The P0300 - with a twist.

[Danny-VE]

Hello everyone,

Have a bit of a problem with a continuous P0300 error code and the check engine notification with no other code.
Car is a 2011 VE 3.0L Omega Sedan.

Here is the tricky part:

Initially I believed that it was from the timing chain as the check engine light came up under multiple conditions. I got that replaced about 2 months ago.
Most of the check engine problems have resolved except under one particular circumstance, when engine braking.
As I am going down the freeway, I move to sequential mode, I place the car in 3rd gear and let it maintain the speed, with RPM sitting at about 3000 all of the sudden check engine light comes on, Traction Control Off, keeps beeping like crazy until I put it in normal gear and accelerate a bit and then it goes away. No change in feeling or drive.
Check ECU and get P0300.

Mechanics did the simple things like new spark plugs, cleaned valves, timing chain... but I am wondering if there could be anything else that they have not checked that could affect the car only in the above circumstances.

What I have noticed that has developed:

1. Around the 2500-3000 RPM mark I can head a sound coming from the engine that I would compare it to something like two plastic geared wheels slipping on each other or like a chain slipping on a geared wheel. Below those RPM is disappears and above the engine sound could be louder.

2. Starting the engine, it hold a high Idle for about 15 -20 seconds which I find a bit long for a modern car. Would that be normal?

3. Very strong hissing sound, pointing to a vacuum leak but I know that it would affect mostly the idle, nothing to do with high RPM.

Anyone has any idea what I can check next?

Any information if highly appreciated.

 

[DAJOKER]

Basically this P0300 code means that the the car's computer has detected that not all of the engine's cylinders are firing properly. A P0300 diagnostic code indicates a random or multiple misfire. ... Unfortunately, a P0300 doesn't tell you specifically which cylinder(s) is/are mis-firing, nor why.
OBD-II Trouble Code: P0300 Random/Multiple Cylinder Misfire Detected

https://www.obd-codes.com/p0300

 

[Danny-VE]

Basically this P0300 code means that the the car's computer has detected that not all of the engine's cylinders are firing properly. A P0300 diagnostic code indicates a random or multiple misfire. ... Unfortunately, a P0300 doesn't tell you specifically which cylinder(s) is/are mis-firing, nor why.
OBD-II Trouble Code: P0300 Random/Multiple Cylinder Misfire Detected

https://www.obd-codes.com/p0300

Hey DAJOKER, thank you for the reply but unfortunately I have done quite a bit of research in this matter and I know what the codes are and what the common symptoms are. That is what led me here, mine does it only in that particular scenario but seems to be running great the rest of the time.

I am hoping that someone here came across this or heard someone else that had the similar problem.

 

[ZXTC]

I would check all your spark plug leads are on tight. Had this issue before. Simple fix.

 

[Fu Manchu]

I would check all your spark plug leads are on tight. Had this issue before. Simple fix.

Doesn't have leads. It's a coil on plug design.

 

[Fu Manchu]

According to Holden these are what can set a P0300

"• A misfire DTC could be caused by an excessive vibration from sources other than the engine.

Inspect for the following possible sources:

- A tire or wheel that is out of round or out of balance

- Variable thickness brake rotors

- An unbalanced drive shaft

- Certain rough road conditions

- Transmission operation

- A damaged accessory drive component or belt

• High resistance in the circuits of the injectors could set a misfire DTC without setting an

injector DTC. Test the injector circuits of the affected cylinder(s) for a high resistance if you

suspect a condition."

There should be a freeze frame data file stored when the code is set. Can you access that?

 

[Fu Manchu]

Make sure all the accessory drive components are going ok. If the belt is not aligned correctly a misfire code can be set.
You can run the car with the belt off a short bit. Heaps of codes will be set, but you'll then know if the hiss is engine or accessory.

Check vacuum lines and connections regardless. Soapy water is safe enough.

Make sure the PCV isn't gunked up. I think Holden suggest a pipe cleaner soaked with carby cleaner is suitable down the hole. (PCV in the drivers side valve cover)

 

[Immortality]

Does this engine use much oil?

You say it only happens when engine braking? Possibly a PCV issue, engine braking creates the highest vacuum condition of any of the driving modes, if there is a PCV issue you may be getting oil contamination into the intake causing fouling and misfire condition. I always recommend a catch can system be installed regardless of vehicle use/age. Oil in the intake/combustion chamber is never a good thing.