Got a new motor for my 99 Z28. Idled real bad on initial start up. took it to my tuner and he hooked up his laptop and HP Tuner interface did some things in his laptop, cranked the engine and it ran and idled good. Was going to drive it off the trailer to set up on his dyno and when he unplug his interface it started running bad just it did when I first started it. He plugged his interface back in and it started to run good again. He told me to splice the purple wire at the data link connector under the dash to the drk green wire going into the to pin 58 in the blue ecm. I don't see how this will help and I don't see how the engine ran fine only when his HP turner interface was plugged in.
Below is the schematic for the data link connector, and my question is if anyone knows where SP200 is located in the car? SP=Splice Pack. and how could the car run good with the interface hooked up to the data link connector.

 

Its under the dash, drivers side, by the DLC, its tucked up next to a flasher.
Why do you want to splice into it? The purple wire from the DLC already meets the wire form the pcm at the splice pack?


I would check your grounds, and just check the splice pack, make sure connections are good. Dont cut any wires.

I actually had a bad connection by the firewall on the passenger side, under dash, inside car, so maybe check that too

 

Thx fucter for the info. I just rang out the purple wire at the DCT to the #58 pin on the blue connect to the ECM and it has continuity.
on your car was the ground on the inside passenger side hard to get to? Why was yours loose? Had someone been in there previously and didn't tighten it?
next thing to do is to go into the splice pack, most elec problems are gounds.

 

But why would the motor run good with the HP tuner interface plugged into the DTC and when it was removed from the DTC the motor ran bad?