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What plug gaps?

Hal Mercier

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I had the engine anomaly light come on on Saturday. It had come on before, run on two cylinders, I ordered NGK plugs, then it decided to run properly again. So second time I changed the plugs.....and it still misfired.

I did a quick check and it was the #3 coil.

Ordered a QH part (25€) which will arrive end of the week but as it's my only running car I got a used Denso coil (another 25€) as it's not a smart idea to run on 2 cylinders.

It immediately ran perfectly with the new/used coil but the anomaly light is still lit!

Does this need removing on a diagnostic suite or is there a sneaky workaround?

Oh yeah....check the plugs! I think they are the originals, 10 years and 135,000 km later. I wonder how many times the owner,(who had it from new) paid to have them changed?


What's the plug gap meant to be? These have to be 4mm +



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You need to read the codes to find out what's stored, misfires are not always caused by plugs or coils

you could drive a bus through that gap, those plugs are (want for a technical description).................. shagged


Honestly i would put some Iridium plugs in the car they give a much cleaner spark (Denso IKH16TT)


Off the top of my head 1.1mm gap

edit. Here you go


Product specifications

Diam (mm)  - 14
Electrode 1 - Earthed Electrode
Electrode Gap (mm) - 1.1
Ground - Nickel
Hex mm - 16
Spec - Nickel
Terminal Shape - Solid
Thread Length (mm) - 26.5
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  • Devon Aygo changed the title to What plug gaps?

It seems happy with it's new NGK plugs but I'm highly impressed that it was running well enough to give over 60 mpg on what has been politely referred to as 'totally shagged' plugs, a pretty accurate description.


In my many decades experience with IC engines I have never seen the like....it speaks volumes for Denso's quality.

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  • 1 year later...

Urgent appeal to Devon Aygo and flash22

I am thinking of changing the spark plugs on my 2016 Aygo. This afternoon I gave my local Toyota dealer my reg. number and he said the plugs I need are Denso SC16HR11.

I found this thread this evening and now I am very confused. Is the local dealer well out of date with that ref. number, if Devon Aygo says it should be K20HR11 and flash22 says the equivalent Iridium, should be IKH20TT.

I don't want to be a Doubting Thomas, as I have always found both contributors to be very accurate and generous with their knowledge. Any help would be greatly appreciated, again.



Kind regards,

Bob Sutton. 

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According to the the Denso spark plug / part finder -

05-14 Denso recommend IKH16TT if Iridium desired, which is what I have in my 08


2016 Denso recommend IXEH20TT if Iridium desired


My question to you all, would my 08 benefit from putting in the later IXEH20TT ??


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Sorry for the late reply

unless you use the at username, we don't see a notification, unless following a thread




Standard Iridium plug is a SC16HR11 what replaced the old SC20HR11 as they were causing running issues



IMHO there is no point in running the TT plugs in a 1.0

IXEH20TT is listed for the CNG or LPG version of the 1KR-FE due to the way gas burns under combustion

Higher the number the colder the plug, lower the number the hotter the plug




Fast moving SC20HR11 Iridium Spark Plug superseded with SC16HR11

Part Number SC20HR11 will be phased out. Due to OE requirements all demand will continue to the existing SC16HR11.

In the past only the 2014 Aygo/108/C1 and Yaris had 16 heat range, however going forward all other engines will move from SC20HR11 to the SC16HR11 Spark Plug. For Aftermarket it is safest to switch gradually to SC16HR11 for the whole connected car parc and sell out the current stock
of SC20HR11. We will supersede SC20HR11 with SC16HR11 automatically in terms of ordering and delivery, following Toyota’s decision. Please refer to the DENSO Spark Plug catalogue for the correct crossing.

Due to OE requirements DENSO has to change the heat range from 20 to 16. These connected applications are mainly Toyota engines. The OE car manufacturer has already switched to SC16HR11 for newly manufactured vehicles. The Aftermarket will follow this consequently.

The level of heat range is connected to low or high speed driving. The initial choice for the right heat range is a result of expectations towards average use of the engine. After a few years of experience with this engine, the manufacturer decided to lower the heat range.

In all digital catalogues like TecDoc and MAM, the change will take effect in June 2017.

From June 2017 onwards we will automatically supersede SC20HR11 with SC16HR11. This will ensure delivery of the correct Spark Plug in case you order the old reference.


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Hello Bob,

Thanks very much for taking the time and trouble in posting this very clear description and advice. It looks like it will be the SC16HR11, as the best choice of spark plug.

Thanks again for sharing your knowledge.


Kind regards,

Bob Sutton. 

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