Engine Misfire Detect p0304 - LS3 - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

JaysSS · 06-27-2023, 08:54 PM

Reaching out for some troubleshooting ideas.

When code comes i have noticed engine switches to OpenLoop and fueling swings +/-0.2 lamba. It strikes me that it swings both rich and lean. I have a Wideband on bank2, post-cat (pulled out stock O2 sensor). I have an AEM OBD2 scanner too, that's how i knew the Loop control mode.

So far i have swapped to different cylinders:
Fuel injector
Spark Plug
Coil Pack

New spark plug wire.

Spark plugs look fine and the few i have pulled all are in the same state of wear. All injector's looked fine.

Performed leak down on cylinder 4 and cylinder 1. ~1%. This mostly rules out mechanical.

On my radar to do next:
Put engine back together, run at idle and jiggle wires.
Flash ECU back to stock (via HP Tuners).

gtstorey · 06-28-2023, 08:59 AM

Do you have an auto or manual? Is #4 a DOD cylinder? You might have a failing lifter that would not show up with leak down test. I'm not sure if a broken valve spring would show an intermittent miss. Of course you didn't tell us anything about the car or how often it throws the code.

Could be wiring although a lot of times (but not always) it would throw other codes with it.

Very doubtful that reflashing to stock will do anything. Not really much in the tune that would affect only one cylinder, unless the others are misfiring also but just not quite bad enough to throw a code.

JaysSS · 06-29-2023, 05:55 PM

Verdict: new plug wire failed. Why? Likely heat from shorties or re-routed heater-core hoses. Noticed immediately when I started my "jiggle the wires" test.

My mistake was thinking "new plug wire, no way it's that!"; it was that...

Any suggestions for protecting from heat/rubbing? I have noticed that my plug wire sleeves are rather ragged, so those are getting replaced...

I could wrap the shorties, but they are a royal PITA the remove/install...
I could wrap the heater-core hoses, but also a PITA.

Short term -> keep a box of plug wires close by

It's an LS3, used to be my daily, now it's my road course, nice day out or 2003 Tahoe out of service car :-)

06-27-2023, 08:54 PM	#1
JaysSS Drives: 2010 Camaro 2SS RS Join Date: Dec 2017 Location: Palatine, IL Posts: 54 View My Garage	Engine Misfire Detect p0304 - LS3 Reaching out for some troubleshooting ideas. When code comes i have noticed engine switches to OpenLoop and fueling swings +/-0.2 lamba. It strikes me that it swings both rich and lean. I have a Wideband on bank2, post-cat (pulled out stock O2 sensor). I have an AEM OBD2 scanner too, that's how i knew the Loop control mode. So far i have swapped to different cylinders: Fuel injector Spark Plug Coil Pack New spark plug wire. Spark plugs look fine and the few i have pulled all are in the same state of wear. All injector's looked fine. Performed leak down on cylinder 4 and cylinder 1. ~1%. This mostly rules out mechanical. On my radar to do next: Put engine back together, run at idle and jiggle wires. Flash ECU back to stock (via HP Tuners).

06-29-2023, 05:55 PM	#3
JaysSS Drives: 2010 Camaro 2SS RS Join Date: Dec 2017 Location: Palatine, IL Posts: 54 View My Garage	Verdict: new plug wire failed. Why? Likely heat from shorties or re-routed heater-core hoses. Noticed immediately when I started my "jiggle the wires" test. My mistake was thinking "new plug wire, no way it's that!"; it was that... Any suggestions for protecting from heat/rubbing? I have noticed that my plug wire sleeves are rather ragged, so those are getting replaced... I could wrap the shorties, but they are a royal PITA the remove/install... I could wrap the heater-core hoses, but also a PITA. Short term -> keep a box of plug wires close by It's an LS3, used to be my daily, now it's my road course, nice day out or 2003 Tahoe out of service car :-) Attached Images

06-28-2023, 08:59 AM	#2
gtstorey Drives: 2010 Camaro SS2,L99, LSA SC Join Date: Aug 2017 Location: Huntsville, AL Posts: 2,450	Do you have an auto or manual? Is #4 a DOD cylinder? You might have a failing lifter that would not show up with leak down test. I'm not sure if a broken valve spring would show an intermittent miss. Of course you didn't tell us anything about the car or how often it throws the code. Could be wiring although a lot of times (but not always) it would throw other codes with it. Very doubtful that reflashing to stock will do anything. Not really much in the tune that would affect only one cylinder, unless the others are misfiring also but just not quite bad enough to throw a code.