4l80e swap VSS issue

[titan101]

On the 7.4 schematic I am seeing f12,f13 (buffer) f2,f3 VSS. B5,B6 show something different.

[1project2many]

Finally got some diagrams and information that I believe I can trust.

The 7060 has pins A1 through D16. There are no E or F pins. If you're looking at a diagram for a '94 C/K truck chances are high that it is not correct for the 7060. I am sure of this. Your ecm may have been in a truck titled as a 94 but GM's service info does not believe they ever put a 7060 into a 94 C/K, and the calibration that you listed for the 7.4 computer was only certified for use in 1992.

-----

/AXRD/ ***Found!!!
BCC year is 1992

BCC= AXRD2296 Scan id= 2061 Part number= 16162295
Release date= 01/15/91 Engine size= 7.4 Trans Type= Auto trans
ECM/PCM: ECM #16147060
Used in trucks: GMC
Possibly used in:
K2500,4WD,3/4 TON K2500,4WD,3/4 TON K3500,4WD,1 TON
K3500,4WD,1 TON

Options:
With C7L GVW RATING (12000 LBS)
With GT4 AXLE, REAR, 3.73 RATIO
With GT5 AXLE, REAR, 4.10 RATIO
With HC4 AXLE, REAR, 4.56 RATIO
With L19 7.4L GAS 8 CYL TBI V8
With MT1 AUTO 4 SPD THM R2 (4L80)
--------

According to this info, the 2wd truck used a DRAC and the 4wd did not. The 2wd VSS signal is routed to the DRAC and a brown wire supplies a speed signal from the DRAC to B11 on the ecm. The 4WD VSS is routed directly to the pcm. The 4WD VSS is connected to B5 and B6 using light blue and dark green/yellow wires. Two different diagrams indicate the same connections. My memory tells me it was the other way around, that the 4WD used the DRAC and the 2WD did not, but I'm getting old and may be wrong. It's easy enough to check your harness to see what it's configured for then switch it around.

The connector pinout shows B11 between a dark blue/white wire and a dark green wire, and B5 and B6 between pink and light blue/white wires. Check for either the brown wire or the light blue and dark green/yellow. If the brown wire is present it will connect to the DRAC at the other end. The choices will be to change the calibration to 2wd or to change wiring to match 4wd vehicle.

[titan101]

Ok thank you I will check my harness asap.

[fastacton]

Ok, I had a few minutes to look at the 7060 harnesses that I have here. I only had two left, one was a 454/2wd and the other was 350/4wd. The 2wd harness was actually the same as the 4wd harness except for the pigtail that goes to the VSS. The 2wd pigtail only had one VSS connector and those wires (green/purple) went through the DRAC/VSSB. The 4wd pigtail had the transfer case VSS wires (green/purple) going to the DRAC and the transmission VSS wires (blue/green) going to the ECM.

One other issue that you might have: Since you had to add the VSS to the newer 4L80E, it is likely that it's a '94 or newer version which has a different force motor than the early ones used with the 7060 ECM. I don't think it affects your shifting, but I have heard that there might be problems eventually (I think there are some other threads about this on here).

[1project2many]

The 2wd pigtail only had one VSS connector and those wires (green/purple) went through the DRAC/VSSB. The 4wd pigtail had the transfer case VSS wires (green/purple) going to the DRAC and the transmission VSS wires (blue/green) going to the ECM.

Did you happen to check the ECM pin locations for those wires?

Thanks.

[fastacton]

It's B5 & B6 for the VSS that goes straight to the ECM. I haven't checked yet, but I'd bet there's a setting in the .bin that would keep the ECM from looking for input on those pins.

[1project2many]

There probably is a setting. I'm not sure if the OP has the tools to make that change.

[titan101]

Yea I have no clue how to do that. So I just need to wire the rear vss right to the PCM?

[1project2many]

That's correct.

[titan101]

And the .bin setting?

[fastacton]

It might be for it to work properly with a 4wd MEMCAL, you'll need the rear VSS to go to both the DRAC and the ECM/PCM. Ideally, you need a 2wd MEMCAL or an adapter so you can install a flash chip and disable the second VSS. You would also need to make sure that your VSS is going to the DRAC and not the ECM.

[titan101]

Ok I will try and wire it up. Where would I get a flash chip?

[1project2many]

You could have your 4wd chip reprogrammed by someone.

[fastacton]

You'll need a G1 adapter from Moates if you want to run a custom chip. I'll look around and see if I have any 2wd 454 MEMCALs here, that would be another way to go.

https://www.moates.net/g1-memory-ada....html?cPath=64

[titan101]

Ok thank you.