After reading this I have no doubt that most of you will put it in the “too hard basket”, but you shouldn’t look at it with such negativity, just treat it as a challenge and a chance to learn far more about your car than you ever wanted to know.
So here's what I see as the options;
Option 1. Separate loom, probably the easiest way to get the engine running. Provided you know enough about the sensors and the requirements of the coils/injectors this method would get the engine running in the shortest time. However it may not be the best answer when it comes to getting the car fully functional, as there may be some issues with the other circuits that will cause problems, e.g. Tacho signal. This is the option I would choose if I were installing the motor in a different car with fewer interconnected systems, and is the approach I chose when I installed the M800 in my MR2.
Option 2. Plug & play adaptor loom. This requires that you know what the wires in the existing loom connect to and what the specs of the various sensors/actuators are. As there seems to be a lack of documentation on the GT-T wiring this will involve a lot of time spent with an ohmmeter and oscilloscope and a fair amount of trial and error accompanied by a large amount of frustration trying to get the aftermarket ECU to accept the sensors or provide the required output signal. The virtue of this method is that you should be able to get a fully functioning car provided the chosen ECU can supply/interpret the required signals. This is the option I would choose when installing an aftermarket ECU in a GT-T.
Option 3. Piggyback the ECU on the existing loom. Possibly easier to do than Option 2. However it would require some duplication of sensors and the stock ECU may still complain if it doesn’t have all the required ignition/injectors connected. That coupled with the messy wiring required to share looms make me very vary of trying this option.
So, assuming you choose option 2, then the required steps are as follows;
- Get a connector block from an ECU and design a circuit board to allow you to connect the aftermarket ECU to the Toyota loom. This is quite a common connector and is used in most modern Toyotas for both ECU & ABS computers so sourcing one of these devices from a wrecker is probably the best bet, provided you can convince them that the item in question is not likely to be an easily saleable proposition you should be able to get the connector for <$100.
- Get a wiring diagram or trace all the wires in an existing loom, even a Japanese wiring diagram would suffice but to date I haven’t been able to locate one. Tracing the loom out is not an easy task. Even with a loom already removed from the vehicle I would estimate it would take several days of checking and rechecking before you had anything usable.
- Obtain the specs of the sensors/actuators and/or replace them with known items. In most cases the sensors should be standard items for which at least some basic documentation is available, or calibration can be easily worked out with an ohmmeter or oscilloscope. Outputs to other devices such as the Tacho, ABS/TRC/VSC computers may be a little bit harder to determine and/or get the ECU to emulate.
- Make up and test the adapter loom. If you have done all the above steps properly this shouldn’t take very long, but it is a very important step to get right as one small mistake here can lead to big problems further on down the track.
- Set up the ECU. Again provided you have determined the signal requirements properly this shouldn’t be too hard to do, but given the lack of documentation this process may be the source of a great deal of frustration.
- Tune the ECU, that’s the easy part.
Based on some estimates I made when I first looked at doing this, I reckon there’s at least 100hrs work required before you get to the tuning phase. That’s a lot of work for a one off project, especially if you’re paying someone else to do it. However any subsequent installs would be a simple matter of making up the adapter loom and tuning, so it would make sense to get as many people involved as possible to share the costs/time involved and that way differences in models (eg Autos) could be easily allowed for.
Using this approach would mean that you could connect any ECU capable of interpreting/producing the correct signals by using a different adaptor loom so the work would still benefit those that wanted to use a different ECU to the one used on the prototype install, though IMHO it’s false economy to try and save money using less capable equipment.
Now for those of you that are thinking this looks too much like hard work, you're right, but then again so is replacing blown motors
And if you're thinking you'll just wait until someone else has done it and get an easy ride. Forget it, because if everyone thinks like that it'll never get done. Well not at least until I find some spare time to do it, and if I end up doing myself there's no way that anyone else will be getting a free ride from my efforts
