A4 (2.8L)
NOTE:
When ignition coil is triggered, spark is supplied to 2 spark plugs at one time. One spark plug fires during compression stroke and the other plug fires during exhaust stroke (waste spark).
Check for a strong Blue spark at coil wire and at each spark plug wire by holding wire terminal no more than 1/4" from chassis ground while cranking engine. Disconnect and inspect all related ignition system connectors and harness. Clean or repair as necessary.