Hi all,

I've been having some recent problems with my Cobalt (car details below) randomly going into Engine Power Reduced/Limp Mode as well as a cylinder one misfire. We have been some difficulties diagnosing the cause so any insight would be appreciated. Here are some details:

2006 Cobalt SS - Supercharged
When I originally bought the car from a dealership I was told that it was all stock but an exhaust and intake. Come to find out it has a Stage 2 kit.

Known Mods and recent replacements:
Stage 2 Kit (assumed to be GM)
Intake
ZZP mid-length header
ZZP Catless Downpipe
ZZP Exhaust
Recently replaced intercooler pump
Recently replaced MAF
Recently replaced Throttle Body
NGK BKR6E plugs gapped to .035"

Bought a scan tool and I am only getting a P0301, a P0069 and a P0420 (catless). How related can these codes be?

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 coil packs, also purchased a new coil pack for Cyl 1.

I checked the MAP reading in the scan tool and compared it to the gauge, I'm 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.

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.

Any thoughts, ideas, insights that could help diagnose the issue would really be helpful. Thanks!

 

Ok, little more info. Upon inspection I found the injectors are Siemens Deka 60lb injectors. 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 an actual GM kit. Maybe someone threw injectors and a smaller pulley on it without tuning? Any input is greatly appreciated

 

How many bolts is your pulley held on by and what color?

 

I'm not with the car now but I know that the pulley is black and bolts are blue. I'm pretty sure that there are 4 (stripped) phillips-head looking bolts.

 

I'm not with the car now but I know that the pulley is black and bolts are blue. I'm pretty sure that there are 4 (stripped) phillips-head looking bolts.

 

Thats a gm pulley then

 

Just talked to ZZP as well and they say they are confident that it's in the tune. After discussing with them, they say that the header/downpipe more than likely threw off the fuel trims enough to make it misfire. Any opinions on this? I just want to be sure that's the issue before purchasing a tune and not them wanting to just sell me a tune. I have heard good things about them in the past and had a good experience with them when purchasing my header/downpipe so I'm sure that's not the case.

 

Doubtful to me. If your car does still have the gms2 flash with 60#, that would make sense. A header/dp is not gonna cause massive misfires and limp mode like they are stating. I drove mine with a shorty and catless for a long time with no issues on gms2.It would still be a tune issue tho for the bigger injectors and i would not recommend their canned tune. Get a custom tune done by someone.

 

All the issues with the car rides once installing the header/downpipe. The car ran fine with no CEL for 30k miles with 60# injectors

 

Now that I think about it I wonder if the 60# injectors made the cat go bad...

 

The only way i would see the header being the problem is if you fuel trims were already whacked out from your 60# inj on, for all we know, the gms2 tune. Otherwise there shouldnt be an issue unless you accidentally broke something during your install. Ive known quite a few guys including myself, to run them without a tune. If you do end up going with the zzp tune, know that it is made to be a temp fix until you can get a custom tune done by someone.

 

Is your boost higher than before?

 

Boost didn't change from adding the header/catless downpipe

 

Well you cant have a bad cat if you are catless. You should actually have less boost at wot after the install.

 

Boost at WOT hits 15psi, after 6k or so it climbs up to 17psi. Redline is around 7k Rpms. I believe it's a stage 2 tune, just curious if the 60# inj could cause th issue we are experiencing, even after driving the car for 30k miles with no issue until the header mods, than we start to experience a random cyl 1 misfire. Along with the p0069. I installed nothing besides the header/dp. The car was bought this way. And everything I tested is installed back in proper order.. Would you guys recommend trying 42# inj and a tune or just stick with the 60# inj and tune?

 

The MAP sensor is in the manifold, the one you found is the outside barometric pressure sensor, it's supposed to be open.

Remove the sensor on the top of the manifold, right next to the blower snout, by Cyl #1. That's the MAP sensor that feeds the PCM and boost gauge. If it's saturated with oil, clean it and see if it helps. I've seen a few fail.

 

Thanks I'll try that today and see what results I get. Still considering a tune since I have no idea if it's been tuned with the 60s

 

Got home early, pulled the injectors again and took a look at the MAP sensor, looks pretty dirty (see pictures). Going to try cleaning it and see what it does.

 

Cleaned the MAP sensor and it didn't seem to help any. Any other insight?

 

That MAP looks like death, not a good sign. How nasty was the intake manifold inside? If there's oil all over that sensor, you may have a PCV valve stuck open causing way too much oil in the manifold. Or you have a cracked ring or some sort of mechanical problem.

 

Would a cracked ring still yield good compression? Even on all 4 cylinders. I'm going to check the pcv today. Thanks

 

definitely seems like a map issue if its not reading right at idle or reading boost. does the boost gauge go up when in boost? because that gauge is referencing the sensor.

i recommend checking the intake mani for excessive buildup like joe said