P0306 and P1404 on chuging 3800

G6superman

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Maybe its the picture but the gap seems excessive, are you using a wire gap gage?
The other thing is those are not the same type of plug, or again it's the picture, the one on the left has an extended center insulator compared to the one on the right. Use the correct AC-Delco plug for whichever engine you have 3.1 or 3.8.
Try swapping the coil for that cylinder with another to see if the P0306 goes away and you get a P030X.
Have you done a compression test?
The old plug is Bosch double platinum bought at autozone, according to them was correct plug and gapped at .060. When pulled out it gaps at .065 after about 5 years. The new plug is ac delco iridium 41-101 gapped to .060 with feeler gauge. I'll check full pack tonite. I did notice damage to wires on 4 and 6, but after replacing plugs and wires on all cylinders little change. Engine is 3.8L non supercharged vin K. A couple of friends have pointed me towards clogged catalytic or flat lobe.
 

melsg5

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clogged cat wouldnt cause only one cylinder to have a P030X. Dont know what year you have but if you have 3 coil packs switch the pack that is firing number 6 to a different position and compression test.
 

G6superman

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clogged cat wouldnt cause only one cylinder to have a P030X. Dont know what year you have but if you have 3 coil packs switch the pack that is firing number 6 to a different position and compression test.
I was taking to a buddy about that yesterday, we also found that the pcv valve has been in the car since it was new, 20 years, because it's hidden under the map sensor housing. I ordered a new map sensor and bought pcv valve, going to do those this afternoon. It's a 99 Chevy lumina LTZ 3.8L K vin, also worth noting it's from the Ottawa plant in Canada, seems like a ridiculous thing to add, but it mattered when it came to fixing a few things now, mostly electrical. We also have done recently a seafoam treatment though the vacuum lines.
 

G6superman

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Update replaced map sensor and pcv, checked again for vacuum leaks, swapped coils, plugs and wires (correct gap), oil and filter, air filter, seafoam treatment. All that's left is injector and egr valve, which I'll get tomorrow.
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G6superman

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*****Update*****
It was the egr valve, had a parts buddy of mine test the old one and said it was fine. Come to find out he never actually tested it, he just noticed the pin wasn't froze and assumed. New part installed and the misfire cleared in seconds and she smoothed out before the end of the drive. Thanks everyone that gave suggestions, you are greatly appreciated. I would have saved about 200 dollars if my friend had tested it but never hurts to replace old equipment. The car is rocking ac delco iridium's, duralast wires, a new map sensor, new air and oil filter plus oil change, 4 new falken tires. Ok wife literally just walked in from test drive, light did come back on for cylinder 6, but I could've fouled the new plug driving it to work this week so stand by while I check. Also could be phantom code from blowing out the built up crap over the past 2 weeks. Overall though installing egr valve made significant difference went from sounding like a tank to smooth idle le she used to. I will look into compression test, I don't have equipment.
 
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