So there's a couple of issues that have come up that weren't an issue before. Quick history, started life as a fleet vehicle, well maintained. Then owned by a friend of my daughter who continued with maintenance and was never hard on the vehicle. Now to me...I got the lucky task of learning that it's similar to my Eclipse in that if the IAC dies, it takes the ecu with it. 3 ecu's and an 2 IAC motors later all is good and I get to drive it. 2 weeks later I was late for work and managed to pull out in front of a vw bug that bounced off the front right corner of my QX4. Damnit. So starts the research and turns out while it destroyed the front end(bumper, support, headlights, radiator support, etc)the damage was all in the front clip. Long story short, after much cussing and throwing things, I have the frame rails straight and almost ready to put it all back together as I pickup parts. Up to this point it started and ran fine, best I can tell only runnin it 30-45secs at a time since I had no radiator but everything sounded like it did before the accident.
Once I replaced the inner fender that holds the battery I'm able to back it up to the garage and continue working on it. The last time I start it up, back into the area in front of my garage unit, all is good, with the exception of the 4WD light is on but more on that later. I finished the last of the straightening I had to do at the end of the frame rail, which required much pounding with a sledge hammer. Go to start it up to move it back and it won't fire up. It cranks just fine, but won't even try to start. It's getting spark, spraying starter fluid in the intake results in it roaring to life for a few brief seconds. Check both fuel pump fuses and relays, all is good there. Check for power at the fuel pump, getting none. So what am I missing, fuses and relays are good, but it's still not powering up the fuel pump. I assume at this point all the pounding is responsible, but what could be the problem then?
Oh, one other thing, when I turn the key off, the dash lights stay on and there's a strange buzzing coming from behind the radio area. If i turn the key on and off a couple times it will shut off as it should with no strange sounds...

sorry for the long winded post, but wanted to get as much info in as I could think is relevant....

Thanks for looking and Happy Holidays to everyone!!
Bernard

Check your eccu2 fuse in the passenger side engine compartment fuse box.

Checked it before , but here now and double-checked it to be sure and is ok. All fhe fuses in the engine bay are good, gonna doucheck the ones in the passenger compartment as well just to be safe.

In that case, the issue could be the anti theft system not registering the key. Is the security light blinking, on, or off?

The theft system appears to be functioning fine. blinks when key not in, stops when key is turned to on position. are there a lot of other systems or circuits that can cause fuel cut?

Make sure your battery is charged up. Any codes at this point?

As far as the fuel pump, when you first turn the key to "on", the fuel pump will run for 1 second or so to pressurize the system. You should be able to verify that by ear or by voltmeter. The ECM then turns the pump off till you turn the key to start. That will verify the pump works.

Also, there are two crankshaft position sensors on early R50's - one back at the flywheel, the other is up under the front crankshaft pulley - kind of hard to see. The front one sends a couple of reference signal pulses (REF in the manual) to the ECM. If the ECM does not get the pulse from the front crank sensor, it shuts off the fuel pump. So maybe the sensor or wiring to that is damaged.

You can find the fuel pump wiring diagram in the manual.

Many thanks to everyone's suggestions. Work got insanely busy and the Qx4 got pushed to the back burner, but now I'm back on it and moving right along finally. So to answer the question of if there were any error codes, yes...there was like 6 error codes that made no sense whatsoever, until I discovered what the issue was. Turns out in the process of securing the wiring harness so it didn't get melted or damaged during the straightening, I had disconnected not one, but both of the ground points....the grounds that go to the relay boxes, one on each side of the engine bay. Once I reconnected those, it fired right up like nothin had ever happened. Needless to say I felt a bit of that newbie shame, but I chalk it up to lack of familiarity with not just the manufacturer, but the platform as well. Spent the last 15yrs with my main focus being the DSM(Eclipse/Talon). Never ran into anything like that with those....oh well, live and learn.
So with that all taken care of now, it's just a matter of time, money, and finding the rest of the parts to make it whole again!! Decided when I was first pricing/sourcing parts that it was gonna be the most cost effective to just convert the front end to a Pathfinder, especially when i got to the cost of the headlights alone. I've seen the stock HIDs range in price from $150 each used, to over a grand for brand new OEM unitsll No thanks, the cost of 1 new light assembly would have easily covered all that it's taking to do the conversion...minus paint of course.
I'll post pics of the before/after once I get it done and at least covered with primer.
Thanks again for all the suggestions from everyone, and for a damn good knowledge base! I have no doubts I'll be back before long!!

Bernard