Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
So a 4.0 2009 Xterra, will turn over all day long with spark pulse and spark presnent. good fuel pressure, but wont start due to no injection pulse. every now and then it will start and run perfectly, I can drive it for miles. heres what ive checked: new ecu, flash updated, checked power and chassis ground, new negative cable, 5 & 12v reference. continuity to ecu for injectors, coils, crank, cam, maf, tps. Proper waveform on cam and crank and in time. IPDM not dropping under 10v under crank for fuel pump supply, ecu power, and bat supply. Fuel pump supplying good power and ground, always has good pressure. I CAN NOT find whats killing injection pulse. Its weird that its getting spark pulse but no injection pulse. According to what I have found with nissan books, NATS and ECU cuts spark for any detected issues. and No codes btw.
My first thought is to disconnect one or both of the CMP sensors and force a backup strategy. See if it now starts consistently after a long crank time. I see that you've checked the CKP/CMP waveform, but these things are picky. :silly:
My other thought is a bug in the MAF sensor. Nissan relies heavily on the MAF to determine the cranking injection pulse width, and will take it down to almost nothing if the MAF indicates no air is coming in.
