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Something going on in with Cylinder 3 (Misfiring)

I

ice334

New member
Ok , my car didnt have any misfires until after i changed my Lower Intake Manifold Gaskets. After changing the gaskets and putting everything back together. The car ran fine. The next day i took it an hour and 30 min away, while driving there it started misfiring and shaking,rough idle at an hour into the trip. The check engine light went to blinking. The Next day i drove it all the way back home in the condition. Put code scanner to it, and received P0303 "Cylinder 3 Misfire":
KRQXPQM.jpg


So i automatically assumed it was the coil pack because i just installed new wires and plugs a week before changing Lower Intake manifold Gasket. Bought new coil pack. Still getting rough idle and P0303 code. So i decided to take a look at Cylinder 3 Spark plug and it was dry black, carbon fouled:
A9Y2kGS.jpg


So went and bought new spark plug, installed it, started car and still rough idle and misfiring. Took the new spark plug out and it had been FOULED also ( DRY BLACK AGAIN). Thats when i gave up on the problem.

Any help would be appreciated AGAIN..thanks!

SN: If i can figure this out i will fully have my car back to running correctly.
 


could be a bad injector, or plug wire, try moving those, one by one, see if the miss moves. make sure the injectors are clipped on fully too.
 
Sounds like a leaky injector. You can remove the rail and have all the injectors installed and them prime the system. The result should be obvious. I had one that stuck completely open.

Jeff
 
Looks like a i found a leaking Injector??? Its the only one thats wet greasy looking. How do i take it off? I tried turn it but it just continues to turn without loosening.
3SnfXxu.jpg
 
To me it sounds like the Lower intake manifold gasket did not seal on the #3 intake cylinder port on that head causing it to run lean (due to a vacuum leak), the computer ends up over compensating by adding to much fuel fouling out the plug. With the engine running try take throttle body or carburetor cleaner and spray it where the lower intake and the cylinder head meet, if its not sealed you should noticed a temporary (a few seconds) difference in how the engine runs. I hate to say it but you might have to take it all back apart to fix it. When I had to replace those gaskets on my car I ended up taking it apart and putting it back together twice due to a very bad vacuum leak that I caused by not reassembling it correctly. I hope you are using the redesigned one that GM did a recall for with an alluminum base instead of the plastic one. Hope this helps.
 


my guess is that was nice and clean after the lim job? now its filthy?

the O rings can tear when installing them, that maybe the mess. you need to oil the o rings then slide them in.
 
I just noticed something:

When i first start the car it only runs smooth for about 3-5 seconds then it starts shaking (Misfiring) . I tried this 5 times back to back and it did it everytime. Runs smooth for about 3-5 seconds then the misfiring comes in.
 
Since you have to pull the injectors for the LIM job, sounds like that is the problem (as said above). Maybe you yanked on that one too hard? They are supposed to spin freely. There are clips holding them in to the rail. I don't know how to remove the clips, but that's what's holding them in place. There is also another o-ring at the top where the injector hooks on to the rail. Change those too.
 
UPDATE:

Just switched the SUPPOSINGLY GREASY fuel injector with the one in the middle (Swaped them out). Put everything back together and still getting Misfire (Cylinder 3), the same way. I guess next is the Intake Manifold gasket check again. SMH
 


ScottyDoggs said:
swap the coil pack around next. did you swap plug wires round yet? and the plug swap too.
Click to expand...

Already swaped the plug and wires ( I swaped #3 and #5 Plug and wires), still got "Cylinder 3 Misfire" and also the #5 plug i put in Cylinder 3 got fouled also. The coil pack for Cylinder 3 is new. Think im going to buy a whole new Spark plud and wire set before going back to the Intake Manifold gasket (long job) smh.
 
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ScottyDoggs said:
no, move the plug wires to where they were before you moved the coils.
Click to expand...

Just switch the coil packs. Took Coil pack (6,3) and switched it with Coil Pack (2,5). Put wires back where they were, just switch coil pack around. Started the car and the severe Shaking disappeared/Went away , idle is way smoother !!! So i hooked scanner to it still getting "Cylnder 3 Misfire" but the idle is smoother and car is not shaking as bad. What you all think?
 
are you seeing active misfires on the scanner? or a po303 code is still there? if the code is still there, clear the code, see if it comes back.
 
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