I have a 740b that has regen issues. It will fail a regen and set a code for loss of ignition and ard nozzle heater voltage above normal. Customer replaced the spark plug, ard head and nozzle heater. Ard nozzle heater code was cleared, but will still fail a manual regen and set a failure to ignite code. I put the nozzle heater/dpf inlet heater on. I have also tried a engine ecm, air control valve and fuel check valve. Fuel pressure during manual regen is 270 psi., there is spark at the spark plug with an inline tester while in regen and the nozzle heater is 4 amps. The flame tip temp always cools down during regen, it will never warm up. I have 11 psi boost at high idle no load. I am running out of ideas and wondering if anyone has had this problem.