LO3/5 ECM tuning - Chevy Impala SS Forum
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post #1 of 2 (permalink) Old 11-25-2001, 09:11 AM
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Cheston and others,

I mentioned the use of Tunercat in another thread, and there was some questions about this program so I started a new thread on ECM tuning for the TBI B-bodies.

Tunercat is a program that allows you to change the fuel and timing parameters that are stored in the stock EPROM, along with some flags and constants related to MIL codes, TCC lock-up, etc. It consists of the main Tunercat program and a "definition file" for each ECM/PCM that you wish to work with. To tune a '91-93 B-body with the '965 ECM, you'll need the $62 definition file (which wasn't available until I asked for it 3 months ago - I kinda wonder why no one bothered asking before me). If you've got an LT1 B-body, you can also get the $EE def file. If you've got other GM vehicles, check out the list of available files (by the way, the website is www.tunercat.com ).

Once you have the software, you need an EPROM burner, and a EPROM eraser. Tunercat creates a .bin file (an image of the EPROM) - the programmer is necessary to "burn" that file into the EPROM chip. There's a lot of different ones available - check out Digikey for some decent ones, or keep an eye on eBay (use "eprom programmer" as your search string). An eraser is available from Digikey for $40 - it basically consists of a UV light that erases the EPROM (since it's not electronically erasable). You'll also want a supply of spare EPROMs on hand; the '965 uses a 2732 (8x4kb) 24-pin EPROM that's not commercially-available anymore. Either use an electronics surplus store, or go back to eBay and find them there. I bought 10 of them for $15 on eBay.

Now, here's where things get a bit tricky. The stock EPROM chip is removable from the ECM, but it's in a non-standard socket You'll need to replace the ECM socket with a standard 24-pin DIP socket (I used a nice 3M ZIF socket from Digikey in my wagon's ECM). If you're handy with soldering and desoldering techniques on PCBs, it's a simple job (I've got pictures, if needed). If not, contact me and I'll rework your ECM for a reasonable price (I'm thinking around $50 right now). If there's a better way to get around this problem, please post it!

OK, so now you've got your reworked ECM, a supply of EPROM, Tunercat, and a EPROM programmer. First, use the EPROM programmer to read the stock .bin from your stock EPROM and store it away in multiple safe locations. You don't want to loose this file, or else you may need to go buy a new stock EPROM later on. In fact, it's a good idea to just not mess with the stock EPROM.

Now, take that stock .bin and open it with Tunercat. You'll find that you can edit all sorts of things. I'm still learning my way with the TBI stuff, and I'm not nearly as comfortable with it as I am with LT1 tuning (but I'm getting there). Before you go messing with everything, set some goals for yourself - what's wrong with the current tune? A big part of that is using WINALDL software to determine what the hell your car is doing. This 160 ALDL stuff isn't great, but it's better than guessing. You'll also need a OBDI ALDL cable, like the one available from AKM electronics or any number of the DIY designs available on the web (there's one shown on the WINALDL site that I've been using with success).

Hopefully that's enough info to get people going. Programming a custom EPROM is much better than playing around with the "quarter mod" BS or any other "hacks". For example, my wagon was lean at WOT but rich at idle - playing around with the fuel pressure could have fixed one problem, but only at the expense of making the other worse. I also had some spark knock counts, but only in a very small range centered around 1600 RPM and 40 kPa - retarding the timing via a distributor adjustment could have fixed this problem, but I would have also retarded the timing in every other area, too.

Cheston, feel free to copy this post to the GM_TBI list - I'm having problems sending outgoing mail right now.

Hopefully this gets some good dialog going. The Thirdgen.org forum is a great resource for TBI tuning tips - there's a lot of guys there with a lot more experience than my own when it comes to TBI tuning.
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post #2 of 2 (permalink) Old 11-25-2001, 09:12 PM
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<BLOCKQUOTE>quote:</font><HR>Originally posted by Eric Bryant:
Cheston, feel free to copy this post to the GM_TBI list - I'm having problems sending outgoing mail right now. <HR></BLOCKQUOTE>

Done! ThankSS!! And I don't even use email for the list anymore. I just go directly to the homepage and Yahoo lets me post from there.
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