Spark plug problem... again.

[ramnakhle]

Hi. keeping this short so here's the deal.
97 Vr-4 bone stock.
-Engine was missing on WOT
-Changed spark plugs, NGK plats (6J-11) Noticed one of the old (bosch, previous owner) plugs had a black line along the ceramic insulator, like a very thin but long crack through which some soot was comin out.
-Tested the car, drove perfectly 1st pull then another, then a third. On the fourth, the miss came back like nothing had happened.
-About 2 weeks later i took out the front bank plugs, one of them had the same mark i saw in the old plug. (don't know if it was the same one). Also noticed that the plugs had some brown stuff at the point where the insulator meets with the metal body of the plug. These had less than a 1000 miles on them so why are they so old-looking? is this normal?
-replaced the 1 damaged plug, cleaned injectors and the car's been running fine since.

questions: what's that stupid crack??? could it have been caused by clogged injectors (they were a bit dirty that's for sure)
how can it be avoided?
thx

[leet]

I don't know about the crack, but have you tried gapping the plugs down, start at .032 and go from there

when I was stock .032 worked well

[defgh1]

Originally Posted by ramnakhle

questions: what's that stupid crack??? could it have been caused by clogged injectors (they were a bit dirty that's for sure)
how can it be avoided?
thx

I hope I am wrong, but it sounds like Detonation which is most frequently caused by hot spots in the combustion chamber. Hot spots will allow the air/fuel mixture to pre-ignite. If you have been having Pre-ignition for a period of time due to lean air/fuel mixture you may have damaged the piston surface resulting in hot spots. If it is a damaged piston then only correction is to replace it!

Doug H

[ramnakhle]

Originally Posted by leet

I don't know about the crack, but have you tried gapping the plugs down, start at .032 and go from there

when I was stock .032 worked well

I don't see how that would help... I'm running stock and the NGK plats come pregapped... if i have to gap them down something else must be going wrong...

Originally Posted by defgh1

I hope I am wrong, but it sounds like Detonation which is most frequently caused by hot spots in the combustion chamber. Hot spots will allow the air/fuel mixture to pre-ignite. If you have been having Pre-ignition for a period of time due to lean air/fuel mixture you may have damaged the piston surface resulting in hot spots. If it is a damaged piston then only correction is to replace it!

Doug H

ok...I'm worried now! how does pre-ignition / detonation feel like in the driver's seat?
I see... But since i replaced that plug and cleaned the fuel delivery system, the car's been runnin great... bout 500 miles now, better than ever...
any particular symptoms of piston damage i should be looking out for?

PS i really baby that car around... no racing, mostly cruising with a few pulls here and there...

[defgh1]

Originally Posted by ramnakhle

ok...I'm worried now! how does pre-ignition / detonation feel like in the driver's seat?
I see... But since i replaced that plug and cleaned the fuel delivery system, the car's been runnin great... bout 500 miles now, better than ever...
any particular symptoms of piston damage i should be looking out for?

PS i really baby that car around... no racing, mostly cruising with a few pulls here and there...

Depending on the amount it can be not noticeable to engine rattle to sudden loss of power. I would keep an eye on the plugs. If they continue to look and run normal then hopefully you only had a lean condition that only affected the plug. If you keep damaging plugs then most likely you have a hot spot (damage) in that cylinder.

Doug H

[ramnakhle]

Originally Posted by defgh1

Depending on the amount it can be not noticeable to engine rattle to sudden loss of power. I would keep an eye on the plugs. If they continue to look and run normal then hopefully you only had a lean condition that only affected the plug. If you keep damaging plugs then most likely you have a hot spot (damage) in that cylinder.

Doug H

OK. well right now it's purring like a kitten so i'm hoping it'll stay that way. I'll check the plugs soon to make sure all is well. I'll have some pics cos i'm no expert

Thanks for the help

[leet]

Originally Posted by ramnakhle

I don't see how that would help... I'm running stock and the NGK plats come pregapped... if i have to gap them down something else must be going wrong...

I had to gap mine down when I was stock, as have many many other people on the boards

[ramnakhle]

Originally Posted by leet

I had to gap mine down when I was stock, as have many many other people on the boards

oh ok...
but did the gap cause DAMAGE to the plug? I will get a picture of the old plug to show you that crack... pretty nasty imo for a gap

anyways i am planning to change the plugs out soon... will regap.
was power loss an issue though?

[ramnakhle]

Ok so i found that old plug. Wanted to post a pic just to make sure you guys knew what i was talking about.


Well?
And what's that brown stuff? the new spark plugs got this deposit very quickly, but i was driving with clogged injectors. stupid.

[donniekak]

Everybody thought you were talking about the part of the plug that is actually in the combustion chamber. Looks like maybe the valve cover gasket around the plug is leaking.