I have a 2009 Cobalt SS with an Injen cold air intake and a Modern Performance catback exhaust muffler delete. Ever since I put these two mods on, the car has been running rich and starts backfiring when Im WOT around 4200 rpm through all five gears. Ive went through and checked all the sensors to make sure something wasnt hooked up all the way, Ive replaced both o2 sensors last week and nothing changed. I put the stock air intake on and it still does it. Could not having a muffler be causing my problem due to not having enough backpressure.

 

Ive also had a guy try and hook up to my ECU using his software which was EFIlive and it wouldnt communicate, so no luck there. What is the best software/program out there to tweak on the ECU factory settings? I did forget to mention that I did unhook the battery and the ECU after putting the mods on and it didnt do anything either. No one around here in Anderson,Indiana seems to have any idea or can help me figure out the problem, so maybe someone out here can. Please help.

 

Trifecta tune or hptuners

 

I know the stock VE tables are usually pretty rich. If for some reason the MAF failed and the PCM went into open loop, that could cause you to run super rich and backfire on shifts....at least thats what my car did while running on stock VE tables, but I have an LSJ.

I have HPTuners, if you can't figure it out I might be able to meet you and log your car. I home on leave in Kokomo right now. Let me know.

 

Between Trifecta and HPtuners, which is the best software of the two to allow more tuning capabilities? Once I or someone else can fix my problem, I want to tune my car to straight performance and raise the boost up to around 19 lbs. Can u raise the boost with either of those two programs? Jdam, I would def like to meet up some time and have u hook up to my car because Im really tired of chasing a problem that I cant solve and its aggrivating me to no end. Thanks for the offer, I appreciate it.

 

Yes you can raise boost with these tunes
If you want to tune yourself, get hptuners..

 

If you cannot get communication with a scanner tool, check your 12 Volt cigarette lighter fuse, its probably out.

If your running rich for no apparent reason, you could have a dead Ho2 Sensor, usually Bank 1 Sensor 1.

When you have a dead Sensor, the ECM gets incorrect data and thinks your running lean, then adds more gasoline to the engine, thus messing up the air/gas ratio, thus getting a rich smell.

1st off, check the fuse for the cigarette lighter 12V output, get it scanned and see what info you can get.

 

John, I just replaced both o2 sensors last week, the one on the manifold and the one after the converter. I didnt check fuses though so thanks for that info.

 

Did you make sure you got the right sensor, its an easy mistake to make. I had a problem with mine, since I have a scanner and I have communication with the ECU, I found that my o2 sensor was not giving any voltage output and the heater circuit was shot, same thing happened when I bought a new one, it happens that I bought the sensor for the cobalt 2.0 engine, while wired the same was its not compatible with the 2.2. Check where you got the sensors from as this could be your issue, if not we'll move on.

 

JDam, I can meet up with u next Saturday after noon if thats good for u. I work nights monday-friday so u pick a time and I'll c u then. Thanks for the help.

 

Did you ever switch out the coils/plugs/injectors? How'd it go?

 

My cas has been doing somethig similar lately. Runs fine on idle, but it will sometimes go very rich and almost stall when cold. Goes to like 10-11 air fuel on my wideband. I also hear the bypass valve having a hard time and opening / closing for no reason. Then I'm on the highway, at let's say 65 pmh and sam ehappens it goes rich for a second, engine sputters and I hear bypass open / close.

Basically all is fine on WoT, but it runs like **** some other times. It started doing it a few weeks ago but I ordered and got replaced the purge selenoid and the bypass valve selenoid. Hasn't changed anything. I may get it to the dealer as it's getting very aoonying. Any idea on what I coud be? Spark plugs are OEM ones and they have at most 15 000 KM they were changed recently too.

 

For the benefit of others that may end up reading this:

Checkers problem was solved. We logged it and he was getting multiple misfires in cylinder one starting at about 4500 rpm. He checked the plugs after we narrowed it down to cylinder one, and turns out it was a bad plug.

As for you, Doomtor, I'm really not that familiar with LNF's but I'd say if its still under warranty, take it to the dealership and make them fix it. Good Luck!

 

WOT is open loop so O2s are not used.