, plus checking crankcase pressure too, maybe a worn piston ring causing blow by under no and high load..

[josh.huber]

I'd buy a genuine MAF before paying anyone. Or at least drive 3rd gear full noise, look at flow rate

[josh.huber]

Doubt its an injector, petrol one's are so easy to clean. I've got a cleaner I made at home. 9v battery and some wd 40 and your done. Very easy for a proper shop to test accurately. Totally different scenario then with diesel injectors

[Bundalene]

Help folks.

Still the same car here- 2005 V6 petrol D3.
Some time last year I replaced the engine for a major timing chain mishap and it was cheaper to replace than repair. Sourced a lowish km motor from a forum member in NSW.

Now I have a new misfire problem. At idle and with throttle. From cold and hot. It is driveable and intermittent misfiring but I don't like to tempt fate here and not pushing it. Under load it is much more prominrnt

OBD code only for cylinder 5 misfire and occasionally 'misfire in first 1000 revolutions'.

I have changed all plugs and leads, cleaned and checked connections, swapped coils around, and even spent good money on injector cleaning and testing (all 6).
Still the misfire persists.

I am operating on an assumption which I just realised, that the 5th cylinder is at driver side firewall. Can someone confirm this is the correct cylinder?

Alternator is a bit noisy and putting out 30V AC at idle but de-energising this before starting changes nothing and the misfire persists.

I am lost here. I am thinking one of:
- a higher level electrical issue, such as the AC ripple damaging the ECU/PCM
- spark issue with wiring
- incorrect cylinder getting my attention as I have not changed all the coils- need confirmation re layout of cylinders as above
- sticking valve (based on the intermittent misfire) but you'd think this would change as it warmed up
- another mechanical issue, but it runs very quiet

Any help here would be very gratefully received. I have made this a really nice car and it has been treated nicely in my hands and this is making me crazy.

Julian

Hi Julian, we have been away for a few days but back now. Unfortunately we do not have a petrol MAF at this stage, last 3 vehicles dismantled were diesel. Sorry but I can't throw any light on your problem but it does sound fuel / air related rather than electrical

Regards Erich

[Julian B]

The solution came from a scope test of the firing voltages. Plugs were found to be the culprit with very poor dwell on 5 cylinders.
Unbelievable.
At least it runs butter smooth now with new injectors!

Thanks to all contributors. I hope the journey helps my future friends with similar issues.

[Dagilmo]

The solution came from a scope test of the firing voltages. Plugs were found to be the culprit with very poor dwell on 5 cylinders.
Unbelievable.
At least it runs butter smooth now with new injectors!

Thanks to all contributors. I hope the journey helps my future friends with similar issues.

Great to hear you got it sorted. It was driving me spare also...Thanks for closing the loop.

[Eric SDV6SE]

Glad you sorted it.

[josh.huber]

You started the post saying you changed the plugs?

[DiscoJeffster]

You started the post saying you changed the plugs?

Not all plugs are made equal that’s for sure. I’d be keen to know the plug model and spec before and after.

[josh.huber]

no there not, these engines like everything in the last 15 years no doubt calls for platinum or iridium plugs, theyre not cheap $15 to $20 each, but you can get the ngk $5 versions that do the same job but just not for as long, 20,000ks vs 80,000ks.

the chances of having a dead plug in number 5, then buying 6 new ones , and puting a dead one back in the same hole have gotta be good enough to buy a lottery ticket

[DiscoJeffster]

no there not, these engines like everything in the last 15 years no doubt calls for platinum or iridium plugs, theyre not cheap $15 to $20 each, but you can get the ngk $5 versions that do the same job but just not for as long, 20,000ks vs 80,000ks.

the chances of having a dead plug in number 5, then buying 6 new ones , and puting a dead one back in the same hole have gotta be good enough to buy a lottery ticket

That’s why I’d like to hear from the OP - did he replace with like for like plugs. I suspect not ...

[Eric SDV6SE]

That’s why I’d like to hear from the OP - did he replace with like for like plugs. I suspect not ...

Fully agree, i once battled to get a Suzuki GSF600 started wirh no luck. Turned out one plug out of 4 was rated 1 step colder than the others, engine would not fire. Swapped all out for new correct grade and started first go ran smooth as silk. Difference was 1 letter or number in the designation, easy to miss if you dont know

[Julian B]

When I had a previous misfire fault which turned out to be skipped time on one cam I bought a set of OEM plugs from Land Rover. They were motorcraft units. I installed these and the car was never driven subsequently, just a cheap experiment for me towards confirming a dead engine.
I kept the plugs, even in the original boxes.
I used these to replace the ones in the current engine that was misfiring, and it seems this was a bad move.
This car had a low km engine replacement sourced here on the forum from a regular contributor. Part of the exchange was new plugs and leads and the plugs were OEM also, but lasted less than 10,000km.
Not planning on using these plugs in the longer term. This is a great lesson on plug technology for me and that using OEM is not necessarily better.

I hope this explains the issue, but yes I think hellishly unlucky to get repeat misfire on that cylinder.

[josh.huber]

When I had a previous misfire fault which turned out to be skipped time on one cam I bought a set of OEM plugs from Land Rover. They were motorcraft units. I installed these and the car was never driven subsequently, just a cheap experiment for me towards confirming a dead engine.
I kept the plugs, even in the original boxes.
I used these to replace the ones in the current engine that was misfiring, and it seems this was a bad move.
This car had a low km engine replacement sourced here on the forum from a regular contributor. Part of the exchange was new plugs and leads and the plugs were OEM also, but lasted less than 10,000km.
Not planning on using these plugs in the longer term. This is a great lesson on plug technology for me and that using OEM is not necessarily better.

I hope this explains the issue, but yes I think hellishly unlucky to get repeat misfire on that cylinder.

Ha ha that's terrible luck. But then again if it wasn't for bad luck sometimes we wouldn't have any at all.