2004 Ford 3.9 liter question

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I replaced the camshaft sycronizer assy on my 2004 3.9L engine. I started it up and it ran fine for a few minutes, then runs really rough. Is it possible I did not have the engine at TDC when I installed the Cam Position assy? It talked abut the fuel timing being off if its not installed with the engine at TDC. In these newer engines, how do you find TDC on the compression stroke? There doesn't seem to be any marks for timing?

Any help??

Thanks