P0304 (cylinder 4 misfire)

[MUDCVRD]

Has anyone experienced a P0304 (cylinder 4 misfire) DTC on 5.3 with AFM that was NOT caused by a stuck value, collapsed lifter, bad lifter solenoid or flat spots on the #4 cam lobes? I have an obvious misfire at idle which makes the engine stumble about every two seconds and I notice a slight RPM fluctuation on the tach. The fluctuation never changes more than 100 to 200 rotations. When it is revved up and held at any RPM it stumbles still, but is not as noticeable. I don't hear any valve-train noise, but while sitting in the truck, I can definitely feel it shaking.

While driving, I don't notice the anomaly AS much, but it is still present. Haven't pulled the #4 plug out yet, nor have I performed a compression or fuel pressure test with leakdowns.

I haven't had any DTC or DIC readings that indicated the traction control or stabilink was malfunctioning, only the P0304 #4 misfire, so I don't suspect, but cannot rule out a throttle body or TPS fault. Doesn't appear to be burning any oil either.

Has anyone ever solved the P0304 DTC with just a spark plug, coil pack or plug wire? I would rather not have to pull the top end off to fix a craptastic AFM issue.

 

 

**Update from today: I erased the P0304 DTC and drove it about 50 miles today. The misfire is not completely gone, but it has seriously improved. It did not activate the MIL. I'm inclined to think that it's probably not internal because it somewhat improved, I hope.

On another note, how many times must the ECM detect the anomaly before it activates the MIL? I seem to remember 3, but maybe there are more specifics to it than that.

[Dnt]

Probably just a fouled plug. Pic from my 2009 5.3 engine but it did use a good bit of oil. That plug had about 70000 miles on it. I cannot remember what the cylinder number was but seems like it was on drivers side maybe 2nd or 3rd one from the front. It fouled that plug more than once over the years.........

 

[Andy Seibel]

Just yesterday I took mine in for cylinder 7 misfire. I would have looked around more on my own, but I was in a hurry and its still under warranty, so I figured I'd drop the truck off and let them waste their time diagnosing.

 

They told me the plug wire was loose. They replaced with a new wire. I drove it home last night, no issues anymore.

[rdnkcpa]

Compression test on #4?

[Coby7]

 

Conditions for setting P0304

 

 

• DTC P0010, P0011, P0101, P0102, P0103, P0106, P0108, P0116, P0117, P0118, P0128, P0220, P0335, P0336, P0502, P1258, P3401, P3425, P3441, and P3449 are not set.

 

 

• The engine speed is between 650-6,200 RPM.

 

 

• The ignition voltage is between 11-18 volts.

 

 

• The engine coolant temperature (ECT) is between -7 and +130°C (+19 and +266°F).

 

 

• The fuel level is more than 10 percent.

 

 

• The antilock brake system (ABS) and the traction control system (TCS) are not active or detecting rough road.

 

 

• The power management is not active.

 

 

• The ECM is not in fuel shut-off, or decel fuel cut-off mode.

 

 

• Excessive drive wheel slip is not detected.

 

 

• Power Take Off is disabled.

 

 

• Cylinder Deactivation is not in progress.

 

 

• A manual transmission with a throttle position less than 95 percent.

 

 

• DTC P0300-P0308 runs continuously when the above conditions are met.

 

[MUDCVRD]

@MyFavTruck - That plug doesn't look that fouled! Ha

 

@coke813 - Thanks, I'll give the wires a good look.

 

@rdnkcpa - That's on my list.

 

@Coby7 - Does that mean all of those conditions must be met to activate the P0304 misfire DTC?

[tbarn]

yes. all conditions

[Coby7]

Got that info right ''OUT'' of the GM server maintenance manual. Cut and paste

[MUDCVRD]

Hook, line and sinker.

 

@MyFavTruck - Does this look familiar? Haha