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My car passed SMOG despite the potential of P0171 at idle:
Test 2021-Final → 2021 (prior 2 tests)
15mph 81 → 357-> 578 (from highest 578 to 81)
25mph 44 → 1079-> 639 (from highest 1079 to 44)This is a 1999 with 144k miles. Emission levels are amazing! These are better than what I had 10yrs ago.
I still have to figure the Fuel Trim maxing out on idle! I was going to change the IAC but saw some improvement (unsure its lasting improvement) so instead went for the SMOG. I will be pursuing a diagnosis.The problem started when shop put a new gasket to IAC valve recognizing a vacuum leak. The following were done while on Park and Closed loop
– so I loosened the bolts on the IAC (introduced a leak) and watched the FT for over 2 mins (130secs) – LTFT did not increase. RPM had few spikes as per OBDII but did not here a significant engine rev sound.
– After tightening the bolt, it took 50secs for LTFT to increase.Thoughts?
Also lat year P0505 was thrown. I just cleaned the IAC.
I am going to swap the IAC with a borrowed part. If it does not fix, I will be smoke testing.
Are u saying leak on the intake before MAP can also be the culprit?
In this car, the MAP is on the throttle body. Plastic intake doesn’t have a crack but it has a port where a hose from the engine (not PCV) connects which is loose.
– This is soon after changing the MAP – car was resting for just 1 hr. You can see the STFT slowly ramping. The red is the front O2 sensor.
– This issue started soon after vacuum leak on IACV was fixed with a new gasket. Wondering if I should remove the IACV gasket and see if the issue goes away?
https://lh3.googleusercontent.com/_8FEwqOpKaoxI_-2H7rFL9SxHUmqEMzDxGQ4wTkaEF2kyetP8tWi3zz_bhSdLkpCB0obOPhW1yUtTOBUqliigQvAoDyeYRVyHgW78nLr9J5YubfnD24wn32ALveji2UFeBR8B6Lx9xjHVOMn23-CBvAdkYXVcIV0mrH7UzG2GCGWbDr_ZvwAzfhIv2O_wm8v7wqeybgRp_W4VxioyAIVG30qx2M7tr-t6UbhbIqF_wrmlMaCLu7lz__SVB4inTv4bybgCOBcAjeicorCgWGgLDludL1QEER0yOYFcqTzL2Nci8v0CGGkH_l0hdJosv-3pUdINhIUJq_fUO52n29K3_C5BqSGToq3DLpXwxXGBiVPMLsBRWCEktRW4SenuDrJq9rLDiYwfLa1mXa_dWyGhrrKy4UiCtEbHJS8ODuIwzD-g0NTDzBSfz–1g4_LNF_siao6y9mz1qFoJ3exm10y0oJ3rm0aMOKkume2oLmLZTUF0U5_IJek6sTp7rxFDA51wFS2NtkXKmv5RYHut-EtMCyBGDUdIMPywgMKbZeHGZzAXkiJmu7zINZOFtYJhb4mjVwVCFkwABKyqcaNRkkZW18TQRm5dNJcLBi0NBfiWxLsBxcXyWiVMg36OnzvwgIU12aZN3_7ft14IjtDNqTWDMAVm0Ai8YJZGUi7UAEeeDjwHlrCm47RLfBoVeIbKsqhbXTJryx6hEafybUEpLvy1iH=w353-h763-no?authuser=0– I called around shops and asked if they have a smoke test m/c. Two of then never answered the question. Another might give a time soon. Not sure if he has it either
– I had a used, but newer, MAP sensor – so I swapped it – seems a little better.
– With the newer one, when the car is idling (Closed loop) on Drive gear, MAP is giving higher reading of 5.36psi. If I shifted to Park (still idling), MAP gives lower value, 4.2psi and STFT increases, hence LTFT increases. You can see it in the photo below.
– Does this have anything to do with Idle Air Control Valve? Faulty?– The O2 sensor in the photo is the rear one. The takeaway is that FT level didn’t get better with RPM.
