LS won't crank

[57FleetsideC4]

Hi All, I am to the point on my 57 pickup project that I am getting ready to start it. This is a LQ4 DBW with 4L80E trans. I can communicate with the pcm with my tech 2 no coded stored but won't crank. Trans data shows it is in park and have power at the purple wire going out of the switch. There is a start relay and if I cross the big red to purple it cranks. The green wire on the start relay has power and if I touch the yellow wire on the starter relay it then cranks. I also am getting the 2 second fuel pump prime signal. I am really not ready to start it yet but trying to get everything in order when it comes time. Thank You Steve

[bigmoe]

So no power to the start relay when the key is at Start position? You would have to work back from there. Do you have a neutral safety switch in that circuit?

[57FleetsideC4]

Originally Posted by bigmoe

So no power to the start relay when the key is at Start position? You would have to work back from there. Do you have a neutral safety switch in that circuit?

Thank You it does have a neutral safety switch but it is a many wire connector and don't know which pins are for that but the pcm is seeing the car in park so it might be ok. I am going to call the business that sold me the engine/trans/pcm/harness setup to see if they can help. It will probably be something simple. Steve

[D-n-Tyke]

These threads may help you if it is the neutral saftey switch on the 4L80 trans. They are from when I was researching how to wire up my NSS.

http://67-72chevytrucks.com/vboard/s...d.php?t=845747

https://ls1tech.com/forums/conversio...l#&gid=1&pid=4

[57FleetsideC4]

Originally Posted by D-n-Tyke

These threads may help you if it is the neutral saftey switch on the 4L80 trans. They are from when I was researching how to wire up my NSS.

http://67-72chevytrucks.com/vboard/s...d.php?t=845747

https://ls1tech.com/forums/conversio...l#&gid=1&pid=4

Thank You. I looked at the one with the starter relay and it looks like the dark green wire becomes hot when in park or neutral so I think that part is good. What feeds that yellow/black wire is where my problem must be. Steve

[D-n-Tyke]

Originally Posted by 57FleetsideC4

Thank You. I looked at the one with the starter relay and it looks like the dark green wire becomes hot when in park or neutral so I think that part is good. What feeds that yellow/black wire is where my problem must be. Steve

Are you using the factory fuse box out of the donor vehicle? Or are you using a standalone fuse/relay block as part of the modified LS harness? Similar to this (https://lt1swap.com/fuseblock_obd2port.html)

[57FleetsideC4]

Originally Posted by D-n-Tyke

Are you using the factory fuse box out of the donor vehicle? Or are you using a standalone fuse/relay block as part of the modified LS harness? Similar to this (https://lt1swap.com/fuseblock_obd2port.html)

This is modified factory harness and I found the problem. There is several wires that have to be connected to the truck to run. The purple start signal wire from the switch was corroded and broke inside the harness (I was poking around and the purple wire pulled out of the harness. Just had to solder the wires together and piece of shrink tube and all set. Thank You for the replys. Steve

[D-n-Tyke]

Originally Posted by 57FleetsideC4

This is modified factory harness and I found the problem. There is several wires that have to be connected to the truck to run. The purple start signal wire from the switch was corroded and broke inside the harness (I was poking around and the purple wire pulled out of the harness. Just had to solder the wires together and piece of shrink tube and all set. Thank You for the replys. Steve

Nice. Glad you got it working. Wiring gremlins can be a pain.