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

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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

What did the answer turn out to be????

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Auto Zentral Ltd.

A vacuum leak on that one cylinder would cause it to miss.

if i read your post correctly this engine was rebuilt 3 yrs ago and #1 hasn't fired since that time.you also say that there is no valve noise.perhaps it would be a good idea to do a cold leakdown test and see if the valves in #1 are leaking.it is not uncommon after a rebuild to find a lifter stuck or that the spacing shims need to be replaced with smaller ones.if lifter wide open and filled with sludge not allowing valve to close all the way or when head resurfaced old spacer shim too big.[if valves making a little noise at least you know they are closing] good luck david poole european performance dallas tx.

i dont see why a worn lobe would make noise.

could you kindly explain. i agree a worn rocker would rattle.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I have never seen a cam lobe wear without damage to the rocker. And generally the wear starts with a weak ball stud, or lack of lubrication and that will certainly make noise.

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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