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Madison 7/26/2019

2008 Buick Lucerne CXL 6 Cyl 3.80L


I have a miss in my 6th cylinder.

I had a miss in the 5th cylinder so I changed all the plugs and wires and the 2&5 ignition coil, after doing that I ran a scan and now there is a miss in the 6th cylinder so I changed the ignition coil for that position also but I still have a miss in the 6th cylinder. What else could be causing this.

1 Answer


Jimm 7/27/2019

P0306 = Cylinder 6 Misfire Detected

Conditions which promote storage of a P0306 fault code are likely to cause catalytic converter and/or engine damage. This code should be classified as severe.

Symptoms may include:

Diminished engine performance
Rough or unstable feeling from engine (at idle or under light acceleration)
Odd odor from engine exhaust
Flashing or constant MIL (malfunction indicator lamp) illumination

A code P0306 may mean that one or more of the following has happened:
Defective ignition coil(s)
Bad spark plug(s), spark plug wires, or spark plug boots
Faulty fuel injector(s)
Malfunctioning fuel delivery system (fuel pump, fuel pump relay, fuel injectors, or fuel filter)
Major engine vacuum leak
EGR valve stuck in the wide open position
Clogged EGR ports

Diagnosis & Repair Steps:
A diagnostic scanner, digital volt/ohmmeter (DVOM), and a reliable vehicle information source will be required to diagnose a stored (or pending) code P0306.
Begin your diagnosis with a visual inspection of the affected ignition coil, spark plug, and spark plug boot

Components that are contaminated with liquid (oil, engine coolant, or water) must be cleaned or replaced.
If the recommended maintenance interval demands (all) spark plug replacement, this is a good time to do it .

Inspect primary wiring and connectors, for the ignition coil in question, and make repairs as necessary Key-on-engine-running (KOER), listen for the presence of a large vacuum leak and make repairs if necessary.

If lean exhaust codes or fuel supply codes accompany the misfire code, they should be diagnosed and repaired first.
All EGR valve position codes should be rectified prior to diagnosing a misfire code.
Insufficient EGR flow codes should be addressed before diagnosing this code


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