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Engine misfires

89K views 67 replies 34 participants last post by  norsi1023 
#1 ·
I have a sporadic engine misfire, more prevalent at idle, but shows up almost all of the time. I have performed a throttle-body cleaning and replaced the spark plugs with AC Delco 41-103 Iridium plugs. These had no affect at all on the problem. Initially the trouble code indicated a mis-fire on cylinder 4. Upon replacement of the plugs, it is now showing a "various misfire" code. Does anyone have any suggestions. I did swap the cylinder 4 coil pack with cylinder 2, anticipating that the trouble code would show a misfire on cylinder 2. But this did not happen (although the definition did change). Help and suggestions would be appreciated. The mileage is 77,000.
 
#34 ·
P0301 - Cylinder 1 Misfire '02 Trailblazer

Wow I feel so lucky to be at the very beginning stages of this issue that you've all already been through...

The check engine light came on a couple days ago and would flash every once in a while, since spark plugs are cheap and relatively easy to replace I did that last night. Didn't help. I guess I'll move on to the coil.

OBDII scanner gave the P0301 code.

Thanks for all the info posted here!
 
#35 ·
...I'm brand new here too, ...and will be following closely.
We have an '02 TB, ...and just last night noticed the rough idle (and I did notice check engine light on)
Hope to hook it up to a scanner today and see what it says.

Is there a breakdown of the codes on this site? ...like I said, I'm new so I haven't had a chance to look around much.

Thanks,

Kevin
 
#38 ·
Wife just called me today at work and said that our 02 TrailBlazer is running rough and actually died 3 times on her today. She says it runs really rough even when she is driving - not just at idle.

I appreciate all previous post and the work that has been done already as this will give me a great jump-start on things!

Life before great threads like this must have been expensive:eek:

I'll keep ya posted - Ronnie
 
#46 ·
Just a follow up here guys - I think the majority of the trouble came from me disconnecting the battery the day prior. This must have done something to the main computer. Anyway - the thing was due for a throttlebody cleaning a new plugs anyway. So the cleaning and new plugs - it has ran great. Runs very smooth. I did find someoil on the #5 plug, but after reading various post on here it might not be as big of a problem as I anticipated.

Now I need to figure out why it smells like fuel when we get in & start it up.

Again - thanks for everything. This is a great site.
 
#39 · (Edited)
...to follow up, ...I hooked up the scanner, ...and sure enough, Code "P0306" ..."misfire on cylinder #6".
A quick trip to Autozone (and about $65 later) problem solved.
Replaced the coil pack for #6 (which was literally a 15 minute job) and it's been running fine since.

...also a comment on the part, ...I found an ebay seller selling these (with shipping)for a little over $50, ...so I ordered one as a backup. The one I got from Autozone was 'Duralast', ...yet in both cases, ...it's a Delphi part.
 
#40 ·
Lucky for me I get to replace a coil too. I just finished replacing fuel filter, air filter, plugs, cleaning throttle body, cleaning IAT, trans filter/gasket, seafoam in fuel tank... I think that's everything lol. It has 84,xxx miles and all of these things need attention. Took the TB for a drive and it felt like a brand new car, for a day. The second day driving it (today) I was going down the interstate trying to burn some of the fuel out to get the seafoam through and all was well for the first few miles. All of a sudden it stumbled a bit then cleared up. This went on for a few miles until it was a constant problem and then the SES light came on. Headed home and stopped by the parts store to have the light checked. Said cyl #5 was missing. Great. Took it home went and checked it out. Sure enough #5 coil wasn't sparking at all. Got a coil coming in the morning at local parts store. What a coincidence I do all this work and I get hit with another $60+ bucks to shell out for a coil. Oh well, hope this thing gets us to our Thanksgiving destination next week :D
 
#42 ·
I have an 06 trailblazer with 90,000 miles on it i was having a misfire problem for quite a while now. it alstarted when water got into the spark plug chambers where the coil connects. i blew all the water out and changed all the spark plugs to boch platnum 4 and the coil packs to acdelco, it was ok at first and then it started misfiering again just on 5 and 6. then i decided that those plugs sucked so i replaced all of them with acdelco plugs and it ran perfect for a week and now my light is back on flashing just when the car is idleing. I am just ready to blow the car up... HELP.
 
