The Gm Aldl Information Page

This page is like that old pair of Levi's. I just can't seem to throw it away, even though it's out of date, faded, and worn stale. I started building this page almost 6 years ago, when hardly anyone else was interested in hooking their laptops to their cars. I poked around the 'net, found a guy in Canada who had done it (PPF, who provided me with GCAR and the schematic), and I started playing around with this stuff. I built a web page, "became an expert" (LOL), and at this point have built and shipped hundreds of ALDL cables all over the world. I still enjoy the heck out of this stuff, but don't have time to play with it anymore. I'm too busy with the wife, kids, 2 jobs, and keeping my 3 Camaros running (err, I'd be happy with 2 at a time running, but right now, we're down to 1, and even that one is scheduled for major work soon :) ).

This page contains information primarily related to the 1994/1995 GM LT1 engine and PCM. I do know that the interface and software (GCAR) will work on some other cars (starting with late 80s GM's), but I couldn't tell you which ones. There's software popping up all over the web these days that use this interface, so look at the links and see the sights. ;^)

This interface and information is for the 8192 baud rate serial interface only. Earlier GM cars (early - mid 80s) used a 160 baud Pulsewidth Modulation scheme. This interface will work with them with the addition of a 10k resistor between "A" and "B", and using software like Jonas' WinALDL free software for 160 baud vehicles. See the link to Dan's page below for more information on those 160 baud cars. Also Peter's page below has good info (and some software).

Remember, my focus is the '94/'95 LT1 based 16188051 PCM. If these methods happen to work with other cars, great! If not, well, then, you were warned. ;^) I know it works with mine. :)

THis is a zipped file that contains the executable, source code, and whatever other junk was in the directory when I zipped it...(ooh, shouldn't have left that naughty .gif in there! j/k)... Click on this link right here to see my notes on what it does (recommended before even thinking about trying the code). Click this link for the software to download the code and .exe for GCAR.

Here is the schematic for the interface. The car has a bidirectional single wire that operates at TTL (5 volt) levels. Your laptop/PC wants separate RS232 transmit and receive ( /- 12 volts). This interface converts the single wire ALDL to RS232. The interface board needs 12 volts from somewhere - for '94s, I recommend the cigarette lighter adapter. For '95s, the OBDII D-shaped connector has 12 volts available. Take your pick. But the boards I sell are capable of drawing power from the RS232 port, so you may not need external power from the car.

A long time ago I put together a parts list required to assemble this board - along with some notes on how I built it. I've built this board several times now, and here is a picture of my last protoboard-style unit. Here are the notes on building my circuit board.

Now that you've seen the board, and the software that will only spit hex numbers at you, it's time for some real documentation. Here is the 8192 baud ALDL datastream information for the 1994/1995 F-car with AUTOMATIC transmissions. Here is the datastream for the MANUAL transmissions. You can see they're a little different, but still close enough to work with the same diagnostic tool. Do these codes apply to other cars and motors? No. Datastreams are engine and transmission specific. I have a copy of the 1993 LT1 datastream decode. And looky here - I have an '89 TPI datastream around here too...

Aww what the heck. Here are ALL of the datastream docs zipped up in a big phat file. Have fun. :)

This is how the over the counter diagnostic softare is written (see Diacom, Autotap, and Dave's Page). Slap some similar code in a microprocessor, put on a small display, and you have the AutoXray, Scanmaster, TechII, and other cool tools... Or, if you're really enterprising (like the fellow with the EV1, link below), you could use a PalmPilot to display the data. That's the coolest ALDL trick I've seen yet! His datastream stuff is completely incompatible here, but the concept is similar.

