quote Originally posted by Romsk: I did some searches on this site for this subject but nothing turned up. I have been studying the ECU/Fiero V9 wiring diagram. It all makes total sense except for Manual vs Automatic Transmissions. There is a wiring option in the harness from the TCC OR SHIFT LT signal from the ECU: For Manual Transmissions: The signal option is routed to the SHIFT lamp on the Instrument Cluster. That is what I have. For Automatic Transmissions: The signal option is routed to the TCC Switch on the Transmission and to the ALDL Connector (they forgot to draw the GND on pin A of that connector). From the schematic it is difficult to tell if the TCC signal is 'ECU TO TCC Solenoid Switch', or if the switch sends the signal 'TCC Solenoid Switch TO ECU'. I am guessing the ECU 'SENDS' the signal to the TCC circuit on the transmission because this pin on the ECU is an output (SHIFT LIGHT) for Manual Transmissions. Which way is it? How does the ECU know it is using a Manual or Automatic Transmission? I found this page on the web that says it uses different PROMs to do that... it that correct? https://www.fierofocus.com/fierosails/ECM.html I don't see a pin or jumper on the ECU connector. In many electronic applications, a pin is left open or shorted to ground to select options, but there is no such pin on the ECU connector. Is there a jumper inside the ECU to set for Manual or Automatic transmmision or is it just embedded in the PROM code? Thanks.

Hi, that is correct. The ECMs themselves are totally identical between the manual and automatic... and across a couple of different years. The 84 is different than all, the 85 V6 is different (has provisions for a knock sensor and a couple of other things), and then 86-87 is the same, and then 88 is unique I think...


This diagram should help...




EDIT: Look at that, the ECM itself is identical from 86-88... just the proms were different.

[This message has been edited by 82-T/A [At Work] (edited 11-23-2024).]

[This message has been edited by Raydar (edited 11-24-2024).]

[This message has been edited by Romsk (edited 11-25-2024).]

The ECM in the Fiero uses just a basic 2732 EPROM.

I have all the Factory EPROM (and some others) files here: https://drive.google.com/dr...fDOqV08k?usp=sharing

You need an EPROM eraser and programmer to make the changes.

[This message has been edited by Mickey_Moose (edited 11-26-2024).]

quote Originally posted by Romsk: I agree, these ECMs all share the same Calpack (just a bunch of data tables right?). I'll bet the code is all the same in the PROMs as well, except: Transmission is used mostly to determine which Speeds/RPMs relate to the gears and for the Shift Light response (thus not using that pin for TCC). Tires sizes for Speedometer calculations.

I think the Calpack is a very basic, rudimentary set of data tables.
As I understand it, it provides the "limp home" parameters, in case the PROM just outright dies. i.e, It provides steady state, but very rich fueling. Fixed ignition timing. Fixed idle speed. Etc, etc, etc.
I've never tried it, but I wouldn't be surprised if you could actually unplug the PROM, and still drive your car. It would still run - albeit poorly.

I had one PROM that was heat sensitive. (GM PROMS seem to not like being erased and reprogrammed.) I got caught in traffic, and the heat from the engine compartment caused the PROM to "zone out". (A good reason to not remove the insulation from the firewall.)
The CEL started flashing quickly, the engine didn't have nearly as much power as it had before, and worst of all, the dadgum A/C cut off.
Shortly after I cleared out of the traffic jam, and got some air circulating into the engine compartment, everything returned to normal.

[This message has been edited by Raydar (edited 11-25-2024).]