m300cab: Thanks for the tip on the 'in pump' filter. These small hidden traps can really keep us scratching our heads. I removed and cleaned the one in my pump so I'm pretty sure it's ok. I also replaced the return check valve in the other orifice thinking that I might be getting air in the lines because of the missing check.
ja17: Thanks very much for the clear explanation and analysis. You have pointed out several areas that I need to look at. I read somewhere that the pressure was around 14 psi and assumed that that was all the pump was capable of producing. I plan to take another reading with the return pinched off. I believe my 230sl is the later one because the only thing I can find in the return line is the one at the exit end of the injector pump. I had a look at that and was surprised to see that it is such a tiny hole through which the returning fuel must pass. I guess this is what keeps the injector reservoir full of fuel, only allowing the excess to return and maintaining the pressure within.
So, checking through your list, it appears that my problem is a pump unable to produce the required psi. I intend to test it as you describe, first on the car with the return line closed, and if I don't see the required pressure, I will test it on the bench, though I don't expect that will show any different result. At that point I will look at the after market pumps you mention. The Carter will serve while I have another look at the original. I seem to remember some talk of shims in there that might be use to make better seals. I don't think I would want to stay with the aftermarket if I can rebuild the original.
Thanks again. I'm feeling re-motivated. There is a classic car event this weekend at the old Mosport raceway, now called the Canadian Tire something or other. I plan to check it out tomorrow but will get back at the 230sl on Sunday.
