Hey all new to the forum. My friend has a 2003 eclipse with a 2.4 SOHC. Thing had originally blown off ground strap on #2 spark plug. Swapped plug, tested coil. Week later started running like crap again. Pulled plug, #2 ground strap bent, minimal gap clearance. Could see pock marks on piston. Yesterday we pulled the oil pan thinking possible rod bearing or wristpin. No results. Pulled head, obvious signs of detonation. Any ideas to help here? Valves look ok, seats not burnt. Only #2 cylinder seems to be having a severe issue. Head gasket looked ok. No possible way for piston to be making contact with plug. Engine has around 90k on it. Upon inspection of piston its obvious it has been happening for a while....Help! I am pretty experience mechanic of 10 years +....

 

timing.
Or coolant in the cylinder.

 

o yeah, and dont run crap fuel.

 

There is no evidence of coolant in the cylinder> Fire rings were good and coolant was clean. No residue either. I put system under pressure and there was no bleed off. I was thinking a timing issue, but you would think that it would be doing the same in other cylinders....Belt and tensioner are not that old and OEM parts were used on replacement. I was starting to lean this way but wasn't convinced since there was no other evidence or timing issue. I am starting to think it can be fuel related....manual says 87 octane. Possibly use higher quality plugs?
Thanks for your response Az

 

A timing issue would not cause the electrode to get hit.

Stick a screwdriver down each cylinder, find TDC, and measure if that piston is sitting taller than any of the others. You may want to rent a bore scope to see if any foreign material is stuck to the top of it.

You shouldn't get detonation because it's naturally aspirated and not high compression either.

 

detonation will happen with crap fuel evn on carbys.
I always run premium. In nz its 95 ron.
But yes as sebba says, maybe bent crank or slipped bearing..?
Not that youll do damage with a screw driver gently, but there are nicer ways to get tdc...

 

edit.
Read 'no possible way to make contact'...Itll be the old plug bit that did the damage.
Gotta be something. valve train? Cams ok? Springs?
Did you do a comp test before/after the leak down?

 

Yes did compression test and a leak down...pulled #2 piston and rod bearings look good slight movement in wrist pin. if the piston were to hit anything it would be a valve first. There is noticeable signs of detonation on the piston, surface of head, etc....This one is bugging me...

 

Really? Maybe you have a bad injector causing that cylinder to lean out.

Get a screwdriver and stick it to each injector while it runs, and put your ear to the handle. You should hear it click nice and crisply. If they all check out, I would remove one at a time and place them in a water bottle. Then crank the car and check the spray pattern.

 

but valves aren't damaged eh?

if it looks like det, it's probably det. wrist pin may cause slap, but unlikely to cause det.

didja look at the valve train?