You know what else you could do with those documents? BUILD YOUR OWN WINDOWS BASED TOOL! Starr Performance has created a very nifty program called Carbytes / EFILive. Allows graphing, logging, etc. All you need is a protocol description document - which I've provided for you above! Starr Performance Website but that's where the main site is. It's a MUST SEE software package! Works with my ALDL converter too. =8^)

I've received emails asking "why not just go buy an AutoXray or whatever"...Well, that's not my point. My point is to *learn* what's going on over that little computer interface. I plugged in *because it was there*. Not 'cuz I'm cheap (well, I am, but that's not the reason I started messing with this stuff). Some people like me just enjoy tinkering with protocols. I do it for fun at work... I do it for fun at home... :) Ever sniffed an ethernet network? Same type of thing. Just watching what's going on can be fun! (OK, my idea of fun is not the same as a lot of folks...)

Where does this lead? Well, I first posted this page about six years ago. I've learned a *lot* since I wrote the (well, crap) that was on here, and posted the software/schematic.

There seems to be a dearth of information on actually tuning fuel injection systems. Too much is protected by a few people. I picked up a magazine dedicated to fuel injection systems this past weekend (one of those Hot Rod / Car Craft / Super Chevy combination deals...). I looked at it, and decided - what a bunch of CRAP! It was nothing I hadn't seen before a million times... You need a coolant sensor, an oxygen sensor, some fuel injectors, blah blah blah... NOTHING about actually tuning the firmware. When it came to that, they turned in to advertisement mode. "Buy or call one of our sponsors of our crap magazine". The vendor stuff is cool, and they know what they're doing, but what kind of "information" for guys like me is that? Nothing. So I'm determined to learn - without their kind of help.

There are dangers in doing this - some not too harsh, some very very expensive... Locking up the PCM (oops - power cycle will fix it - been there, done that - I'm one of the few people who can claim that they've locked up the computer in their car and had to reboot...), corrupting the flash (umm, either need surface mount component repair or a new PCM - that's why I bought a spare PCM from a junkyard), slagging the motor (running lean can really suck...), or grenading the transmission (uh-oh). So, it's not for the guy who just wants to start randomly playing - study and caution are highly advised... Stay tuned for more details. I'll be working on it. ;) As a slight update, I have had one friend smoke two PCMs, and I reparied them both - so all is not hopeless if you doorstop your PCM! I can fix 'em.

Wanna taste? Here are some maps from the LT1 PCM... They look good at 800x600. Don't blame me if you haven't replaced your CGA/EGA/VGA monitor yet. ;) ;)

"LT1 Edit Dump of Table -- Spk Adv 400-4000 RPM

Filename = Untitled
400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2800 3200 3600 4000
25 KPA 16.0 24.0 27.0 32.0 34.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0 35.0
30 KPA 16.0 24.0 31.0 38.0 40.0 40.0 41.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 41.0
35 KPA 27.0 27.0 32.0 39.0 39.0 41.0 41.0 43.0 43.0 43.0 43.0 43.0 43.0 43.0 43.0
40 KPA 28.0 30.0 33.0 36.0 38.0 40.0 41.0 43.0 43.0 43.0 43.0 43.0 43.0 44.0 44.0
45 KPA 28.0 30.0 33.0 34.0 37.0 38.0 40.0 41.0 41.0 42.0 43.0 42.0 42.0 43.0 43.0
50 KPA 26.0 29.0 32.0 33.0 35.0 36.0 38.0 39.0 40.0 40.0 41.0 41.0 41.0 42.0 42.0
55 KPA 24.0 27.0 29.0 31.0 34.0 35.0 37.0 38.0 39.0 40.0 40.0 40.0 41.0 41.0 41.0
60 KPA 24.0 25.0 26.0 29.0 33.0 34.0 35.0 37.0 38.0 39.0 39.0 39.0 40.0 41.0 41.0
65 KPA 20.0 24.0 25.0 26.0 29.0 32.0 34.0 36.0 37.0 38.0 39.0 38.0 38.0 39.0 39.0
70 KPA 20.0 21.0 22.0 23.0 25.0 28.0 31.0 34.0 35.0 37.0 37.0 37.0 37.0 38.0 39.0
75 KPA 18.0 18.0 19.0 20.0 22.0 25.0 27.0 30.0 31.0 34.0 35.0 36.0 36.0 37.0 38.0
80 KPA 14.0 16.0 16.0 16.0 18.0 22.0 23.0 26.0 28.0 31.0 34.0 35.0 36.0 37.0 38.0
85 KPA 12.0 13.0 14.0 14.0 16.0 20.0 20.0 23.0 25.0 28.0 32.0 35.0 35.0 37.0 37.0
90 KPA 11.0 11.0 11.0 11.0 14.0 17.0 18.0 21.0 24.0 28.0 31.0 35.0 35.0 35.0 35.0
95 KPA 9.0 9.0 9.0 9.0 12.0 14.0 16.0 19.0 23.0 27.0 30.0 34.0 34.0 35.0 35.0
100 KPA 8.0 8.0 9.0 9.0 12.0 14.0 16.0 19.0 23.0 27.0 30.0 33.0 33.0 33.0 33.0
"

