I have a 2003 Silverado that I just pulled the 4.3l out of.
I have a Harness and ECM out of an earlier (99-02) Silverado. I prefer the DBC setup over the DBW. That's why I got the earlier Harness and ECM.
What issues am I going to encounter trying to make the earlier Harness/ECM combination work in my 2003 Truck?

 

Oh my god I think I am having deja vu.

 

The 99-02 and the 03+ wiring harnesses are not compatible with one another. Not sure how to to go about converting to DBC on the 03+, but I'm sure it's possible somehow. IIRC the early LS Express still had DBC.

So you are doing a V6 to V8 swap?

LOL. I think that other thread was by a member called something Jesus. I haven't heard from him lately. I'm sure he got it figured out and is doing donuts somewhere. ☺️

On a side note, is there really a difference between DBC and DBW? I can't really perceive any difference between my trucks that have either. I don't do burnouts, maybe that's why? I was reading this book and it said the engineers put the dbw on the LS1 because they wanted driveability from all kinds of folks. I understood that as they didn't want Grandma spinning out of control when she tapped the gas a little too much on the Corvette at a stop light? 🤷

 

Yes, in the process of swappingbout the 4.3l and replacing it with a Crate 5.3l from Summit.
Turns out, the older 99-02 harness isn't going to work. The older harness doesn't play well with the 03+ chassis harness. Causes all kinds issues with the headlights, ignition, HVAC, ect...
Gonna just run the correct 03+ harness and ecm and add IAT and TPS pigtails to it.

 

I Remembered there's a thread somewhere where they show you what to look for when you open the ECU to see it's capable of running a DBC. I can't remember where I saw that.

Your factory ECU may be able to be reflashed to the V8 though and probably keep it DBC, as that's what you have. It's the silver box ECU, right? Not the black box? Do you know anyone that has HP Tuners?

 

Official NBS V6 geniii V8 swap guide

How too DBW - DBC swap

 

@strutaeng DBC is instant input/output whereas DBW before a tune is laggy as all get out. Driving my truck and then driving any untuned DBW is the strangest feeling ever.
Plus the pedal just has a genuine different feel to it.