Cruze 1.4T misfire (with carnage pictures)

[sciphi]

My Cruze had a miss right around 3000 RPM that had been there for a few months, but only under 10 PSI boost or more. I originally attributed it to its aftermarket tune not having enough flexibility to adapt to the constantly changing weather and gasoline at this time of year. It was also coming up on a spark plug change interval. Mileage is 120,000 miles. So it's had a good long run.

Last night the car started shaking at idle and disabled traction and stability control. A scan showed a code P0304 (cylinder 4 misfire) as pending, but no CEL was lit yet. I limped the car home, popped the hood, and heard a faint sound of electrical arcing. This is what I found:

How to read the coil pack: Cylinder 1 is the left, cylinder 4 is on the right:



I did spill some oil onto that cylinder 4 coil a long time ago during an oil change, and that spark plug subsequently loosened itself up over the course of a few thousand miles. Not the factory's fault, I was in there messing with the plugs early in the car's life. So that coil #4 has seen some things it shouldn't see.

With the cylinder 4 boot removed:



Yep, that's a weak area in the plastic of the boot. It got poked and the plastic crumbled into dust.

Comparison to cylinder 3 coil:



So there's the culprit. $150 later for 4 new plugs (since it was due) and a new coil, no misfire.

 

[Kool1]

It's always nice to fix something yourself, know why it happened, and to experience job satisfaction!!

 

[CT8]

When are the plugs supposed to be changes? I wonder if the spark was finding the easiest place to jump?

 

[Ram01]

Change the assesory belt also good work

 

[friendly_jacek]

so, why was the color change? oil or arcing?

 

[KGMtech]

Was that GM parts pricing?

 

[michaelluscher]

That 4 coils in 1 unit looks similar to the Saab DIS coil they used

You can't replace individual coils, right?

Have to buy all 4 in the unit?

 

[sciphi]

To respond to everybody who's posted so far:

Originally Posted By: Kool1
It's always nice to fix something yourself, know why it happened, and to experience job satisfaction!!


Indeed!

Originally Posted By: CT8
When are the plugs supposed to be changes? I wonder if the spark was finding the easiest place to jump?


OEM change interval is 100k miles. With the tune I have, I change them at ~60k mile intervals. They were last changed at ~60k miles, so it was due. The interior of that coil was also pretty nasty, with a lot of gunk on the metal spring that conducts electricity to the plugs. So the spark likely found a faster way of going to ground.

Originally Posted By: Ram01
Change the assesory belt also good work


Thanks! Belt is supposed to be done at 150k miles. The belt looks better than some other belts I've replaced with far less mileage on them.

Originally Posted By: friendly_jacek
so, why was the color change? oil or arcing?


Probably the color changed initially because of oil spilling, and then due to spark as the dried-out rubber degraded as an insulator.

Originally Posted By: KGMtech
Was that GM parts pricing?


$150 was $120 for the coil from a local parts house that specializes in GM parts, and $30 in new iridium spark plugs.

Originally Posted By: michaelluscher
That 4 coils in 1 unit looks similar to the Saab DIS coil they used

You can't replace individual coils, right?

Have to buy all 4 in the unit?


Correct, the whole unit needs to be replaced for a failure.

I drove the car all around today and it was fine. Glad to see the misfire gone.