Nissan 370Z Forum - View Single Post - So ive been fighting an intermittent misfire for ever...

SonicVQ · 09-10-2019, 08:33 AM

If you want to troubleshoot this yourself, get a cheap OBD scanner ($15) and a good OBD app like OBD Fusion.($15)

Then you can find out your fuel trims which will tell you if your engine is running lean or rich. You can also see your air/fuel ratio in real time. Also, OBD fusion has a very good diagnostic report that will show the mis-fire counters for each cylinder.

Low fuel pressure would result in a high fuel trim as extra fuel is being added trying to get the engine back to the proper air/fuel ratio.

Also as mentioned, the factory spec for fuel pressure is 51 PSI and a special tool (fuel tap) is needed to check it. The old style "T - tap" gauge won't work as all our fuel lines are steel or hard plastic - no rubber.

The codes P0171/P0174 indicates that both banks are too lean.
This tells us that issue is common to both banks. So look for intake leaks, torn intake boots, loose hoses.

If your fuel pressure is 30 PSI, that is too low and I would start there.

09-10-2019, 08:33 AM	#46 (permalink)
SonicVQ Base Member Join Date: Jan 2016 Location: Ontario Posts: 230 Drives: G37 Sport Rep Power: 6720	If you want to troubleshoot this yourself, get a cheap OBD scanner ($15) and a good OBD app like OBD Fusion.($15) Then you can find out your fuel trims which will tell you if your engine is running lean or rich. You can also see your air/fuel ratio in real time. Also, OBD fusion has a very good diagnostic report that will show the mis-fire counters for each cylinder. Low fuel pressure would result in a high fuel trim as extra fuel is being added trying to get the engine back to the proper air/fuel ratio. Also as mentioned, the factory spec for fuel pressure is 51 PSI and a special tool (fuel tap) is needed to check it. The old style "T - tap" gauge won't work as all our fuel lines are steel or hard plastic - no rubber. The codes P0171/P0174 indicates that both banks are too lean. This tells us that issue is common to both banks. So look for intake leaks, torn intake boots, loose hoses. If your fuel pressure is 30 PSI, that is too low and I would start there. Last edited by SonicVQ; 09-10-2019 at 08:41 AM.