ENGINE PERFORMANCE • UNIT 2 • LESSON 2

Starts, Then Stalls

The Challenger’s diagnostic decision lab: capture the moment that running changes to stalling, compare independent evidence, and identify the system that stopped supporting combustion.

Diagnostic mission

The engine starts and runs, then stalls. Does it lose idle airflow, receive unexpected EVAP vapor/airflow, lose fuel pressure, or lose its crankshaft reference? Four service tickets share a complaint but fail at different times and for different reasons.

Teaching model, not OEM specifications. Timelines, pressures, voltages, RPM values, and test results are illustrative. On real vehicles, capture freeze-frame and live data during the event, follow manufacturer service procedures, and use appropriate fuel, electrical, and moving-part safety precautions. Do not disconnect fuel lines or defeat emissions systems based on this exercise.

1 · Select a service ticket

CUSTOMER COMPLAINT
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0 / 4 solved0 tests recorded

2 · Capture the stall

Select a moment or run the short simulated event. Compare what is normal before the fault with what changes at the stall.

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Crankshaft-reference trace (schematic)

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RPM and CKP trace are two clues, not two independent physical measurements: scan RPM may be derived from the CKP signal.

3 · Select diagnostic tests

Test results describe the selected ticket at its failure point unless specified. The live-data snapshot captures your selected timeline moment.

Evidence collected

No tests yet

4 · Evidence log

  1. Choose a test to record evidence.
The Challenger asks: Does “engine stalled” prove the fuel pump is defective? Which signal changed first, and what independent measurement would you use to separate a pump-feed fault from a lost CKP reference?

5 · Defend the diagnosis

6 · How to think about a stall

Observed changeWhat to investigate next
Runs with light pedal input; dies at closed throttleIdle-air strategy, throttle condition, vacuum leaks, and load response; avoid assuming a specific failed part.
Starts after refueling; unexpected purge flow when commanded closedEVAP purge sealing and approved isolation/functional tests; investigate mixture clues as supporting evidence.
Fuel pressure falls after pump supply disappearsSupply/ground/control circuit before replacing the pump.
CKP reference vanishes; spark and injector commands ceaseCKP waveform, circuit integrity and related inputs; rule out a shared ECM-power issue.

Important: During startup and some fault states, fuel-trim readings may be unavailable, frozen, or unrepresentative. Never diagnose a brief stall from fuel trims alone.

Learning check: what should be captured first?

When an engine starts normally and stalls only after warming up, which record most directly helps separate a fuel-feed failure from a lost CKP reference?