I'm about to begin my first gen 4 harness for a swap. I've done many gen 3 . I'm having a hard time finding good information for making one stand alone. I keep reading mixed information.

 

I though about this same project and sold my harness for $150 and purchased PSI harness, along with the harness can all the support I could ask for. I have PDF of 2008 G/H Full size van Electrical Manual I could email, PM me with your email address.

 

did you look see what LT!Swap.com have for your needs. If not listed e-mail him he probaly can head you rite way on it.

 

I have L92 and 6L80. I had issues with the harness when both trans TCM and PCM turned off by the same relay. This was causing communication errors as they are supposed to be turned off in series vs in parallel. I ended up rewiring .... the main PCM now triggers a relay which supplies power to the TCM. If you turn off the TCM and PCM simultaneously it gives a low voltage error and loses memory so the trans resets its learned behaviors. In short it starts out very jerky until the trans re-learns pressure settings and clutch actuation.

There is a ground output from the PCM that in the OEM application which energizes an accessory relay.
Wouldn't be surprised if you will have to wire yours the same way. I could find the reference thread if need be.
Hope that might help.

Doug

 

Very helpful info Doug !!!

 

Glad to help. BTW - I have E38 and T43 computers. If you have different, perhaps don't expect the same issues.

 

I'm not 100% sure but you may need the BCM to make everything work correctly. I have an E38 on an LY6 and the speedometer is not happy without the BCM. Im using a T56 tho.

 

Theres a lot more "oddities" lets just call them for lack of a better description with gen IV vs genIII swaps. Its a similar process, you just get forced deeper into the digital side of things whether you want to or not as making a true stand alone out of the ECM is no easy task, its looking for a lot of "go" calls from the other computers ( TCM, BCM, SDM ). Unlike 24x systems which have one PCM that does all so it can be repinned and easily tuned/commanded into pretty much whatever OS and set up you want. Its just not so with the GENIV trickiness and some things are so called hard coded into the genIV ecm's so your stuck with OEM settings on the fan control for instance and theres almost always VSS feed problems.


*edit* Also the bonus of using the LY6 controller is you can retain VVT which I really like, and keeps setting records for LS builds I might add.

 

Cam described it well.

Dakota Digital makes the STA - 1000 which can extract speedo and tach data from the OBDII port via the CAN bus. It drives analog gauges with its waveform outputs. It also has a test mode which you can use to ensure your tach / speedo wiring and calibration... I found that useful for a system test before startup.

I paid about $110 for the DD device. It provides the flexibility to use a variety of (even stock) gauges which is great.
It also can drive speed input to a cruise control unit.

Doug

 

DW SD, id like some more info on the tcm being on a seperate relay. Now I'm kinda worried about this harness. Dang gen 3 stuff was so easy but these e38 pcm's with seperate tcm crap.i wouldn't worry as much ifit were minebut it's for someone else and you know when you do something like this for someone it somehow comes with a lifetime warranty. I might just tell hi to give psi a call.

 

So I'm confused on the can bus wiring. Does pins 27,28 go from the pcm to the obd2 port ?