Why change your ECM?
I have several vehicles of which consist of a 1989 GMC 2500 with an ECM with the broadcast code on it of 1227747, and of course my 1986 Pontiac Fiero, and a 1989 Dodge Shadow, recently painted due to a accident that was not my fault.
I am going to start with my truck. 1989 GMC C2500 305CID AUTO 400 TRAN
I have rebuilt the 305 in the truck with flat top pistons, RV cam etc. I really was particular about the re-assembly of the motor. I rebuilt it in the middle of winter so even my torque settings were redone to compensate for the temperature several times at different temperatures.
The truck had a bad hesitation at about 1200 to 1600 rpm at 60-70 KPA. This is what I was mostly after to get out. I have noticed a service update for the truck as replace EPROM, so GM is aware of this problem. I looked at my main spark table and found it to be pretty rough. This is strange thinking that the old way of managing the spark advance was just rpm vs. advance. So first of all I smoothed it out, keeping the highest advance and the lowest only 1 degree advanced. I put up to 6 degrees at the area I maintain highway cruise speeds.
Well it really made a difference! Now I am going to redo my fuel tables. I have noticed with a scan tool that the BLM is at some areas 108 which is the lowest that the ECM will go to lean the fuel out. OH yes, by the way, before I even started I replaced the O2 to get accurate measurements. I have leaned out the fuel tables in all areas to the point that I now see 128 which is the correct air/fuel mixture 14:1:1. I have also pulled the plugs after some use and found that they were the correct color of being tan.
Well with this truck I have tested up to an %80 increase in mileage with more power! This is a worthwhile project to build. I did end up buying a Snap-On MT2500 with all domestic up to 96, with transmission module. The reason for this is because I am working on other projects that I wanted an easy interface to. The following will get you going on some OBD I systems and also newer OBD II for newer PCM's.
UPDATE ON HESITATION AT 50 - 60 KPA AT 1200 rpm
My Hesitation after all my work re-mapping my fuel tables and doing my spark table, was not related. After getting it all out, I ended up finding a bad EGR Valve. Not the switch but the one behind the carburetor. Then I had to start my mapping all over again. I had to also disable the fault code for EGR and disabled the spark advance for EGR % corrections. Now it runs excellent and I think so far I am getting about 25 miles to the gallon without an overdrive transmission. Excellent! I also have tons more power. I have noticed with the fuel table that they like about 10% more fuel than original to get an 128 BLM on my scanner, but I figured this might be the modifications over factory when the motor was rebuilt. I think for stock vehicles with this hesitation, just replacing the EGR valve will solve the problems and make a huge difference. I bet there is a few vehicles out there that no person can figure what the problem really is, it took me some time too for the hesitation problem.
Another Update on the above having %10 more fuel needed for correct mixtures. I have found that the EGR programming was getting in the way for volumetric efficiency. An easy way to totally disable any EGR in the computer is to enable the EGR at %100 of the TPS. I also disabled all spark advance based on percentage of the EGR just to be safe, considering that I am only 2 degrees retarded off the point where my engine would knock.
I have also only 2 degrees retard in the event of a knock and 2 degrees advanced while in power enrich mode. At the worse it will have 0 degrees difference from my main spark table. I do have more retard for the timing based on higher RPM's while in PE mode, so if I am flooring it, I don't want the motor to fly apart if it has knock. I also corrected my cold advance with max of 4 degrees for any temp under 55 degrees C. This gets rid of any chance of a knock while startup.
What I have found is that the stock fuel table is dead on now everywhere (128BLM) but at 80KPA it is (131BLM) at 1600RPM to about 2800RPM. This is very acceptable. I have tons of power, cant trip the knock sensor, and PE mode seems to work fine. For a 305CID motor I bet I would beat most stock 350CID motors right now.
I have a 26 foot trailer I pull and I can do 100KM/H to 110KM/H. Not up a hill though. I still have to check mixtures and knock while I pull the trailer. I am building a LED display fuel mixture indicator though as the computer updates are very slow for this ECM. This will help the last stage of refinements. Here is how to build your own Air/Fuel indicator.
I seem to be still getting excellent mileage out of my truck also. I will post results soon as I collect them over time. I am doing about 18 Miles to the Gallon while pulling the trailer.
Update: years later
still running, still get extremely good gas mileage. I get about 28 and pulling I still get 18. the motor has run extremely well and is abnormally easy to start in really cold weather. if the motor has lasted this long, I guess the programming is good! no major problems to date.
AND EVEN MORE YEARS
I have had no issues, the truck starts good, runs good, and still gets good mileage. Its now been about 5 years or even 6 years since I played with the program in the ECM. now the EPROM burner has a layer of dust on it! I should pull it out and play again.
How to Build your own interface
I have downloaded the ECM bin editor from www.tunercat.com but I wanted a scan converter to try to see what was happening when I tested my changed with the engine management.
first of all you need to convert the data out of the car to a logic level that a normal computer serial interface will be able to see. This is easily done with a chip from MAXIM 232. It will convert any logic level to a 5V level.
Here is a schematic I found on the Internet and it works.
This works with the OBD II systems
I built mine out of a breakout box with DB25 connectors on it. I was able to put a 5V regulator inside of the box and it turned out really nice. Now all you have to do is find some sort of Scan Tool Software to use this or use it with existing software available. Try www.tunercat.com for links that will give you access to software that will work. I will post some links as I verify and test my own software.
This is for OBD I systems
Also there are links on www.tunercat.com to find a software called ALDMON.exe that you will have to use to view the data.
Do you want your own computer chip for your Automobile?
First of all you need to have some basic knowledge how to run an EPROM burner.
If you know how to read an EPROM and get it as a *.bin format from INTEL hex then save it to a disk.
You might need an EPROM eraser also, Unless you are using new EPROM's which are already BLANK.
Link to this site to get a demo version of there software. I found by default that it was enabled to edit my bin for my 1989 GM 2500 truck.
The above is the pin-out of the chip found in your ECM
you can edit your own chip and play with different things and see what you can do. Also at the above site it has many links to various information available on the Internet that is extremely useful.
Programming on-the-fly
Well, its been a few years since I have really done anything with this truck for programming. This project has saved me so much money in fuel and has been working perfectly all this time. Now there is a unit made that will allow me real-time updates to my software. I have ordered a unit and will post my results soon. Boy, this will be nice! I have been wishing I could do this for so long!
Bill at Speedtronics said this has to be soldered into place in the ECM. They offered to do this for me, but I will do it myself. If you decide to try it, have them install it for you so it is correct. You will have to ship your ECM to them.
I also got a switch for it that will enable several different BIN files to be active in this unit, and I can switch between different programs when I want. The PRO version of the prominator allows programming on the fly without any interruption with you vehicle running.
I CANT WAIT !
I will be using the CATS RT tuner software for this unit
I'll let you know how it works, l8tr
