USB TTL drives the output high which could potentially cause the ECU output to blow. ALDL is half duplex: The ECU output is a 10 kohm resistor to +5V with a switched transistor to 0V. The interface must also have a switched transistor to 0V only. The maximum current that can flow in the ECU output transistor is 5V/10k ~ ½mA.If the interface is switched via a transistor to 5V in the off state, then when the ECU starts to respond, the maximum current in the ECU transistor is determined by the output capability of the interface and could be 100s of milliamps. You would be advised to put a diode in series (Anode to the interface output and cathode to the ECU). The interface low output will increase by ~0.7V but should still be recognised as a low by the ECU.
Hoe do you plan to select that baud rate on your PC when it doesn't exist on the terminal program settings menu ?
A number of people have produced free software of varying complexity and platform support that will work with the above interface. We don't have any 8192 baud software yet, but we do have 160 baud simple and generic software for DOS.
That's not fair..
So far, I've come up with the circuit shown here. Then someone else said the diode might be the wrong way round.