This took a long time!!
The E92 ECM on the ZL1 and any LT4 engine acts as its own boost controller. It provides a PWM signal to control the boost cutting mechanism. In its native state, the ECM commands 95% (or similar) PWM to allow the supercharger bypass valve to actuate using vaccum. When the ECM determines that boost should not be allowed it will pull the PWM signal down to 5%, which will prevent the bypass valve from closing.
There is a mismatch between what the ECM provides and what smoothboost expects. When the ECM sends 95% PWM in order to allow the bypass to actuate on vaccum, Smoothboost interprets this as a disable signal and will not allow any boost to build. This mismatch was an oversight when starting this project.
Unknown to the mismatch, I started with the assumption that boost was disabled at 95%, and enabled at 0, since that is what smoothboost expected.
Continuing on, I was determined to make the ECM operate in a way that it was not programmed to. This led me down many rabbit holes and locating a handful of tables that make a blown LT1 engine behave very smooth with no errors disabled.
For all the Digging, I compared side by side the de-compiled source from a 2016 Camaro against a 2016 Cadillac. (more on de-compiling later) This allowed me to see that the core of the Boost controlling code in the ECM was the same. The parameters were however different. From here I started mixing and matching differences between the two calibrations. After a lot of trial and error I stumbled upon some DTC calibrations that looks suspicious. I had landed on the Master enable switch for the P0033-35 error routines. Once I enabled this, I immediately got a p0033 error code.
Later i found out that the P0033 code is because the Smoothboost actuator has different electrical characteristics than the standard LT4 Boost controller. I was able to locate the expected resistance values for the P0033-35 codes, and was able to make the ECM happy.
From here, I dug into the P101, and P1101 error conditions that appeared. The SCIAP sensor has a extra table that adds into the P101 error routine. These are enabled under a specific Pressure ratio of the engine. In LT1 vehicles this was set to 1.0, while on LT4 it was set lower like .97. This small difference curbed all the P101 and P1101 errors I was seeing.
As I continued on, Attempting to make the LT1 behave as close to a LT4 as possible. This was the last time I ever saw the Bypass pwm go to 0. After fixing P1101 and P101, the ECM never commanded 0% duty cycle. Even though I did not accept that it was working as expected it very much was. I continued to Fight to find a table that would allow the bypass valve to actuate. But I was not able to…
I was stopped here for a long time, Until i requested a ZL1 log and put 2 and 2 together and saw that a factory ZL1 boost PWM actuated in the same manner that I was seeing. This is when I realized that I had the logic backwards….
For now, I have set the experiment down, Since the ECM is always allowing Boost unless an error condition occurs (or we are overboost) The benifet to me became minimal. As for now, I have accepted this limitation. I am currently using the Smoothboost’s pedal functionality to control the blower.
I suspect that once Smoothboost gets a product that has the same electrical characteristics as the stock controller that this will work much better.