So you’re interested in doing your own OBD1/1.5 tuning?

First let me say, it is not easy, it is expensive, and there is nowhere near as much support for it as OBD2 guys have. So, if you want a professional to make chips for you for cheap, See Ryan and Sinister Performance (http://www.gmtuners.com).

Now, if your OCD and can’t stand not knowing how to do things yourself, read on.

Lets start with the general idea.. Your pre-96 PCM has a removable memcal with a flash-able prom (programmable read only memory) and a knock/calibration circuit in it. This is generally called a chip. There is a bin file on that prom which contains all the algorithms, variables, and tables needed to control your engine, transmission, and other misc. components. This bin file needs tuning software and a definition file in order for you to make any sense of it. So, you will need to extract the file from the stock memcal, alter the file, and reload it back onto a prom or emulator.

With that said there are two ways you can go. You can either continuously burn new proms for every set of changes you want to make. Or, you can use a prom emulator and make changes to the file whenever you want via USB cable. The second option is more expensive however.

Hardware

First off, you need to get your stock bin off your stock prom. If I don’t have it and you can’t find it on the web, you will need a prom reader and an adapter to get the bin.

Lets figure out what type of prom you have..
90-93 L27 and 92-93 L67 Bonnevilles have a 28 pin 27C256 prom.
94-95 L67, L27, and 95 L36 Bonnevilles have a 28 pin 27C512 prom.

To read this prom you’ll need to make an adapter or get one from Moates.

Now you’ll need a burner/reader. There are many options for this. As long as it works with the proms you’ll be using, that’s all you need. I opted for the Moates Burn1. They now have the Burn2 available.

You will also need to either hack up your stock memcal and put a prom socket on it so you can remove the prom, or you’ll need an adapter that reads that knock/calibration chip from your memcal and has a socket for a prom. I know the 94-95 crowd would need this adapter but the 90-93 crowd would need shoot off an email to Moates to figure out the correct one.

Up until this point I outlined all you would need hardware wise except for spare proms if you were to only burn chips.

If you want to do real-time tuning instead of burning chips all the time you will need an emulator. I have a Moates Ostrich 1.0 but they have since made improvements and came out with the more compact Ostrich 2.0. This will work with the two aforementioned prom types. With this, you can literally change parameters as you drive.

Software

There are two different programs that I am aware of as far as tuning goes; Tunercat/RT and TunerPro/RT. They both have a version for basic chip burning and Real Time tuning.

I’ve only used Tunercat/RT so I can only really comment on it. Tunercat’s programs are both free to try however you need purchase a definition file ($19.95) for your particular year/engine. After 30 days the temporary license will expire and you will need to purchase a license. ($69.95 or $99.95 for RT)

IIRC TunerPro is free but RT is $30.

Actual Tuning

You can get the basic ideas of how to tune from a good Third gen F-body site. Look for posts relating to MAF only PCMs. Those cars along with that era of Vettes are the only GM setups I found to be similar to ours as far as tuning goes. Majority of tuning now is MAP based or MAF/MAP based. So, it makes it difficult to learn because our setups need to be modified differently.

Off the top of my head, I have a decent hold on the following and could explain specifically how to make these changes:
Dial in the fuel trims, WOT O2s, modify all the EGR tables & spark tables, do gearing changes, modify lockup tables, performance shift, tune for different injectors or throttlebody, and I also know how to read the load tables since they are based on LV8 instead of MAP.

That’s it for now and I may add or make changes to it as more info comes to mind.

Feel free to ask any questions.

Here's a short run-down on how to tune using TunerCATs:

When logging, take LTFT, STFT, and MAF air flow data for fueling.

First thing you want to do is dial in the fuel injector constant (you may have a summer and winter constant) to something a little better suited for your mods. This will help with keeping your MAF tables within their min/max values per table. There are 8 tables and they all have min/maxes You don't want to have to make large compensations there because you'll hit the ceiling.
After the LTFTs have dialed themselves in, pick a MAF range you commonly find yourself in, such as what you cruise at on the highway and record the LTFT. If the LTFT is greater than 128 (lean) you want to divide it by 128, subtract 1 and multiply it by your current fuel injector constant to get the amount of the fuel injector constant you should subtract. Then subtract the calculated value from the current fuel injector constant to get your new one. This is basically making a percentage of how much more fuel you need, or how lean you are and reducing the fuel injector constant so that the pcm thinks the injectors flow less and it adds more fuel.
I know text is difficult with calcs so it's like this:
([(LTFT/128)-1]*FIC) = FICS (fuel injector constant subtracted)
FIC-FICS = NewFIC

Now if your LTFTs are low (rich) you do the following:
[1-(LTFT/128)]*FIC = FICA (fuel injector constant added)
FIC+FICA = NewFIC

So the first one figures out how much to lower the FIC to make the computer squirt more and the second figures out how much to raise the FIC to make the computer squirt less. Kinda backwards but it makes sense.

Now once you have a base FIC you can move onto MAF table tuning. This is relatively easy but you'll be doing it over and over since there are so many points to cover. Some pay attention to STFTs when calculating this but I just wait till the LTFTs settle and use those.
Log LTFTs and the MAF flow rate they occur at.

If the LTFT is higher than 128 just:
[(LTFT/128)*MAFRT] = NewMAFRT (MAFRT = logged maf rate; NewMAFRT = New MAF flow rate for corresponding frequency)

If the LTFT is lower than 128 just:
[(LTFT/128)*MAFRT] = NewMAFRT

So the first calc increases the MAF flow rate at a given frequency to make the computer think more air is coming in and will in turn add more fuel. The second, decreases the rate for a given frequency and will decease fuel.

Quick recap:
If you're running lean off the bat, reduce the FIC using the calc above. Rich, use the next calc.
If you're running lean after an adjusted FIC, increase the MAF flow rate for a given frequency using the cal above. Rich, use next calc.

That'll get the fueling spot on. And if you're concerned with changing the FIC, don't be. It's not exactly accurate to begin with and neither are the MAF rates.

For WOT fueling just use the PE Trim vs. RPM table to dial in your WOT O2s. This should be done last.

For spark, it's difficult to know where exactly to add timing since a scan (well at least my current scantool) will not tell you the LV8 or load value. Not to mention, there are a few tables that add and subtract to the base timing maps..

For non-WOT I came up with a trick for adding spark advance at low load situations. This is ideal for cruising MPGs.
I figured out what load cell I was in by EGR position. IIRC there is a EGR position vs. load table and a EGR spark advance vs. load table.
So, you can log EGR position, commanded spark advance, and KR. Then you know how much spark you have at a particular load cell by referencing the EGR position table and you can add spark to the appropriate cell on the EGR spark advance table.

Once I got a feel for what load cell I was in I also added spark to some mid load cells in the main spark table.

And for WOT spark, there is a PE spark advance vs. RPM table too.

Changing idle rpm, coolant turn on temps, etc are easy and straight forward.

That's all I got off the top of my head. If you're unclear about any parts LMK and ignore any grammatical errors. I just ran through this.

I'm not sure if this is ever really going to get used (besides me since I periodically forget all of this) but here is more info:

How to tune for FDR changes:

(Old shift point in mph) * [Old FDR/New FDR] = (New shift point in mph)