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Help figuring out a misfire and misc codes

J

jrmac88

New member
I drive a 2002 gt. I was getting groceries today and everything was fine driving in, got back in the car to go home and it was vibrating like crazy and misfiring. I happened to be near a parts store so I checked the codes. Heres what I got:
p0128 (twice)- Something about the coolant temp being too low? I never replaced my Thermo on this car I'm thinking maybe its time.
P0300- Random multiple cylinder misfire
P0420 (twice)- below catalyst efficiency threshhold yada yada; I've had this ever since I replaced my cat with an aftermarket one someone suggested I add a spark plug defouler or some jazz to get rid of this.
P1811- Maximum adapt and long shift- something about taking too long to shift. This one confused me a bit my fluid was slightly low so hopefully topping it off will help
P0306- misfire cyl. 6

About a year and a half ago (when I got the car) I had a clogged cat. Before figuring this out I changed the plugs and wires. Not sure if this is relevant but the car was outside for the blizzard, it seemed fine during/after the storm. I cleared the codes when I got home, took it around the block and the only one coming back is the P0306. I'm thinking bad coil? I'll take a peak at the plug anyways. Probably wont be trying to fix this until tomorrow or the day after but any tips or advice is greatly appreciated. Thanks in advance.
 


I'd bet that the wire or the plug is shot. Since #6 wire can lay on the O2 sensor or manifold back there, it's possible it just melted the wire and is arching. Worst case, swap the coil w/ another and see if the miss follows since all the coils are the same. If it stays on #6 then you know where to look.

The P0420 is due to the high flowing cat.

P1811- Did you ever notice your car slamming into gears, even under light throttle? This is usually caused by a failing PCS solenoid. A trans fluid and filter change, a bottle of lucas stop-slip and a shift kit should help eliminate this.

P0128 could either be a faulty thermostat, or a bad Engine Temp. Sensor, which this is located under the thermo. neck in the LIM, kinda at an angle.
 
Thanks! I did notice the #6 wire was resting against some kind of sensor, it looked a little shanky. I haven't noticed the car slamming gears but its something to look out for. Rather than moving the coils can I Just swap the wires? I believe 3 and 6 are on the same coil, so if I put 6 where 3 is and 3 to where 6 is, and the misfire should move to cylinder 3 if its the coil.... right? I think they fire at the same time if they are on the same coil, but I could be mistaken.
 
Yes..if you swap 3/6 wires on the posts and the misfire moves, then it's the coil. It's not common for our coils to break in that manner though. This is because the coil fires both towers at the same time. Hence why our system is called a waste spark setup. One of the two cylinders is always firing on the exhaust while the other is on the compression.

More than likely it's the wire at the O2 sensor where #6 is touching.
 
Well, guess I'm just that kind of lucky. I swapped the wires and the misfire moved to 3. New coil fixed it.:th_scratchhead: I see what you guys are talking about with that #6 wire routed poorly, but mine were fairly new. Thanks for the help.
 
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