My problem is with an ls1 swap into a 86 Iroc. Before i did the swap I I made sure that the engine would run, just to take any guess work out. I did have to bypass the fuel pump relay because of vats, but it did run. Well after completing the swap, I tried to fire it up and nothing!!! the lights work, radio works, but it wont crank. I went to the fuse box and jumped pin 30 and 87 on the relay and the starter cranked and the car ran for about 5 sec but then shut off. I know the starter is good and I know it probably only ran for a few secs because of the vats not being bypassed yet, but why wont i get any signal to my starter. I checked and I do have 12v at the starter coming form the batt. I evenput the starter relay back in and had my wife try to crank it while I checked the reading on the little purple wire coming in to the starter and it read neg -12v. Why would it read negative 12v? Do I have a bad ground somwhere? Bad BCM? how can I by pass the BCM just to get the signal to the starter? Any help is greatly appreciated. I just cant wait to hear it run and idle!!!! thanks again for your help.

 

Anyone have even an idea? right about now Ill try anything

 

The VATS system in the BCM has two ways of disabling the vehicle. It will not send a fuel enable signal to the PCM thus disabling the fuel pump. And it won't provide ground for the coil side of the starter relay thus preventing the starter from engaging.

It's easy enough to provide an alternate ground for the starter relay - just run the yellow with black wire at the relay directly to ground instead of back to the BCM.

 

Whitebird,
thanks for the help, I didn't know vats also diabled the starter. So before I start cutting wires I'll try to bypass the vats with a resistor and if it still doesn't fix it then I'll d what you recommended. Thanks again and I'll post if I get it running.

 

Whitebird,
thanks, you were right! All I did was bypass the vats and it cranked! Thanks a million, I didn't know that the vats also disabled the starter. I literally learn somthing new everytime I visit this site.