Well, you could pull the rocker/cam cover off and look at the cam lobes. But if the cam lobe or rocker arm were worn enough to cause the cylinder not to fire, there would be a huge amount of noise.

My suggestion for diagnosis:

1. Do a compression test to make sure that the valves are closing
2a. Swap the plug wire with a firing cylinder's
2b. Put a timing light on #1 and see if there is spark
3. Pull the injector out and test or swap it with another cylinder. Install the injector with a new seal.
4. Blow the line from the FD to the injector out with compressed air
5. Swap the line to #1 to a different position on the FD

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe