15/06/2026 10:54 am
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Automotive Q&A
What fuel-trim checkpoints make a road test useful instead of a screenshot dump?
Review the evidence, add a focused answer, and distinguish confirmed measurements from assumptions.
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Our scan files can contain hundreds of parameters, but the repair order still needs a concise comparison. We want repeatable checkpoints that distinguish idle air leaks, load-related fuel delivery and purge effects without burying the conclusion.
What states do you capture before and after repair?
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16/06/2026 10:23 am
Use a small parameter set and record closed-loop status, RPM, load, MAF or MAP, STFT and LTFT by bank at hot idle, steady 2,500 rpm, light cruise and a safe moderate-load event. Add purge command, fuel pressure and upstream sensor equivalence ratio when relevant. Hold each state long enough to separate correction from transition.
Repeat the same route, ambient range and fuel condition after repair. The value is in the shape: high only at idle suggests unmetered air; correction that grows with load points toward delivery or measurement.
Topic starter
17/06/2026 9:40 am
The new sheet reduced one 40-channel log to four comparable checkpoints. On a lean case, idle correction fell from +22% to +4% after the repair while cruise remained nearly unchanged. The cause-and-effect was obvious in one page.