P1273 code, with slight rough idle

Maintenance/Repairs
1

I got a 04 Nissan Sentra that has a p1273 (Air Fuel Ratio Sensor 1 Bank 1 Lean Shift Monitoring) with a slight rough idle on cold starts most of the time. There’s also a hesitation/kicking from a cold start when going 0-20 mph till I drive about .5 of a mile, after that .5 mile or so the symptoms go away and the car runs fine.
I got some live data readings that are a bit confusing. My fuel trim readings (last week were, short term: -18, long term 7). (Now short term: 7.8, long term -10.2). Why if I have a lean condition are my numbers negative? And why did my fuel trims completely flip flop from positive to negative?
My O2 sensor 1# reading that reads .240 has always read that since I had my car (5 years) and only oscillates + - another .025, my O2 senson 2# did oscillate from .100 to .900 before this code but now it’s at .050. Right now I do see sensor 1 spike up near .900 when I’m going down a steep hill when I take my foot off the gas and it does the same thing on the highway when I take my foot off the gas and my sensor 2 goes to .000 the same time.
Here are some checks/tests I did already.

  1. Did a vacuum leak test, shot some smoke from the brake booster hose. No leaks.
  2. Exhaust check, put my hand over the tail pipe and had good pressure build up. So that’s good.
  3. O2 senson 1 has 12.25v going to it and had 9.6 ohms.
  4. MAF sensor, looking at it by eye, I don’t see any dirt build up at all. I shot it with some maf spray and nothing changed. I also did unplug the sensor connector and the idle did dip for a sec. like it was about to stall but then ran fine afterwards for 1 min with sensor unplugged.
  5. Fuel pressure, I didn’t check fuel pressure because I don’t have a test port, I would have to disconnect the line, little more involved. I want to add that I always had a problem with the check valve in the pump, after driving the car and car sits for 15-90 mins in a warm state I got to prime the pump 4 times or the car won’t start correctly, cold starts no problem.
    Looking to see from what I described does it point out to a specific problem or is there something else I should check or look more into?
    Here’s my live data PID and a link to the full list with me revving the engine if that’s more helpful. https://filebin.net/6eojdyilflbgilnb
    Fuel system 1 statusOL-Fault
    Fuel System 2 status–
    Calculated Load Value(%)22.0
    Engine Coolant Temperature(¡£C)93
    Short Term Fuel Trim -Bank 1(%)7.8
    Long Term Fuel Trim - Bank 1(%)-10.2
    Engine RPM(rpm) 812
    Vehicle Speed Sensor(km/h)0
    Ignition Timing Advanece for #1 Cylinder(¡£)17.0
    Intake Air Temperature(¡£C)46
    Air Flow Rate from Mass Air Flow Sensor(g/s)2.33
    Absolute Throttle Position(%)1.2
    Location of Oxygen SensorsB1S12–B2S----
    Oxygen Sensor Output Voltage Bank 1-Sensor 1(V)0.230
    Short Term Fuel Trim Bank 1-Sensor 1(%)8.6
    Oxygen Sensor Output Voltage Bank 1-Sensor 2(V)0.050
2

I also want to add, I checked the fuel injectors with a mechanic stethoscope and they all sound the same.

3

Potential causes of a P1273 are

  • Faulty Air fuel ratio (A/F) Sensor 1 Bank 1
  • Air fuel ratio (A/F) Sensor 1 Bank 1 harness is open or shorted
  • Air fuel ratio (A/F) Sensor 1 Bank 1 circuit poor electrical connection
  • Fuel pressure
  • Faulty Fuel injector
  • Faulty Air Flow Meter

Notice the 1st 3 possible problems… Probably not a bad sensor with just this code. Check the O2 sensor wiring re: points 2 and 3.

Find the pressure regulator, pull the vacuum line off while the car is running. If it squirts fuel, that’s bad. Replace it.

See if you can rent a fuel pressure tester. They have fittings that fit between the feed and the injector rail to allow you to test this. I don’t expect that is a problem but…

4

Idle air control valve

5

So I was able to do a fuel pressure test and got 51.5 psi with the car running. Looked it up and spoke with Nissan, I’m suppose to get 51 psi.
Priming the car before I started it, it goes to 51.5 psi then the psi drops right away, goes down to 5 psi in about 22 secs. Again, car running I get 51.5 psi, and same thing when the car is turned off, the psi drops to 5 psi, but in about 12 secs and then slowly goes to 0 psi.
I did pinch off the line to see if the gas bleeds to the fuel pump and by pinching the line it held pressure. So when the pressure drops on the pressure gauge when the engine stops running, it’s draining into the tank, not draining threw the injectors.
I assume the pump can be ruled out for the problem for this p1273 lean code? So what’s the next things to check into? Injectors? If so what’s the best way to check them?

6

On some cars a signal of low oil pressure will cause the fuel pump to shut off, once the key is back to Run position. You might have low oil pressure but more likely an OP sensor is the problem. Good luck.