This section of our Gen V blog may or may not take two separate blog entries to cover. However, this is one of the more important things in considering a Gen V swap.
One of the scariest things I personally encountered in building my Nova and utilizing this new combo is the great unknown of wiring, electronics, and what is and isn't needed. While the build front to back was uncharted territory for nearly all of the car world, the electronics were like some mythical creature everyone claims to have seen and know but nobody could tell me they have actually touched, seen, or directly how to deal with things. Most conversations started with "oh yeah I've done tons of those, only to find out they have just dealt with Corvettes or Camaros that came into their shop running fine. After describing our combination, folks eyes had a tendency to glaze over and we were issued a "be careful" type of strategy from them and a good luck before the signed out.
I will add this disclaimer because I think its important. I live my life in the aftermarket auto industry as unbiased as possible. I am quick to praise quality, good components. In the same breath, I have ZERO issue calling out products that are huge embarrassing failures or that are just plain nightmares waiting to happen. If any of this offends you, I suggest you stop reading now.
To start with, we ordered for a GM swap ECU and harness Part number 19331517. This was an LT4 manual transmission swap specific harness and comes from Gm Performance parts, we ordered ours through our friends at Scoggin Dickey Performance Center. Although I was not very impressed with the harness quality or the documentation with this GMPP piece (much of their instruction manual was inaccurate or incomplete), it was about the only option out there as far as a stand alone system that would control Direct Injection and offer factory reliabilit. For under $2000 it seemed like a pretty good price, keep in mind this came with harness, ecu, drive by wire pedal, MAF, two 02 sensors, and a number of other necessary components. Note that I emphasized factory reliability. I find it quite scary to think of some of these ECU manufacturers controlling Direct Injectors, lets face it, many of them struggle enough with Port Injection, a place where there is much more room for error that will go un noticed. But I digress...
Our GM harness came with so many plug ins, it was scary to even myself who I consider a seasoned EFI enthusiast. Many of the same plugins you will see in a standard Gen 3 or 4 motor including cam, crank, coil packs, map sensor, maf, 02s. However, there are some very NOTABLE (read important) pieces that need to be addressed. Vehicle Speed Sensor, otherwise known as VSS. This sensor plays a pivotal roll in the tuning of these engines. Without getting too deep into it, fueling is calculated on estimated torque numbers, which requires a vehicle speed to calculate as one of its factors. Try to run these engines without this sensor (atleast on a GM harness) you will be unsuccessful. Many of the people we spoke to said (oh you need a stock Corvette abs wheel otherwise this won't work). This simply is not true. With the help of our friend Scott Clark at Real Tuners, we were able to wire up a standard VR sensor to one of our Motion Raceworks Billet High Def Driveshaft Reluctor Wheels, and scale the data in HP tuners to provide the appropriate data. Simply put, bolt on one of our billet wheels to your rearend yoke, hook the two supplied wires in the harness up to the two wires of a vr sensor that faces our billet wheel and you're set. Additionally, if you are unfamiliar with a VR sensor, they're a very common form of sensor that exists in many different engines and other applicatons. When we discovered the need for this we were pressed for time and just went ahead and stole a sensor out of a 2017 Coyote Ford Motor, the crankshaft sensor. We made a bracket and went along our way. There are MANY different options available and most all will work fine. If you are unfamiliar with our driveshaft wheels, click below.
In addition to the VR VSS sensor, there are a few other sensors that deserve notable mention. Always plug in the Fuel Line Pressure sensor. This is the sensor that gives feedback to the ECU on incoming pressure for the High Pressure Fuel Pump that is cam driven (next component in line). There is a solenoid on top of said fuel high pressure fuel pump that allows fuel in and out as necessary, thus needing to know whats coming and whats after it to control fuel flow properly to the direct injectors.
