hey everyone, I am looking for some advice. Would a bad injector by symptomatic of leaks around a glow plug, longer cranking times, lots of black smoke upon firing, and carbon on the side of the glowplug. Also, the glow plug was difficult to pull out and remove from the hole (carbon build-up maybe?)

Thanks in advance.

Any codes?
Have you checked the turbo?
Any boost leaks?

You can do an injector return flow test. I use this kit:
https://www.amazon.com/gp/aw/d/B0186OY51Q/ref=mp_s_a_1_1?ie=UTF8&qid=1488163562&sr=8-1&pi=AC_SX236_SY340_QL65&keywords=diesel+injector+test+kit
The return flow should be about the same from all 4 injectors. If one is returning less, that injector is injecting too much.

Or pull all 4 and send them to a qualified diesel injection shop.

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U.S. Army Retired