I have a 2012 QX56 that is backfiring, loss of power, won't rev up. Is it the fuel pump? There is no light on the dash and it's not throwing a code. I replaced the O2 sensors and cat 12 months ago but that was for a different issue. Is there a place I can test the fuel pressure on the rail? Any other suggestions?

Sounds more like a disconnected MAF.

If it's not revving beyond 3k, and backfires, but there's no CEL, are you sure there's no code? Have you scanned for a pending code?

There was no code after driving it for 4 hours this way. I got a new battery today because in checking over things I noticed the old one had a crack in it by the negative post. The 1st time that I started it after putting the new battery in it revved and acted fine. I shut it off and about 20 minutes later I went to drive it and it went back to the way it was before the new battery but it did throw a code this time, P062B.

That's kind of a generic catch-all code.

My concern would be damage to the harness from a leaking battery. The code *could* be leftover from before, and low battery voltage can cause all manner of drivability issues.

Clear the code and see how it drives - but let's also check battery voltage (while running and with the car off).

Battery voltage tested fine, it was 14.7 while running. Battery didn't really leak as the crack was on the top, no damage to the cables. Plus we put a new battery in it. We even load tested the battery & both the old battery and the new battery were good, outside of the crack that was on top of the old one. What should the fuel pressure be and is there a schrader valve that I can put a gauge on?

Any other suggestions from anyone?

Not sure why the obsession with fuel pressure. That would throw a clear and obvious code.

Does the CEL light up with key on (not running)? That indicates if the diagnostic function is even working (some shady sellers remove the bulb).

Backfiring, loss of power, and no revs past 3k is typically MAF-related.

Get some electronic contact cleaner (aerosol) and clean the filament (NO substitutes). Check wiring to the MAF as well.

Do you have a code reader? If so, we need to see pending and current codes.

We cleaned the MAF and checked the wiring and it all looks good. Every time we have cleared the codes it runs like crap right away and then the P062B code pops up. We pulled it in the shop this morning to check if there were any other codes like you asked and there was still just the P062B. We cleared it again and it came right back but this time P0300 also came up.

Here are some pictures of the MAF wiring. You can see the insulation is cracked and the wire is showing through right where it goes into the plug but none of that is touching each other or looks really bad.

https://photos.app.goo.gl/FAwP5kSGrKPeH2618

Is the shrink wrap on the white wire from the factory?
Should there be 1 green wire going to 2 green wires as it goes into the plug?

Still trying to figure this out. Our local Nissan dealership put it on their diagnostic machine and recommend replacing upstream O2 sensors, spark plugs and testing compression. We are going to do the work ourselves. We are getting 150, 170 & 190 on the compression test on the different cylinders. Any thoughts and what should we be getting on the compression?

I drove it back from the dealership and it idles rough when you start it until you hit the gas pedal and then it smooths out. I was doing 80mph on the highway on the way back but you cannot punch it as there is no power. It will just slowly build speed. If you drive it long enough it will just all go to crap and you can only go about 40mph.

Sounds a lot like what I had for behavior but I did get specific OBD2 codes. It's only ~ 30min check to pull off the HPFP to see if it's this lifter issue (only suggesting since nothing's fixed it for you yet)...

I ran into similar stuttering under load and unable to go past 3k RPM, unless slowly building up to it, just before my high pressure fuel pump (HPFP) lifter (part 13231+A) failed completely. I got codes P0087 and/or P0090. If you have a worn lifter (flattened to or passed the 4 little holes on the bottom) you'll want to replace it before it completely fails and scores the eccentric camshaft assembly (part 13020+B) and the timing cover and you get a very expensive repair bill (or failed engine).

Here's a pic from a youtube video that shows lifter wear (although for a different car, it's the same general design):