hey there ladies and germs, I've got this nice little '84 240, and it's got this problem, you see...

on starting the car more or less cold, i've found that it can take many attempts to actually get it to start up and stay running. To be more specific, it seems as if there is little or no fuel early on in the ignition process, that the engine is simply misfiring again and again. It'll fire a few times, possibly backfire, and then stall. in the past, cranking it a second time was all that was needed to start it up, but this has been failing recently, with the car needing as many as four attempts to get running. I do not have a fuel pressure gauge, so I can't even be sure fuel pressure is the problem or not. On top of this, lately there have been severe issues with the engine, right before stalling, making a number of **extremely** loud "THUD" and "TONG" (think of some Mr. Universe hitting the block with a sledge hammer) noises, some of which are outright frightening, which bring me to that second part of the subject...knock. Recently, as well, the engine has been starting to knock very loudly on all amounts of throttle. I do not have the money to try to take the car to a proper service center and being as it one of only two working cars it is necessary to keep it operational, so diagnosis has been difficult. It has been getting progressively worse, but since I offered the suggested to my parental units to fill it up with midgrade instead of regular, the knock as more or less gone away with exception of very light throttle. What could possibly cause this problem? And being as it has potentially been hapenning for six to eight months (the time I have not been at home :D), what sort of engine damage could possibly have occured, if any? any solutions, outside of midgrade or premium?

my suspicion regarding the start issue is that the check valve is bad, but I had read that this valve mostly plays its role in preventing bubbling in the fuel lines after shutting off the engine, so...whaddaya think? is it the check valve, or is it something else? think I would be best wiring up a momentary switch to run the fuel pump to "prime" the fuel lines? affordability is a big issue when it comes to getting new parts right now, but I may be able to pull a couple of spares off of a nearby parts car. and any Macgyver-isms are very welcome here. Anything to save a buck. ;)

Cheers
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1980 240DL, 1984 240DL, 1988 740GLE, 1993 850 GLT