Originally Posted by
Aaron1989
I have a similar ftdi usb. I connected the rxd and txd together and ran them to the serial data (pin m) then ran the ground to the ground (pin a).
When I connect it to the car and get tuner pro opened up and start data logging the readings are erratic and are all over the place. I even tried putting a resister between pin a and b. And still nothing. With the key on engine off if I push the accelerator the volts for the TPS sensor raise.
I talked to a guy that used to be a mechanic and is an electrical engineer now and he said I may be able to put a diode on the rxd side with the positive facing the Aldl port. He said what it sounds like to him is that the signals are getting mixed up. And from other research I've done says that serial is the best way to go
92 Buick LeSabre 3.8