if that strainer is clogged, you can fill her up with all 24 gallons and she wont sputter. To test, feed the engine from a cubie of diesel in the engine room - if the engine starts easy - you just found your problem. I also would suggest to find a hand bleeder bulb to push the fuel through the pump to ensure no air is in the pump.

You said you removed the prefilter and saw no contaimnants, when did you change the secondary (big) fuel filter, and in my experience if you disturb these things when cold - you are in for a miserable time unless you have a portable jumpstarter with you. I always service them when the engine is hot - and keep the engine above 2000 rpm immediately after start.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)