P0303 Misfire - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
Problems and Service Talk about any mechanical problems you are having

Closed Thread
 
LinkBack Thread Tools Display Modes
post #1 of 22 (permalink) Old 10-17-2013, 07:04 AM Thread Starter
Newcomer
 
Join Date: Oct 2013
Posts: 7
P0303 Misfire

Hey folks
New here and have searched a number of P0303 misfire threads but never really saw anything with a resolved repair.
Cobalt is 2007
I'm getting the code P0303 misfire cyl 3. At first it was random now it seems to be permanent. I also ran Live Data on my scan tool it its reading Fuel System 1 Open Loop Fault only at idle. This kind of leads me to the H02 sensor but theres no code stored for that in the computer.

I've done the normal maintenance stuff
plugs
air filter
oil change
swapped coil pack 1 to 3
fuse check

Any and all advice will be appreciated.

thanks

Last edited by moto515; 10-17-2013 at 07:09 AM.
moto515 is offline  
Sponsored Links
Advertisement
 
post #2 of 22 (permalink) Old 10-17-2013, 07:23 AM
YourCobalt of the Quarter Winner
YourCobalt of the Month Winner


 
BankerBalt's Avatar
 
Join Date: Oct 2010
Location: Eagan MN
Posts: 4,647
Garage
Injector or bent valves. Does the engine shake on you or cut out? Try swapping injectors

Sent from AutoGuide.com Free App

Forged L61 BW S252 Turbocharged Showoff Thread
BankerBalt is offline  
post #3 of 22 (permalink) Old 10-17-2013, 09:18 AM Thread Starter
Newcomer
 
Join Date: Oct 2013
Posts: 7
Quote:
Originally Posted by BankerBalt View Post
Injector or bent valves. Does the engine shake on you or cut out? Try swapping injectors

Sent from AutoGuide.com Free App
I don't think its a bent valve. If it was it would be constant.
I just got in from more troubleshooting and found the TB was pretty dirty so I cleaned that up and it ran great. I though I had it. Nice smooth idle, steady at about 910rpm and only a P0102 pending code after clearing the codes, since I had it running with the intake off. I shut it down, and reinstalled the intake, and it progressed down hill from there until the idle dropped to 655rpm and it started shaking, logging the p0303, and my open loop fault was back.

I then removed the intake boot shroud while running and it eventually, not instantly, smoothed out, cleared the open loop fault, and the idle ran back up to 910rpm.

I'm starting to think the MAF is in play now.
moto515 is offline  
 
post #4 of 22 (permalink) Old 10-17-2013, 09:44 AM
YourCobalt of the Quarter Winner
YourCobalt of the Month Winner


 
BankerBalt's Avatar
 
Join Date: Oct 2010
Location: Eagan MN
Posts: 4,647
Garage
Or it could be some sort of restriction in the intake piping itself. Clean the maf, blow all the crap out the intake and see if it does anything

Sent from AutoGuide.com Free App

Forged L61 BW S252 Turbocharged Showoff Thread
BankerBalt is offline  
post #5 of 22 (permalink) Old 10-17-2013, 10:49 AM
Super Moderator
YourCobalt.com Premium Member


 
Coby7's Avatar
 
Join Date: Oct 2011
Location: Magnetic Hill, New-Brunswick
Posts: 11,820
Garage
P0303 is only valid if it is accompanied by a double digit amount of misfire error counts.

Every minute spent angry is a happy minute lost for ever and ever!!!
Drives 2016 Cocoa Buick Encore 1.4L Turbo auto KL4CJDSB2GB652675
Drives 2016 Sunset Orange Trax LT1 1.4L Turbo auto 3GNCJPSB8GL142716

Never drive faster than your guardian angel can fly
Coby7 is offline  
post #6 of 22 (permalink) Old 10-21-2013, 03:42 PM Thread Starter
Newcomer
 
Join Date: Oct 2013
Posts: 7
Updates

I've since replace the MAF and that did nothing to resolve this issue.
I also removed the intake and checked for restriction, and it was clear.

