04 Silverado 4.3 to 4.8 Swap Need Help

[00_Silverado_Z71]

I hate to do this but as I cannot find any info where it seems anyone has had a similar problem...I posted on performance trucks with no help however I have a 2004 Silverado started out as a 4.3 5 Speed truck I scored a 4.8 out of a 2000 with low miles for cheap and also came with the harness from the 2000 maybe someone can help me out with a few problems i've ran into. We currently have it in the truck and all hooked up every ground and every plug minus a couple that go to the transmission because apparently this harness out of the 2000 is out of an automatic is it possible to use this harness or will I need a different one? As of right now none of my gauges are working in the truck and when you turn the key on and try to start the truck as soon as you engage the clutch without even turning the key it tries to start itself however it is not getting fuel and will not start. Hopefully someone can guide me in the right direction here in what i'm doing wrong or what I need to change. Everything off the 2000 harness seemed to plug into eveything on my 2004. Are the fuse blocks different is why i'm receiving these problems or do I need to get a newer style harness? I want to retain the cable style throttle body as the truck was drive by cable is why i've refrained from picking up a newer style harness. Ive read the nbs v6-v8 threads over and over trying to get a solution. Also I forgot to mention the pcm has already been flashed for the 4.8 and mods by nelson performance so once i can work out all the small problems it should be good to go.

[danger_ranger83]

with the truck being an 04 u need a harness for DBW i dont think u can use the harness for a DBC with an 04 but i may be wrong

[00_Silverado_Z71]

Well my truck is currently drive by cable as the 4.3 was when I pulled it out

[danger_ranger83]

i know this but with the v8 they are DBW

[00_Silverado_Z71]

Yea I understand...Nelson has already set up the pcm (red/blue connectors) for the drive by cable i'm thinking my biggest problem with the harness is that its a 2000 harness and with my 2004 fuse block the pin outs are different in that harness causing numerous things not to be working. If i'm not mistaken the 03+ are blue and green which are different pin outs as well

[danger_ranger83]

the pinouts for red/blue and blue/green are for the pcm....i think your problem is the bcm in your truck isnt liking the 2000 model computer and thats causing it not to run..you might be able to swap bcms but you would have to swap gauges too... im not sure that would work though

[00_Silverado_Z71]

What about the 2 plugs on the trans since mine is a manual truck not an automatic and will my current tuned PCM from Nelson work with the 03+ harness? I know theyll have to retune it for the drive by wire

[00_Silverado_Z71]

Alright well got back to work on my truck again...now more problems. I ended up buying a 2004 manual trans harness from GM with dbw and then went and got the pedal and all the stuff to make it work. Got it all installed in the last couple of days I have double and triple checked every plug, wire, and ground to make sure i'm good to go. I go to start the truck and it does nothing its like it is dead from the ignition. Called Nelson today to make sure my VATS was turned off and indeed it had been. Security light hasn't been on but it was another check to make sure it had been turned off. I can get it to start for a few seconds by jumping the starter relay under the hood with a wire but it wont stay running. Tonight we went through every circuit and relay and switch in the truck to make sure they all had power when needed when the clutch was pressed and key on etc...and I still have nothing when I try to start it. Everything comes on and works accordingly but it just will not fire. If anyone might have any insight on what this might be or have had the similar problem please let me know i'm about at my whits end trying to figure it out.

[00_Silverado_Z71]

What about the 2 plugs on the trans since mine is a manual truck not an automatic and will my current tuned PCM from Nelson work with the 03+ harness? I know theyll have to retune it for the drive by wire. And I'm guessing I'll have to get a different throttle body as well

[00_Silverado_Z71]

Also my buddy that's doing the swap works for gm and we located a part number for an 04 4.8 engine harness for a manual truck with drive by cable and with his discount I can get it pretty reasonable I may go that route to keep from having to buy so much extra stuff. Should all the sensors from the 2000 motor work on an 04 harness or will some have to be changed.