Hello,
I have a 2010 cobalt SS turbo, 103k miles, with no catalytic converter, but I installed a muffler on it about 5 years ago. Since then it has never backfired so as soon as I heard it I knew there was a problem.
I was no lift shifting, and first to second I can never hit it for some reason but I tried like a SOB (bad idea) completely missed, engine red lined, so I waited for it to go down then popped it back into second. The car jerked really bad, and that was the start of the issues. Backfiring, can't accelerate properly above 3k without hesitating and backfiring.
so far I've changed the map sensors with ZZP, $120 later, still the same issue. The car is decked out in ZZP, and a k&n
cold air by the way, with a zzp tune. I also cleaned the MAF.
As I was reading live date from idle I noticed absolute throttle position was at 22%, not sure if that's normal for this car, I've never looked ?
Also noticed that it's jumping to about 3psi boost when I accelerate in neutral, which I also never paid attention to but I don't ever remember it boosting while reving in neutral.
Any ideas what this could be? Bringing it to the dealer on Tuesday.

Live reading

 

Throttle position is fine. It sits around 20% at idle, and only actually opens to something like 90% at WOT, iirc.

Have you checked your plugs? Might be time to change them.

Does the car run properly, other than when trying to go WOT/high RPM?

 

I changed the plugs at 97k and coils. All oem. I will check them tomorrow when I have time. It does not run normally at idle. It's erratic. RPMs jumps then dip. Air to fuel ratio starts normally at 14.7 but then will go to 19, then down to 10 and jump back and forth, mostly on the high end. There are no codes. I'm fearing for the worst here lol it's hard to detect any rod knock due to the tick from the injectors, but I don't think it's that because once I'm able to pass 3k (its a struggle) it revs fine. It certainly does feel like a misfire

 

I'd check plugs and compression... and maybe go ahead and pop that valve cover off and give everything a look.

 

Here are the spark plugs. I'm not an expert but that doesnt look normal for only 6k miles. It feels like the engine is struggling to get air. When I gas it, the RPMs actually go down, then slowly creep up. Any ideas? I'll have to hold off on the valve cover for now... No time


Spark plugs

 

​​​​​I have wot and it gets stuck at this rpm heres my air to fuel ratio fyi

 

Use this: https://ngksparkplugs.com/en/resources/read-spark-plug

Might be a fuel injector problem. Might be an O2 Sensor problem. With limited data, it's hard to say. Kind of need to see a log of sensor data.

Check your intercooler end caps for cracks, as well as any other plastic charge piping. Boost leak check would be easiest.

 

I can log live data. What do you suggest I monitor? I'm off today so Im gonna dive deep into it. I'm gonna hold off bringing it to a dealer

 

I would check the piping first. The more I think about it... the more I think you have a boost leak. Hopefully @ECaulk can offer some advice; he's more familiar with the LNF side of things.

 

Just unplugged my MAF sensor and started it. Idling fine and reving fine. Bad MAF??? I didn't think u could break a MAF by driving like a maniac

 

Yes, a bad MAF will do crazy things. And Cobalts have a weird habit of having things break either when you install something new or when something unrelated breaks and/or gets replaced.

 

Just replaced with an Hitachi one from advanced auto to test it. Driving like a champ again. Only issue i see is the air to fuel ratio seems off while driving. It'll go real lean to 18 when I coast in gear. Could this be because of the type of MAF and it's giving false readings? I'm thinking of ordering OEM GM from ZZP.
edit: doesn't seem like a boost leak, I'm able to hit 21 psi, and it feels strong, not missing a beat while accelerating. Idle however is a little jumpy. A/F will not stay at a constant 14.7, goes from 14.1 to 15.1 erratically
edit2: finally got some codes
P0100
P0113Ed

 

When coasting, the AFR should shoot lean. Totally normal. DFCO (Deceleration Fuel Cut Off).

And the AFR will oscillate around 14.7; that's just how cars work. You might have been better off unplugging the negative lead on the battery to reset fuel trims, but it's fine, the car will readjust soon enough.

I'd clear the codes and see if they come back. Funny how that works. Dead MAF, no codes. Replace MAF, get MAF codes.

Hitachi might be an OE-supplier, so it may not be worth ordering an OEM one. I'm not sure on LNF's though. That info is usually a bit harder to find for GM stuff, imo. Pretty easy to find OE-supplier info in the VW world.

 

Thank you for your help! I will update this soon after a bit of driving. Hopefully this will help someone else out

 

Just checking back in, everything is working great. MAF sensor was definitely it and the cheap one from advanced auto seems to be working great.

 

Good to hear!

 

I totally dropped the ball on this one. Last week was a **** show for me, but it seems you got the problem fixed.

For others reading into this, if the code is P0101 its 99.5% of the time a boost leak not a bad maf. If the car runs like crap but no codes, unplug the maf and if it runs great, you likely have a bad maf. I still suggest doing a boost leak test as unplugging the maf will cover up a leak, and with these cars its always good to confirm everything is sealed up proper.