You would likely need to compensate by increasing the amount of air that was delivered to the cylinder to get the optimal fuel/air ratio. I'm not sure about diesels, but I'm pretty sure that when you increase the fuel/air ratio, it's also a good idea to tweak the spark timings and cams. I know that diesels have glow plugs and not spark plugs, but I would assume you would need to compensate similarly, where possible.
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