Thread: spark plug problem

hey guys help me out on this one i have ask everyone in the world no one knows i know i have the correct spark plugs ..to start off i have a stock 1999 3.8 super charger motor in a grand prix ..every once in a while when i kick it down to pass a car or just out ripping up and down the roads pretty hard my car starts missing so i start digging to find the problem and i find that the prong on the end of the spark plug is bent shut first time it was number 3 cyclinder this time it was number 4 cyclinder ..now this motor runs like it just left the car lot new not a sound or knock ..(carbon maybe) ?? i know someone out there has had this problem before ..what could it be ..could a back fire cause this maybe due to bad wires or bad coil i have no idea plzz help me out thanks in advance

that is mechanical damage usually, backfire would blow the plug out before it would bend the electrode I think. I would pull them all and get a bore scope (it looks kind of like the thing your doctor uses in your ears and nose) if something is damaging the plug, it can do the same to the piston or at least the rings

Originally Posted by VinnieGTP

You really need to look in the bore. If they were like that, 99.9% of the time a piston hit them.

you mean he's chipped more than one piston. while it's possible, its doubtful that would have happened and he not have noticed extra noise while the chipped part was still in the cylinder.

if the actual piston hit the plug, due to wrong application or what not, it would have been all of them, likely not just one then the other.

I agree, I have only seen a piston hit a plug once, and it was catastrophic, but I have seen carbon do similar things

Originally Posted by dr456931

yes it seems very strange the first time it happened to #3 cyclinder it was knocking very bad sounded like a rocker arm checked with a code reader it said #3 misfire so i pulled the pluged and it was bent over so then i changed the pluged but still had a miss and knocked i drove it prolly 5 mile then it stoped missing and knocking ran perfect then prolly 200 mile later...#4 cyclinder started missing but NO knock so i pulled the plug and it was now bent changed plug and now it's fine again ...u just have to hear this motor it runs great just like a new car when plugs are good ..NO knock No smoke DONT use oil this car has 125ths miles on it ..ooh when i looked at the plugs there is no scrath on the electrode no where it is bent so far that it would lead u to believe that the piston is busted but it isnt ..so what do i do???

ah-ha!

more info is the key here.

get a bore-scope (or find a shop that has one) and get those cylinders checked out. it's possible that you did indeed experience a chipped piston. i suppose it's possible it was carbon, but not likely.

a few factors can contribute to this, bigger one being KR/detonation.

i recall someone on cgp had this same thing happen and pulled the heads off to find perfect pistons....he did find larger chunks of accumulated carbon in the EGR passages and at the time the EGR was still enabled...i have seen it before on a different car, the carbon chunk ponged around smashed the electrode and left the building... he deleted the EGR at that point if i recall
i suspect that toasty has it in the bag...that sound you were hearing was likely the ring land making love to the cylinder head....