So, on the assumption train (all aboard the assumption train!), I had another one to test today.
The drivetrain combo in my car is a little weird, because I have an early(ish) LT4 (2016) with a total bastardization of rear drivetrain (C6 bellhousing, late C5/early C6 torque tube, late C6 Grand Sport transmission and diff). This ended this way because I wanted a TR6060 not T56 trans and the stronger Z06/Grand Sport diff and gearing. The bellhousing and torque tube came from a guy that damaged his torque tube and bought a built one, but he had a first year C6 which apparently had a C5 style torque tube? I dunno, but my torque tube and bellhousing didn't match and I had to build a spacer to get the stack up right. I could not do a C7 transmission as the 7 speed is >1" longer and I don't have that kind of room to spare in the back of the car.
Annnnyway, long story short the C7 ECU expects a hall effect (3 wire) speed sensor for VSS. The C6 has a VR (2 wire) sensor. They make a setup to put a hall effect on a C6 diff (technically it's for the side of a T56, but it could be made to work), but it's about 2" longer than the stock sensor, and I have about 1/16" of clearance (it's a 10 minute job to plug in the damn sensor, I'm going to address that this winter) between the sensor and the trunk floor.
So, I need to put a VR sensor on an ECU that wants a hall effect. Here's where assumption comes in. GM sells an LT4 crate motor with control pack. This control pack, which is also an E92 ECU of the same generation as mine, has an input for a 2 wire VSS. This is on a different pin which is unused on the Corvette ECU. So I wired it up to that. Unsurprisingly I didn't get speed readout on the ECU when I drove the car. Not optimal. But then the question was this: Is this a tune setting, a segment swap, or an entirely different OS required (and if the latter, what else does that impact). I downloaded a crate motor tune, did a compare and found a setting (TOS, aka Transmission Output Speed, hardware). Changed that to match the crate motor and tested.
Works! Speed is WAY low, I put it in 6th (I have no axles just stub shafts right now) and spun it up and it showed like 19 MPH, but it does increase in speed proportionally to output shaft RPM, so I should just need to adjust the pules per mile until it lines up. This is great news as otherwise I was going to have to use the hall input and build a VR -> Hall setup and mess about with all of that which is a PITA.
About time I had a victory. I also have my updated CAN gateway in and validated that all functions now work properly. Tach, speedo and temp read from the GM ECU correctly and update on the dash in real time, control of the engine start button status/enable is correct, and dash "wake up" and control of the ABS and TCS lights work. Victory.
I also played with the idle tuning a bit to try and get it happier. It's not happy yet, but it's much less angry, so that's a good start. The big goal is everything is generally working now, before I rip it apart to build the new wiring harness and put the high flow GDI injectors in. I do need to decide if I want to snag a high output GDI pump and port the blower/throttle body while it's apart, but honestly I'm not sure that ~800 RWHP is better than ~700 RWHP in this car, or at least not sure it's worth $4k, anyway.
