The above refers to the general thought that injectors should be checked about every 100k miles.This is true for commercial trucks, also. The injectors need to be "pop" tested and the spray pattern observed. This is a very simple and fast procedure, but you need the specialized equipment. Thus, I would pull the injectors and take them to any "fuel injection pump shop" (or "fuel injection service") that you can find in the phone book.Try not to take them to a car or truck dealer because they will be more expensive. A small fuel injection pump shop should be a lot cheaper: maybe $10 per injector to check. They can also try to clean any slightly clogged injectors. If you need parts, go for the whole injector because the nozzel only isn't that much cheaper. This web site has great prices on injectors - in the low $40's I believe. Good luck.

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Paul 1987 300 SDL; 2000 ML; '69 MGB; '68 VW Fastback