How do you know that they are failing without removing them and testing them?

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Currently driving a very clean 1985 300SD from the West Coast.

There are plenty of indicators to point you towards failing injectors without actually pulling them out and looking at them.

Possibly the easiest is running through a few cans of diesel purge, if your problem goes away for a while, then reappears it could very well be an injector problem. I'm sure there are more definitive means of doing this.

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-justin

1987 300TD, 1987 300TD
2008 R32, 2000 Passat Wagon