My car: 2005 Cobalt SS/SC

My mods:
- 3" Fujita cold air intake w/ AEM dryflow filter
- 3"/2.5" Downpipe w/ highflow cat

Misc:
- Operating temps have stayed below 200 consistently, no excessive heat has been observed.
- My average fuel economy is between 30-32mpg mixed driving
- The spark plugs show even and normal wear
- No codes of any type are currently being thrown and all connections have been checked as I recently detailed the car.

The problem:
While driving I notice my car will experience a fluctuation in boost around when it reaches 7psi it will surge to 10-12 psi then drop back down to 8-9 during acceleration. When I near redline the boost will sometimes fluctuate between 12 and 14psi. The boost will do this at varying cruising speeds as well but i observe it most under the said conditions. I have only noticed this after I installed the performance downpipe. I don't fully understand how the addition of a higher flowing exhaust component would cause the boost to fluctuate in this manner. Has anyone else experienced this problem? My initial thoughts are maybe some type of leak in the hoses, or an ecu hiccup. I would love to hear any useful suggestions based on the information I have provided.

 

Do you feel the car surging as well, or is it just seeing the guage move? Also, if the car is totally stock minus the intake and downpipe I believe the ECU will limit boost to 12.5. Do you have an aftermarket exhaust or just the downpipe? It almost sounds like this could be a cat problem.

 

Are you checking your rpms too? Do your rpms move with the boost because you could have a slippy clutch.

 

The rpms dont really have time to move, it happens really quick so there isnt enough time for the car to surge forward. The exhaust is completely stock and so is the manifold. The only thing I have modified is the downpipe.

 

I paid attention to the problem tonight, The rpms were non responsive to the boost gauge. I also tested the clutch and its not slipping. Any, other ideas folks? How would i be able to tell if it was a cat problem?

 

bump

 

maybe you have a bad gauge. that or im mis understanding the problem can you FEEL the boost bleed off? or is it just the gauge going crazy?

 

defective gauge

 

must be. changing your downpipe and intake wouldnt do anything. they may make your car feel jerky because of a bad maf or bad o2 sensor but it would NOT affect your boost

 

ftw er ftl

Actually don't you get a decrease in boost from swapping exhaust components particularly header/downpipe?

 

i was thinking it might be a bad gauge. I would expect boost to drop after the intake, due to a loss in pressure, but hp could be had due to a gain in volumetric efficiency.

 

slight decrease... nothing redic and it wouldnt cause it to fluctuate