Vintage Cars: 77 Mercedes 450 SL odd cranking but no ignition, engine cranks, fuel pump relay

Question
When I bought a '77 450SL Roadster (107.044 Chassie,117982 Engine),it was hard to start. Got new coil but then the battery was dead most of the time. Replace battery. Started everytime for 8 months. Recently ascending a hill (not steep), I heard an audible "pop" under the hood and car died immediately. Still cranks with vigor but there's an odd sound, it knew it wasn't going to start. Am checking fuel system & spark. But today I noticed that less than an inch from the breather hose was a larger diameter hose hooked to something that looked like it was vacuum related. Immediately, I thought maybe the "Pop" I heard before engine stopped were these hoses separating from pressure. I connected them and they fit perfect and duct taped them. However, no change, same cranking-but-not starting. Before the problem, I always smelled gas in the cabin-always. Now, though the engine cranks mightily, I smell no gas even when trying to flood it. My ques: 1)Can I just check the fuel injectors or fuel injector to see if gas has been being pumped? 2)Can I physically remove the fuel filter to check for blockage/do cleaning; 3)I think the fuel pump is out but its hard to check because its only me working on it, so how can I find out if the fuel pump is dead or just not getting juice from the relay? (I've read you're statements about where the relay is-- but then what do you do with it?) Finally, should I "un" duct tape the air breather hose from that other hose?How does finding the fuel pump relay tell me whether the pump is working and the relay is bad? Sorry so long, I'm exasperated. It was running so well one week ago!!

Answer
well lets start with the pop, I suspect it is your line you see that blew off. Coincidental , perhaps??
Now then - a car dies suddenly for only three reasons, no air, no spark or no fuel.
I doubt it is the air
Spark - have you checked for spark?
Fuel - you may need to pull an injector or the line to the rail, or at the line into fuel distributor and see if you have fuel on cranking
Can you hear the pump spin up to presurize system
?


that is where I would start, let me know what you find