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-   -   Po302 Misfire (https://www.cobaltss.net/forums/problems-service-maintenance-69/po302-misfire-327524/)

05misfire 03-17-2019 10:20 PM
Po302 Misfire
 
My 2005 lsj has a P0302 cylinder 2 misfire. It is tuned for 94 octane and I ended up having to put a full tank of regular 87 with STP octane booster to bring it up to a reasonable octane level. (I know I shouldn’t have put regular but I was far from home) about 4-5 hours down the road I started to get a misfire (blinking check engine light). I burnt about half the tank of regular then topped up with 94 octane and it stopped misfiring for about 10 minutes. Then I took it downtown and it started misfiring again and hasn’t stopped since yesterday. I tried wiggling the injector harness and no change, any advice to where I should go from here would be great! It has NGK 1 step colder plugs and zzp stage 3 kit with 60lbs injectors with zzp coils as well

jdbaugh1 03-18-2019 08:23 AM
Hopefully you didn't get into the boost much when you had 87 octane in the tank. I would run the car and then pull the spark plugs and compare them to cylinder 2. With it being specific to cylinder 2 you essentially have 3 possibilities for what is wrong, fuel, spark, or low on compression.

ECaulk 03-18-2019 09:40 AM
I'd rule out the fuel as it is a single cylinder misfire, but not rule out that the injector could be fubard. First step, look at the plugs and try swapping cylinder 3 with cylinder 2 (spark plug only). If the misfire moves you need spark plugs, if it doesnt try moving the coil pack to a different cylinder. If it doesn't move it's time for a compression test and leak down.

Sharkey 03-18-2019 03:18 PM
myself, id go straight for a compression test, but thats just me. do a compression test and then swap 2 and 3 plug around and see what happens, if the problem doesnt move to 3 then swap 2 and 3 coil, if the problem still doesnt move you can try swapping injectors around.

05misfire 03-19-2019 02:00 AM
Po302 misfire gone
 
Originally Posted by jdbaugh1 (Post 7708775)
Hopefully you didn't get into the boost much when you had 87 octane in the tank. I would run the car and then pull the spark plugs and compare them to cylinder 2. With it being specific to cylinder 2 you essentially have 3 possibilities for what is wrong, fuel, spark, or low on compression.
Originally Posted by ECaulk (Post 7708785)
I'd rule out the fuel as it is a single cylinder misfire, but not rule out that the injector could be fubard. First step, look at the plugs and try swapping cylinder 3 with cylinder 2 (spark plug only). If the misfire moves you need spark plugs, if it doesnt try moving the coil pack to a different cylinder. If it doesn't move it's time for a compression test and leak down.
Originally Posted by Sharkey (Post 7708813)
myself, id go straight for a compression test, but thats just me. do a compression test and then swap 2 and 3 plug around and see what happens, if the problem doesnt move to 3 then swap 2 and 3 coil, if the problem still doesnt move you can try swapping injectors around.
The misfire has gone away after driving for roughly 10 more minutes to drain the rest of the regular gas out.

jdbaugh1 03-19-2019 08:10 AM
Originally Posted by 05misfire (Post 7708823)

The misfire has gone away after driving for roughly 10 more minutes to drain the rest of the regular gas out.
You could of had some water in your fuel or something. 87 by itself should cause misfires under low load cruise conditions.


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