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TexasJohn55

'98 3800 seriesII, P0171, scan data stream, what do you think?

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TJ55,

I don't know if this will help but, sometimes if the photo files are too large the system won't load them.

Try resizing the images (smaller) then try uploading them again.

John F.

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TJ55,

I don't know if this will help but, sometimes if the photo files are too large the system won't load them.

Try resizing the images (smaller) then try uploading them again.

John F.

Yeah, I always resize to appx 60 KB before attempting upload.

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I still cannot upload attachments!

After replacing PCV valve and removing vacuum from fuel regulator and boosting pressure from 36 psi at idle to 45 psi at all times, my STFT numbers are 3-5 at hot idle and it passed emissions with no codes. P0171 gone for now. I may later try hooking back vacuum line to regulator and see if problem returns. The one unknown is whether the PCV valve had any effect on it running lean. It did rattle and appeared ok.

The new MAP sensor reads a little lower than the original I tore up, 29.2 ambient instead of 29.6 or 29.8. Weather change can affect that. I don't anticipate that little difference is a factor on tuning. Car seems to drive the same at 45 or 36 psi, really cannot tell any difference.

Still don't know what was the definitive cause of P0171 running lean at idle. I will update thread if I learn anything worth passing along.

Thanks for the help and future comments on subject are welcome.............John

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Well, I thought it was time for an update on the running lean code P0171. If you recall, I had mentioned that the honeycomb screen in the intake was damaged. There was a lot of comments about the MAF sensor and also maybe intake leaks. Came time for another inspection and the code was showing up regularly. I removed the intake boot and sure enough, the screen was held in with a thin snapring. I removed the screen and noticed that the damage was directly inline with the channel to the MAF sensor. I straightened the honeycomb as best I could and rotated the screen so the damage was away from the MAF channel. Long story short, that fixed it. The code has not reset since appx 2 mos ago.

 

Thank you all for your input, I have learned alot from this.

 

PS: those MAF sensors are not cheap so I decided mine might work after fixing the cause of the upset airstream to the MAF.

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Time for an update. Still running good, Moral of the story: Engine will not run right and MAF CANNOT READ CORRECTLY IF THE HONEYCOMB SCREEN IS MISSING OR DAMAGED OR UPSETS THE LAMINAR AIR FLOW ACROSS THE SENSOR.

Edited by TexasJohn55 (see edit history)

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