P0302 cylinder 2 Misfire

[tlijun]

My buick Century 2003 V6 3.1L 142K miles, failed emission test with P0302 cylinder 2 Misfire. All sparks and wires are replaced half year ago. Right now the service egine soon light is not on, but it did randomly ON and blinked soemtime ago. I do not think the cynlinder 2 ignition coil has problem. If the coil is bad, the misfire will beconsitently happen, and the SES loght will be always on.

Is it possible the air leak? How can I check the gasket and o ring? Does the computer scan will read this kind gasket and o ring leak code?

Any input and advice will be great help.


tlijun

[richtazz]

Never rule anything out without checking first. If I had $1 for everytime I've heard "it can't be _____, I just replaced it", I'd be a billionaire. First thing I would do is swap two plug wires and see if the misfire moves with the wire swap. That would finger the plug wires as the cause. Also inspect the spark plug in cylinder 2 for cracks in the ceramic insulator. If the miss stays on cyl-2 after swapping the wires, then you need to check compression and injector function on that cylinder.

[tlijun]

Richtazz,

right now the service engine soon SES light is not on or blinking. If I pull out the cynlinder #2 spark wire, the SES light is on immediately. So the spark and wire seems are not a problem. I guess it could be the injectot's problem, but I do not know how to check it. Bought one bottle Sean Foam Injector cleaner, and is waiting if the SES light comes back.
Do you know how to check the Injector?

[FishFind]

You have a few things too check.
you need to check the psi on your heads, You can rent a tester from a auto part store.
you should also rent/borrow a vacuum tester and test the vacuum on your valve cover. If you have a Haynes manual it will tell you how to do several different test with it. If you have a missfire and bad emissions you need to check the valves, head gaskets and your CAT. All can be tested with the vacuum and it is easy to do.

Also check and see that spark plug for #2 cylinder is working. pull the fuse for your fuel pump and let the engine use up all remaining gas."Don't pump gas into the cylinder if you have the sparkplug pulled" and test it against the block while someone tries to turn it over for you.

[richtazz]

Do you have access to a scan tool that can show you your misfire counts? If the misfire pops up every now and then, I would suspect it's ignition related or a bad injector, not a cylinder compression issue. Even though the factory ignition coils have the cylinder numbers marked on them, they are interchangeable. You could swap two coils around and see if the miss moves with the coil that was originally on cylinder 2 to whatever cylinder it was moved to, indicating a bad one. If the miss stays on cylinder 2, you're back to either a bad fuel injector or plug.


You can check the injectors using a digital multimeter and check the resistance. the resistance should be around 11-12 ohms, and if the # 2 injector is way off from the rest then it should be the cause of your misfire. The problem is that your injectors are under the upper plenum, so it would have to be removed to check them.

[BNaylor]

Originally Posted by tlijun

All sparks and wires are replaced half year ago.

What brand ignition wires and spark plugs to include heat range?

If the SES light is not on or flashing and no codes stored in history you should pass emissions testing. Using an odb-ii scanner clear the old history codes, if any are stored but depending on the type DTC you should have a SES light so this doesn't make sense.

[tlijun]

I took Richtazz's advice, "Never rule anything out without checking first", replaced a new Cylinder 2 ignition coil, and cleaned the car computer code last Saturday. It runs 220 miles so far, the SES light is not on and no flash, it looks normal. I thought the issue was killed by replacing the coil., but when I scan the the car again at Advance Auto Part today, it shows the P0302 cyclinder 2 misfired PENDING. This time it is PENDING. I do not really understand what the Pending mean.... Does the computer need more time to confirm the cylinder 2 misfire, or needs more time to confirm the cylinder 2 misfire is cleared.

[Scrapper]

the 3100 or 3.1 you can call it was bad on head gaskets would leak i got one in a 1993 buick skylark grand sport and after 120000 i finaly had to replace it. do that compression test he talked about and you'll know that way. but after replaced it i've went up to 175000 on it now and still going. if that's not it try replacing the tps sensor if check engine lite comes on long enough to get it hooked up at zone or advanced. but still sounds like head gasket.

[richtazz]

A pending misfire code indicates the PCM detects a higher number of misfires from that cylinder than the other cylinders, but not quite enough to trip a P0302 code.

[tlijun]

My car gent to Buick Dealer few days ago, the diagnosis result is
Scan engine data, power balance test passed,
performance injector drop test, passed.
check compression, all within 10 psi. ohemed injectors, passed.
Added cleaned near cylinder two, engine runs better, reading shows normal.
Lower intake gasket breach. EST to repair:$1500

Is it the Lower intake gasket breach a popular problme with buick engine?

[richtazz]

the 3100 is infamous for intake issues. The factory gaskets are plastic, and cannot control the different expansion rates of the aluminum intake/heads and cast iron block. They commonly fail around the coolant transfer ports causing mysterious coolant loss and overheating. They rarely cause misfires, unless the coolant passage failed near the intake port. This will cause coolant to get in the cylinder. check the plug in cylinder 2 for coolant discoloration (Orange/pink if you're running Dexcool coolant, Green/yellow if the coolant has been changed to generic coolant). If there is coolant in cylinder 2, then the intake gasket is the cause of the misfires. $1500 for an intake job is absolutely robbery. A competent independent shop should do it for less than $800 (depending on where you are). Here in Flint, MI, 3100/3400 intake jobs using the updated metal framed gaskets go for about $550-$650, just as an example. If they want to take it all the way down to include head gasket replacement as a precaution (which depending on how long you have been driving it like this may be a good idea), you should still be under $1000.