Lean AFRs - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

Quiche2192 · 12-04-2022, 01:37 PM

My SR20DET seems to be running lean according to my innovate wideband.

I've checked fuel pump (hardwired to battery), fuel pressure (50psi no vacuum), injectors are good, no exhaust leaks, cleaned MAF, calibrated O2 sensor.

My AFRs used to be 11.3 at WOT, now it's like 11.7 pretty consistently, and I am getting a knock sensor code 34. I do remember the car running bad after I cleaned the engine bay. I think some water may have gone into the intake. I did clean the MAF, but still.

Could the MAF have gone bad?

slider2828 · 12-12-2022, 09:21 PM

You can just check the reading on resistance to see if in spec. I would do the same with the TPS sensor and the ECT sensor..... Its all in the manual.

Kingtal0n · 12-13-2022, 08:29 AM

Get an AEM wideband without stupid calibration.
A difference of .5AFR is negligible if the reading is in the 11's any 11 is fine
I've seen some sr20 stock ECU run 12.5 in the boost
Replace the knock sensor, check the timing, basic maintenance.
Very unlikely maf is bad. Could be dirty but rarely they go bad.

They do get old though and that seems to influence more than anything.

I tried 5x different mafs once and all of the give difference AFR at wide open throttle.
only real way to control is to use a stand-alone like Power FC

make sure maf is installed right, no air leaking around it, straight tubes in front and back. Recirculated bypass dumping after the maf. If there is open blow-off or if the blow-off closes prematurely or at low rpm the backflow into the maf will cause problems.

Quiche2192 · 12-15-2022, 09:15 PM

Thanks for the advice guys. I have yet to find the problem. I haven't tested other MAF's yet. Knock sensor is new, timing is good. I have an open blowoff, but didn't have problems before. 11.7 isn't bad at all, but it used to be 11.3 so something happened to cause it to go to 11.7 and that's what I'm trying to find out

tunermt · 01-14-2023, 09:57 PM

(Assuming MAF is ok/nothing was damaged during engine bay wash)

If the pump is on its way out it will still make fuel pressure at idle just fine but will not be able to keep up under full load/high rpm.
You may just have a tired pump and or dirty fuel filters. You can check by logging a fuel pressure sensor or monitoring a gauge through a WOT pull. *Fuel pressure should rise/fall 1:1 with boost\manifold pressure.

12-04-2022, 01:37 PM	#1
Quiche2192 Join Date: Oct 2018 Location: FL Age: 33 Posts: 49 Trader Rating: (0) Feedback Score: 0 reviews	Lean AFRs My SR20DET seems to be running lean according to my innovate wideband. I've checked fuel pump (hardwired to battery), fuel pressure (50psi no vacuum), injectors are good, no exhaust leaks, cleaned MAF, calibrated O2 sensor. My AFRs used to be 11.3 at WOT, now it's like 11.7 pretty consistently, and I am getting a knock sensor code 34. I do remember the car running bad after I cleaned the engine bay. I think some water may have gone into the intake. I did clean the MAF, but still. Could the MAF have gone bad?

12-12-2022, 09:21 PM	#2
slider2828 Post Whore! Join Date: Oct 2004 Location: San Francisco, CA Posts: 6,040 Trader Rating: (13) Feedback Score: 13 reviews	You can just check the reading on resistance to see if in spec. I would do the same with the TPS sensor and the ECT sensor..... Its all in the manual. __________________ Turn and Burn!

01-14-2023, 09:57 PM	#5
tunermt Zilvia Junkie Join Date: Aug 2008 Location: MT, AZ, Seoul, Bangkok Posts: 393 Trader Rating: (0) Feedback Score: 0 reviews	(Assuming MAF is ok/nothing was damaged during engine bay wash) If the pump is on its way out it will still make fuel pressure at idle just fine but will not be able to keep up under full load/high rpm. You may just have a tired pump and or dirty fuel filters. You can check by logging a fuel pressure sensor or monitoring a gauge through a WOT pull. *Fuel pressure should rise/fall 1:1 with boost\manifold pressure. __________________ GTR Parts Buy JDM Cars

12-13-2022, 08:29 AM	#3
Kingtal0n Post Whore! Join Date: Jul 2005 Location: South Florida Age: 42 Posts: 4,829 Trader Rating: (17) Feedback Score: 17 reviews	Get an AEM wideband without stupid calibration. A difference of .5AFR is negligible if the reading is in the 11's any 11 is fine I've seen some sr20 stock ECU run 12.5 in the boost Replace the knock sensor, check the timing, basic maintenance. Very unlikely maf is bad. Could be dirty but rarely they go bad. They do get old though and that seems to influence more than anything. I tried 5x different mafs once and all of the give difference AFR at wide open throttle. only real way to control is to use a stand-alone like Power FC make sure maf is installed right, no air leaking around it, straight tubes in front and back. Recirculated bypass dumping after the maf. If there is open blow-off or if the blow-off closes prematurely or at low rpm the backflow into the maf will cause problems.

12-15-2022, 09:15 PM	#4
Quiche2192 Join Date: Oct 2018 Location: FL Age: 33 Posts: 49 Trader Rating: (0) Feedback Score: 0 reviews	Thanks for the advice guys. I have yet to find the problem. I haven't tested other MAF's yet. Knock sensor is new, timing is good. I have an open blowoff, but didn't have problems before. 11.7 isn't bad at all, but it used to be 11.3 so something happened to cause it to go to 11.7 and that's what I'm trying to find out