– I hear you – smoke test on the engine and EVAP – I will find a different shop and take it there.BTW, Should I ask to diagnose for P0171 or leak via smoke?
I repeated the experiment Scanner-Danner did.
As u can see LTFT step by step increases with time irrespective of RPM – RPM went from around 750 to 1500 to 2500.
As I said before, LTFT comes down when I drive normally. Around city LTFT settles at 12.5. So this does not readily support vacuum leak as supported by Scanner-Danner. If u click the link below image opens on a new page. Some sort of sensors malfunctioning?Part 1:
– Shop diagnosed a IACV (idle air control) vacuum leak. When this was fixed with a new gasket, P0171 symptoms started while it is also misfiring.
– Shop properly diagnosed and figured one of the 4 injectors was Mechanically bad. Previously they all passed ohm test. No flow test. Moved injectors around to see misfire moving with it.
So all 4 were changed with reman Honda injectors from a lab.
– Shop also tested for fuel pressure with and without regulator – all were good. I saw with my eyes Pressure gauge was connected with and without the regulator and the engine was running – all normal including pressure being held.
– Does Redline injector cleaner send more fuel to injectors?Part 2:
– Car was released to me and I had it idle a lot before changing oil – resulted in P0171
– Took it back to the shop and he tested as per the manual: Fuel Pressure, O2 Sensor (he did say somewhat slow at times – NTK O2 is new), EVAP purge solenoid. The next step is adjust valve followed by replace injectors (again)
– We wanted to think about it so took the car away.I have been driving around without P0171 – IM Monitor is still not ready on EVAP yet – I let the gas to empty and filled it half way today. 6 out of 7 on IM is complete/ready.
It looks to me when it idles on D4, trim (FT) is not surging – but it surges on Park which eventually triggers P0171. Symptoms might have lessened but I am cautious.
When I drove on Freeway with AC on, LTFT increased to 14 from 7. It has come down to 12.5 around city.
So again, idling on Park gear causes P0171.
If I were to take it to another shop, I need to ask them for a specific diagnoses – which one are you recommending? The shop was busy to write up diagnosis so I only have the CC receipt. They are buying time to give the diagnosis report to me.
Also, am I safe to go for SMOG in California (San Jose area) despite this lean condition? Last time it failed due high NO – HC was low so were others. Just the NO was high once at 25mph and later at 15mph. By this time misfire developed.
Actually, the shop diagnosed my car for 2hrs – they changed the injectors and the IACV gasket. Beyond that they could not diagnose.
Shop said valve adjustment (which I had it done 20k miles ago) and there is no guarantee that it will fix it. Shop did not have a Smoke m/c. Valve adj cost another $300.Does this condition has anything to do with idle Air Control Valve (IACV):
– the car earns the P0171 CEL at idle
– When driving steadily, CEL goes off.The car last yr gave P0505 – also AC would shuts off at idle.
So I cleaned the IACV and AC started working fine.
I didn’t change the IACV gasket that it introduced a leak which shop fixed – Ever since shop fixed it, the P0171 came.I tried with the throttle body butterfly open!
I might need to use two Cigars – some smoke escaped through my improvised connection.
Spark plug was upgraded to Platinum at 80k and I maintained it at 144k too. I bought it at OReilly store not online. It is the correct fitment with upgrade.
At 80k, I upgraded to Platinum NGK spark. No issues. At 144k, replaced with new Platinum NGK spark.
Could this be causing it?Also, this time, I put 5 gals of 91 gas + 7 gal of 87 gas. I have always used 87 gas only as recommended by the Honda. Hope this is not causing it.
I did a smoke test using this mtd. https://www.youtube.com/watch?v=GOhl4r0GSiE
I didn’t find a leak. I might have to re-do and use 2 Cigars instead of one.Is there any special procedure to do to the car before smoking?
Today I did the pinch test on EVAP and Brake booster cables when the engine is on closed loop. No change in fuel trim. I am going to build a Smoke m/c and test it or find another shop with smoke machine.
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