Found a puzzling problem- after running with little or no load for 5 or 6 sessions of 1 to 3 hours each (in my driveway) the late-model A4 began to miss and run a bit rough. Removing each spark plug wire in turn proved that #4 was not firing. But when putting the spark plug wire back onto the spark plug, the engine smoothed out briefly.
Experimenting showed that if the wire was pushed fully onto the spark plug it would not fire but if the wire was close enough to the plug to jump a small gap, the plug would fire and the engine would smooth out.
The #4 spark plug tip was black and covered with a wet soot, not yet clearly oil-fouled but certainly not clean like all the others. Switching plugs between #3 & #4 solved the misfire, maybe temporarily.
I suspect that the light fouling in #4 indicates some ring problem but the compression is good (112psi) and similar to other cylinders.
Is there any hope that running under load may improve this?
I've already squirted some Mystery oil onto the pistons, But I don't understand why the spark plug works only after jumping a gap to the plug.
Any suggestions would be appreciated, thanks.
Experimenting showed that if the wire was pushed fully onto the spark plug it would not fire but if the wire was close enough to the plug to jump a small gap, the plug would fire and the engine would smooth out.
The #4 spark plug tip was black and covered with a wet soot, not yet clearly oil-fouled but certainly not clean like all the others. Switching plugs between #3 & #4 solved the misfire, maybe temporarily.
I suspect that the light fouling in #4 indicates some ring problem but the compression is good (112psi) and similar to other cylinders.
Is there any hope that running under load may improve this?
I've already squirted some Mystery oil onto the pistons, But I don't understand why the spark plug works only after jumping a gap to the plug.
Any suggestions would be appreciated, thanks.
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