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In ignition waveform analysis, a low firing voltage combined with an extended burn time indicates that the spark easily initiates and sustains combustion, which is typical of a rich mixture. Rich mixtures contain more fuel, making it easier for the spark to ionize the gap, resulting in lower firing voltage. Conversely, lean mixtures require higher firing voltage and often have shorter burn times. A wide spark gap would increase firing voltage, not decrease it. Weak coil output would present as high firing voltage demands with misfire tendencies. ASE emphasizes waveform analysis as a key diagnostic tool, teaching technicians to interpret voltage and duration patterns accurately. Recognizing mixture conditions through ignition waveforms allows technicians to isolate whether misfires are fuel or ignition related, a vital skill in advanced engine performance troubleshooting.

Simultaneous misfire on paired cylinders in a DIS/waste-spark setup points directly to the shared coil. PCM, plugs, or fuel rail would not explain paired misfires. ASE emphasizes recognizing shared components in paired-cylinder misfires for efficient troubleshooting.

If fuel pressure is stable but the mixture is lean under boost, the PCM may be under-fueling because of incorrect airflow reporting. A faulty MAF sensor that underestimates airflow will cause insufficient injector pulse width. A restricted intercooler or dirty air filter would restrict airflow but also lower boost, not directly lean the mixture. A weak fuel pump would lower pressure, but here pressure is stable. ASE emphasizes comparing calculated vs. actual airflow to confirm MAF accuracy, a key skill in diagnosing boost-related lean conditions.

If all injectors drop less than normal, they’re not getting enough fuel volume, despite correct pressure. This points to a clogged filter or line. MAF issues skew airflow readings, not injector balance. Throttle bodies affect idle, not volume. PCM faults don’t limit all injector balance equally. ASE stresses using both pressure and balance tests for systemic faults.

High backpressure indicates exhaust restriction, most often a plugged catalytic converter. TPS, ignition, or injectors don’t create excessive backpressure. ASE stresses mechanical confirmation of restrictions.