Long time lurker, infrequent poster here. First, the backstory on my GFs 2008 Cobalt SS/TC. We bought the car a year ago and the previous owner had added some HAHN components; MaxFlow CatCon Down Pipe, 3" SS Catback, and the Cool Ram intake. That was all, according to him and that I verified.

Fast forward to a week ago and it develops what I think is the ECOTEC tick. It was due for an oil change anyways so we took it to the dealer and asked them to troubleshoot the noise. The dealer informs me that it's not what I think, they say it's the turbo bearings. They also say that the boost was turned up which caused the bearings to fry.

That doesn't make sense to me, I thought the stock boost was around 15lbs max. I called a dealer friend back in Colorado and he pulled up GM Document ID# 1830792 which basically says the Turbo is capable of 20PSI. Full document in second post.

They are saying that they won't cover it under warranty because it was "chipped". I pressed the shop forman about it and he says he can't see anything that the original tech was talking about but that he can't guarantee that it's covered under warranty until he disassembles the waste gate to make sure it's not modified and that the computer has the correct tune.

Any ideas?

Document ID# 1830792
2008 Chevrolet HHR


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Boost Control System Description




(1) Evaporative Emission (EVAP) Canister Vent Solenoid Valve
(2) EVAP Canister
(3) Non-Return Valve
(4) EVAP Canister Purge Solenoid Valve
(5) High Pressure Fuel Pump
(6) Camshaft Position (CMP) Actuator Solenoid
(7) Charge Air Bypass Valve Solenoid
(8) Charge Air Bypass Valve
(9) Mass Air Flow (MAF)/Intake Air Temperature (IAT) Sensor
(10) Turbocharger Wastegate Solenoid Valve
(11) Turbocharger Wastegate Actuator
(12) Camshaft Position (CMP) Sensor
(13) Ignition Coil/Module and Spark Plug
(14) Fuel Injector
(15) Charge Air Cooler (CAC)
(16) Turbocharger Boost Pressure Sensor
(17) Throttle Body (TB)
(18) Manifold Absolute Pressure (MAP) Sensor
(19) Fuel Rail Pressure (FRP) Sensor
(20) Engine Coolant Temperature (ECT) Sensor
(21) Engine Exhaust Manifold
(22) Turbocharger
(23) Heated Oxygen Sensor (HO2S) 1 and 2
(24) Catalyst
(25) Crankshaft Position (CKP) Sensor
(26) Fuel Pump Module
(27) Accelerator Pedal
(28) Theft Deterrent
(29) Data Link Connector (DLC)
(30) Malfunction Indicator Lamp (MIL)
(31) GMLAN Serial Data
(32) Engine Control Module (ECM)

Boost Control Description and Operation
A turbocharger (TC) is a compressor that is used to increase the power output of an engine by increasing the mass of the oxygen and therefore the fuel entering the engine. This BorgWarner™ dual-scroll TC is mounted on the exhaust manifold and the lightweight turbine is driven by the waste energy generated by the flow of the exhaust gases. The turbine is connected by a shaft to the compressor which is mounted in the induction system of the engine. The compressor vanes compress the intake air above atmospheric pressure, thereby greatly increasing the density of the air entering the engine. The TC is capable of producing up to 20 psi, or 1.40 bar, of power-enhancing boost.

The TC incorporates a wastegate that is controlled by a pressure differential, that is determined by the engine control module (ECM) by means of a PWM solenoid, in order to regulate the pressure ratio of the compressor. A TC bypass valve is integrated within the unit, and is also controlled by the ECM by utilizing a remotely mounted solenoid to prevent compressor surging and damage from vibrations by opening during abrupt closed throttle conditions. When the valve is commanded open during closed throttle deceleration conditions, the bypass valve allows the air to recirculate in the TC and maintain compressor speed. Within a calibrated range during the closed throttle event, or upon a wide open throttle command the valve will then close to optimize turbo response.

TC Wastegate Closed




(1) Turbocharger Wastegate Solenoid with Duty Cycle at 100 percent
(2) Compressor
(3) Turbine
(4) Exhaust Gas Pressure
(5) Spring Force
(6) Turbocharger Wastegate Actuator

The wastegate is completely closed at idle. All of the exhaust energy is passing through the turbine. There are three reasons that the wastegate remains closed:

• There is a lack of compressor outlet pressure. Lower compressor outlet pressures tend to close the wastegate via the pneumatic connection to the actuator.

• The return spring within the actuator is helping to keep the wastegate closed.

• The low energy of the exhaust gas flow is not enough to overcome the return spring force.

During normal operation, if a wide open throttle were to be requested at lower engine speeds, the ECM will command the boost control solenoid with a duty cycle of 100 percent to minimize any turbo lag. During engine loads in the middle and upper RPM ranges, the ECM will command the boost control solenoid, with a duty cycle of 65-80 percent. Manifold pressures of up to 240 kPa are possible.

TC Wastegate Open




(1) Turbocharger Wastegate Solenoid with Duty Cycle at 0 percent
(2) Compressor
(3) Turbine
(4) Regulating Pressure
(5) Exhaust Gas Pressure
(6) Spring Force
(7) Turbocharger Wastegate Actuator

When certain DTCs are set the ECM will limit the amount of available boost pressure. Limiting boost pressure is accomplished by the ECM controlling the TC wastegate solenoid and maintaining the duty cycle at 0 percent. This means that the ECM will not actively close the wastegate during greater engine loads. The system at this point is limited to mechanical boost. Mechanical boost means that the wastegate will still move, but the amount of motion is limited by the mechanical properties of the return spring within the actuator, the pneumatic properties of the actuator, and the physics of the exhaust gas flow in the exhaust system. In this mode of operation the manifold pressure will attain a maximum pressure of 140 kPa.

The TC wastegate actuator assembly has a threaded rod and nut that connects the diaphragm of the actuator to the wastegate. This rod is adjusted to BorgWarner™ factory specifications and is not adjustable.


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Document ID# 1830792

 

Wow.....yeah stock boost on average is 15. The car makes more or less boost depending on where you live to make 260/260....gm stage 1 upgrade takes the boost to 20 and the same thing goes for that. Some people seen up to 22psi on their car stock to make 280/320

 

I knew it was a variable system, I've tried like hell to get this thing to hit 20PSI and can't. I'm really starting to think it was a lazy tech because the shop foreman didn't even try to stick up for him.

 

Stock boost is 15...

 

You might wanna take that car somewhere else. When they start making up excuses that make no sense of why it's broke and they might not fix it, you are in for a fight. And once they definitively decide that and write it up in the computer you are screwed. It voids your warranty completely and not even calling gm customer service helps because they just talk to the dealership and hear the same story and stick up for them. I had this happen to me when my head started leaking oil from a hairline crack somewhere and took it to the dealership. They did a few minor things first without a problem, but when they found out that they were going to have to do more extensive and expensive work like replacing the head, the excuses started rolling in. They claimed that the mods I had were the cause of an oil leak. At the time all I had was an intake, 2.4 IM, header, downpipe, and exhaust. They went as far as to say that my aeroforce interceptor gauge was a performance device and was a partial cause in voiding my warranty. This may not be the case with your dealership, but just trying to help you out. And from my experience when they start telling you things you know aren't true, watch out.

 

GTOhaas07,

I would be happy to verify with our Technical Assistance Center about the boost operation. Would you please send me the last 8 digits of your VIN?

Best,
Sarah
GM Customer Service

 

Thanks for the offer but the dealer came through after some pressing. They are replacing the turbo under warranty.

 

Very glad to hear it! Keep me posted on how everything is running after the turbo replacement.
Best,
Sarah
GM Customer Service