04 Silverado 4.3 to 4.8 Swap Need Help

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.

Anyone?

If you're sure 100% that everything is wired correctly pay NP to ship you another PCM and see if it's just a bad load or something, cover that base.

Im more than a 100% sure it's all correct I've went over every single wire from the dash harness to the motor to pcm

Maybe ns switch? I know if that is not working correctly it won't do anything...

Reading through this real quick, but are you trying to use a RED/BLUE pcm with a 2004 harness?

Quote:

---

Originally Posted by PitchBlackC3

Reading through this real quick, but are you trying to use a RED/BLUE pcm with a 2004 harness?

---

No, Nelson swapped it out and sent me the right one the blue/green and everything is wired just as it should be from the factory my truck is throwing a bunch different codes now and still is only able to start it by jumping the starter relay cannot get it to crank with the key. Here are a list of codes its currently throwing according to a tech2:

P0068 throttle body air flow performance
P0102 maf circuit low frequency
P0412 secondary air injection solenoid relay control circuit
P0418 secondary air injection pump control circuit
P0801 reverse inhibit solenoid control circuit
P0803 skip shift solenoid control circuit
P0804 skip shift lamp control circuit
P0856 traction control torque request circuit
P1516 tac module throttle actuator position performance
P1630 theft deterrent learn mode active

Keep in mind me and my mechanic buddy have went over every bit of the wiring we have schematics for all the starting circuits, engine harness, pcm harness and body harness and still cannot find an issue of why it will not start with a key everything has power where it needs to go and ground when needed but no dice when trying to start it.

Some of those codes are odd, you shouldn't have AIR codes at all on a 2004 and the NV3500 doesn't have skip shift or reverse lock out solenoids so you shouldn't have those codes either. Almost makes me think you have a F-body tune loaded, but if that was true your DBW throttle wouldn't be working at all.

Also the theft deterrent learn mode code is a little strange. That should be a self clearing code after the key is turned off.

I imagine VATS was turned off, but maybe Allen will chime in with what he did for your tune. (I see where you said he checked it already now)

After talking with Allen this is the email he sent me yesterday:

Here's everything you requested we tune for:
4.8L, 224/224 562/562 114
longtubes, exhaust, cai
remove: cats/o2, egr
31lbinj, 4.10
87/89 oct
* speed limiter 150


Those codes below are definitely harness related.
When the pcm sees for example a low freq maf code, that is a ground or the
maf wiring between the maf and pcm.

When the pcm sets the tac and throttle body codes, it's wiring and tac/pedal
related.

I can turn off the air injection codes, the theft deterrent, skip shift
codes, but those codes are showing up because there are no devices present.
But they aren't causing the pcm to act up.


The theft codes is coming from the body control module, the pcm has vats
turned off due to the engine conversion.
Vats is not on in the pcm.

We are definitely dealing with wiring, ground and power issues here.

I would agree all the PO800 codes seem to be F-Body codes that don't have anything to do with my truck and not sure how I could possibly have any harness issues the harness is one I ordered specifically for my truck from GM for a 2004, 4.8, 5 Speed with DBW damn thing was $500. I have checked all grounds and circuits and still not getting anywhere with this thing. Indeed the DBW stuff is not working with my pcm and it was removed from a running driving truck at the salvage yard even the same year as mine. I'm about to go light it on fire and roll it out of the shop its getting to that point.

Did you check at those sensors and make sure you don't have gnd on the signal side when it shouldn't be there? What about the voltage on the 5v reference circuits? You checked the gnds on the back of the heads?

Try unplugging the BCM connectors and see if it will start without it plugged in.