P0302: Cylinder 2 misfire deteced.

[Blackstar]

Problem started last week on the way to work. During drive coolant temp at half ways between operating temp and feels like it's almost stalling. Another 30 seconds and it's back to normal. Did this twice more but the third time it didn't come out of it and developed a misfire.

I understand what the code means, either a bad plug or coil but could this misfire occur because of something else? Whatever was causing the near stall? These plugs were replaced along with one coil that went bad about 5 years ago, probably 40- 50K on them now.

Any ideas??

 

[Redbeard]

When was the last time you cleaned the throttle body? And what type of spark plugs did you use when they were changed out?

 

[Mooseman]

Plugs rarely cause a misfire unless overdue, wrong type or brand, or broken.

Try swapping #2 coil with #1, clear the codes and see if the problem follows or.not.

 

[Kelly@PCMofNC]

The "good" news is that the miss is bad enough for the PCM to pin it to one cylinder. Like Mooseman said, start swapping components from a good cyl to the bad one. Plug, plug wire, coil, injector (all one at a time). When the misfire "moves" to that cylinder then you've found it.

As for the stalling, that may or may not be related, but I would address the misfire first. When they are down a cylinder or two they really don't drive that great.

 

[Blackstar]

Yup. She's not driving very well right now. Idles like my old Harley.

I'm gonna get at this on Saturday. Nice weather and a weekend off...

Thanks for the replies and suggestions.

 

[Blackstar]

I tried a couple things today. First moved the #2 coil to #3 and got a multiple misfire. Pulled the 2 plug and changed with 3- no change.

Pulled all the plugs and coils. (I found a video that says I can check the coil with an Ohm meter. All tested the same)

Also, poured a 1/4 can of Seafoam in the tank and sprayed some in and around the throttle bogy opening while running.

Changed the plugs with an old set I had that still looked good. Cleaned and gapped them and installed. Put all back together again and it seems to be running better but still feels like a slight misfire.

Droved it up the road a bit and check engine light flashed on and off a few times. No codes set but a pending Misfire Code #2 cylinder.

I mentioned in my earlier post that when I changed the plugs a few years ago with AC's I was mistaken. The new plugs then were NGK's. The ones I installed today were the AC's.

My next step is to see if I can find a coil to replace #2. The one I changed a few years ago was #3.

 

[mrrsm]

The Misfire Problem involving GM Vehicles with the 4.2L LL8 Engine and the solution covered in this document probably are not involved in your present circumstances... but since you mentioned anticipating "Good Weather"... this information might still be worth a look... "whether" it is or is not involved:

http://ww2.justanswer.com/uploads/heavychevy396/2010-05-22_150734_dripping_rain_water.pdf

 

[Blackstar]

We haven't had rain here for about 3 weeks.(besides a little mist and drizzle) Everything looked dry inside the wells.

So, is it better to run AC plugs rather than aftermarket?

 

[Wooluf1952]

"Also, poured a 1/4 can of Seafoam in the tank and sprayed some in and around the throttle bogy opening while running. "

The throttle body needs to be removed to fully clean it. Just spraying it while the engine is running will not clean off the gunk on the back.

 

[Mooseman]

So when you swapped the coils, did you clear the codes? If so, it's normal for it to have a pending P0300 until it decides which cylinder is misfiring. If you left the coils as you were trying other things, if it did settle on P0302, then the misfire remained at cylinder 2 so the coil isn't at fault.

Next would be to check if you have spark at cylinder 2 and the wiring for that coil. You could check for spark by using a spare spark plug grounded to the engine and inserting it into the coil and check for a nice regular spark. If no spark, it's time to check the wiring.

If spark is good, next would be to check compression just to eliminate a mechanical issue.

If that checks out, next would be the fuel injector. To check that, it would be best to do an injector balance test. For that you would need a high end scan tool or a Tech 2. Because removing the injectors involves also removing the intake manifold, I would have this test done before going any further to be certain that the injector is at fault.

This video is pretty technical but explains the injector balance test as well as checking the wiring although he went the other way around since he has the tools.

 

[Blackstar]

I didn't wait a very long interval when I was swapping coils. I will try that tomorrow.

Today I removed the throttle body and cleaned it. (Thanks Wooluf1952). The back side was terrible. Had to spray several times and scrubbed between sprays. Came out looking great after that.

Test drive. Still a P0302 but running a lot smoother. Took a quick run out the highway and it runs smooth all the ways up to 70 mph. But as soon as I stop I have that loping idle. Need more experimenting tomorrow. Will swap out a couple coils and see if the misfire moves to another cylinder... after a little more time (Thanks Moose).

 

[Blackstar]

Solved! Went out this morning and swapped #2 for #4 coil. Right away got P0300- Multi cylinder misfire. Drove it up and down the road a few times with no change.

Jumped on the bike and rode out to a local used parts place and picked up a used coil for $30.00 (Cheapest new one was $65.00 and 2 -3 days away. Installed the new(used) one in the #2 slot and returned the #4 to #4.

Fired her up and she again is purring like a kitten.

Thank you for the info and tips. This is a great forum!

 

[fletch09]

been dealing with this for a week, misfire on #2. check engine lite came on Sun the 16th. had advanced auto check it, CEL went off. after reading thru this thread, decided to try the least expensive fix w/ fuel injector cleaner in tank of gas. after 1 week and 400+ miles CEL came on again. had Advanced Auto check again. same code(s). misfire still there. it's not bad, only notice it when sitting at a stop light, but it get's worse the warmer the engine gets. so getting a coil and replacing it. Rock Auto has the least expensive AC Delco one. just have to wait a couple days.
just to clarify, cylinder numbers start w/ #1 at the nose and work back to fire wall, correct?

 

[mrrsm]

Yes...

 

[fletch09]

I'll continue here instead of starting new thread;
my misfire was barely noticeable, only could feel it while sitting at a stop light. did not notice any reduction in power. i drive 45-50 min one way to work with the later half on back roads where i can do 60-70 mph for long stretches.
replaced coil,(RockAuto had best price, 31.00 incl. shipping) Mon night after work
CEL light went away, back out of garage and just sat idling, still had misfire and CEL came back
with in 3 min.
Tues drove to work and later that day replaced the spark plug in #2.
misfire gone. had O'Reilly's A P clear the codes. (my work is right behind an O'Reilly's)
she's run fine ever since.
below see a picture of 2 spark plugs. the one on the top is the one i took out at 98K, when i did them all. (don't know what cylinder that came out of)
the one on the bottom is from #2 after 22K.
was it just a bad plug? did a bad coil cause the plug to go bad?
no, i have not check any other plugs at this point. anybody's thoughts?

 

[Mooseman]

Did you notice they're not the same number? The worn one is likely the original with that original part number, which was subsequently replaced with 41-103.

 

[fletch09]

the older one (original) has 12598004 w/ 41-103 on the other side.
the newer one has 126525058 also w/ 41-103 on the other side.

 

[Mooseman]

Ah, OK. Either way, that plug was done.

 

[fletch09]

do i chalk that up to a bad plug, or could a bad coil cause the plug to fail?

 

[Mooseman]

I doubt a coil could do that to a plug. Maybe the tip was damaged and broke off. Did you gap them when you installed them? You're not supposed to.

 

[fletch09]

do not recall gaping them.

 

[Mooseman]

Could just have been bad then. Happens I guess.