Spark plug keeps breaking

[Psion]

Hi all

this is my first post, my daughters Polo 52 plate AZQ engine keeps breaking the insulation around the electrode, I have 15 bar in all 3 pots from cold and have tried Bosch and NGK the only difference is the NGK will last longer than the Bosch. Color of all the plugs is fine and it only happens in pot 1.

i have a genuine VCDS and all I get is an intermittent missfire cylinder 1, the car starts and runs fine does not loose coolant and burns no oil.

At first I thought it might be a burned exhaust valve, but as above just this morning a carried out a stone cold compression check and all 3 pots returned 15 bar, it is truly driving me nuts

thanks in advance

[Flash2]

Maybe cyl 1 is running lean for some reason causing the plug to over heat. It might be worth swapping cyl 1 injector to another cyl and see if the plug problem moves too. At least that would rule out a fuel delivery problem.

[Psion]

Hi

thanks for reply, I have already tried that and needless to say it stayed on pot 1, I do have a genuine VCDS do you know if it is possible to maybe trouble shoot with that as I tend to just run output tests and clear codes with it. Just haven't had time to learn how to use it for more in depth diagnoses.

[Psion]

Today I put VCDS back on and had a look at fuel trim and the first block was reading -8.6% i.e rich, now I am no expert but that value does seem high I would expect it to be closer to 0%, It still doesn't give any glues as to why it is always cylinder 1 plug that gets broken, as below pic this is now the 3rd one in the space of a year.

26781

[niall campbell]

Try replacing the coil on top of the spark plug

Also what RON of petrol are you putting in ? Plain unleaded ?

NGK Spark Plugs USA (http://www.ngksparkplugs.com/tech_support/spark_plugs/p2.asp)

Could also be that the Knock Sensor needs replacing if the timing is causing it

NGK Spark Plugs USA (http://www.ngksparkplugs.com/tech_support/spark_plugs/p5.asp?mode=nml)

[niall campbell]

Also how often are you replacing the spark plugs, should be 20,000 miles.

The gap looks big in your photo.

Can you check at 10,000 mile oil service ?

[Psion]

Hi all

When this started to happen first thing I done was a compression check all good, I must have swapped everything around 3 times and still it remains on cylinder 1. Just yesterday i checked the compressions from cold all 3 15 bar, I then warmed up to operating temp and scanned the engine with a thermometer and found no hot spots.

My other daughter has the same car so going to see what the fuel trim is on that and compare as from my understanding although -8.6% long term is within limits i.e. +/- 10% it is still high and would expect to see short term trim at a comparable +8.6% to bring long term closer to 0% and yet it is doing nothing. Pretty sure this is not a vacuum leak as that would cause a lean condition. I am no expert at VCDS and if someone knows better I am all ears.

Took the car for a drive yesterday and its fine no knocking no hesitation, accelerated hard in high gear from low speed absolutely fine. Every time it breaks the insulation I know because there is a slight misfire at cold start, blip the throttle and it runs fine, no codes!

Have even spoken to a VW tech and in all his years he has never come across anything like it as there is just nothing such as detonation low compression timing issues.

Plugs are all new as used Bosch before and have found the NGK's seem to last longer, the cap is .8 which is what it should be, I would say its driving me nuts but as my daughter is now in AOZ the car is being sold, but I would like to cure this before, if not its bought as seen. When she comes home I'll be getting her anything other than a car with this pile of crap that VW have the audacity to call an engine.

Will report latter with the comparison I am going to carry out this morning.

[zollaf]

are you certain the right plugs are being used ?
what ngk ones are you using.

[Psion]

yep plugs are as stated in the Haynes and I have had the same happen to VW plugs 101 905 601B capped at .8.

Have just taken some readings from the other POLO which is long term -2.3% as compared to -8.6% on the problem car.

Really have run out of ideas as there is nothing in the measuring blocks that would throw a code and yet it still breaks plugs!

[niall campbell]

Some mechanics will always replace No 1 as its known as the problem cylinder

[Psion]

Hi All

thanks for all the suggestions, but have now sold the car but just to throw something else in, I read on the NGK site that if the plug is not properly torqued down it can cause the above. However I'm sure it wasn't the case in this instance as I always use a Tourque wrench so as not to over tighten.

other than the above the car started and run fine very bazaare!

when she gets back from AOZ will be looking for a 1.4TDI, anyone know of any weak points on this modal?

[niall campbell]

Excellent engine, I have it in the Fabia and its great.

Mind you I have the PD engine which is now shipped to India !

I had to buy the 1.2 petrol for the insurance for my boy, otherwise it would have been diesel, the 1.4 tdi is Group 9, alongside the 1.9 non turbo.

The 1.9 tdi is a Group 18

[niall campbell]

I still think the ignition coil was suspect in your No 1 cylinder by the way

[Psion]

I swapped the coils around on numerous occasions and it still remained on pot 1