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Low MAP at WOT with high backpressure confirms exhaust restriction. A plugged catalytic converter is the most likely restriction. A faulty MAP would not coincide with backpressure findings. Ignition and throttle body faults affect combustion or idle quality, not exhaust flow. ASE emphasizes confirming restrictions with backpressure tests for accurate diagnosis.

Negative trims indicate the PCM is reducing fuel because of enrichment. Elevated CO and HC confirm incomplete combustion due to excessive fuel. If spark and compression are normal, a stuck injector is likely flooding fuel. A bad catalyst may allow emissions through but would not cause trims to go negative. Vacuum leaks cause lean conditions, and O2 faults would cause false trims, not negative with rich gases. ASE stresses correlating gas patterns with trims to confirm injector faults.

If injector balance and fuel pressure are fine but MAF reads low, the sensor is underreporting airflow, causing the PCM to underfuel. A weak pump would drop pressure, not MAF readings. Vacuum leaks affect idle more than load. Dirty throttle plates influence idle airflow, not WOT. ASE stresses verifying sensor plausibility by comparing MAF data to expected airflow.

A rich mixture reduces ionization resistance, resulting in low firing voltage, while the abundance of fuel extends combustion, causing long burn time. Lean mixtures would raise voltage and shorten burn. Weak coils lower overall spark energy but do not lengthen burn time. Wide plug gaps increase voltage. ASE stresses waveform interpretation for accurate identification of mixture conditions.

Excessive pressure overwhelms injectors, leading to richness confirmed by negative trims and rich O2 readings. Ignition would raise HC, not CO specifically. Injectors or catalysts may contribute but not with matching pressure data. ASE emphasizes verifying fuel pressure against spec before condemning other systems.