I thought about this a bit today:

Pull the injector lines off the IP. Crank and fuel should shoot out.

If not then you have a problem, it could be a bad lift pump or an air locked IP.

I was told by a Bosch shop that if you put fuel in a bottle and suspend it above the engine then gravity will help you out. I think that should help purge the air.

The only way to time a 603 is with the MB timing tool. The dealer should have one. It is a little box with two lights, and a probe that screws into the side of the IP.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200