Okay, so now I know at least one reason why I can't run a 180* thermostat, the TCC won't lock due to ECM parameters. There are likely other issues dealing with enrichment and maybe ignition timing as well that need modification/tuning...

Is there a listing of ECM parameters floating around somewhere? I guess I'm gonna have to modify this thing in order to get my 180* thermostat working properly...

 

The tuning definition (ECU/XDF/TDS) file IS the list of parameters.
Each "Mask ID" has a different set.
Finding out what each parameter does will take some reading and research.

 

I know how to read and write PROM's and have the tools do do that. I suppose the next step is to yank the N828131 prom from my 1226519, stick it in my reader and make a binary file.

Is there a better way to go about moding than just guessing which bytes to change with a hex editor?

Thanks,

 

Well, to expand on what JP86SS said, you are going to need to do some research. From using the BBC lookup on moates.net I see your car is either an 85 or 86 with most likely the 3.0 with an auto. WinALDL support 84, 85 and 86 CLCC cars, so you should be able to datalog and view all the data coming out of your ALDL port. My guess is that you will have to search using your BCC to see if anyone has disassembled it already for you, otherwise you will be disassembling the binary image. Because it is not a commonly use ECU there doesn't appear to be any XDF's to look at so you are in for a lot of work. good luck.

 

Thanks,

Yea, it seems the emphasis has been nearly all on TBI ECU's, my 84 is a carbed CCC 231 Buick and runs pretty well but I think I could make it run better (especially idle, too lean).

I also want to make other changes, so I'm gonna try disassembling the PROM and see what that does for me.

Luckily I learned 68K Moto assembly back in the early 90's, so I can probably do it. Anyway, if I'm successful and in the spirit of contributing to this great resource provided here, I'll be posting the details of how I accomplished it along with disassembled original and modified versions of my code.

Good luck!

 

Okay, so what I decided to do was just an ECM hardware hack instead of trying to redesign the software. This addresses my CTS offset issue so I can run that 180* thermostat.

So what I did was change the Coolant Temperature Sensor (CTS) circuit impedance by adjusting the pull up(supply) resistor. I removed the factory 360 Ohm chip-style resistor and in it's place installed a 470 Ohm 1/4 W film resistor. This added about a 20* offset so the ECU now believes engine temp is 200* when in fact it's actually 180* and so locks the TCC on que as it should. I should mention, the PROM version is known as "DFS", which is a California emissions compliant version, so this issue may be specific only to my particular circumstances.

Neutral idle still rather lean for my tastes (Vacuum and O2 crossovers are good along with carb dwell, but rough and stinky idle), life goes on!

 

A second solution which I've discovered was to change the PROM from DFS to BSX, the BSX locks the torque converter at an engine temperature of 160* and at 35 MPH instead of the ~190*/45 MPH constants for the DFS.

So now I'm back to an unhacked ECM with a BSX PROM instead of the DFS PROM.

Still haven't discovered the best way to fatten the idle mixture though, hoping not to have to go to a mechanical carb and vacuum distributor having hit a brick wall on moding the ECM PROM.