LS swap electronics

[mhiscott]

Over the past few months, I've been toying with the idea of transplanting an LS2/T56 from a 05/06 Pontiac GTO into my 2013 FRS. I am comfortable with the mechanical aspect of doing this swap, but I've been mulling over the best way to make it work from an electrical standpoint.

I'm no stranger to running aftermarket EMS systems, with a Megasquirt standalone and custom harness in my AE86, and reprogrammed ECUs in my Evo 3, DSM an Evo X.

The idea of running a reliable OEM ECU setup, however, has always intrigued me. I would like to use the OEM LS2 ECU, with an aftermarket painless wiring harness typically used for transplanting these drivetrains into classic muscle cars. The harness allows complete functionality with the GTO's ECU, minus emmissions controls. The original GTO drive by wire gas pedal would be retained, as well as the corresponding drive by wire throttle body. The only connections inputs required as a bare minimum to allow this sort of setup to "piggyback" off an existing chassis would be power, ground, ignition, and start wires.

What I was considering, was to remove the FRS's drivetrain, retain the FRS ecu and harness, which would be powered up as normal on key advance to the ignition position. The car in such a state would think the engine was not yet started, or stalled out. From what I can gather, all systems other than ABS/TCS/Gauges/PS/AC would work in such as state.

If I were to simply add in my new drivetrain's power harness and ECU, tied into the original harness for power/ground/ignition, I would have most of the functionality I would need to drive the car with the swapped engine.

Has anyone run a setup similar to what I'm suggesting (engine type does not matter), with essentially two harnesses working in parallel with one another independently?

To build on this, has anyone found a way to add in your own engine control solution while retaining operation of systems like the power steering?

[Calum]

I'd give Motec a call.

[taylork057]

gauges will never work unless you have an aftermarket can bus system, similar to the way hinson does for the rx8. Ps, ac, abs are all separate from ecu and will function normally if you install them correctly. You can do it im sure, but some creative thinking is necessary

Originally Posted by Calum

I'd give Motec a call.

dont waste their time.

[mhiscott]

I would be running an aftermarket cluster most likely. Unless there is some sort of canbus interface module on the market, I doubt there'd be an easy way of retaining the original instrument cluster.

Calling Motec would just have them tell me to run some standalone EMS system of theirs. The whole point with this swap is I want to retain the OEM Chevrolet electronics.

[Calum]

My bad I was thinking of this.

http://www.ft86club.com/forums/showthread.php?t=46362

"- Different Engines. Don’t want to run the FA20? Want to drop in your monster EJ257, how about an EZ30R H6, Supra 6, LS V8….no problem with the Hydra EMS as we make custom ecus for this very thing so you don’t have to rewire you chassis and loose your car’s features!!!"

[RickyB]

PS, AC and ABS will not work unless the ECU is properly integrated with the CAN bus. For example, the PS looks at a specific packet sent out by the ECU that tells it the engine is running and how much assist is required for current operating conditions. Without this, the PS motor stays off. The AC compressor is controlled by the engine ECU. It looks at the body and climate control packets to determine if the AC compressor is requested and without this, the compressor will not run when required. Without an ECU that speaks the same CAN language as the factory ECU, the dashboard is essentially dead and useless.

The only way to drop in a foreign engine and not replace or give up on most of the electronics in the vehicle is to put in an aftermarket EMS that can speak the FRS CAN protocol and run the transplanted engine. The only two units currently available that can do this are Hydra and Motec.

[SmsAlSuwaidi]

WGP already managed to do it, maybe they could sell you the harness which integrates both the 86 and LS ecu's together if I'm correct

[RickyB]

To make the dual ECU setup work, you would have to have some kind of trigger simulator to translate the engine speed of the hosted engine into what appears to be the 36-2-1 crank trigger wheel of the FA20. This would make the factory ECU believe that the engine is turning so that it would send the appropriate CAN packets out to switch on the PS, ABS and run the dashboard tach. If the host ECU uses an old style AC request pin to do AC idle up, then you may be able to feed the AC compressor request to that. You will have to do something to make sure that both ECUs see the right coolant temperature (probably install the FA20 coolant temp sensor into the new cooling system), or have the host ECU take over the function of the cooling fans. Even after all that, the factory ECU is going to quickly figure out that it really isn't in control of a real engine and various idiot lights are going to be on constantly. Also, the fuel gauge is always going to be reading incorrectly, since whoever designed this car had the bright idea to have the dashboard trust the ECU fuel consumption data on the CAN to adjust the fuel gauge.

You can certainly get the car to drive down the road with a dual-headed harness, but you will still have several annoying issues that will make the setup seem more like a science project than a great road car. Of course, if the entire idea is to build a pure race car, then who cares?

Most shops able to handle something like this will wisely choose the EMS route since that will be most in keeping with the principles of least surprise and keep the customer satisfied.

[DoctorNick]

I was under the impression WGP had it running on the LS ECU with no idiot lights on.