ECM programming calibrataions between models

I have heard many places that the ECM calibration between the RMW and Caprice wagon is essentially identical. Since that I found out that the Buick uses a different protocol so my new DST tuner would not communicate with it, but that has been resolved by Jet with and update so now I can read it.

Anyway, when I was unable to read the Buick, Jet said about all I could do was swap out the PCM for a Caprice version so the DST could communicate with it. I ordered a preflashed ECM with the factory program the dealers use to flash the units to current updates for a Caprice wagon VIN# I got off a used car ad on the internet. It was wagon that had the trailer towing package and our Buick does not.

I installed and read the Caprice ECM and then put the Buick on back in and read it with the modified DST tuner and went to work on my PC to learn the programs. I was particularly interested in the gear/speedo automatic calculator by tire size or revs/mile and rear axle ratio and what they did to the shift points.

Long story short is that what found out was pretty surprising.

If I set the Buick and Caprice to the same revs/mile and rear axle ratio, they spit out different shiftpoints and lockup points by MPH. The Caprice was considerably higher than the Buick. Very contrary to the all the same idea. Since I only have the two ECMs, I can't check any others at this point, so I don't know if the difference is because of Buick vs Caprice differences or trailer tow vs no trailer tow.

What it does tell me is that if you are looking for more performance in a Buick with a stock engine, you would likely get a boost by just changing the ECM to a Caprice towing version and change the gears to match the towing 2.93 (which you should do anyway). Junk yard donor car would be perfect and cheap to do.

Now I really wonder what calibration an Impala SS has in it.

So, the order in which you do modify values is important. It is quite possible that the editor program actually recalculates the shift points after you modify the rear axle ratio. What were the starting rear axle ratios of both programs?

A similar issue occurs when adjusting the spark advance tables. There is a "spark bias" value that is subtracted from the spark tables to get the actual spark advance. This is done because the tables are stored in the PCM as unsigned integers which can't go negative. So the stock B-body table has a 20 degree spark bias value; if you alter that number, some editors automatically adjust the spark advance tables and some don't. I don't recall which but the information is out there if you search.

I'll also say that most all of the source code needed to run the powertrain is in the BIN (binary) file you download. The Buick program has additional code to provide messages to the climate control head. This is the main reason I'm not plowing ahead on a Torqhead or 0411 PCM swap on my 96 Roadmaster at the moment; I don't know anyone who's gotten the climate control to work right. It occurred to me that it might be smarter to lift the buick-specific programming from the 96 PCM and add it into the 0411 PCM if there's room, then the climate control head could talk with the 0411 PCM. Just need to find the time to do all that...

I was starting with clean read of each of the calibrations, but one being trail pkg and one not they had different axle ratios in them, even though the DST does not show what the current one is. Since per the specs, the Buick would have the 2.56 gears and Caprice would have the 2.93 gears, so they certainly showed different shift points.

I changed the Buick 2.56 to same as the 2.93 and got different shift points than the Caprice showed, with the Buick being lower.

I then changed the Buick back to 2.56 and it went back where it was in the first place.

I then changed the Caprice to the 2.56 ratio and it went to different shift points, higher ones, than the Buick showed.

I changed the Caprice to 2.93 where it started and the shift points went back to where they were.

I then changed both of them to 3.08 ratio and they both changed shift points, with Caprice being higher.

Changed both back to the starting points of 2.56 and 2.93 and they were both back where they started.

This all would tell me that that the program is using the gears to directly calculate the shift points and doing it consistently as it always give the same answers for each vehicle.

I would certainly also guess that there is a base shift point/gear ratio chart built into the program, but they don't show that anywhere I could find. Then there probably is a modifier that is based on the VIN of the vehicle or the part number of the calibration. If the VIN pulls up a Buick without trailer pkg, it gets a different modifier to put on the base map for the shift points than a Caprice with trailer pkg does.

The calibrations I started with from the reads appear to both be GM generated, with the Buick being the original calibration number and the Caprice being a just done calibration install from the GM data base based on VIN.

I don't know if a hidden base chart even exists in aftermarket software like JET. Something like that might only exist within GM. For the'94-95 definition file, TunerPro does have the base MAF calibrations stored for B, F and Y cars, but these are gleaned from factory calibrations.

At any rate I would not be terribly concerned about this.  The tables are starting points, and when I did transmission tuning on my last wagon, I adjusted the shift points for my exact commute. In fact it was so good that I ended up never manually shifting it using the Blazer floor shifter I had installed.

sherlock9c1 wrote:

I don't know if a hidden base chart even exists in aftermarket software like JET. Something like that might only exist within GM. For the'94-95 definition file, TunerPro does have the base MAF calibrations stored for B, F and Y cars, but these are gleaned from factory calibrations.

At any rate I would not be terribly concerned about this.  The tables are starting points, and when I did transmission tuning on my last wagon, I adjusted the shift points for my exact commute. In fact it was so good that I ended up never manually shifting it using the Blazer floor shifter I had installed.

Totally agree, and I am sure the base map isn't in the Jet program. That would be why the Jet can't load a clean PCM, it has to have a GM program on it first and that would be where the map would be.

I also agree that programming to your particular driving style and loads, plus the engine mods or not is by far that best.

My point was that if someone didn't have a tuner and didn't want to spend on a tune, they could probably get better results for what they are tying to do by finding the right donor car and getting the gears and PCM from it. Want a high MPG low rpm turning highway cruiser, get a non trailer pkg Buick. Want more performance at the expense of a little MPG and rpm noise get a Caprice wagon with trailer tow, or maybe Buick with trailer tow (at this point unkown if the difference is the trailer two, brand, or both). Want the 3.08 gear get the gears and PCM from and Impala SS or cop version Caprice.

Only issue is without a programmer, the VATs value will change if you just throw in another PCM. I swapped a 9C1 PCM into my 94 RMW which was a non issue since the 9c1 don't use VATs with the single key option. I figured the difference between 3.08 and 2.93 was a non issue and it really wasn't and it woke the car up quite a bit.

Sprocket wrote:

Only issue is without a programmer, the VATs value will change if you just throw in another PCM.   I swapped a 9C1 PCM into my 94 RMW which was a non issue since the 9c1 don't use VATs with the single key option.   I figured the difference between 3.08 and 2.93 was a non issue and it really wasn't and it woke the car up quite a bit.  

That is pretty interesting. Didn't the 1991 9C1 have gen I engine in it at about 200 hp?