Code
P0284
HUMMER
P — Powertrain
Cylinder 8 Contribution/Balance Fault
AI status
Completed
Completed
100%
Causes
- Faulty fuel injector for cylinder 8 (stuck, leaking, clogged, or electrically open/short)
- Ignition fault on cylinder 8 (bad coil/coil pack, spark plug, or plug wire)
- Low compression or mechanical failure in cylinder 8 (valve, piston, rings, head gasket)
- Wiring or connector fault to injector or ignition (open, short, high resistance, corroded)
- Low or fluctuating fuel rail pressure or fuel trim issues
- Intake air metering problem (MAF/MAP) or vacuum leak affecting cylinder balance
Symptoms
- Malfunction Indicator Lamp (MIL/CEL) illuminated
- Rough idle or visible shaking at idle
- Misfire detected or misfire count on cylinder 8
- Reduced engine power or hesitation under load
- Poor fuel economy and increased emissions
- Possible fuel smell (if injector leaking)
What to check
- Read all stored and pending codes plus freeze frame data with a capable scan tool
- Record misfire counts by cylinder and monitor cylinder contribution/balance PIDs or tests
- Check short-term and long-term fuel trims and compare with load/idle conditions
- Inspect wiring and connectors at cylinder 8 injector and ignition coil for damage, corrosion, or looseness
- Measure injector resistance and compare to specification; check for injector activation on a scope or with a noid light
- Scope ignition primary/secondary waveforms or swap coils/plugs with another cylinder to see if issue follows component
Signal parameters
- Injector resistance (ohms) — compare to factory spec for that vehicle
- Injector pulse width (ms) at idle and under load as seen on scan tool or scope
- Short-term and long-term fuel trim (%) at idle and load
- Per-cylinder misfire counts and cylinder contribution % (scan tool PID)
- Ignition coil primary voltage/current waveform and secondary spark waveform
- Fuel rail pressure (kPa or psi) and regulator response under load
Diagnostic algorithm
- Verify the complaint and capture freeze-frame / live data. Note misfire counts and whether P0284 is current or intermittent.
- Clear codes and re-run engine to see if P0284 returns and observe which conditions trigger it (idle, cruise, load).
- Visually inspect wiring/connectors for cylinder 8 injector and coil. Repair any damaged wiring or poor connections. Retest.
- Swap the cylinder 8 injector with another cylinder’s injector (or swap coil/plug) and re-scan: if the code/misfire follows the component, replace the faulty part.
- If swapping components does not move the fault, check injector operation with a noid light or oscilloscope to confirm pulse and waveform. Measure injector resistance.
- Check ignition: inspect/replace spark plug, test coil with scope or known-good coil swap. Verify strong, consistent spark at cylinder 8.
- Perform a compression and/or leak-down test on cylinder 8 and compare to other cylinders. Repair mechanical faults if compression is low.
- Test fuel pressure and flow; inspect fuel rail and pressure regulator. If fuel pressure is low or unstable, repair fuel supply before continuing.
- Check MAF/MAP, vacuum lines, and intake for leaks or restrictions. Fix any air metering or vacuum issues and retest.
- Verify cam/crank timing and check for related timing codes. Repair timing or sensor issues as required.
- If all hardware checks pass and wiring is verified, consider ECM/PCM testing or reflash as a last step (follow manufacturer procedures).
- After repair, clear codes and perform a road test with live-data monitoring to confirm cylinder 8 contribution is within expected range and code does not return.
Likely causes
- Faulty fuel injector for cylinder 8
- Ignition component failure on cylinder 8 (coil or spark plug)
- Mechanical issue (low compression or valve problem)
- Wiring/connectors for injector or coil on cylinder 8
- Fuel pressure or fuel trim problem causing poor injection
Fault status
Status
MIL on. ECM detected cylinder 8 contribution/balance deviation from expected values and stored code P0284. Freeze frame and live data captured when fault occurred.
Repair difficulty: Medium
Diagnostic time: 1.0 - 3.0 hours
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