I just swapped the motor on my qx56 for the same model and same year engine, everything works except it does not want to start, it has perfect compression and fuel delivery, but something is stopping the spark, the car produces spark on the first attempt, and them stops.

In other words every time I crank the engine it sparks but only the 1st time and then i have to crank again and again, its like something is preventing the car from producing a continous spark. i read alot about the IPDM recall but i do not have a lot of information on it other then it causes the car not to start. i have not seen the security light show up when starting but my girl said she did see it once when cranking. any ideas are welcome!!! thank you all in advanced

IPDM, BCM, TCM are all important parts that must match up to everything else in the system.

the nissan engine has many sensors that talk to the BCM (Cam angle sensor, piston position, knock sensor, etc) and if one of them are faulty or if the wiring is damaged (the canbus is a serial computer network) you can get issues.

IPDM is easy to start with. its a relay in the black box in the engine room. use a fog lap relay to make a temp swap to see if it works. you can read up on ipdm issues with the nissan armada/titan of the same year since they are all the same engine.

also check for any DTCs at the obd port.

Thank you very much for the reply @Marctrinixx. you've been a great help.
another thing: will low oil in the tranny cause the TCM to not allow the vehicle to start, i forgot to mention that the tranny dumped some fluid on its way back into the truck because of the tilt when going in since i pulled the engine out with the transmission. The cardan shaft left a huge opening for the fluid to leak out. i have been rebuilding this entire truck from scratch pretty much including interior and some paint work plus swapping the engine, the only thing i never touched was the wiring so its why i am at a stand still, I will be putting in the radiator and the rest of the front of the truck back on and ill update tomorrow.
I will also try the IPDM thing first, and i was getting a P1051, every time i clear it it comes back.

low fluid may put the tranny in emergency or "limp mode" but i dont think it prevents the car from starting.

that code could be fixed by resetting the ECM. there is also a ecm learn procedure online that you can do. it involves pedal presses and key ignition sequences. i may have posted it in this forum but if you dont see it search for "nissan armada titan ecm learn" and you should find it that way.

could be a faulty sensor or could be a short in the wiring harness. checking for continuity at the different sensors would be the only way to accurately find out.

thank you so much, you've been a great help once again, I swapped the relays and now i am getting spark, i have great compression and fuel coming from the tank, but the code for p1051 keeps showing up and the car still not starting. i am guessing bad fuel because is about a year old so i am currently emptying the tank.

but if the air/fuel sensor is bad, can that cause the car not to start?
one issue resolved and thanks in advanced, almost through hopefully by tonight.

air fuel would just make the car run rich i think.

if you are not getting spark, could be the petrol pump, fuel lines, cam sensor.... could be a million things.

faulty spark plugs, coil packs/wires....

To whomever sees this post, and relates. the car finally started yesterday. after a long battle with the truck. The engine was swapped for an engine from the same model and same year.
- the wiring hardness belonged to an AWD and mine was RWD. what i learned was that It does not matter that there are extra plugs, because if the car does not code/require them it won't even notice them. but if it does require them and does not have them, the computer will pick it up in a sec.
- the code U1000 & u1001 is usually for bad ground connections as anyone will tell you, however, their locations evade big time. there are 2 right under the steering wheel on the walls that hold a plate above your knees. the easiest to notice is on the left side behind the lift gate switches.
- there are 3 grounds around the battery bay area, two on the fender wall and one right between the battery and the ipdm under the mass amount of wires.
- there are three on the left side of the engine bay, on the inner wall of the engine bay below the intake box, need to remove intake and also fan shroud.
- another note, this cars mean business, the damn truck WILL NOT start with a weak battery, it must be fully charged, i had to buy a new one and even with that i had to charge it to the max.
- if the car cranks and does not turn over, check the spark, if it sparks once and only once, after every time you hit the ignition, replace the ECM relay on the IPDM. you know what replace it either way, it is only $3 at the dealer.
- if the car still does not turn on but cranks non stop, check the DAMN camshaft sensors and crankcase sensor. In the end after 6 months of war with my truck, it was the DAMN crankcase sensor. picked one up at Advaced auto for $30.00 after all the struggle and jumping the truck and 6 months of wrecking my brain. a BMW mechanic told me to replace both sensors, i only had to replace one to get it started.