Right so this story is as follows -
Car bought S/H from Fiat with 7300ish miles on the clock, has driven all round Europe twice with out any issues since purchase last June.
At 20000 miles I had the car serviced (full service + waterpump and cambelt) by my local Alfa Fiat Specialist and the next day (less than 50miles after full service) the car started to misfire badly and the engine light came on.
Managed to limp the car back to the Specialist, who checks the fault code , replaces the coil pack to discover that its actually a duff spark plug.
Indecently all four plugs look fine, almost new.
States this is very unusual and pops back the old NKG spark plugs that he had from the service the day before..... car returns to normal.
The mechanic then fits a second new set of Bosch Spark plugs on my return the next morning and all seems fine.
I have just driven 1250miles to Valencia and all was still fine, until this afternoon. Engine misfires badly again and engine light returns.
I limped the car to the house and popped out the YR7 DC+ Bosch spark plugs... they all look fine.. no visible issues at all!
I have two Fiat boxed sets of NKGs that I had from Shop4parts, so these are fitted and the car returns to normal.
When this happened the last time, the mechanic tested the plug with the tuning business next door and it was deemed that it had failed internally.

Has anyone seen this before? Plugs in two sets fail

I would suspect the plug leads, spark plugs hardly ever fail nowadays especially two sets, was the fault on the same cylinder?

I don't have the equipment to tell. I watched the guy getting shocked trying to earth each plug to see if there was a spark. In the end he went off to borrow a probe from the Smart car business next door.
You mean that the lead is somehow damaging the plug? or that the lead is faulty?
As when the mechanic tested the plug it was dead!

It's very rare for a new plug to fail let alone two new plugs leading me to think it could have been/be the plug lead see how it goes if the fault cones back look at the leads.
One of our plug leads failed although the car was 6 years old leading to misfire and engine light, you could clearly hear and see the spark jumping from the lead to the engine.

If the plugs have been dropped at any time the ceramic can crack leading to a leakage of the spark.

D

I will pick up a new spare set of leads anyhow I think, that would be a good idea.
This definitely isn't about the lead breaking down and the spark leaving the insulation. This is about the spark plug failing.
The last time the mechanic borrowed a probe that sensed the charge/spark down the lead and no2 was not firing at all, this is why he thought it was a duff coil pack.
Coil pack was changed and still the same problem... his line of thought was also it is very unusual to be the spark plug.
Since I was driving 1250miles a week later, I kept the new coil pack installed (old one as a spare).
The spark plugs were replaced (same supplier/batch) and the car returned to normal.

Double check part No.s

Could be the wrong heat grade..or even fundamentals like its a non resistor plug.

Then swap around the cylinders..see if the misfire ' moves '

Yes, last time this was tested with a probe and the non firing cylinder moved with the spark plug. They are the Bosch plugs specified for the 1.2 alright

ok,
does sound like the plug - especially as refitting the original NGK set restores good running.

there can be some VERY strange scenarios that can damage plugs..

but for the time being.. I would just stick with what works without issue,

Charlie

p6baseunit said:

At 20000 miles I had the car serviced (full service + waterpump and cambelt)

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Out of interest why did you have these replaced, "so early" ?

Car is coming up to 4 years old and we are starting a new life in Gandia/Valencia Spain. It made sense to me to get the guys I trust to do everything needed on the car, so that we can just import it and the TwinAir.
So brake discs, pads, rear shocks, 4 new tyres, water pump, pully and cam belt have all been done with a fresh MOT, so it gives me time to go through the import process...and before you ask... Second hand cars here are very expensive compared to the UK. WeBuyAnyCar were offering £6K each for two cars that cost £18K new and then I would spend €12K each replacing them.
Also TwinAirs are rare here

Spark plugs really don't need replacing very often at all, so if the old ones are fine leave them in modern cars with electronic engine management tend to run at their optimum as long as everything is well maintained so the plugs don't get fouled or burnt, nor covered in oil or soot.

Could just be you got unlucky with a bad batch of plugs or could be someone dropped a box load of them somewhere in transit, who knows and you might never find out

I changed the plugs on our 1.2 Lounge at 69k and I replaced like for like. I fitted NGKs and the car is running well.

I did this due to numerous issues with other makes in other engines. Especially the old SOHC M20 BMW engines that ALWAYS perform better with NGKs over any other plug. I also had issues with Champions in a Micra a few years back and so these days I always stick as close to original spec as I can.

Put a set of NGKs in there and see how they do. But I have to agree, i'd be sticking the 20k ones back in there as they are good for many many more miles.

I put Denso iridium in our 1.2 now I don't need to change them for 5 years

B7TMW said:

But I have to agree, i'd be sticking the 20k ones back in there as they are good for many many more miles.

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I wish I could, they went in the mechanics bin a few weeks ago.
Anyhow a new set of NGKs have been fitted and normal service has been resumed

John202020 said:

I put Denso iridium in our 1.2 now I don't need to change them for 5 years

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Lets hope they do not require major surgery after being in place for so long

I did put anti seize on the threads and wondered about silicone grease on the plug lead to plug interface?