Code P0171 System too Lean. (not the PCV hose) - Page 3 - Ford Focus Forum, Ford Focus ST Forum, Ford Focus RS Forum
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Old 07-02-2019, 02:39 PM   #21
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Yeah. Honestly try unplugging the MAF and seeing what happens. It will default to just using the o2 sensors and should level out in ~5 minutes after.

But again, you need a live data scan tool to know wether this fixes it.

Cal

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Old 07-02-2019, 03:15 PM   #22
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I'll reset the PCM, unplug the MAF and check the results with my live data scanner. I'm not sure exactly what I'll be looking for so I'll post the results.
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Old 07-02-2019, 03:32 PM   #23
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Originally Posted by Stangfire View Post
I'll reset the PCM, unplug the MAF and check the results with my live data scanner. I'm not sure exactly what I'll be looking for so I'll post the results.
Use the proper PCM reset procedure.

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Old 07-02-2019, 03:52 PM   #24
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You'll be looking for the fuel trim numbers to go to or near 0% long term fuel trim (ltft) or short (stft) 0% fuel trims along with the first 02 sensor fluctuating from .1-.9v means it's running level.

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Old 07-02-2019, 05:17 PM   #25
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I guess I don’t know how to reset the PCM. I thought that just meant to clear the codes. Anyway, first thing I did was unhook the MAF sensor. Started the car and instantly the CEL was off. I erased the codes. Ran the car for 5 minutes and got the attached readings. O2 sensors are reading same as before. #1 is .1-.8v. The other 2 are steady.
Attached Thumbnails
Code P0171 System too Lean. (not the PCV hose)-794a2121-fee9-495f-bda5-b70d7a82f141_1562105557015.jpg  

Code P0171 System too Lean. (not the PCV hose)-533adc27-b289-44c3-8fcb-7e9fd07d227e_1562105627558.jpg  

Code P0171 System too Lean. (not the PCV hose)-b6da47eb-43c0-4883-a5b5-11add6e62cc8_1562105671255.jpg  

Code P0171 System too Lean. (not the PCV hose)-048f77cc-bc83-49f5-ae8b-c6dd673e24c9_1562105725679.jpg  

Code P0171 System too Lean. (not the PCV hose)-e63a3720-1507-45ed-a03f-f6194940a6d4_1562105763182.jpg  

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Old 07-02-2019, 08:10 PM   #26
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Quote:
Originally Posted by Stangfire View Post
I guess I don’t know how to reset the PCM. I thought that just meant to clear the codes. Anyway, first thing I did was unhook the MAF sensor. Started the car and instantly the CEL was off. I erased the codes. Ran the car for 5 minutes and got the attached readings. O2 sensors are reading same as before. #1 is .1-.8v. The other 2 are steady.
PCM reset:

RFP is right at 41psi (282 kPa) which is good. Is this data with the MAF plugged in or not?

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Old 07-03-2019, 01:06 AM   #27
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Quote:
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Yeah I've cleaned the MAF sensor. I'll try again. I've used propane all over the engine trying to find a vacuum leak. I can't find one. I don't hear any hissing or sucking either. I put a vacuum gauge on a line and it shows ok.

I wonder if the O2 sensor can sometimes work and not work?

What would be the next step? Test the fuel pressure with a manual gauge? Why can't you trust the fuel pressure readings from the scanner? (or can you?)
The reason we don't trust the FRP sensor reading, is that we don't know if it's accurate until the reading from it is verified with a manual pressure gauge.
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Old 07-03-2019, 08:08 AM   #28
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Quote:
Originally Posted by Paul1958 View Post
PCM reset:
https://www.youtube.com/watch?v=hZAsoqmqhdM

RFP is right at 41psi (282 kPa) which is good. Is this data with the MAF plugged in or not?

Paul
This was with the MAF unplugged.
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Old 07-03-2019, 08:25 AM   #29
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Does it seem normal for the CEL to turn off immediately when I unplugged the MAF?

I erased the CEL code and drove 30 miles with the live data scanner on and the MAF plugged back in. Light did not come on yet.

The O2 sensor 1 cycles between .1-.8V like it should. So that seems fine. O2 #3 and #4 are mostly at .8V sometimes a little lower like .5 maybe I saw. So they seem good.

The LTFT bank 1 is always around 17%
The STFT bank 1 is mostly around 5%

The STFT sensor 1 is about +-8%
The STFT sensor 2 is 99.2% and it NEVER moves.
The STFT sensor 3 is 99.2% and it NEVER moves.

Should I be focusing on STFT bank 1 or sensor 1, sensor 2, or sensor 3?

Thanks for the help by the way! I’ll reset the PCM as well.
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Old 07-03-2019, 08:36 AM   #30
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One more thing. From what I read if my MAF sensor is working properly when I unplug it and drive the car is should drive poorly. If no change then the MAF might be bad.

Does this sound right?
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