A friend of mine has an IROC that he has put the engine and trans out of a 93 F-body into. Months ago he just needed me to see if I could disable the VATS in the computer chip. I know you can't do this on an LT1 C4 (I've tried) there are two components to the system and disabling the chip is only half the story. I thought it might work in his case though since he doesn't have the CCM to deal with.

At the time I didn't really think about the differences so I just slapped the stock 92 image from my Vette onto a chip for him. The only thing I changed was that I unchecked the VATS Select option. Low and behold the car fired up right away worked fine. Ultimately though he had a lot of other bugs to get worked out and the project got seriously delayed. Now he's working on the project again and he called me with some questions. Some of his questions act like they would be related to the fact that he's running the Corvette program with his Z-28 wiring harness. There aren't a whole lot of differences but there are a few. I had him give me the broadcast code from his stock chip, BDZL. I found it quickly enough on DIY-EFI. I thought I would just uncheck the VATS, burn the chip and see how many of his phantom problems go away.

When I open up the BDZL chip it required the DA3 definition, fair enough I expected that. What I didn't expect was to only find ONE field in the ECM switch table. That constant is VATS DIAGNOSTIC and it is unchecked. The DA2 chip in the Vette has both VATS DIAGNOSTIC and VATS SELECT, with VATS DIAGNOSTIC being off by default as well. So now what? I really think the DA3, BDZL chip would work better for him, except that it very likely won't start because there is no way to defeat the VATS. The engine is stone stock, it could run on the stock chip if it weren't for the VATS.

He's working on it tonight and was really hoping for an answer. Any experts out there?

 

Well it turns out this is easier than I first thought. My TunerCAT DA3 definition file dates to 1999. The new definition file will provide the options I need along with a bunch of other cool stuff too.

BTW a friend of mine suggested that this thread might be locked because it mentioned disabling the VATS. Not that it matter so much now because I have my answer, but here's the way I see it. Yes disabling the VATS might be a miniscule security threat to somebody but there are perfectly legitimate reasons to want to do so, IE engine swaps, etc. It would be one thing to be asking how to disable it under the hood, but your average car theif isn't going to be burning computer chips to kill VATS.

Even though I didn't get an answer I would like to thank the moderators for allowing the thread to live and give me the opportunity to get an answer.

 

continuing the VATS question, I'm curious whether the VATS VALUE (not the enable), whether the VATS value is stored in the MEMCAL, or is it hardwired into the ECM circuit board, or is it also stored in the EPROM with the VATS enable.

If I swap out my ECM module 1227730 for another ECM 1227730, and transfer in my original MEMCAL and EPROM, will the same VATS ignition key still work, or will my car not start then?

I'm guessing it's in the MEMCAL, since I think folks have swapped out their ECMs when they fail. And the chip burners ask if you want the VATS disabled on the custom chips. I don't recall them asking for the VATS value.

I'm just wondering, before I start swapping out the ECM box to mod that, keeping a spare handy. Just don't want to screw things up too badly. If anybody knows...

 

I actually don't believe it is stored in either place. I have replaced the ECM in my car (92 Vette) and had no problems. I've also reprogrammed the EPROM on several VATS enabled cars without first reading their stock chip and it worked just fine. If it is in the MEMCAL it is in some of the other logic, not the flashable chip. You should be fine to swap it out

 

As I understand it...
The resistance of the key is detected by the VATS module. If the resistance is correct the module will output a square wave signal to the ecm. In the ECM prom there are calibration values of 33 to 66 hz for this input.
If the signal from the VATS module is there(60 hz from what I have read), then the injectors are permitted to fire.
The VATS module itself does the resistance check, not the ECM.
The VATS module also can have a relay to disable the starter if the resistance of the key is incorrect.
The starter relay can be jumpered out if the module is removed and then all thats lleft is to turn off the VATS in the EPROM in the ECM to not look for thesuare wave "OK" signal from the VATS module to allow the enginge to run.
Jp

 

Double post ?
Don't know how that happened.

 

thanks for the scoop. didn't even know there was any significance to the VATS module, I'd heard it mentioned, thought it was some passive device, although if I had stopped to think about it in these days of a microchip in everything...

makes sense, good explanation. much appreciated.