2021 Chevrolet Silverado 5.3L Cylinder 5 Misfire Diagnosis
I have a 2021 Chevy Silverado 5.3L with a consistent misfire on cylinder #5. I’ve already replaced the plug wires and the spark plug (the old plug was consistently fuel-soaked). I swapped the coil pack with cylinder #3 and the misfire stayed on #5. I also replaced injector #5. I can visibly see spark when testing the coil while it’s running, and compression on #5 while cranking is about 160 psi. Given these results, what are the most likely remaining causes and the next best diagnostic steps to isolate why cylinder #5 is still misfiring?
You’ve covered the basics well: spark, plug, coil, injector, and compression all check out solid on cylinder #5. The fact that the misfire stays on #5 after swapping coils and replacing the injector points away from ignition and fuel delivery. Compression at 160 psi is decent, so mechanical failure like a bad valve or piston ring is less likely but not impossible.
Most likely causes now are timing-related sensor issues or valve problems that don’t show up in a static compression test.
Most likely culprits
- Camshaft Position Sensor or Timing Signal Issue: If the cam sensor or its circuit is faulty, the ECM may mistime injector or ignition events on cylinder #5.
- Valve Lash or Valve Damage: A valve that’s sticking or burnt can cause intermittent misfire even with decent compression.
- Wiring or ECM Ignition Control Circuit: Less common but possible if the coil is getting spark but timing is off or intermittent.
How to narrow it down
- Scan for codes and live data: Check for camshaft position sensor codes or misfire codes with freeze frame data. Look at cam/crank correlation.
- Perform a running compression or cylinder leak-down test on #5: This can reveal valve sealing issues missed by static compression.
- Check camshaft position sensor wiring and connector: Look for corrosion, damage, or loose pins.
- Swap camshaft position sensor with a known good unit if possible: See if misfire moves or clears.
- Use a lab scope or scan tool to monitor ignition coil firing and injector pulse on #5: Confirm timing and duration match other cylinders.
- Inspect valve train on cylinder #5: If accessible, check rocker arms, lifters, and valve springs for damage or looseness.
- If all else fails, consider ECM or wiring harness faults: This is a last resort after mechanical and sensor checks.
Possible parts
- Camshaft Position Sensor (only if scan data or wiring checks indicate fault)
- Valve components (rocker arm, lifter) if valve train damage is found
- Wiring harness repair or ECM replacement only if confirmed by diagnostics
A few questions
- Are there any stored or pending trouble codes related to camshaft position or misfire?
- Have you checked the wiring harness and connectors for cylinder #5 coil and injector for damage or corrosion?
- Does the misfire occur under all conditions or only under load, idle, or certain RPM ranges?