Curious spark plug conundrum

[techieboi]

This is my first post on this Forum, although I’ve been a member for a few months now.

Anyway, I’ve had an interesting weekend. I have been doing some preventative maintenance on the Cupra to get it ready for next week’s Stage 1 Revo Remap. I jumped onto Awesome GTI’s website and ordered a new set of NGK Iridium BKR7EIX Spark plugs, a set of Red ‘R8’ Coil Packs, a new ‘D’ Version DV, a version ‘R’ PCV and a Pipercross Panel filter. All went in without any issues.

So I’ve driven about 200 miles this weekend and noticed a 4mpg drop in my overall fuel economy, which for a Cupra isn’t good. I was averaging only about 29-30mpg. Normally if I’m driving that way I’m looking at around 33-34ish mpg.

Also on full boost I think that the car was experiencing a strange vibration, but I was having trouble finding the cause.

So after looking for PCV and DV leaks and swapping out the coil packs I came to the conclusion that the spark plugs must be the culprit. I changed them back to the Bosch FR5KPP332S plugs that were installed by TSR Performance back in June when I bought the car. They only had 8K miles on them, but I thought the NGKs would be better after reading other people's posts on this Forum. Obviously my car didn't think so as I’m now looking at 36mpg and the vibration has gone. I assume that the vibration was a misfire, but can’t be certain as I don’t have a VAG-COM. The engine feels much smoother and pulls harder than ever.

I have a CDL engine in my FL Cupra and understand that the NGKs are a popular choice for other owners. Are they more suited to the BWJ engines?

 

[OldManPooley]

I have the CDL engine in my Cupra R and put the same NGK plugs in with no issues at all.

Its a mystery?

 

[lsg60]

Maybe the new spark plugs weren't properly gaped? I've had that before on a polo

 

[techieboi]

I thought that too, I checked all 4 of them and they are bang on 0.8mm as they should be. The Bosch plugs are gapped at 0.7mm though. Perhaps the 0.1mm makes a big difference.

 

[Aok82]

The iridium plugs has 5k ohm resistance as the normal ones have only 1k ohm. (normals i mean the double platinum NGK)
that makes the coils work harder to produce decent spark and can fail in high rpm.
Usually people have solved this by gapping the iridium plugs at 0.6mm. (its pregapped 0.8).
That should sort the issue.

 

[techieboi]

Thanks for that info, really appreciate it. It makes complete sense and I'll probably have another go at refitting the NGKs when the weather warms up a bit. Cheers.

 

[Aok82]

Actually this got me thinking why people use those iridium plugs when even the ngk program does not suggest them. There are a lot of people that have problems with misfire in high rpm and i suddendly started to think could this be the cause?

Surely they might come in need in stage 2 or after but really dont see any reason to change them before that.
Mainly they seem to work just fine.

 

[techieboi]

I must admit, now that the original plugs are back in, the car is running perfectly. As you say makes sense for running stage 2 and beyond, where heat is going to be an issue. But the impact on mpg was quite a shock for me, especially as I thought it should get better.

Also with 5k Ohm resistance instead of 1k Ohm, aren't we just going to get through coil packs 5 times faster?

On my Cupra, there was a noticeable misfire in the higher rev range and on full boost (well it was noticeable once I figured out what it was).

 

[techieboi]

NGK recommend the PFR7S8EG plug for the 2.0 TFSI, which only has 1K Ohm resistance according to their parts catalog. Same plug that they recommend for the V10 Audi R8 apparently.

 

[Jfox]

Very interesting info.

Cheers, i would assume the 1k ohm sparks are a lot cheaper than the 5k as well?

 

[Madscientist]

Interesting! I though it was just something with my car or plugs. Same plugs on my stage 1 cupra. Im sure i logged more ignition timing pull too. I might try relogging the iridium plugs standard gap and then gapped 0.6mm.