Got my 1987 2.8 Firebird with swapped T5 in it but originally it had auto trans. Previous owner re-programmed the ECM and wrote about changes in it on it's surface.
Don't know what exactly he did...

Now T5 has mechanic speedo cable, though speedo itself is electronic. I need to buy electronic VSS and don't know whether there's any difference in ECM for manual and auto trans.

Any suggestions?

 

Some people report no issues and some people say they have a high idle after swapping to a manual trans. When I do my swap I will be getting a chip burnt for a manual transmission as well as VATS delete and probably some emissions delete.

 

The PROM installed right now in your 87 should be the HNR... Manual PROM is the HNL. Both use the same ECM. All you need is the VSS for the trans tailshaft housing (make sure it's for the 87 and not a 90-92 as those are different). Provided you got the right trans for your gear combo, you should currently have a 19T white nylon driven gear on the speedo adapter run by a 7T purple nylon drive gear on the trans output shaft for the proper 3.42 gear ratio. The gear on the speedo adapter SHOULD just swap over to the VSS. If the gear is one piece with a nylon cable shaft, you will need to find one for a metal shaft that will go on your VSS (I've tried cutting the gear off of the shaft and drilling it for the VSS, but the speedo was bouncy).

 

I also can't find buffer box in my car, there are no connectors to it too!
I read on thirdgen that V6 Firebirds came without buffer (speedo is electronic), ECM reads signal straight from VSS. Is it true?

Thanks a lot for information!

 

It's the yellow box on the backside of the ECM bracket... Facing towards the seats rather than the ECM which is facing the engine. The buffer wasn't integrated into the ECM until 1990.

Unless you actually have the cable operated speedometer, that is. If there is a big fat cable running from the engine compartment next to the steering column up into the dash, the speedo is mechanical.

 

I've inspected everything, no buffer box, but only mounting place for it on ecm. No wiring connectors fot this too... somebody totally deleted harness to buffer box, i think.

Speedo is electronic, i'm sure. Only swapped T5 has speedo cable which i need to delete.

Originally PROM was HNR, you were right, as you can see on photo it was changed to HNT, besides some digits below read 601 633 154.

Lots of work for me to do with speedo.