Malibu Misfire!

[Shaun Bass]

I have a 2008 Malibu LTZ with a misfire under load on #4 and intermittent on #3 , changed plugs, the coil packs, and checked for intake leaks. Also did a compression test, no more miss on #3, But #4 is still there. Codes : P0304, P0300.

Topic

[Mike]

The 08 Malibu came with 5 different engine choices.
To get helpful replies, it’s best to tell us which engine yours has.
Not everyone is familiar enough with the model to know which trim levels came with which engines.

[Shaun Bass]

3.6 VVT Transverse

[Mike]

Did the compression test show all cylinders roughly equal ?
No pooled oil in the spark plug well to short out the plug?
Which plugs did you install?

If you haven’t already checked, make sure there isn’t a fuse that controls Injector #4 or Coil #4.

I’d get a spray can of Mass Air Flow Sensor cleaner (not carb cleaner or other type of cleaner) and clean the MAF sensor hot wires, since you’re getting a general misfire code (P0300) in addition to the P0304.

Check the wires for the #4 injector and for the coil to be sure each is getting power and ground.
Next up to to swap the injector for #4 to another position and see if the misfire moves with the injector.

You could try running a bottle of Techron complete concentrated fuel system cleaner (not the weaker fuel injector cleaner).

Fuel pressure check would be a good idea, too.

[Shaun Bass]

Mystery solved, I had someone sit in the car and hold the RPM at 2500 for about a minute, then sprayed throttle cleaner around the intake. Leak at #4. Turns out that I couldn’t find it with the engine at idle. Thank you for all the tips though. I did try them all and found that the miss stayed on #4 which prompted the mid-range RPM test.

[Mike]

Glad you found the cause.
Appreciate you posting again.
Nothing worse than an unsolved mystery!

[Author]

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