240sx wont start?

[zeause]

i bought my all stock 92 240sx the other day and the guy said it was hard to start. Well it quit starting. It runs great when its running but it usually takes 6 or 7 times of the motor turning before it will hit. It just quit starting all together a couple of days ago. It has spark and fuel. I checked the timing when it was running so i know its fine. The ecu shows a code 55. Ive searched and came up with no real answers. Ive changed cap rotor plugs plug wires fpr fuel pump checked the injectors swapped distributors and coils. I have no idea what else it could be?