I've read a few threads saying it's normal for boost to drop off a bit towards the higher RPM's, but I wanted to get people's opinions on what mine's doing. I actually threw a 0299 code (turbo under boost) while boosting in 3rd gear (no data log for that one because I forgot to hit the button!) If you could take a minute to look at the datalog below I would REALLY appreciate it. The datalog is a 2nd and 3rd gear pull. I had to back off at 90 mph due to traffic approaching. Hopefully someone might be able to help me out. I see similar drops in boost when the tune is active and when it's not.

Just in case the graph is hard to see:
Max boost in 2nd gear = 22.6 psi @ 4500 RPM dropping to about 16 psi at 6300 RPM.
Max boost in 3rd = 21.5 psi @ 5000 RPM dropping to 19 psi @ 5500 RPM before backing off on the throttle.

MAF sits fairly constant @ ~26.5 to 27.0 lb/m even when the boost drops down at higher rpms.

https://www.cobaltss.net/gallery/sho...hp?i=76434&c=3

 

It shouldn't be dropping that much. You may have a leak.

 

That's what I was thinking. Any ideas on how to find the boost leak? Visually I can't see any cracks in the boost tubing or IC. I'm thinking about flashing back to stock and taking it in to the dealer. Just tell them the boost isn't holding. I might have to get it to pop a code again...

 

Look like you started to drop off at 5000 in 3rd...my car holds max boost (around 20.5-21)
all the way to red line.

 

I imagine a leak that small (really hidden) will be very hard to spot. I would tighten up all hoses and look for any cracks in tubing/IC end caps.

 

What are your mods? I'm wondering if the stock airbox/charge piping may be restricting the flow.

 

No, your problem is not your intake or charge piping, so don't go modding it before you fix your car. You either have a leak, or your wastegate actuator arm isn't properly adjusted.

 

I think I'm just going back to stock tune and then try to get it to pop a 0299 code, then take it to the dealer. Like you said I think there's probably a small leak in the intercooler or something.

 

Check the wastegate actuator arm. It may not be set correctly. There's a TSB about it.

 

I'm pretty sure I found the leak. There's a bolt near the bottom of the intercooler that is too long and rubbed a small hole in the boost tubing. Seems like I've heard about a TSB for that. Off to the dealer I go!

 

Think I found it..is this it?

https://www.cobaltss.net/forums/4870788-post1.html

 

Glad you found the leak X- Ray I check my car also no hole from that bolt but I can see where tha bolt rubbed on the pipe some I think having aftermarket inter cooler helped it is just a little higher everyone should take this bolt out asap or get a shorter bolt in there it being in there is just asking for trouble IMO. Really GM should be doing this on all the ss/ tc's.

 

I wonder if this is a problem with 2008 models only? Looks like both of you here plus the one I posted about are all 2008 models?? I have a 2009, but can't *see* the area just looking around. Guess I'll have to jack up the car to get underneath to see for sure.

 

my car logged 27lbs bone stock...

 

Yes my car is an 08. I had checked this a month or so ago and thought it was ok I was looking at the other bolt that sticks up. but checked just a min ago that bolt where circled in red looks like it sits about a 1/16 of an inch from that pipe you cannot see it you have to feel for the end of the bolt it is behind the little spoiler flap. It may even be riding on the bolt I can see silver marks where the bolt was rubbing. I Dont think it rubbed through though, I am going to take it out and put in a shorter bolt in the am.

 

OK....deal is if you're not *tuned*, ECU will put ya into limp pronto with that goin' on

 

Service Information 2008 Chevrolet Cobalt | Cobalt, G5 (VIN A) Service Manual | Document ID: 2195686
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#PIP4485: Low Boost, Reduced Power and/or DTC - keywords air cac charge control cooler driveability ecm engine gas hole lnf low maf mil P0101 P0299 P2178 pipe power reduced reducdpwrmde rub ses start stall - (Sep 26, 2008)


Subject: Low Boost, Reduced Power and/or DTC


Models: 2008-2009 Chevrolet Cobalt SS Only




--------------------------------------------------------------------------------

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
If a technician encounters a low boost/power condition and/or dtc, the following may help.

Recommendation/Instructions:
When a technician encounters a low boost/power condition and/or related dtc on a 2008-09 Cobalt SS they should inspect the right side CAC-(Charge Air Cooler) pipe for contacting a radiator support bolt. Due to the location of the CAC on 2008-09 Chevrolet Cobalts a radiator support bracket bolt on the right front may make contact with the lower charge air cooler/hose from below. This contact may cause the CAC to leak boost or vacuum if a hole is present. Review the illustration to see the location of the suspect bolt. A thick washer may be added to the bolt to increase clearance.

Note: Bulletin 07-06-04-029 should be used to diagnose the charge air system when leaks are suspected. This bulletin may be aided by using the evap smoke cart to introduce smoke to the CAC system.






(1) Right lower radiator support bracket

(2) Right front lower Charge Air Duct concern

(3) This bolt will wear a hole in the Charge Air duct

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION


Š 2009 General Motors Corporation. All rights reserved.

 

Thanks! Looks like it came out Sept 08, so maybe 09 cars like mine built later on were *taken care of*?

 

Shoot some dish soap around the duct and watch for bubbles. Simple. Got a Dremel?

 

I just dropped it off at the dealer. I just want to get the pipe replaced. It's a pretty significant hole in the pipe, so I just want it replaced. Hopefully the part won't be on back order or something. Maybe they'll put in aftermarket piping and I'll just pay the difference. I'll post back after I hear from the dealer.

 

Aftermarket pipe's are most likely cheaper than new OEM from the dealership...... even at their cost lol.

 

You're prly right! Lol. And my dealer is pretty cool so maybe I'll start looking around for aftermarket cold side pipe and see if anyone has it in stock.

 

It's not the pipe...bolt ate a hole in it.

 

OP take your car to the dealer there are a number of tech bulletins out for that issue just don't tell them about your tune and it should be warrenty take it from me i'm a tech at a chevy dealer and just fixed a car for the same problem

 

Yeah, I know. I was thinking that if the stock pipe was on backorder and was going to take months to get it I would try to go aftermarket. But turns out the pipe will be in on Monday or Tuesday next week.