missfire

[tooo_much_fun]

I have a 2009 cobalt ss/tc and have done a few mods to it, and after a few months it has started to missfire and backfire when I hit 4800 rpm in second gear only. I am thinking it may be the dumb down on the car kicking my butt for the mods and not doing a tune yet. I have put on Injen cold air intake, intercooler piping, and a Megan catless downpipe. Anyone have any guesses as to what may be causing this? I have already checked all the piping clamps for leaks and my air filter is clean.

 

[Intmd83r]

throttle body clean ?

 

[YelloEye]

Cold air intake is skewing your MAF readings which is messing up your fuel trims. Get tuned or remove the intake.

Also when did you change plugs last? Make sure you use the stock NGK ILTR5D plug unless you are pushing more than 50 hp more than stock, even then NGK or die.

 

[tooo_much_fun]

Just changed plugs last week to NGK's. Has to be the tune then. Thats what I was thinking. Thanks for the info guys.
Mike

 

[YelloEye]

Fuel trims for sure then. Get tuned or back to stock air box.

 

[tooo_much_fun]

Okay, I got a trifecta tune and my car is still miss firing after I hit 4200RPM in second and now third. I have no clue what is going on with this thing. I have checked all the piping for leaks, TB is clean, I have new NKG plugs in it. Can anyone help?????

 

[tooo_much_fun]

I went and had the codes checked and it said random misfire in cylenders 2 and 3, and purge valve low flow. I was told there may be a problem with the ECU. Anyone got an ideas on it?

 

[Drumrush]

ive heard that the injens on the ss/tc are hard to tune for because of the MAF position

 

[tooo_much_fun]

I am going to put the stock air box on and see if that fixes it. Thanks for the info.

 

[tooo_much_fun]

Okay. I put the stock airbox and the stock downpipe back on and the car still misfires with the tune on or off when it's under a load. It only misfires between 4000 - 5000RPM in 2nd and 3rd gear. Idles perfect and drives perfect. Not sure what else it could be.

 

[Tuner923]

i had a miss and backfire issue, i started using gas from sunoco 93 octane only fixed my miss and back fire problem. if i go to other gas stations when im in a pinch.. backfire and misfires return.

to rule out the coils as the source of the misfire take coil 2 install at cyl 1 take coil 3 install at cyl 4. now if the misfire follows to a misfire at cyl 1 and 4 instead of 2-3 its the coils.

if the misfire remains at 2-3 someone should look at the trigger pattern on a oscilloscope. from there you can rule out if the coil is burning out or if the pcm is glitched.

also did you ensure the plugs were gaped? i NEVER trust the gap from the manufacturer, they bounce around in shipping and can lose the spec. also small cracks in the ceramic can cause misfires.

---------- Post added at 01:21 PM ---------- Previous post was at 01:11 PM ----------

also fyi i had a complete coil failure at less than 25,000 miles.

 

[tooo_much_fun]

I moved the coils around and put new plugs in. The misfire seems to be gone idle. i will drive it a bit and let you know how it all works out. Thanks for all the good info.
Mike