I also noticed on my live data scan I have Bank 1 Sensor 2 reading .965v STFT 99.0%.
Were Bank 1 sensor 1 is reading STFT 0.0% at idle.

I don't know what those are an indication of, but I have no o2 sensor codes.
Can anyone help?

thanks
moto515 is offline  
post #7 of 22 (permalink) Old 10-21-2013, 04:28 PM
Super Moderator
YourCobalt.com Premium Member


 
Coby7's Avatar
 
Join Date: Oct 2011
Location: Magnetic Hill, New-Brunswick
Posts: 11,820
Garage
Those readings look about right. You kinda need a scope for the first one because it's going to be all over the place. Second HO2 is more stable at just under a volt.

---------- Post added at 08:28 PM ---------- Previous post was at 08:19 PM ----------

How many misfire counts do you have for cylinder 3?

Every minute spent angry is a happy minute lost for ever and ever!!!
Drives 2016 Cocoa Buick Encore 1.4L Turbo auto KL4CJDSB2GB652675
Drives 2016 Sunset Orange Trax LT1 1.4L Turbo auto 3GNCJPSB8GL142716

Never drive faster than your guardian angel can fly
Coby7 is offline  
post #8 of 22 (permalink) Old 11-04-2013, 03:19 PM Thread Starter
Newcomer
 
Join Date: Oct 2013
Posts: 7
P0303 misfire resolved!

I think I can finally put this problem in the past.

Running a live scan on my OBD II scanner indicated a open loop fault condition when idling at running temp.
This should have been an alert to a faulty o2 sensor.
I bought both the up stream and down stream o2 sensors, and received 2 up streams. So I went ahead and replaced the up stream. And I'll replace the other one soon.
After 30min driveway run time, the problem is gone. No codes and no open loop fault.
moto515 is offline  
post #9 of 22 (permalink) Old 11-04-2013, 04:09 PM
Super Moderator
YourCobalt.com Premium Member


 
Coby7's Avatar
 
Join Date: Oct 2011
Location: Magnetic Hill, New-Brunswick
Posts: 11,820
Garage
Well, that's a bit funny because if it was an HOČ sensor you would think you'd get an HOČ code. The ECM checks for 6 different possible fault with each HOČs. One possibility though is that the HOČ in question might be out of specs enough to make your engine run like crap enough to set a P0303 but not enough to set an HOČ fault code.

Every minute spent angry is a happy minute lost for ever and ever!!!
Drives 2016 Cocoa Buick Encore 1.4L Turbo auto KL4CJDSB2GB652675
Drives 2016 Sunset Orange Trax LT1 1.4L Turbo auto 3GNCJPSB8GL142716

Never drive faster than your guardian angel can fly

Last edited by Coby7; 11-05-2013 at 06:42 AM.
Coby7 is offline  
post #10 of 22 (permalink) Old 11-05-2013, 06:22 AM Thread Starter
Newcomer
 
Join Date: Oct 2013
Posts: 7
Quote:
Originally Posted by Coby7 View Post
Well, that's a bit funny because if it was an HOČ sensor you would think you'd get an HOČ code. The ECM checks for 6 different possible fault with each HOČs. One possibility though is that the HOČ in question might be out of specs enough to make your engine run like grap enough to set a P0303 but not enough to set an HOČ fault code.
I agree and I'm a little pissed since I replaced MAF ($35), Injectors ($25), and Plugs($24), + countless hours, all unnecessarily. At least the parts were cheap...
Those same parts for my motorcycle would have been 2x the cost each.

One interesting note, after replacing the up stream 02 I am now seeing much different voltage readings on both o2's running live data on my scan tool.

Hopefully this info is of some help to others in the future. I have seen posts of dealerships service shops indicating new heads or complete engine rebuilds were required to resolve P0303. I was 100% sure that was a load of bullsh*t.

Last edited by moto515; 11-05-2013 at 06:29 AM.
moto515 is offline  
Sponsored Links
Advertisement
 
Closed Thread

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome