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Discussion Starter #1
2012 qx56 150k plus miles
bought the truck for a deal, and I'm understanding way now lol
drove it to the house and it ran like it was running on 4 cylinders.
I went through my check list
replaced mass air flow/ looking at live data and saw it was bad.
replaced spark plugs and check fuel pump.
checked hpfp
timing recall was done,
long story short.
went through more checks, to come to a computer issue, sent off for repair, they comfirm damage unrepairable, so bought another one from lkq and sent it to the dealer to get it reprogrammed.
its gets up to speed better but still sounds the same with a lean and Multi misfire code
paid them to figure it out, 6900 to replace cats and o2s, clogged cats.
I wanted checked that before I go replacing cats, I deleted them and it still runs the same.
I go ahead and replace spark plugs again because they were fouled out again. and still runs the same.

I was looking at the fuel pressure live before the ecm replacemnt and the commanded fuel pressure rail pressure were jumping around so I looked at it on another truck just like it and it was steady at idle and with gas.

after ecm replacement its steady but low at idle 300-500 psi and same while driving when you let off gas, and sometimes when under acceleration its low but most of the time its up 1300- 2100 psi.

truck about to run me crazy. HELPPPPPP!
 

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man you got a car that was not taken care of. i had a 2012 qx fully loaded and never had any issues at 96K. of course i bought it new and took care of it.

what i suggest is pulling more codes because they for sure are there. you mentioned the air flow sensor but its obviously more going on that that.
 

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Maybe try replacing the fuel pump. I had a 2006 SE and boy that was fast and zippy even with around 350k kms on the clock.

Now I just replaced it with another 06 LE with 180k on the clock and it's like around I would say only 60% as fast as the older SE. But drives and idles just fine.

And from looking around and asking other mada owners seems like replacing the fuel pump is one of the first things to get it back as they are known to start going bad.
 

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Regarding the lean and misfire DTCs, I had was able to diagnose and fix those DTCs on my '14 QX80. I posted it over at another forum: P0171/P0300. Fixed.

It seems you have a diagnostic tool since you've mentioned looking at live data. Do you also have a copy of the service manual? Have you looked at fuel trims, short and long term, along with 02 voltages. Those are important PIDs that will help rule out a clogged cat-converter(s). It just too bad you have Nissan/Infiniti service techs who don't even follow the specific steps to diagnose some of these DTCs.
 
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Discussion Starter #5
man you got a car that was not taken care of. i had a 2012 qx fully loaded and never had any issues at 96K. of course i bought it new and took care of it.

what i suggest is pulling more codes because they for sure are there. you mentioned the air flow sensor but its obviously more going on that that.
that's correct they didn't but its just a p0300 that's confirmed and running piss poor.

Regarding the lean and misfire DTCs, I had was able to diagnose and fix those DTCs on my '14 QX80. I posted it over at another forum: P0171/P0300. Fixed.

It seems you have a diagnostic tool since you've mentioned looking at live data. Do you also have a copy of the service manual? Have you looked at fuel trims, short and long term, along with 02 voltages. Those are important PIDs that will help rule out a clogged cat-converter(s). It just too bad you have Nissan/Infiniti service techs who don't even follow the specific steps to diagnose some of these DTCs.
cats were clogged I deleted them. and when I was checking the fuel pressure my intake gaskets did look like yours and if the cats were clogged I'm pretty sure injectors have build up I replace spark plugs and when put the second set in they where black like I didn't just replace them so I guess I will try the cleaning you did, you had to use a special tool to get the injectors out right?
 

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No special tool needed to remove fuel rails and injectors. If they're difficult to remove, just use a plastic panel remover tool to get some leverage.

Check compression as well. Standard: 242 psi, Minimum: 178.
 
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Discussion Starter #8
No special tool needed to remove fuel rails and spark plugs. If they're difficult to remove, just use a plastic panel remover tool to get some leverage.

Check compression as well. Standard: 242 psi, Minimum: 178.
I was referring to the injectors
my live data shows this
@ 1000 rpms
fuel rail pressure 377.1 psi
short term ft 25% both
long term 0.0% bank 1
9.4% bank 2

@ 3350 rpm
561.3 psi fuel rail pressure
25% both short term
long term 0.0% bank 1
8.6% bank 2

those just do not look right to me and I have all data but it doesn't show me spec for fuel pressure.
 

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I just corrected my post. I didn't realize I typed spark plugs. Sorry about that.

Those STFTs are very high and will definitely trigger lean DTCs, along with misfires.
At idle, fuel pressure should be around 65 psi.
 
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I just corrected my post. I didn't realize I typed spark plugs. Sorry about that.

Those STFTs are very high and will definitely trigger lean DTCs, along with misfires.
At idle, fuel pressure should be around 65 psi.
so I let it run for about 2 hrs and and I saw the short term fuel trim start stabilizing and I went outside and it was running correctly first time since I've bought it did 100 and everything, running strong and good then the next day it slowly started to run rough again the misfire code came then I saw that bank 2 start commanding for 25% more fuel then I cleared the codes boom back to square one with the injector module code that made me change it to begin with man man man man
 

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Did you physically check the injectors and also test the ohms (1.44-1.73Ω) for each injector? Also look for any cracks or exposed wires on the injector harness/pigtails.
 
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