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Discussion Starter · #1 ·
Okay, I've searched high and low, read a billion threads (okay, not THAT many, but enough) been from site to site, group to group and I just can't nail this one down.
Full story, back in November-ish, I bought my '05 Aero (Automatic), there were issues. It wouldn't boost and had a loud shrieking noise when spooling. Dealer replaced turbo, boost controller and vacuum lines coming off it, new DIC and plugs. Car still wouldn't boost. Figured out it was a plugged cat. Replaced that and the car boosted to 15 psi max (according the Torque app) and felt great. Still had an odd shrieking noise. Tightened down all the exhaust manifold bolts (including the turbo manifold). Things seemed great for a while. Then my exhaust started vomiting the hair of the Adams Family out the tail pipe. Muffler was now blocked up since all the packing was, well, now unpacking (it even spewed out of the joint right at the start of the muffler box. I got a whole new OEM Resonator and muffler. Now it flows free as a bird, BUT... Using the Torque app to monitor boost levels from MAF, I'm now getting 19+ psi. There's still a shriek, only at max boost. (I think it's this ONE stud I can't tighten down enough on the turbo manifold). I've checked the wastegate arm, seems fine and while driving, I can see the boost fluctuate here and there as it normally should given the air request/torque demand etc. I can run the engine hard, the boost doesn't creep up as I've read in some other posts about overboost issues.
For example, I can do, say, 1/2-3/4 throttle, up a hill, and the boost will climb to where it needs to be and stay there, then slowly taper off when the demand isn't as high. It's ONLY when I push for max pressure, it goes into the 1st 1/8 (just shy of 1/4) into the red. No misfires, no hesitations, no fuel cut. Car just flies.
I have zero way to know if this thing was tuned previous to me purchasing it (which, hey! I'm okay with it being tuned). If it is stock, am I in for a world of trouble with this issue? I'm at a loss as to 'Leave it as is since the car does actually run fine' or 'pull what little bit of hair I have left' out trying to find this damn paranormal overboost ghost.

Any ideas?
 

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Could you be seeing the 20 second (or whatever it is) overboost function? WIS has a detailed explanation.
 

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It won't have the factory overboost function if its an automatic. Maybe it has a tune? If you hold the - and + keys on the SID does it show open SID? Was the turbo replaced with a genuine mitsubishi td-04, or off brand? It could be something with the wastegate, but it's odd there is no fuel cut. Maybe there is a tune?
 

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How do you know for sure that it is over-boosting? Is the torque app actual pressure read from the MAP sensor or just some type of calculation?
 

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Discussion Starter · #5 · (Edited)
How do you know for sure that it is over-boosting? Is the torque app actual pressure read from the MAP sensor or just some type of calculation?
The torque app streams data direct to your android device from the OBD II port through an OBD II reader. Boost is measured from MAF, you can change it, but the most accurate is from MAF. When I had a 9-3ss Linear and read boost data from torque. 8 psi was pretty much max consistently so it is pretty dead accurate.
My assumption on over-boosting is that the needle on the dash shouldn't cross over into the red since I don't live out in the mountains where the air is thin, so I'm just assuming it is over-boosting. Plus the fact that since I've cleared all the exhaust restrictions, I went from 15 psi to 19 psi. 19 is a bit much for stock no?
 

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Discussion Starter · #6 ·
It won't have the factory overboost function if its an automatic. Maybe it has a tune? If you hold the - and + keys on the SID does it show open SID? Was the turbo replaced with a genuine mitsubishi td-04, or off brand? It could be something with the wastegate, but it's odd there is no fuel cut. Maybe there is a tune?
Checking for open-SID was the first thing I did when I got the car and I don't have that (bummer). As far as I know it's genuine, if not it's a damn good knock off. Since the wastegate is okay (I can move it with my hand even while the arm is connected) that's where I'm perplexed, plus the fact that I have no fuel cut or any other indication that something is wrong. It just cranks out the boost like it wants to eat whatever is front of it. It drives perfectly fine and smooth. Just goes into red at WOT.
 

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I see, kinda what I figured. I'll have to disagree with you on the accuracy of the MAF for boost. Boost is a measure of the pressure in the manifold. MAF = Mass Air Flow, measuring the amount of air "flowing" by the wires on the sensor. This is also how the load/turbo gauge gets its reading as well. The ECU assumes boost pressure should be X based off what the MAF is reading. The MOST accurate way to measure actual boost pressure would be the MAP = Manifold Absolute Pressure, which measures the actual pressure that is in the manifold (many of them read atmospheric pressure KOEO, not sure about SAAB). To see exactly how much boost pressure you have it should read off of the MAP sensor, or T in a gauge to one of the lines from the manifold to see true pressure.

The point I am getting at is you are assuming the car is over-boosting based off of a calculated number from a sensor not designed to measure pressure. All signs currently point to an unmodified ECU on a vehicle with no other symptoms of over-boosting so I personally would get a more accurate boost reading before I chased down a suspected problem that might not exist.

BTW - I see the turbo gauge hit the lower part of the red on both my SAABs when I go WOT and there is only flat ground near me too.
 

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I'd switch torque back to MAP and see what it shows. I use the MAP sensor for boost in my car and it seems pretty accurate. Sounds like everything else is stock. I too get the needle a little in the red and usually see 14.5psi-15 on torque
 

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Discussion Starter · #10 ·
I'd switch torque back to MAP and see what it shows. I use the MAP sensor for boost in my car and it seems pretty accurate. Sounds like everything else is stock. I too get the needle a little in the red and usually see 14.5psi-15 on torque
I will go for a test run set as map and see what I get.
 

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Discussion Starter · #11 ·
I will go for a test run set as map and see what I get.
Just came back from a run with Torque set to read from MAP. Seems that nothing is wrong. 15.2 psi. On my 9-3ss if I set it to MAP it would read like 27 psi but in MAF 8 or so psi. Different car, different setup I guess.

Thanks everyone! Now to get some silicone hoses to replace all the vacuum lines. Yipee!
 

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I know nothing of t8, ie, your SS.

However, T7 systems shoot for a requested air mass; not a target boost pressure. Ie, on a cold day, it will build 'less boost' because the air is denser. You may hit 12-13-14 psi. On a hot day, or at altitude, a stock aero will hit high teens if I am not mistaken.

The turbo is there to provide the requested airmass to the ECU; altitude and weather will have an effect!

T5, ie, NG 900's and '99 9-3 units are solely MAP based, and shoot only for a boost pressure target. This is why on chilly days, the car goes a bit better; at altitude, a bit less so, etc,etc
 
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