misfire......only under certain circumstance

[one1]

So for 2 days in a row while in 5th gear on the freeway my valves have started to chatter wildly and loudly when I put my foot on the throttle, then it will go away...... down the road it will do it again. Threw a code yesterday misfire on cyl 4. Doesn't do it around town. Didn't do it going up a steep mountain for 5 minutes of ascension. Just does it on the freeway randomly. Seems like when I am going down the road for a bit it loses fire on at least that cyl... I was thinking maybe one of the coil packs is going down. The timing is sketchy though on when it chooses to misfire.

 

[one1]

Mystery solved, These two plugs are from cyl #2

This is the third AP104 Autolite plug to fail on me in 3 months. All different issues in different cyls, but all insulator failure.

 

[Mark_88]

Hmmmm...I just had a similar problem with #2 cylinder...my plug (one only) was so bunged up with crud it could barely fire...just cleaned it up and it runs much better...

With my engine, I'm looking at possible issues with the valve seals...hopefully that's all it is...

With yours...it could mean you need to run a higher temp plug...if they are failing in different cylinders in a similar fashion then it means the heat in your combustion chambers exceeds the plug rating...

 

[one1]

I just put a new head gasket, timing belt, plugs, wires, etc done at 150k, which was 3k miles ago..... no idea if relevant.

 

[Mark_88]

Depends on whether this was happening before you did the work or not...if it wasn't happening before then it could mean either something has changed in the dynamics of the combustion or the plugs are simply not the right ones for this engine..