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So i have been meaning to ask this sometime now. What are the option for persons that have automatic and what to that best of they both worlds and have all the cars daily functions, but still have a other EMS control fuel, spark and boost control.
How does one start to walk that road? Note i just using Automatic as the example, as it is a topic that i done see coming up much.
The short answer is it's difficult. The auto computer relies on seeing certain signals from the factory ECU and when you remove the stock ECU these signals won't exist. Your options are to either piggyback the stock ECU so that the required signals will still be sent to the auto (not your first option by the sound of it) or use an ECU that can replicate these signals in a standalone installation. I believe Pro EFI can run a factory auto but it's not something I've investigated.
Short of these options you would need to consider swapping the auto for a manual or at least for a non electronically controlled auto.
In my experience the piggyback method is solid though and a technique that is viable, effective and affordable. When I say piggy back in this way, I'm only talking about keeping the stock ECU outputting the required signals to the auto. The fuel and ignition is 100% controlled by your aftermarket ECU.
sorry, when i said (piggyback) i was more referring to items like the AEM FIC and Greddy Ultimate... i did mean "Duel ECU". I need to learn this terms better. Do continue... :)
E.G. i see haltech has a "Device Emulator", but i don't or hear ppl talking about it, far less using it and i have been asking myself why is this? Base on what you have said so far, running the stock ecu with a ems ecu is the way to good when dealing with times one need to retain the stock computer. So again, i would love to know more.
Installing an ECU in a piggy back installation isn't always simple as some of the signals need to be shared such as the engine speed and position, coolant temperature etc. In the perfect world you would use an ECU where the internal pullup resistor for the temp sensors can be turned off, otherwise you will need to add additional sensors.
Some later model factory ECUs will also need to be fooled so that it still sees a load on the injector and ignition drives. If it sees these as open circuit then it can often trigger a fault code.