While driving home from work last night around midnight no traffic on i20 inter state highway i decided to stretch the legs on the car a bit. was cruising in 5th gear around 65mph, then down shifted to 3rd and went wot and speed pick up pretty fast, but when i was around 85mph almost top of 3rd gear and rpm around 7300 i looked at my Cobb accesport and it registered 12+ knocks very fast, so i cut off on the gas pedal and limped very slowly back home, wasn't but 3 miles from the house when it happened. AFR was at a steady 12.0afr when i was at wot. When i stopped on a stop light the car was sputtering and idling badly. Got home let the car cool off for 4 hours, then i started checking under the hood. Checked vacuum lines, intercooler piping, fpr hose, FP relay everything was OK, I left the spark plugs for last and behold what i found. the culprit was the closest spark plug to the throttle body or for other reference the drivers side. I did not checked the spark plug gap when i put them in new, i guess i should of have, but i didn't have any issues before. Any feedback would be greatly appreciated. thanks.

 

Oh, wow! Did you replace them yet? Is it running ok now?

 

Welcome to the club.

https://www.evolutionm.net/forums/ev...-failures.html

If you can't find a new set locally I have a spare set sitting here you could use to get you by. Don Herring Mitsu in Irving should have a set though for about $55 after the NTEC discount.

 

Thanks Kracka.

I have 5 new sets. always replaced at 10k intervals.
Funny thing is i always replace spark plugs every 10k miles, since i know about evo x spark plugs failures, i also replace fuel pump relays at the same intervals. I already went ahead and replaced it with new plugs and FP relay. Started the car and it purs like a cat. I think it might have been from detonation, maybe a bad batch of e85. who knows?

 

My guess would be a piston smacked it??? Also 12.0 AFR on E85 seems to rich for me

 

I have never run E85, but isn't 12.0 AFR too lean?

 

12.0 is about right for E85. 12.0-12.5

 

Did it make contact with the piston top?

I would bore scope the cylinder in question just for peace of mind!

 

My fear has been confirmed. Chipped piston, pretty good size as well. Compression 110,120,120, Chipped piston at 100. Will upload pictures later. Sad thing I baby my car, never launched, and hardly ever punch it.

 

How does that even happen? timing was off?

 

+1. I'm confused how this happens without a rod bolt snapping to allow the piston to reach higher than normal, or the plug somehow falling inside the cylinder...

 

It wasn't the piston coming up higher. It was the broken piston piece hitting the spark plug. If the piston it self came up that high, it would have hit the valves way before hitting the spark plug.

 

pictures

 

Ok gotcha, piston broke and a piece hit the spark plug. I was thinking piston hit the spark plug, breaking a piece off the piston. That makes more sense.

Next question is, any idea why the piston broke...?

 

ring land faliour?