Diagnosing the misfire codes P0306, P0302
 

My truck decided to have some issues last weekend coming home from a friends house on Thanksgiving.

After being on the road for about an hour the truck shuddered, lost speed and was incredibly sluggish trying to get up the hill. It flashed the CEL and then went out. I was doing about 75 with the cruise on.

After slowing down to about 60 it stopped the shuddering and resumed operations as normal. Until about 20 minutes later when it repeated the above.

The next day I grabbed my reader and found the P0302 and P0306 codes. I cleared the codes and took it for a "test" drive up and down the mountain to see if it would trip the codes again. It didn't flip the codes. I thought I might have been dealing with a "one off" issue and left it alone for a few days.

Two days ago the CEL light came on and stayed on this time. Sure enough P0306. Cylinder 2 did not throw a code this time. After doing some research on here I ordered two new COPs and bought a mechanics stethoscope and some new spark plugs just in case.

The stethoscope confirms that cylinder 6 is having some issues. The COPs came in today so I'll take it apart tomorrow and see what I see. I'll be looking at both the COPs and the plugs to see what may be causing the problem. The "nice" thing about this is that at least it's one of the easier COPs to get to.

Should be a nice day for working on the truck.

The little woman has the same issue with her Equinox, put in a new EGR "electric type" and plugs with wires. Fixed. Enjoy.

I got into the truck today and pulled out the spark plug on cylinder 6 and this is what I saw.

A side by side comparison of the plug I took out and a new one.
http://i301.photobucket.com/albums/n...s/P1040296.jpg

I think this was the problem. However, this is the original COP
http://i301.photobucket.com/albums/n...s/P1040298.jpg

I don't think this is bad but I had a new one already so I replaced it anyways. I'll keep this in my spare parts bucket 'cause ya just never know.

I took it on a 45 min test run up and down the mountain and don't seem to be having any issues so far. Next up will be a long run to see if the symptoms return. The mechanic's stethoscope reports that the bad knocking from this cylinder is no longer there so fingers crossed.

On a side note, [rant] Who the :-X09 designed the motor to be so far back in the engine compartment? I'm glad I only had to do this on the easy to reach plugs. I couldn't imagine the frustration at trying to get at the back plugs. Now that I think about it, how DO you get to the back ones? It's almost like you have to take the dash off to reach them. That looks to be an exercise in :-banghead and :-X01ok. [/rant]

Plugs aren't that bad, I've seen alot worse. The hardest one is I think it's #8 - the back one on the passenger side. Remove the computer and it's mounting bracket which is easy and you can get to the plug with no problem. Looks like your plug was bad for sure I had a similar problem. If the plugs aren't too old I'd replace the one in # 2 also. If they have some miles on them replace them all. Save that COP I doubt it's bad.

That plug was loose thats why its discolored and the COP has soot on the boot. The cylinder leaned out and burned the plug up.

mine is having the same problem. however I assumed it was the cam phasers but while i'm replacing them, I might has well change the plugs and cop's

Yeah so that's interesting...

I had the plugs replaced by my mechanic, who, shall we say didn't believe that I knew more than he did when it came to these trucks. They did the spark plug change and didn't torque them properly. Enter the nasty gas smell into the truck. I did my research, took it back to them and told them to torque them. They said "we did". It still smelled of gas in the truck so I broke down and went to the dealer. The dealer torqued them and the gas smell went away.

So, my question is... If the dealer torqued them fixing the gas smell how could the plug be loose? Just trying to understand what's going on so I can fix it and stop it from happening again.

Get a mechanic's stethoscope (about $10 from any auto parts store and by far the best diagnostic tool I've ever purchased) and touch it to all the cylinders. If you've got any bad misfires or anything you should be able to pin point which one is giving you the problem with the stethoscope.