Originally posted by: moomba99As far as the plug firing inside the cylinder....I was wodering the same thing. But the ground you would thing would be just as good if not better once it was threaded into the cylinder. It has GREAT spark outside the cylinder and even ignites the fuel from outside the cylinder. Once threaded inside the head....NOTHING.
Yes, the grounding is going to be fine once it's screwed into the cylinder. That wasn't my concern. I was wondering if anything ELSE might cause the plug not to spark while screwed in.
You have air, even if it's only the air trapped within the cylinder when you take out the plug for a moment. You have fuel, even if it's only the fuel you manually squirted into the cylinder. IF you have spark within the cylinder, even at the "wrong time", it will ignite whatever fuel is in there and you'll know it by sound or feel. Bad timing in this case doesn't matter... a spark anytime inside a cylinder containing air and fuel should cause ignition. At this point you're not trying to get the engine to run, just confirm that it will light up an air-fuel mixture.
So I'm still betting that you're not getting a spark inside the cylinder. I'm not sure how to confirm that, though. Perhaps remove the head, put the plug in it, and make sure it sparks while screwed into the head? Or back off the head screws enough that the head isn't sealed to the cylinder, then repeat your test and see if you get ignition then? (Should be even more obvious than normal because of blowby.) Somehow you need to take little baby steps between "plug entirely out" and "plug entirely in" to see when the spark disappears.
Is there anything else you do when testing like this that might affect spark? Any wires disconnected? Engine switch on? Key on? I know this sounds stupid but sometimes it's just something simple that you forget out of habit.