Hi all,

I've been having some recent problems with my Cobalt. It randomly goes into Engine Power Reduced/Limp Mode when on the highway and the idle/boost levels are all over the place. It will idle anywhere from 1200 to 3000rpms and when shifting the rpms tend not to drop. The boost levels are everywhere when driving and at idle. I can be at a stop light and the boost guage will read 5psi or it will be below 0.

I took it to the dealership and they said that they are seeing these three codes: p0300, p0069,p0420. I have been catless about a year with no issues and they are saying that I am having these issues due to not having enough back pressure since I am catless. What are your thoughts? Here are the mods to the car:

2006 Cobalt SS - Supercharged
Bought the car from a dealership with 40k miles and was told that it was all stock but an exhaust and intake. Come to find out it has (what I believe to be) a Stage 2 kit (pulley has 77.9mm stamped on it, injectors look different than stock, revs higher than stock and boost gauge shows 15psi at WOT)
Intake
ZZP mid-length header
ZZP Catless Downpipe
ZZP Exhaust
Recently replaced intercooler pump
Recently replaced MAF
New 1-step colder plugs

Thanks

 

That is the most retarded thing I've ever heard. So incorrect. Stay away from those fools.

Yes, from what you are saying you have the GMS2 kit installed.

The only code you have due to being catless is the P0420 code which is a code to say the cat is not running up to par. This happens when it senses a change in flow. Since you removed the cat a code gets set. It does not affect engine performance at all.

That code can be removed via a HP tuners or buying an O2 extension for your downpipe.

I believe the P0300 is a misfire code & P0069 is a barometric pressure code. From what you are saying it sounds like you have a vacuum leak issue as well.

Inspect your plugs and coil packs. Also, you mention a new MAF sensor... Did you purchase an oem MAF sensor or a cheap aftermarket sensor?

 

That was my thought as well. I tried disputing it with them, but they are not having it. They keep telling me that the lack of backpressure is most likely causing the misfire and limp mode.

 

Just saw your edit:

This issue of going into limp mode happened a few months ago as well. Took it to the same place and they said it was caused by a bad MAF sensor. They replaced the MAF sensor with a new OEM one and the problem went away. Now a few months later, similar issues are happening.

 

They are fools.

Anyways... what do you have your plugs gapped at?

I'd inspect the coil packs and plugs. Misfires usually occur from an improper plug gap or bad coil.

I believe the P0069 code can be caused from the map sensor as well... Might want to have that checked.

 

Well I just talked to them again. They said the went deeper into it and found out 2 things:

1. The throttle body is causing the idle issue and Engine Power Reduced
2. A valve is not sealing and that is causing the misfire.

Plugs are gapped at .035.

 

I don't believe the valve part so much... Only because that is not a common issue and you have low mileage.

A bad throttle body can def cause those problems. I'd start there.

Plugs are gapped correctly but still check the coil packs. Did they tell you which cylinder is misfiring? If so swap a coil pack from another cylinder to that one and if the misfire goes away you know its the coil pack.

 

I am definitely going to start with the throttle body and see where that goes. They said they checked the plugs, coilpacks, and injectors and found know problems. Cylinder one is misfiring.

 

Yes, def start with the throttle body. You can try cleaning it... if that doesn't work replace it.

Might solve all your issues. A rough idle can cause a misfire to.

Let me know how u make out.

 

Got the car back the other day and have driven it about 200 miles since I've gotten it back. It seems a lot better but not perfect. I still have a CEL that I need to check, I assume it's the p0420, but want to be sure it's not that and more. I haven't gone into Engine Power Reduced and the high idle seems to have gone away. Although it does idle around 1.5k when coasting to a stop and then drops down to normal (this is new). It feels like there is still a misfire at idle but it goes away once starting to drive.

 

Good to hear there has been some improvement. The code is prob your p0420 code, that won't go away unless you do what I mentioned a few posts up. It doesn't harm anything though.

The idle dropping when you coast to a stop is normal.

 

So it went back into Engine Power Reduced on my to work again this morning.. I will be taking it to an Autozone at lunch to get the codes scanned.

 

Let me know what they are. Did u replace the throttle body yet?

 

Wasn't able to make it to Autozone, busy day. The throttle body was replaced. I just called the shop that did the work and they are again telling me they think it's happening because the sensors are being thrown off by the lack cats. They did say that they are going to meet together and do some research and see if they can figure something out. I will be dropping the car back off there tonight and plan to have them find the problem this time at no cost.

 

Being catless will only cause the p0420 code (w/o the methods I explained a few posts above)... and will not affect drivability or put the car in reduced power mode. Tell them to go pound sand with that remark.

If you still have the P0069 code have them check your barometric and map sensor, and for the hell of it have them inspect the supercharger inlet pressure sensor.

 

UPDATE, still fighting this issue. Bought a scan tool and am only getting a p0301 and a p0069 aswell as the p0420 but im not to worried about that code. How related can these two codes be? Also did a compression test, 180-190PSI on all cylinders. Pulled the injectors and they all have around 12ohms resistance. All injectors are also firing. I switched coilpacks, also purchased a new coil pack for Cyl 1. Its running NGK BKR6E plugs gapped to .035". I also noticed when i wiggle the MAP plug the car starts to fall on its face. I checked the map reading in the scan tool and compared it to the gauge, Im getting 10.2HG at idle from the map scan tool, and my gauge reads around 20HG at idle, even when i go into positive boost the map never reads positive pressure on the scan tool. Any input?

 

Also pulled the Manifold absolute pressure sensor and there is no vacuum line connected to it? The senser the sits under the Fuel rail on the right side of it if your standing infront of it.

 

also calc fuel % at idle is 25-30%

 

Both MAP and baro sensors have 5 Ohms resistance.

 

Ok, little more info. Upon inspection I found the injectors are Siemens deka 60lb injectors. Anybody have any advice? Calling zzp in the morning to see if I get get some better info. Trying to troubleshoot this issue myself. I am leaning toward smaller injectors and a tune. Maybe getting the zzp kit? Everything seems to be working properly, I've switched coil packs and switched the injectors around, still cyl 1 misfire. Compression is good. I'm not even sure now if this is a actual GM kit. Maybe someone threw injectors and a smaller pulley on it without tuning? Any input is greatly appreciated

 

Good morning! Any feedback on this issue would be greatly appreciated!

 

Do you still have this car?