This might be a dumb question but work with me.

I keep reading all these articles in various magazines or posted online about how some engine was replaces with another EFI engine but nobody talks about how the dash is wired to work with the new ECM.

So I guess the real question is what connections go from the ECM to the dash gauges and what do people do to preserve all dash functionality e.g. check engine light, tach or whatever needs to be wired?

The reason I’m interested in this topic is because I have ’91 305 TBI and I’d like to swap the engine with a 350 TBI I pulled from a ’94 full size van. I have the ECM and the wiring harness from the van plus the transmission (4L80E) which hopefully will replace my current 700R4 but I don’t want to loose the dashboard functionality if I use the new ECM.

 

Shouldn't have any at all. I switched to carb 3 years ago, and removed my ecm altogether, and all my guages work (except the SES light I guess). For a swap like that - might want to get the wiring from the donor ECM to the ALDL connector - since it's probably OBDII it's going to have diffeent codes. Then, you can always at least read the OBDII codes from the new ECM.

 

For V6/TPI cars the VSS is ran thru the ECM
For TBI cars, it runs to a buffer box which distributes signal to the ECM, Speedo and cruise

You have a TBI so youll have no worries losing the original ECM

camaronewbie had no issues with his speedo since his is an older model with a cable driven speedo

 

The ECM from the van is OBDI, OBDII came out in '96.
I do have the wiring, not sure if the ALDL is there though.

I guess I have to trace the connections on diagrams from the service manual.

 

The connector between the ECM and the dash in our cars is called C207 and we have pinouts for it for different years on our page here: http://www.austinthirdgen.org/index.php?pid=19 (scroll all the way down)

There are a few signals traveling through the C207 that I can remember right now, such as the CEL, injector power, VATS fuel enable.

All your dash gauges should get their signals from C100 (the bulkhead connector on driver side).

Hope this helps.
Lou

 

Thanks BigBad, cool site too, it's in my Favorites now.

 

Nope - My car is a 1992 - NOT cable driven speedo - and ALL guages work fine except maybe SES light (since there's no ECM to tell it to light up).

 

So let me get this straigt you heve an electric speedo that works and no ECM?

 

Yes, the TBI cars "branch off" the speed signal before the ECM. So if you remove the ECM, other devices using the speed signal still work. Which you cannot easily do on a TPI engine where the speed signal goes through the ECM.

Hope this helps.
Lou

 

No reason you couldnt retrofit a buffer box into a TPI/V6 car to run the speedo

Fiero swappers have been doing that for years