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Cobalt SS 09 LNF - 80K KM

Bought this car from a dodge dealership a few months ago and now it seems to be acting up. Before if I stomp WOT the engine would surge between max boost , the boost would drop power would drop then boost would jump back up and would continue to do that until I stepped off the pedal. Now lately if I stomp WOT the car I get a big blast of boost then seems to go into limp mode. Note I don't get any engine lights or pending codes at all. The reason I think it goes into limp mode is I hear the turbo spooling and i get about 2psi 13KPA. I pull over and shut the car off and volla I got full boost again.

Now I was told the car was stock when I purchased it, after looking under the hood, everything in fact looks stock but you can see bent rivet and clips around the air box and lights. Any ideas what can be going on? When the engine is in limp mode is there a mechanical movement of the BOV? If so could that mean maby I have a vacuum leak and not getting enough vaccum to open the BOV then its overboosting and going into limp? Other than that the engine seems to run fine, and like I said no CEL's at all.
 

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Yah I know, whatever they are called they recirculate air back into the intake manifold, but if I had low vacuum could it prevent the valve from opening quick enough to prevent overboost perhaps? And no there is not boost controller like I said everything is stock, unless the previous owner tuned it but if he did it would of most likely been a mostly stock tune so I don't think it would cause this?
 

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Did you check for codes or you assumed that if the CEL wasn't on you had no code. Reason I'm saying is because ECM cannot put engine into limp mode without setting a code. Does your CEL lamp work or come on when you turn your key without starting the engine? Something is odd here.....
 

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Yah thats what I mean, I get no codes. I even plugged it in to see the history, nothing, and nothing is pending. It did it again today too, stomped on it in about 4th gear full boost, then nothing until I got it home. Shut it off for a minute started back up and full boost. I am clueless. (I don't know what my vacuum is at idle, got nothing to measure it with or tools until I get home, currently doing some training in a different province) And yes the light works, and I had to clear a code recently because my gas cap wasn't sealing properly which set off a code.
 

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you have a vac/boost gauge... what is your vac at idle? is your turbo hooked to your wastegate with a vac line? i'd say maybe your evap. it's hard to tell without knowing all the codes or hearing the car run
 

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Discussion Starter #8 (Edited)
you have a vac/boost gauge... what is your vac at idle? is your turbo hooked to your wastegate with a vac line? i'd say maybe your evap. it's hard to tell without knowing all the codes or hearing the car run
I have the digital display (RPD) doesn't tell me vacuum. And like I said before there are zero codes. The car starts fine, runs fine, the issues begin at WOT. And I thought the wastegate was controlled by a solenoid? I don't know, whatever the stock setup would be.
 

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it's controlled by the compressor housing. check to see if the vacuum line is still there

---------- Post added at 07:26 PM ---------- Previous post was at 07:25 PM ----------

i'm gonna go ahead and assume either your wastegate failed or it's not hooked up
 

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How could my wastegate have failed if every time I restart the car it works fine until I WOT again? Everything looks connected.
 

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Ok, time to shed my light into this subject.

First off, these cars have an EBC (Electronic Boost Controller) that is built right on the side of the turbo (it's the black electronic control box with 3 vacuum lines on it). Check those lines. Make sure all are hooked up, one is a reference from the engine, one goes to the Wastegate and one goes to the stock BPV (By-Pass Valve (not BOV)). The shortest one goes to the nipple on the turbo housing itself for a boost reference line, the T-off nipple on the boost controller goes to your Wastegate, and the one at the opposite end of the reference line goes to the BPV. If those are wrong, you won't get boost, after the first time you boost.

Now, you say you hit "max" boost, now as these cars have the automatic learning feature where they will automatically increase/decrease boost to keep you at the 260hp/260tq output at all times unless you are tuned, about what is your boost at when you are at "max" boost?

What I am most interested in hearing about is your "surging" you are talking about. To me it honestly sounds like there is something wrong with the tune or something wrong with the vacuum lines for the turbo.
 

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Discussion Starter #14
Ok, time to shed my light into this subject.

First off, these cars have an EBC (Electronic Boost Controller) that is built right on the side of the turbo (it's the black electronic control box with 3 vacuum lines on it). Check those lines. Make sure all are hooked up, one is a reference from the engine, one goes to the Wastegate and one goes to the stock BPV (By-Pass Valve (not BOV)). The shortest one goes to the nipple on the turbo housing itself for a boost reference line, the T-off nipple on the boost controller goes to your Wastegate, and the one at the opposite end of the reference line goes to the BPV. If those are wrong, you won't get boost, after the first time you boost.

Now, you say you hit "max" boost, now as these cars have the automatic learning feature where they will automatically increase/decrease boost to keep you at the 260hp/260tq output at all times unless you are tuned, about what is your boost at when you are at "max" boost?

What I am most interested in hearing about is your "surging" you are talking about. To me it honestly sounds like there is something wrong with the tune or something wrong with the vacuum lines for the turbo.
Thank you for that detailed post I'll have a good look at what you described tomorrow. I am starting to think it is a computer related issue because I am not getting any engine codes when the car goes into limp mode like overboost codes are turned off. And if I had low vacuum I would notice the car running like crap at idle (and no boost conditions) and possibly codes? Everything on the car right now is stock, (I picked it up used). If the previous owner did tune it though I would think it would be a very shy tune to work with OEM components so it shouldnt cause these issues. This is very confusing.
 
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