I used to have a 79 300CD - best car I ever owned. Bought it new and drove it unitil '84 when I bought my current CD - the guy who has it now has over 650K miles on it and wouldn't part with it. Back to your car, if it was sitting on an incline with low fuel for a long time, the fuel tank filter make be crudded up - the easiest way to fix this temporarly (or at least see if it's the problem) is to disconnect the fuel line where it connects to the input to your clear plastic filter, remove the fuel cap, and blow (preferably with an air gun) backwards towards the fuel tank - that will knock the crud loose enough that you can get more fuel. If that ends up being the problem, it's not too big a project to remove and clean the tank filter - I think there's several threads on it.

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Houston, Texas
1984 300CD 235K miles, Elvira, one owner
1987 300TD 180K miles
1974 TR6 78K miles Sarah Jane, one owner
OBK #27