"LT1 Edit Dump of Table -- Spk Adv 4000-7000 RPM

Filename = Untitled
4000 4500 5000 5500 6000 6500 7000
25 KPA 35.0 35.0 35.0 35.0 35.0 35.0 32.0
30 KPA 41.0 41.0 41.0 40.0 40.0 40.0 36.0
35 KPA 43.0 44.0 44.0 44.0 44.0 44.0 46.0
40 KPA 44.0 44.0 44.0 44.0 44.0 44.0 46.0
45 KPA 43.0 43.0 43.0 43.0 43.0 43.0 46.0
50 KPA 42.0 42.0 42.0 42.0 42.0 42.0 46.0
55 KPA 41.0 41.0 41.0 41.0 41.0 41.0 46.0
60 KPA 41.0 40.0 40.0 40.0 41.0 41.0 40.0
65 KPA 39.0 40.0 39.0 39.0 40.0 41.0 40.0
70 KPA 39.0 40.0 39.0 39.0 40.0 41.0 36.0
75 KPA 38.0 39.0 39.0 39.0 39.0 39.0 33.0
80 KPA 38.0 38.0 38.0 38.0 38.0 38.0 30.0
85 KPA 37.0 37.0 37.0 37.0 37.0 37.0 29.0
90 KPA 35.0 35.0 35.0 35.0 35.0 36.0 28.0
95 KPA 35.0 35.0 35.0 35.0 35.0 36.0 27.0
100KPA 33.0 33.0 33.0 33.0 33.0 36.0 26.0
"

There are quite a few more tables worth editing... Especially Performance Enrichment AFR related (I didn't post those), nor did I include transmission shift pressure adjustment. Check out MTI Houston. Under their LT1 computer mods section, they've listed a partial spark map as well... Seems he left a few columns out. ;)

Now, of course, I have to throw in the obligatory linkage. Be sure to check out:

DIYEFI / GMECM Page (where it all started for me!)

Related to DIYEFI: GM Systems Links - a nice place to start

Related to DIYEFI: Programming 101 - The CSH Repository - ESSENTIAL READING

Related to DIYEFI: Bruce Plecan's Tuning Tips (Bruce is the only guy I know who runs ECM's on his dining room table! ESSENTIAL READING PART II

Dave's Homepage (PCMcomm - cool freebie diagnostic tool that uses the same RS232/ALDL interface! Great guy too...)

Dan's ALDL Information Page (160 Baud emphasis - another nice guy!)

Peter's ECM Pages Lots of good info on ECM's of all eras...

Andy Whittaker's Lotus Page (cool stuff once again!)

EV1 ALDL Page (this guy linked a PalmPilot to his car... can you say trick!? :p~~ droolin!) Wander around his site - there's a lot there!

Continue reading here: Diagnostic Scanning Software

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