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Aside from max kudos for all your efforts And the educational value they represent, in your video may I share on bit of feedback: Concerning your video: “Diagnosing Lean Condition from Exhaust Leak using Scan Tool P0171, P0174” At the 20:16 video timer mark: you observed and pointed out the Long Term FuelTrim failed to move or respond or update and that was a perplexing thing at first, but it stimulated me thinking and is subject of my feedback. About that observation, It occurred to me, PCM is unable to distinguish extra air That is not present in intake side but actually present in exhaust side. Mistakenly ratcheting fuel into this … PCM gets to it’s ratcheting limitation and aside from actual divergence away from STOIC it’s ability to compensate has been reached. PCM programming decision tree evaluates To a new value for a LTFT UPDATE value only in the event of actually ratcheting and getting to STOIC but in this case, limitation of ratchet count can never reach STOIC, so it’s OUTSIDE system’s ability to compensate. Situationally. The next ignition start up cycle must rely on the previous last known good LTFT value. Without benefit of a current PCM LTFT UPDATE … as it was unable to accommodate a current LTFT updated newer value … because such value in this instance is beyond it’s ratchet limitation ability to compute. Reminds me of Robot in Lost in Space “THIS DOES NOT COMPUTE! Danger! Will Robinson”
Aside from no way to edit my original share I am relegated to use your reply option to add and further clarify…
I believe I can explain how you did uncover a Definitive “exhaust leak diagnostic tag” your goal of discovery I believe can be shown a success???
Focus is on LTFT Not Moving … WHY … here because intake fuel/air ratio is diverging away from an original STOIC condition.
PCM ratchets fuel in only to see a Ratchet count going out of bounds. PCM defaults with no valid count to display as the new LTFT ASSIGNMENT. All due to extra air responsible for this not at all present in intake side.
He was also observing the o2 sensor behavior so I’d say he still has a good theory since the o2 sensor behavior isn’t that irregular in the test
You can also test it out, as I did, and got the same results as Matt
Even a vacuum leak has to be pretty noticeable to throw a code at least in the car I tried it
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