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Discussion Starter · #1 ·
Hey everyone.

I've owned my 08 GXP for about 5 years now. Just after I bought it, I had the GMPP tune, intake and exhaust done on it. I was seeing boost as high as 26psi. Just recently, I noticed that my boost level only hits a max of 20psi. I don't drive the car that often, however I recently have been home more often and the weather has been nice, so the Solstice gets to come out more. It only has 25k miles and has never had any engine codes. What could be the issue?
 

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Boost pressure depends on a lot of items. Items that can be related to weather (mostly). Just because you're now only getting 20psi, doesn’t necessarily mean that you aren’t getting the same horsepower. The humidity in the air could be a lot less, requiring less air (boost) to mix with fuel. The temperature could be lower, therefore needing more air (boost) to burn the fuel….

Now that being said, I understand where you’re coming from. My old charge tubes I was seeing 22psi consistently. I put new tubes on and saw 25psi for a few days and the car had really come to life. It’s now settled at 19psi. I am just attributing it to the fact that even though I’m tuned, the “learn-down” feature is still enabled in my tune. So, I will be pursuing a new tune in the next 2 months…..
 

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The GMPP tune still has certain safeties built in to prevent you trashing you turbo. That may be what has adjusted the pressure downward.

26 psi is really high for that tune!
 

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Did your dealer solder the 3 Bar sensor MAP connections when he/she did the installation?.
If it was not solder, then you need to do this period, to save you of instances like this.
 

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Discussion Starter · #5 ·
Did your dealer solder the 3 Bar sensor MAP connections when he/she did the installation?.
If it was not solder, then you need to do this period, to save you of instances like this.
It's been a while since I've had the tune. Where do I look for this?
 

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It's been a while since I've had the tune. Where do I look for this?
Driver side IC pipe. The 3 Bar sensor will be attached to it with a single screw and wires attached to it. You need to look at these wires and see if it was soldered or crimpped.
 

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Discussion Starter · #10 ·
Reviving an old post. Everything in the engine bay is tip top. It finally dawned on me that I started to use non ethanol premium gas around the time I noticed my boost numbers go down. Is it possible that the better fuel is making that much difference? Less boost is needed to achieve the same HP? What do you think?
 

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Fuel shouldn't make a whole 6psi of boost difference. I just had a boost issue and replaced my purge valve and it really made a difference. I was at 22psi last year and this winter was only boosting to 18 when I would take my car out...sometimes only 15psi. I decided to take some advice and replace the purge valve, even though the "blow through" test passed. I have consistently seen 23psi since the replacement! But, in my defense I was getting the code p2188 - too rich at idle as well. Haven't driven it enough to see if that code has gone away. The other cheaper thing you might try is replacing the bypass solenoid. It sits right next to the purge valve and costs about $50. It's like the BOV. If that doesn't fix it, you could (I use could lightly!) have the dreaded IC rupture. It might not be bad enough to set a CEL, but you might lose boost because of it.... Here's my thread from this last year on my boost issue: http://www.solsticeforum.com/forum/f43/less-boost-then-expected-123353/
 

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Discussion Starter · #12 ·
I did replace the purge valve a few months ago after receiving a cel. It did blow completely through. I cleared the code and replaced with oem part. I haven't done anything else. I'll try the bypass solenoid next. Please explain more about the IC rupture. What and where is it?
 

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Actually premium fuel should give a higher boost number than regular. At higher compression (higher boost), regular will start to knock and the ECM will reduce boost. Premium (more octane, a knock inhibitor) will allow higher compression (more boost) without knocking.
 

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Discussion Starter · #14 ·
This is true. I've never used regular. Most gas stations have 10% ethanol. I have a gas station near me that doesn't add ethanol.
 

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Discussion Starter · #15 ·
So, I ordered the bypass solenoid. The dealer asked if I needed the pigtails as well. I wasn't sure so I didn't order them. Not sure I would need them. Seem like the bypass solenoid is a 5 minute job consisting of one electrical connection and 2 hoses.

I looked at the intercooler and it seems fine. So...Once the bypass solenoid arrives, I'll install and provide an update.

On a side note, I hit some high speeds today and noticed at that high speed that I could get 21psi. Slower speeds got 18-19.
 

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Discussion Starter · #16 ·
Just an update today, while I wait for the new bypass solenoid. I took a closer look at the wiring that was done for the 2 map sensors. The first one coming off the IC pipe is wired properly and soldered and heat shrinked for each wire.

It's the same for the sensor on the intake manifold except that wire 3 coming off the new sensor is not connected. It's just sitting there. Is this normal? It's not like it came loose or the connection was broken, it was just never connected. Should it have been?
 

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It's normal. In the standard setup, one is a T/MAP sensor and one is just a MAP sensor. The GMPP sensors are both T/MAPs - so the second one doesn't have it's T (temperature) wire connected.
 

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Discussion Starter · #18 ·
Ok. Great. Thanks for the quick response. I guess I'll wait and see what happens with the bypass solenoid.
 

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Discussion Starter · #19 ·
So, I installed the new bypass solenoid and there is no change. My max boost is at 20psi. So, any other ideas? I checked the wiring, which was done correctly with solder and heat shrink, replaced both the purge valve as well as the bypass solenoid. My IC seems to be in good shape as well.

What else could be the issue?
 

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Clean your MAF and see if that helps.
 
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