← Back to list

1996 Chevrolet K1500 P0306 Misfire: Diagnosis and Solutions with Spark and Compression Confirmed

Model: 96 chevrolet k1500 Fault Code: P0306 Posted: 2016-10-30 06:55

I own a 1996 Chevrolet K1500 5.7L V8, and I'm experiencing a persistent misfire on cylinder #6, indicated by the OBD2 fault code P0306 (Cylinder 6 Misfire). I've already replaced the spark plug, wire, cap, rotor, and injector — all new components. A compression test shows 142 lbs on cylinder 6, which is within normal range. Spark is confirmed at the plug, so ignition is not the issue. I've tried installing a different ECM/PCM (Vehicle Control Module), but the problem persists. The vehicle runs with a noticeable miss on cylinder #6 and does not exhibit oil leaks or coolant loss. When I remove the spark plug, it appears black — suggesting recent sparking activity. The misfire is occurring despite having battery voltage (+B) at the injector control wire at the VCM (Vehicle Control Module). I've tested the control wire with a test light while the key is on and engine off: the light flickers when connected to battery positive, indicating that the driver circuit appears functional. I replaced the injector and its poppet nozzle (the small component at the end of the fuel line that opens under ~50 psi pressure). I suspect the issue may be related to a faulty VCM signal or an internal wiring fault in the injector control path. However, since replacing both the VCM and injector did not resolve the problem, I'm seeking further insight into potential root causes — especially whether the lower intake gasket could be contributing (though it seems unlikely based on current symptoms).

Related fault codes
P0306
Comments (13)
Anonymous 2016-11-03 17:06

Any suggestions or troubleshooting steps for a P0306 misfire in a 1996 K1500 with confirmed spark and compression?

Anonymous 2016-11-03 18:01

When the key is on and engine off, you should have battery voltage (+B) on the injector control wire at the VCM. Do you? If not, there could be a shorted or open control wire, or a faulty PCM driver circuit. To test: disconnect the VCM connector from the module and check for voltage at the control wire. If no voltage is present, then use a test light connected to battery positive and probe the injector control wire at the VCM connector — if it lights up, there's likely a short to ground in the control wire between the injector and VCM.

Anonymous 2016-11-03 18:04

If the test light does not illuminate when connected to battery positive and there is no voltage on the injector control wire at the VCM with the key on, then the issue could be an open circuit between the injector and VCM, a faulty injector winding, or an open feed circuit to the injector.

Anonymous 2016-11-05 16:56

I do have battery voltage (+B) at the VCM connector for cylinder #6. I've checked all components — spark plugs, wires, cap, rotor, and injector — and they are all new and properly installed.

Anonymous 2016-11-05 20:29

With +B present on the control wire at the VCM, take a test light connected to battery positive and probe the control wire while the engine is running. The test light should flicker — this indicates that the PCM driver circuit is functional. If it does not flicker, then there may be an issue with the PCM pin at the VCM connector or a faulty PCM driver.

Anonymous 2016-11-06 07:14

I've performed that test and the result is positive — the test light flickers. I’ve also replaced the VCM, but the problem remains. All components including the injector and poppet nozzle have been replaced.

Anonymous 2016-11-06 07:17

No oil consumption or coolant loss. No visible leaks from the engine. The spark plug appears black — consistent with recent sparking activity only.

Anonymous 2016-11-06 16:56

You have +B on the injector control wire at the VCM for cylinder #6. Do you have proper control signal? That means: connect a test light to battery positive and probe the control wire at the VCM connector. The test light should flicker if the driver is working. If everything were functioning correctly, the injector would be spraying fuel into the cylinder. All the details mentioned in this post are accurate — did you replace the poppet nozzle when changing the injector?

Anonymous 2016-11-08 12:34

What is a poppet nozzle? I replaced the entire injector unit.

Anonymous 2016-11-11 15:39

Clarification needed on the poppet nozzle and its role in fuel delivery.

Anonymous 2016-11-14 19:32

The poppet nozzle is a small component at the end of the injector hose that opens under approximately 50 psi pressure. It acts as a check valve to allow fuel flow into the cylinder when pressure builds.

Anonymous 2016-11-17 19:53

I replaced both the injector and the poppet nozzle — I now suspect it might be related to the lower intake gasket, though I don’t see how that would prevent fuel injection.

Anonymous 2016-11-18 19:30

A blown or faulty lower intake gasket is unlikely to cause a misfire on cylinder #6 if the injector is receiving proper voltage and signal. The issue may lie deeper in the VCM, wiring, or fuel delivery system.