I made sure the engine was at operating temps when i watched and adjusted the timing by adjusting the pump sprocket. I went off what the video on youtube said. I also just had a malone stage3 tune done with hopes that it was gonna help the starting issue some. And it did nothing. Battery is new and its cranking just fine. It just acts like the glow plugs arent working. Glow plug light stays on for 15-30 seconds
Do you have the coolant sensor off to cause the glow plug light stay on for 15 to 30 seconds? Way to long unless it's well below 0F.
You indicated the glow plug harness was already replaced, should be OK.
You also saw 3 plugs removed and glowing. OK
I would try a clamp on amperage test on the wires going to the glow plugs.
This would confirm you are getting the current through and no bad connection in the circuit.
Bentley manual indicated 6 amp per plug minimum or 24 amps total or higher.
Someone also posted putting snow around the base of the plugs and listen for hissing when it melts. I never tried it.
Last, if your plugs are staying on for that length of time and they are the correct voltage for the glow plug controller relay they should be more then hot enough to start the car.
My light hasn't stayed on more then 5-6 seconds this winter so far. (Monroe NY)
Have you measured the voltage at the starter while cranking the car?
If it drops below 9.6 volts the ECU shuts off.