The "let's brainstorm how to make a piggyback work" thread

[Loren]

Originally Posted by eTiMaGo

sounds like that could work too, but what really worries me is the self-test check the ECU does (very rich for a second, then very lean, and see how the sensor reacts. If it does not react, CEL)

though looking back at the manual's explanation, The HO2
sensor informs the ECM that the post-TWC air-fuel ratio is lean (low voltage, i.e. less than 0.45 V). That sounds like reducing the voltage of the sensor's output should be enough to trick the ECU into thinking the system is lean, thus enriching the mixture? Problem is, no way to tune that...

I'm not talking about completely faking the O2 signal and locking it down at a fixed value. It would still respond, it would just be "off" a bit, and the ECU would have no way of knowing that.

A system like the LC-1 is VERY tunable. It works like this:
Say the default narrowband O2 sensor output is .45 - 1.5 volts. (not sure if that's right or not, it's something like that) The center of that range represents exactly 14.7.

The LC-1 has not one, but TWO programmable outputs. You could wire one of them to a gauge that would tell you the ACTUAL AFR. The other one you program as a sort of "hybrid wideband" using the standard narrowband voltage range, but centered on something richer than 14.7.

The ECU sees what it expects to see (even though it's not quite the truth), the signal responds to the ECU's commands, and everybody's happy.

Now that I think about it, some additional circuitry may be required to shift the voltage range, but it should be doable. Probably way easier than hacking the ECU.

Tip: The Miata is a far, far more popular car among racers and tuners, and the factory ECU has never been hacked. The closest anyone has ever come is to overclock it with a faster crystal, which has the effect of raising the rev limit and leaning the mixture. I think asking for or waiting for a hack of the Toyota ECU is unrealistic.