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?
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).]
I am pretty sure within the calibration there is a switch to select auto or manual transmission.
Exactly.
There are a few other changes to the tables as well. Idle speed, upshift light function, TCC lockup parameters. Also (as were alluded to) some minor wiring changes for shift light vs TCC lockup.
Either configuration (auto vs manual) will run on the other's PROM. Just won't run - or handle the above functions - properly.
[This message has been edited by Raydar (edited 11-24-2024).]
Thanks all. I found that ECM/PROM chart today as well. Very helpful.
The markings on my old ECM that I have, compared to the chart, shows it is a: ECU: 1227170 1986-1988 Fiero 2.8L V6 MPFI Only
PROM: APR Version APR0164 1986 4 Speed Manual Transmission 205/60R15 Front Tires, 215/60R15 Rear Tires Federal Emissions Calpack 16044802
Yup, it came from my 1986 SE 2.8L V6 MPFI that I stripped years ago.
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. Emissions parameters not tweaked for non California use. All per 1986 regulations.
I bet each PROM has the exact code, just different lookup tables based on the various configurations.
This means if I want to put that ECM in my 1987 GT with 5 Speed Manual Transmission, 205/60R15 Front Tires, 215/60R15 Rear Tires, and Federal Emissions, I need PROM Version: APN0154.
How do I get such a PROM?
I'll bet this old ECM/PROM will work in my 1987 GT: The one year difference was probably just some small tweaks in parameters, and it being 5 Speed would have some minor impact on the Air/Fuel Ratio Learn Blocks, and the Shift Light will probably not come on at optimal times, but it might still be drivable... but I would rather have the correct PROM for my car.
[This message has been edited by Romsk (edited 11-25-2024).]
Thanks for the info. I built my own PROM programmer from an Arduino, shift registers, and a ZIP socket.
Those PROMs I can get from Digikey or Amazon.
I went to your link, but it was broken. Do you have another link?
If the PROM ICs are not too expensive, I may program a PROM for each of the versions for the Fiero 2.8L ECM. This way I can have master copies on hand. Inside the PROM is clearly in a socket. There is a smaller IC near by... is that the CALPACK?
I put these ECM/PROM/CALPACK version tables in the Help in my GUI that I made for Fiero GT owners.
The 85 V6 had provisions for a Knock Sensor. You mean the 1226869 ECU has an input pin for a Knock Sensor?
Hi, yes, that's correct. The only thing is... the factory wiring harness does not have a wire for the pin-out from the ECM. You can edit the PROM's programming though and enable the knock sensor, and then add one.
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).]
Everything is in the EPROMS files\others directory, EPROMS are relatively cheap, but are getting harder to find, there are still a few places as there is still a high demand for them in the "retro" hobbies.
The only files you needs are the EPROM - the smaller chip are all the same as mentioned above contains the limp mode tables.
Oh, and thanks for your link, wish I had that a few months ago. lol
[This message has been edited by Mickey_Moose (edited 11-26-2024).]
Thanks for the info. So the CALPACK has the Limp Home parameters... good to know.
Yes, that would be interesting if the engine could run without a PROM at all. My thoughts... all the ECU has to do is put the EST ICM in bypass mode and pulse the Injectors when the EST signal comes in from the Distributor, and using the TPS to widen the Injector pulse depending on its position. Pretty much a fancy carburetor at that point. Since all 6 Injectors are pulsed at once to better atomize the fuel at each intake port (learned that at this site), no Injector cylinder timing is needed... another reason why all Injectors pulse at once... an eaiser fail safe (limp home) mode.
A simple hardware circuit can do all that with no computer control at all.
I think it is high time for me to get schematics of the ECU and source code for the PROM. They use a 68HC11 microcontroller as the CPU. I wrote 68HC11 assembly code when I was a young pup engineer in the late 1980's. It can't be all that difficult compared to missile system I have helpec designed back then.
These PROMs can become temperature sensitive?... well they are 40 years old and that memory technology is approaching 45 years or so now.
We are on the forefront of witnessing this technology in one of it its widest, oldest, and stil living applications.
