Liam Miller made his debut for Leeds on loan from Manchester and he curled a delightful 25-yard effort that Carlo Nash did well to save.
Leeds boss Blackwell attempted to breath new life into his side's faltering attack bringing on Robbie Blake and Jonathon Douglas.
With seven minutes remaining, the unmarked Blake fired in a shot, but Nash produced another fine save.
Preston manager Billy Davies:
"We should have won the game and I am disappointed that we didn't.
"Leeds started the second half well but we controlled the game after that, but we just haven't had the breaks.
"I am not worried that we are drawing so many games. I would be worried if we were not playing well, but we are. We just need to take more chances."
Leeds: Sullivan, Kelly, Butler, Kilgallon, Harding, Richardson (Douglas 72), Derry, Miller (Moore 90), Lewis, Hulse, Healy (Blake 71).
Subs Not Used: Gregan, Bennett.
Preston: Nash, Alexander (Mawene 86), Lucketti, Davis, Hill, Sedgwick, McKenna, Jones (Nugent 15), O'Neil (Etuhu 45), Davidson, Agyemang.
Subs Not Used: Dichio, Lewis Neal.
Booked: Sedgwick, Lucketti, Nugent, Hill.
Ref: A D'Urso (Essex).