'97 GLT ECU swap (M4.4 to M4.4), no AC afterwards.

[Chuck W]

OK, well I'm stuck at the moment.

Came home and pulled the recently flashed ECU that is suspect. Installed the original 97 GLT ECU. AC works and OBD2 tool connects to scan codes.

Went ahead and grabbed the other ECU I have. Same bin as before. Did the AC mod (At least I think I did. I checked the bin and said it was present), and flashed a new ECU. No working AC and no connection available to the OBD2 scan tool.

[Chuck W]

Well, I can't seem to get logged into VS, nor can I even send the mods a message, as it won't even allow me to get past the "security check". Any request to get a password reset just disappears.

After doing some more digging, I think I see how to get the OBD port functional again.

I still cannot figure out why the AC isn't working. I even checked in the hex editor and found the proper byte values for the "AC mod" (00 in both locations)

The only odd thing that I have found is that if I change something in the bin and save it, the checksum values are not changing.

This is getting kind of aggravating. It should be working...

[Chuck W]

One FINAL update for the evening.

A new wrinkle. With the "new" flashed ECU with the AC Mod, the very first time you start the car after reconnecting the battery and try and run the AC, the compressor kicks on for about a second then stops. After that, it won't re-engage.

With the stock 97GLT ECU, the AC works just as it always did. Cycles on and off, gets cold, like it should.

Ugh.

[erikv11]

Well at least you know it is the ECU, not the car messing up. That's pretty weird AC behavior, I haven't seen that problem. One thing I have experienced, if the voltage is not up throughout the flash you can get some weird results. Is it staying up very close to 16V?

I had a strange problem with checksums that was ultimately related to a Windows update or something, I'm actually not sure why but eventually my setup started flashing properly again. I was able to get a lot of help at VS from user gdog, sending bins back and forth etc. until we sorted it out.

I suspect this will ultimately be solved by just flashing again but I wish I could help more.

You can disable the rear O2 under Emissions > Rear Cat Check there are 5 entries, set all of them to zero.

[Chuck W]

The power supply I'm using for flashing is 14V-3A. Not sure if it's dropping lower than the required 13.5V. There appear to be no glitches/hiccups in the erase/flash process.

If I could actually get logged into VS, I might be able to ask some more specific questions there, but the site is being difficult.

I did find the location for the rear O2 sensors, so that should be handled now.

I'm at the point to where I need to put the original ECU and injectors back in the car and while I sort this out. Once I get it figured out, I can swap things back.