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AFR Sensor and O2 Sensor both hit lean rails when stopping

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2 years 8 months ago #50031 by DIY JoeR
This is in reference to a 2009 Toyota Corolla XLE 1.8L.
Coming to a stop, the RPMs dip a couple of times and then gets corrected. Mode 6 records a handful of misfires on cylinder 1 per trip. On rare occasions, at start up, it'll trigger P0301 which is like 65000 misfires. I swapped coils and misfire stayed on 1. I swapped plugs and misfire stayed on 1. I swapped fuel injectors and misfire stayed on 1. My mechanic says that cylinders 1 and 2 have 90 something psi and the other two have 130 and wants to replace my engine, but I suspect that yes, corollas are known to get low compression but something else is happening here as well.
I wasn't planning to discuss this until I did all my tests but when I saw how the sensors get pegged lean, I thought that might be all I need to see.
This shows a typical stop at a red light. At about 300 seconds my foot comes off the pedal. At about 305, I start braking and come to a stop. The engine bounces low a couple of times and then goes normal. During the decell, the sensors hit the rails and the STFT seems stuck.
What do you think?
 

File Attachment:

File Name: typicalstop.pdf
File Size:217 KB

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2 years 8 months ago #50041 by Tyler
The fuel cut during decel looks perfectly normal to me. B) Pretty typical strategy amongst most manufacturers. I bet that if you watch the Loop status during the same event, it'll say Open or some variation.

P0301 is a different story. Does the Freeze Frame say the code set going down the road? Cold start? Knowing that can narrow your list of suspects.

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2 years 8 months ago #50046 by DIY JoeR
Thanks for clarifying that Tyler. In all my research on either type of sensor there has not been even one example of them maxxing or bottoming out like that.
You were right that it leaves closed loop when I release the gas pedal.
For the times when it immediately gave a P0301, it was always within a few seconds of starting to drive after morning start up. This occurred much more often in the winter and almost not at all in the summer. I'll post some freeze frame data.

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2 years 8 months ago #50047 by DIY JoeR
 

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File Name: freezeframes.pdf
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2 years 8 months ago #50048 by Tyler
Solid Freeze Frame data, sir. B)

I'd be looking for a cylinder head gasket leaking into #1, or a genuine compression/mechanical issue like your mechanic mentioned. If you have compressed air available, you're only about $100 away from being able to do your own compression and leak down testing.

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2 years 8 months ago #50073 by DIY JoeR
Oh man! That's not good. I don't have compressed air. I was hoping you would suggest that the compression is marginal from wear and that some faulty sensor was tipping it into misfire range. Oh well.
Just out of curiosity, what might be the theory explaining how the idle recovers after a couple of misfired?

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2 years 8 months ago #50074 by Tyler
:lol: Sorry 'bout that. How many miles does this engine have on it? It's been my experience that these engines start suffering cylinder head issues above 150K. Not all, but enough that I keep it in the back of my mind when working on them.

Even if you don't have compressed air, you can still do your own compression testing and verify the results for yourself. No offense meant to your mechanic, but I'd want to verify those results before making any repair decisions.

For what it's worth, this is a capture from a known good 2010 Matrix (same engine) during a closed throttle decel:

www.scanshare.io/Share/TJOPOC79uUCa03skNrAyag

 

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