2000 K2500 5.7 to 1996 7.4 swap

[MumMushroom]

Hard to find information for 454 swaps online.

I swapped a 454 from a 1996 (obd2) gmc C2500 suburban,
I was able to swap the whole harness from the suburban and get the engine to run perfectly in-my truck

Only problem is that only certain gauges are not working

Fuel gauge pinging to the left when in park but pings to right when in neutral or drive

Oil pressure gauge pinged to the right no matter what

Tachometer not working at all

blower motor, wipers and windows everything else works, was able to plug harness in from my transfer case to the 454 transmission harness, so even 4x4 works.

at first I thought it was a ground so I finished putting all fenders on and hooking up body grounds,

I do not want to swap dash from the suburban as it does not have an airbag and mine does

Do I need to re pin at the bulkhead connector? Or is it something else?

I do have the cluster from the 454 in my truck and also have the whole donor vehicle still

 

[454cid]

I think you have a mix of early and late black box pcm parts. Fuel guage runs through the pcm on the late box for instance and the sender uses different values.

 

[MumMushroom]

I think you have a mix of early and late black box pcm parts. Fuel guage runs through the pcm on the late box for instance and the sender uses different values.

I found that on the passenger side through the firewall the 1996 454 harness has a six pin connector. However, the original engine harness for my truck has an eight pin , I switched all the wires and connected them as best I could but still had no sensor gauges, I found a schematic that showed the two extra wires that I had from my 8 pin were oil, pressure and water temp. I ran a jumper directly from the sensor to one of the two wires and it read correctly and I watched the temp go up.
I think I’m going to try to do the same thing with the oil pressure and tap off of the sensor and send it directly to the second spare wire , however I’m not sure how I’m going to tackle the tachometer as I’ve heard it gets it’s reading from the pcm, again maybe tapping off of the signal wire from the pcm and sending directly behind the cluster could fix it.
I could probably do the same thing with the fuel level by tapping off of the sending unit signal wire.

I know for now they are jumper wires just to test but if I can do this instead of finding the wires by comparing schematics I’m gonna do the faster way if it works

 

[OutlawDrifter]

1996 pulls the fuel gauge signal from the sender. 1998+ pulls the fuel gauge signal from the ECM.

 

[MumMushroom]

Do you know where the tachometer gets it’s reading from?

1996 pulls the fuel gauge signal from the sender. 1998+ pulls the fuel gauge signal from the ECM.

 

[OutlawDrifter]

Do you know where the tachometer gets it’s reading from?

Not directly, but I would guess it's tied in with the distributor wiring.

 

[MumMushroom]

I think it’s best just to swap the dash wiring from the 1996 454 suburban into my truck instead of having to deal with this headache. Found out that the oil pressure wiring on the 454 is a 3 wire, and on my 5.7 wire it is a one. So going to be more difficult to figure it out especially because I can’t find the right schematics to re pin the main plug (bulkhead). Just for anyone wanting to do this swap, save yourself the headache and buy the same year engine harness that matches your truck

 

[454cid]

I think it’s best just to swap the dash wiring from the 1996 454 suburban into my truck instead of having to deal with this headache. Found out that the oil pressure wiring on the 454 is a 3 wire, and on my 5.7 wire it is a one. So going to be more difficult to figure it out especially because I can’t find the right schematics to re pin the main plug (bulkhead). Just for anyone wanting to do this swap, save yourself the headache and buy the same year engine harness that matches your truck

My 99 454 uses a one wire. I was surprised when I found that out.

 

[MumMushroom]

So I swapping wiring from 1996 dash over and only thing that works is coolant temp, I guess nobody has done this swap before because this is a major issue that anyone doing it would have. haven't found anything related to swaps and gauges. Getting real close to letting truck sit around. Got a lot of time into the swap, gauges are gonna kill me.