Vehicle: 1994 GMC Z71
Engine: 5.3 LS1 Swap
Transmission: 4L60E

My story / issue:
Used LT1Swap website to modify the first harness. The engine start and ran. I noticed the vehicle had poor fuel economy and would choke you out from the fumes. I finally made an appointment with a local tuner. After about 30 mins at the shop, with the truck on the rollers, i was told that they could not connect to the ECU via the OBD2 port. They help me out and added some grounds and fiddled with a few other things for about an hour. To no avail, we could not communicate with the ECU through the OBD2 port. But, those guys were very nice and didn't charge me for their time (HOUSTON HOUSE OF POWER great dudes). From there, the only thing i thought it could be was the wiring harness. So i went and got another donor harness and started from scratch again. After completing the engine start and ran. Again, no communication via the OBD2 port. So i bit the bullet and bought a brand new harness form painless performance. Again, the engine start and ran but with no communication could be established with the ECU. So, i bought another ECU thinking maybe i shorted it through the whole rewiring process. I didn't have the VATS removed from the new computer but figured I should be able to communicate with the ECU. Nope. So next, i thought i needed to hook up the PN switch. So i went and bought one thinking that the ECU wouldn't let me communicate with it if it didn't know i was in park....So i bought on today and still no luck. I am seriously at my wits end with this thing. Its a nice clean truck and i am on the verge of punting the project.

If anyone has any guidance/advice or even a good guy in the Houston, TX area i could call and get it looked at would be greatly appreciated.


Thank you for your time!
John

 

Are you positive you have constant power at the data port on the orange wire? Double check that. Then make sure both grounds in the data port are actually grounded. You will need a voltmeter so you can do a continuity test on them. If you don't have one, in a pinch you can test it with a test light, but you'll probably need to put a piece of wire in it to reach the terminals. Put one end of the test light on the orange wire and the other on the black wires in the data connector, you will obviously need to check both black wires.

 

I'm in Houston, TX if you need some help. I sent you a PM with my phone #-please call me! I also have HP Tuners. I also have MULTIPLE LS wiring harnesses and MULTIPLE PCM's laying around if you want to try other PCM's.. You can easily hook them up, and then just READ them without using any credits. If you can READ it, you can then WRITE to it as well. Have you verified that you have the wires running to the OBD2 connector pinned out correctly?
OBD2 PORT
58 DK GRN SERIAL DATA-OBD2 PORT BLUE CONNECTOR---this wire ties into PIN position 58 on the BLUE connector!

The wires below are for the OBD2 CONNECTOR itself
Pin 2: Diagnostic Signal Wire, PIN 58 DK GRN-this wire goes back to the BLUE CONNECTOR @ PCM
Pin 4: Ground
Pin 5: Ground
Pin 16 ORANGE WIRE-CONSTANT power from the battery

Here is the OBD2 port diagram;
https://www.google.com/search?q=obd2+port+wiring+diagram&tbm=isch&source= iu&ictx=1&fir=p9FUA6zIKPZ27M%253A%252CNL9wycJa6Nhv 9M%252C_&usg=AFrqEzf-ii3jrIHzjlnkY9E1Yr5BHWotNA&sa=X&ved=2ahUKEwimxObd0 NTcAhUPG6wKHREyCN0Q9QEwAXoECAQQBg#imgrc=rncYXtYYOZ 5YrM:

You can also look at the wiring diagram pin out listed at this link. PLEASE pay attention to the fact that you have not indicated WHAT YEAR PCM/COMPUTER/HARNESS/ENGINE you are running so the pin-out may not apply to your specific application;
http://lt1swap.com/99-02_vortec_pcm.htm

 

I have constant power to pin 16 and continuity on pins 4&5.

kawa, giving you a call.

I have a cheap bosch reader to test the port. It know it works because i use it on my suburban.