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So my Trailblazer seems to have developed an intermittent, yet severe misfire. Only seems to happen at idle when in drive, or right when i take off from a dead stop. Car had a ported throttle body for almost a year, I put the stock one back on after this issue popped up. I pulled the passenger valve cover and the rockers are tight so I don't suspect a stuck lifter, nor is there any ticking or knocking from the motor except when cold, and it goes away once warm. Plugs were changed a little over two years ago, and have maybe 25k on them. Any ideas on where best to start?
You are sure it’s number 6 from a datalog I suppose? How does plug look on that cylinder? Check the basics first like a connector with a pin issue for that coil pack, etc. Also check all grounds. Thermal variations can have effects on little things like that. Go back over the manifold bolts as well. Check all the smalls before you dig in. It’s usually something simple.
Pull the coil and plug on #6. If the plug looks ok and isn't carbon tracked, swap it to another cyl anyway, see if your miss follows. If it doesn't, swap #6 coil with any other and see if the miss follows.
You are sure it’s number 6 from a datalog I suppose? How does plug look on that cylinder? Check the basics first like a connector with a pin issue for that coil pack, etc. Also check all grounds. Thermal variations can have effects on little things like that. Go back over the manifold bolts as well. Check all the smalls before you dig in. It’s usually something simple.
Yeah. I had an issue almost a year ago where the check engine started flashing. Was only a few miles from home so I limped it there and hooked up my scanner. Misfire history showed something like 35k misfires on cylinder 6, but the issue resolved itself the next morning and hasn't returned. Now it's just a miss here and there, not enough to set a code or anything, but when it misses it feels like someone is hitting the car lol.
I had a spare bracket with coils from a different car so I swapped those out but the issue remains. I did clean the one ground on the front of the passenger head, but the rest of my grounds are aftermarket (I have a big audio system in the car). I'll pull the plugs and retorque the intake tomorrow and see what happens.
So I pulled all the plugs on the pass side, this is what I found.
Here's cyl 2:
Cylinder 4
cylinder 6
cylinder 8
Cylinder 6s spark plug wasn't fully torqued, i was able to unscrew it by hand (as evidenced by all of the carbon on the threads of number six) and the wire absolutely jusr fell apart when I went to pull it off the plug. Im not a spark plug guru, but my assumption about the node on the spark plug being basically gone is overheating due to a leaner mixture since the plug wasn't sealing fully?
Maybe someone with more plug knowledge can chime in. As of now oreillys is closed but im going there in the morning and getting new plugs and wires. These were ngk tr51x, should I change to a different plug? A little disappointed these only lasted 30k.
Install NGK 3784 double platinum for best performance/life. For future ref, spark plug and wire is the first place to start with on a misfire. In general, spark plugs are always a "go to" when dealing with run issues that aren't obvious. Gives you most insight in what's going on in the CC. Hope this helps.
03-09-2021, 05:45 PM
Misfire LH6 cyl 6 