#43 ·
...sorry to hear that troubles are back.
First (which I'm sure you've already done, ...or are about to do), ...get the scanner back on there and confirm what is shows.
It may just be a coincidence that a new code picked up.
Otherwise, ...It may be possible that while doing the work you did, ...you 'hit' something (unrelated to what you changed) and it's intermittent. I'd check every connector under the hood,....just make sure there all securly seated.
Hard to tell exactly what the problem might be without more detail, ...but hopefully you'll get to the bottom of it...
 
#45 ·
Misfire

tmcat,

I have had the same problem with my 05 envoy, you might want to get a compression test done on the number 4 cylinder. I know with my it was the
#6 come to find out the valves in the head were sticking, it seems like this is an on going problem with the 4.2L engines. Good Luck and I hope this helps.
 
#48 ·
cyl 6 misfire

Ok,i have a 2007 trailblazer 55k ,about a month ago got code po306 ,check engine light came on then off after driving few miles, now 3 days ago same thing,but the check engine light dint turn off this time.
So i took the truck to Chevy dealer,2 hours later got a call,bad exhaust valve cyl 6.
They are replacing the cyl head,valves,etc.(truck still in the shop)
they told me that it has happen to a lots of blazers,and a lots of H3,do to bad manufacture valves
thank god for 100k miles warranty from Chevy,dint have to pay a dime for a $4000+ repair.
 
#49 ·
Hello, I have been lurking here for awhile now, figured it was time to post up. I have a 2005 Trailblazer that is now in the the shop for the second time to have the head replaced. The first time was at 38,000 miles and thank goodness I had the extended warranty as the bill was almost $8000. It all started with the car stahling at idle during prolonged idle at stoplights and drive-thrus. It threw a P300 code the first time. Around 85000 miles started getting P304 codes, went through the usual plugs, coils and wiring. I was dreading the inevitable, but took it back to the dealer last week and found out the #4 cylinder is down almost 70% from all the others. They are pulling the head to have the guides replaced. I think this was the problem the first time on cyliders 2 and 6. I have an aftermarket extended warranty since my GM warranty ended at 72000. I have spoke with Chevy customer service and a District Rep is handling the claim. Have not heard what they will pick up for costs but it can't hurt. My other warranty is balking, but my service advisor is pushing forward. Cost for this repair looks to be around 4K. Will keep all updated with the out come.
-Spo-
 
#50 ·
Misfire Cyl #2 Dealer serviced

New to site. Love the articles and reads.

Well heres my problem:

Been having the check engine light come up (Solid). Scanned it and got an evap code(p0440), reset and thought nothing of it. Came back again probably 200kms later. Scanned again same code. Took plugs out and changed all, and cleaned TB, replaced gas cap. Cleared code. Came back on again.
Took it to GM dealer, and they scanned it and found that p0330 and p0440 where stored in the PCM. They determined that the misfire is coming from #2 cylinder after swapping #2 and #3 coil. The misfire is only at idle.
They also hooked up the fuel pressure tester and preformed injector balance test, finding injectors to be in spec. Also did crankshaft variation relearn and recheck, finding miss still on #2.
At this stage they have said that they believe it to be a mechanical issue and that the cylinder head needs to be replaced. They also said that a compression test would not show anything as doing a single cylinder test would not give an accurate reading. Also said that a leak down test would not be benifical as they are sure #2 is the problem and the head needs to be replaced.
Anybody got any ideas. I have tried FI cleaner but not the AC delco stuff- Is this the same as Carbon Cleaner, worth the money.
I am going to get a compression test done or leak down test, any input on which is more worth the money in this situation.
 
#51 ·
New to site. Love the articles and reads.

