Start here — the foundations
5-Gas Analysis Basics
What CO, CO₂, HC, O₂ and NOₓ each tell you about combustion efficiency.
read →Bretschneider Lambda Formula
Theoretical lambda derived from exhaust gases — sensor-independent.
read →Probe Placement Guide
How depth affects CO+CO₂ totals — and how to guarantee accurate samples.
read →Interpreting 5-Gas Results
A structured approach: observe, hypothesise, cross-check, confirm.
read →Pattern recognition — what the gases reveal
Vacuum Leak Diagnosis
High O₂, high λ, low CO/CO₂ — confirm with smoke and propane.
read →EGR Stuck Open Patterns
Why NOₓ stays low even under load when EGR won't close.
read →Secondary Air Injection & O₂
Normal cold-start O₂ rise from SAI — don't mistake it for a leak.
read →Cold Start Enrichment vs Rich Fault
Distinguish normal warm-up behaviour from an actual enrichment problem.
read →NOₓ Puzzles
When high NOₓ appears with a rich mixture — ECT misreads, lean cylinders.
read →Ignition Timing & Emissions
Late-timing signature: high HC, high CO, suppressed NOₓ.
read →Cross-checking with OBD data
STFT vs LTFT Discrepancies
What mismatched trims reveal about intermittent leaks and sensor drift.
read →Freeze Frame Analysis
Using the snapshot conditions at DTC time to reproduce the fault.
read →DTC P0420 — Catalyst or O₂?
Is the catalyst actually failing, or is the downstream sensor lying?
read →Oxygen Sensor Efficiency
Upstream vs downstream activity as a cat-performance proxy.
read →MAF Under-Reporting
Why low MAF reads produce rich lambda — and how to verify.
read →Lambda Calculator Accuracy
When calculated and measured lambda disagree — which should you trust?
read →Catalyst, fuel delivery, maintenance
Catalyst Efficiency Testing
Conversion calculation, efficiency bars, pass/fail thresholds.
read →The Holy Grail Graph
Lambda vs RPM — visual fingerprints for exhaust leaks.
read →Fuel Delivery Faults
Distinguishing pump, injector, and regulator problems through gas analysis.
read →Analyzer Maintenance
Calibration, filter changes, sensor care — the basics that stop false positives.
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