the concave side goes against the injector. if you hold it up to the tip of the nozzle you can see how it seals. keep a flashlight handy so that after you drop them in you can verify that they are right side up. Did you replace your injector nozzles?

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• 1993 Mercedes-Benz 400E *146,000 Miles*
• 1985 Mercedes-Benz 300SD Turbo Diesel Biodiesel *SOLD @ 346,000 Miles*
• 1984 Mercedes-Benz 300D Turbo Diesel Biodiesel *SOLD @ 284,000 Miles*