Bad gas? Also check for spark on your other 3 plugs and make sure they're wet with fuel also. Just to rule out injectors not firing.
I doubt your timing belt is broken, as I believe you wouldn't get any spark at all if that were the case, since the distributor is turned by the camshaft. If the timing belt were broken, the camshaft wouldn't spin, neither would the rotor in the distributor, and therefore no spark. Also you have compression.
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