Alrighty... After a bunch of research and waiting a few days on DHL International; she's fixed and running great again.
TLDR: If you're replacing the Fuel Pressure Sensor on the fuel rail, you need a Bosch 0261545053
The 'Knockoff' Amazon Bosch sensor I had was SKU Bosch 0261545074. This sensor seems to only register 70 bar (1015 psi) on a 1st gen ECU. For reference, here's the Amazon link:
http://www.amazon.com/gp/product/B07XKG4CB9/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
From a thread in this section, I then tried the GP Sorensen Fuel Injection Pressure Sensor 800-90002 from Autozone. Supposedly for a 2010+ Cobalt SS. To my surprise, when it arrived, it was a rebranded Bosch sensor, with SKU 0261545052. This one only registered 100 bar (1450 PSI).
After my previous post, with my hypothesis of the sensor not reading the correct pressure, I started researching the capabilities of different Bosch sensors. In doing so, I came across this marketing material:
https://www.bosch-motorsport.com/content/downloads/Raceparts/Resources/pdf/Data Sheet_69609227_Pressure_Sensor_Fluid_PSS-140/260/420/600.pdf
As you can see, the 0261545053 is the 140 bar sensor (2030 psi) our cars require.
I don't know why that Cobalt sensor seemed to work for the other dude in his
thread, but it didn't work with whatever programming is going on in a 2008 Speed3.
My next issue was finding one... There doesn't seem to be a US based retailer that sells the 053. I ended up buying one from Finland:
https://www.finjector.com/paineantu...ppi_bosch_compact_bosch_0261545053-p-174996-0
I actually ordered it last Thursday, the April 8th, and received it today, April 12th. All told, after shipping, it was a little over $100 USD. And they threw in a Finish chocolate candy thing that my son enjoyed, ha.
I wanted to throw a bow on this for the interwebs, since there are a ridiculous amount of threads just like this with no conclusions.