My Fiero would start but once it warmed up near operating temperature, if I stopped it and then restarted it a few minutes later, it REFUSED to start. I would have to wait 15 to 30 minutes before it would re-start. This happened at a gas station. It probably was having this problem for a couple of week, but since I was driving it only to work and then home at the time, I never saw it because the car had hours between starts... I was filling up every two weeks and gas was the only place I stopped to/from work.
I guess the ECU has a fail safe to prevent the Engine from starting if it has been running for a while, stopped, and CTS is though the roof. The ECU must have some way of knowing it was off long enough to be safe to start... because the CTS resistance was wide open hot or cold. My SES light was not working at time, I found that to be a loose connection on the Instrument Cluster connector.
I connected my car to the Fiero GT ALDL Monitor tool that I designed, put it DMDIAG Mode, and saw in seconds that my IAT (MAT) and CTS were reading at the end of their scales after sitting all night at around 70 degrees F. I replaced them both and I was running normally again.
You said the SES lamp was blinking rapidly when your ECU/PROM got hot, correct?
We all know the SES lamp comes on steady in Normal Mode (no resistance or shorting on pins A and B on the ALDL Connector) when a Error Code is thrown.
But I think I remember reading somewhere (the owners manual?) that a flashing SES lamp means shut down the engine now. Correct?
That SES lamp tells us a lot:
NORMAL Mode (what users can get): Off: No Errror Codes, nothing bad detected but there may be issues building. Steady on: Service Engine Soon, check Error Codes. Blinking: Shut down Engine NOW.
DMALDL Mode: Need to confirm this. I think it is off in this mode. Other: Not sure yet.
DMFACT Mode: Need to confirm the lamp function in this mode. This mode puts the ECM in Limp Home Mode to test that Fail Safe Circuitry. I forget what the SES lamp does. I think it is on in this mode.
DMDIAG Mode: Ignition On, Engine Not Running: Blinks Error Codes. Engine Running: Blinking Rapidly: ECU is in Open Loop. Blinking Slower: ECU is in Closed Loop. On when the O2 level is slightly Rich (AFR just under 14.7 to about 14.5), Off when slightly Lean (AFR from just over 14.7 to about 14.9). Because a Narrow Band O2 Sensor is used, the ECU constantly adjust the Air Fuel Ratio slightly above and below the Stoichiometric midpoint of 14.7 : 1 as a running check to make sure the O2 sensor is working properly and responding quickly to AFR changes (it does this all the time, even in NORMAL Mode, but we never feel it because it is a slight AFR change but the O2 Senor swings the most volts in this narrow range). It should blink about every second or so and it should go above (light on) and below (light off) 50% of the time... it varies, but on average a 1Hz 50% Duty Cycle blink rate.
Not too shabby for a light most people think is just an "Idiot Light" [smile].
Great web site. I download the APR for my old ECM and the APN for my existing GT ECM.
Thanks!
Would you mind if I posted a link to your page in my web page?
Hi, glad it was of some use. Feel free to post a link (not really a "page" just a google drive directory that can be shared). lol
edit: saw in your other post, I may have a copy of the ECM schematic as well. I will have to look for that - but in my head I seem to think that I have a copy of that.
[This message has been edited by Mickey_Moose (edited 11-29-2024).]
The 85 V6 had provisions for a Knock Sensor. You mean the 1226869 ECU has an input pin for a Knock Sensor?
You just need to add the sensor, the GM ESC module, wire it to the ECM, reprogram to accept knock inputs and you have knock control. I did this on my turbo 3.4L and it works like a charm but ONLY with the1226869 ECM that was used in 85.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Originally posted by Romsk: I think it is high time for me to get schematics of the ECU and source code for the PROM. They use a 68HC11 microcontroller as the CPU. I wrote 68HC11 assembly code when I was a young pup engineer in the late 1980's. It can't be all that difficult compared to missile system I have helpec designed back then.
I finally found what I have for the 7170 schematics - uploaded to the google drive posted earlier.
[This message has been edited by Mickey_Moose (edited 12-08-2024).]
