Wierd one I am having a bit of trouble with. Got the motor runing and idling decent enough to start running some scan software with it. My buddy came over with his laptop and HP tuners software. We werent sure if it would work with an LT1 but since its OBD2 we figured it should. Well we were hooked up and reading fine. started the motor and we lost communications. We figured it was a software issue since we werent sure if the scan part of HP tuners would work.

So we moved on and hooked up my laptop with Autotap... same thing. We did a little investigating and we have communications and data transfer to the laptop Key on engine off. We have it when cranking... reading cranking rpm and what not... as soon as the motor fires we loose communications.

So we figured it was a ground isse and traced out the 2 grounds from the ALDL. I dont have my service manual in fron of me here so I might be wrong about these pin numbers.. but pin 4 ground goes to chassis ground just under the dash on driver side. Ground is good and the wire is good. Less than .5ohms. Pin 5 ground goes to the engine. Traced it out and thru the connector on the passenger side (interior harness to engine harness connector). From there thru the engine harness to the block. Bolted to the stud just above the starter. Again less than .5 ohms.

So we started looking at data wires. There are 2 data wires. tan and Purple one. I think the purple one in pin 2 is labled Class 2 data and I believe thats the one we read and flash thru. The other is tan and I forget what its called. Getting 4.5V on teh tan one but not getting any voltage reading on the other. Is it able to be measured with a meter? Not dure what kind of signal it is honestly.

Power supply is good 12v and its there KOEF and running..

Any idea what the issue might be?

BTW, some info about the car: it is a stripped down race car. Much of the wiring in the car has been removed. I did it personally and I took great car in doing it. Sat with a service manual in one hand and I made certain I knew what wire I was removing before i removed it. (Thats not to say I didnt make a mistake somewhere)... just saying it was not hacked up witout any care involved. I removed the simple stuff... HVAC, radio, abs, interior lighting, PDL, trunk release, BCM, all dash instrument cluster wiring also...

The other stuff is still there. headlights, fog lights ect...

Any help is greatly appreciated.

Seams like we are losing the data on the serial bus when running... and only running....

Could it be interferance?

battery has been relocated to the rear. Good chassis ground to the batery in the back with 1 gauge. Good ground from stock motor mont ground stud to the distro ground stud on wheel well. Also an aditional 1 guage ground strap from the driver side head (bolt/stud for ignition coil)to the chassis again...