Well heres my problem:

Been having the check engine light come up (Solid). Scanned it and got an evap code(p0440), reset and thought nothing of it. Came back again probably 200kms later. Scanned again same code. Took plugs out and changed all, and cleaned TB, replaced gas cap. Cleared code. Came back on again.
Took it to GM dealer, and they scanned it and found that p0330 and p0440 where stored in the PCM. They determined that the misfire is coming from #2 cylinder after swapping #2 and #3 coil. The misfire is only at idle.
They also hooked up the fuel pressure tester and preformed injector balance test, finding injectors to be in spec. Also did crankshaft variation relearn and recheck, finding miss still on #2.
At this stage they have said that they believe it to be a mechanical issue and that the cylinder head needs to be replaced. They also said that a compression test would not show anything as doing a single cylinder test would not give an accurate reading. Also said that a leak down test would not be benifical as they are sure #2 is the problem and the head needs to be replaced.
Anybody got any ideas. I have tried FI cleaner but not the AC delco stuff- Is this the same as Carbon Cleaner, worth the money.
I am going to get a compression test done or leak down test, any input on which is more worth the money in this situation.
P0330 is a knock sensor issue, not a misfire. A compression check will tell you if the head or anything mechanical is wrong. Are you noticing any symptoms or issues?
 
#53 ·
Comp Test results

Ok, so today I had the compression tested on Cyl #2,3,4.
#2-showed 200
#3- 204
#4- 199

These reading are great. There is no sign of a misfire besides the reading from GM. My light did come on again today but my reader showed evap so thinking of switching the vent solenoid and going from there. Good thing I didn't let GM take head apart.
No point of doing leak down at this point as the compression is where I want it to be. Not sure what to think of this.. Update later.
 
#54 ·
Shaunmann:

With the air intake resonator off, see if you can get the #2 cylinder to misfire by wiggling the wire and connector at the #2 coil. I had a broken wire inside the connector. This caused me a lot of headaches before I accidentally found it. Usually, this would show up as a P0302 code (#2 misfire). What scanner do you have?
 
#57 ·
Thank you.

This is the first message I've ever written on any forum. I just had to write and say thank you. I just bought a 2003 trailblazer, and don't get me wrong I love the truck, but they've got more than their share of problems. Anyway back on topic, since buying the truck I've I haven't stopped turning wrenches, and this forum has saved me a lot of time, money and aggravation. You guys have helped with a variety of issues, but after today I felt that I needed to express my gratitude. Thanks to this thread, as of today, no more SES light! I had a bad coil pack on cylinder 2. Thanks everybody for sharing your experiences, I hope that I'll be able to return the favor, and help somebody else with some of mine.
 
#60 ·
This is the first message I've ever written on any forum. I just had to write and say thank you. I just bought a 2003 trailblazer, and don't get me wrong I love the truck, but they've got more than their share of problems. Anyway back on topic, since buying the truck I've I haven't stopped turning wrenches, and this forum has saved me a lot of time, money and aggravation. You guys have helped with a variety of issues, but after today I felt that I needed to express my gratitude. Thanks to this thread, as of today, no more SES light! I had a bad coil pack on cylinder 2. Thanks everybody for sharing your experiences, I hope that I'll be able to return the favor, and help somebody else with some of mine.
this is my first post also. Thank you trailvoy.com
 
#61 ·
02 tb 200000km misfiring

My tb has been hesitating/stumbling when the light turns green. I think the worst is under load going up a hill. I cleaned the throttle body for the first time since I bought it 5 years ago.. shame, I know. Still missing. I will start with plugs. I did those 2-3 yrs ago. I will update as I go through all suggestions in the thread.
 
#62 · (Edited)
Fixed p0300 multiple misfire

Bought a Creader VI from a friend who just started a Mac tools franchise truck here. Pretty decent scanner for 165$ hooked it up. Code 0300. Not very specific. I started with the cleaning tb , fuel filter. Still popped on low rmp load, from a stop light really bad. Up hill really really bad. I could feel the mis at still idle but it got really evident when I would turn on heat or ac. It would calm down when the fan was shut off. So I decide to do some coil swaps today. Bought the last coil in the city. Had to go to gm for plugs. Coil 107.82 at napa. Plugs77.58 at gm. Started with the plug change and started it up. ....it was the plugs or one of them. They were champions. I changed them 5 years ago according to my receipts, before I read anything here about delco being a must. Well I have a spare coil and am glad it's over for the moment. From what I read it could have been and I expected it to be a true PITA. Not a lot of help I know but I appreciate all the help from the site and thought I'd throw in my 2 pennies.
 
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