Next is a sensor that plagued us from almost the beginning, and it requires some attention. This will not be the last we hear of this issue so take notes. The direct injection fuel injector harness (a subharness of the main harness) on the driver side has a built in High Pressure Fuel Rail Sensor connector. This subharness has two variations so far in the LT world, one variation contains a 3 pin connector for the fuel rail sensor, the other has a 4 pin connector for the sensor. Both Subharnesses plug in IDENTICAL to the main harness, leaving you to do nothing but guess on the subharness compatibility. Note, these subharnesses do NOT come with the main harness. These subharnesses are a mid year switch type of item. Even more fun, I believe the GM main harness in this kit may vary also. It is CRUCIAL that you match the correct subharness here with main harness you are supplied. Because we started our journey with the wrong harness, our HP Tuners was showing 4300 psi on the rail (wrong sensor, wrong subharness) and therefore the engine would not command more fuel and would not start. We scratched our heads on this one for quite some time, believe me. Switched to the correct subharness and sensor and the motor popped right off.
Another sensor that can be quite troublesome is the MAF sensor. Most of us GM guys are used to turning that sucker off and running Speed Density and letting er rip. I am here to tell you that this is simply not possible, in stock ECU format, with a DI engine. Plan to run your MAF sensor for the duration, it is not an option. We contacted every single knowledge bank of Gen V tuning including HP Tuners themselves, these ECU's require a MAF to run. Bottomline...
Last but CERTAINLY NOT LEAST do not overlook a Top of Clutch Engagement switch, or Clutch Switch in general. When we embarked on Hot Rod Drag Week our Nova was BRAND NEW and we were wiring the car in the tech lanes, I'm not kidding, my copilot Nick and I wired the Battery cutoff switch, tail lights, and blinkers in. That being said we COULD NOT get the car to open the throttle blades past 40%. The engine had no codes, ran great otherwise, the engine would not make anything over 0 psi of boost. This had me the type of confused that makes a guy just want to scream (imagine how embarrassing it is driving miss daisy down the track in front of all your Drag Week buddies because the throttle won't open).
After combing through some very undocumented and unfinished paperwork we received from GM I found a blurb about a top of clutch switch. We were assured it was not needed, but opened HP Tuners and there was a line in the datalog that says clutch switch engaged, and it said yes next to it. From the factory, these engines are given some built in ECU safeties to protect themselves and their drivelines. Basically GM doesn't want you to side step the clutch on a 630 horse LT4 and shatter everything behind it and then bring the car in for warranty. So in summary when the clutch is in the engine is limited throttle and power. This switch acts backwards, when its released the circuit is closed. When the clutch is depressed the circuit is open, when the clutch is released the circuit is closed (backwards of how a typical switch like that works). The second day of Hot Rod Drag Week we spent our night (see picture of me waste deep in a wiring disaster looking for two stray wires) tearing a beautiful wiring harness that our friend Brad Nagel so tediously built apart and found the two "Top of Clutch Engagement" wires, purple and yellow two colors I will never forget, and connected them (closed the circuit) and voila.
Here is a list of sensor and plugins you can do away with/turn off. AFM, DOD, Boost Bypass Valve, Alternator, Fuel Pump Module/PWM module Main plugin. These as well as a few others (I am sure I am missing some) can be code cleared or deleted from the tune completely using HP Tuners.
In summary, the Gen V ECU in stock form is MUCH more temperamental in terms of what data it HAS to have in order to operate correctly (or at all). Keep in mind these engines also control a Drive By Wire Throttle Body as well. If many of these codes or sensors are not satisfied, the throttle blades simply won't open past 30/40%. In the end of the day, it is nothing to be scared of, and as these non stock form swaps become more prevalent, this may all become basic standard knowledge. My goal for this particular blog is to hopefully put in writing some of the problems WE experienced so future swappers can reference quickly and troubleshoot.
As I mentioned in my previous Fuel System Blog, it is asking too much of the fuel system to push one of these engines above the 1000-1100 threshhold, atleast for any reasonable budget, also from a reliability standpoint. That being said we decided long before the first wire was ran on our swap that we were going to add a "piggy back" ecu to add a second set of injectors for a port injection. Basically we are running supplemental fueling to the motor through 8 port injectors that are installed in to the 417 Motorsports lower intake manifold much the same as a standard LS engine would have. In order to do this we picked up a number of sensors. I will discuss THIS and more in our next blog. Stay tuned...
Go Fast. Be safe.