I think our theory on a bad injector was that if it failed internally, assuming there is a spring that holds the injector valve needle closed until 3.3 bar is achieved, if this needle didn't close completely or remained opened partially under all pressure situations the idle would become rough at idle as the faulty injected cylinder would actually recieve more fuel than could be burned at idle speed. Running the engine at rpm's higher than let's say 1000 would absorb the additional fuel without much effect to engine performance. Although I don't understand the injection system fully, even after reading the site on it's operation, especially when it doesn't go into much info on the break down of the actual injector operation and the parts contained there in.
What other problems do you see as happening if an injector was in fact releasing fuel below the preset 3.3 bar when the engine speed didn't call for this amount of fuel? It seems that this engine has the ability to run somewhat rich with only an idle problem as a result verses trying to add air to an almost properly propotioned mixture, which basically just stops the engine in it's tracks. Any additional light you can spread on this situation would be greatly appreciated.
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'84 300SD 256,000 Gold on Brown (Mileage Award)
'86 300E 246,000 Blue on Tan