Injectors not seated correctly. Simply put a diesel needs three things to run, air, fuel and compression. Were it an ECU problem like a cam sensor it wouldn't be pulsing the injectors regardless of where they are located, be it in the bore or in the air.
Since you're getting fuel, your electrickery is ok so sensors are off the list of culprits, as is fuel, since the manifold is off, there's no air restriction, leaves one thing from the list of necessities for a diseasel engine to run, compression. Where can you lose compression, valves, glow plugs, piston rings and injectors. Given you have disturbed the injectors, and it was working before, it's current inoperability is a consequence of recent actions. It's beyond impossibility that you've coincidentally damaged all four cylinders to the point of having insufficient compression to fire through broken valves/rings/glowplugs.
Were it only one or two culinders damaged / down on compresion, it'd be running on two of three cylinders and missing on the damaged one, but it's not firing at all, so it's a sytemic fault across all four cylinders.
When you eliminate the impossible, whatever is left, no matter how improbable, must be the truth, and going back to out diesel needs triangle, we've eliminated air, and fuel, so it must be compression that is your issue. Given it's across all four, the only thing that's been disturbed on all four cylinders in the injectors. Ipso facto it's only the injectors that can be causing your lack of compression, resulting in a lack of ignition.
It's not an expensive repair, but injector seals can be a right C%&T to sort....