a few questions...

[Steve=Ravet%Prj=Eng%PCPD=Hou at bangate.compaq.com]

faustini at lamp0.arl.army.mil (Lou Faustini) Wrote:
| 
| 
|     Hi. 
|     Does anyone out there have any information on how to decypher 
| the data 
| stream on the GM ALDL?  I have played with it a little, and all I 
| have come 
| up with is the baud rate (8192bps) and what appears to be the 
| markers for 
| start-of-frame. I have no idea what the data it is sending me is 
| supposed to 
| mean. I assume things like airflow  and RPM are being sent, but I 
| have no 
| way of knowing how they are encoded. I really don't feeel like 
| disasembling 
| the 32k of 'hc11 code in the ECU, so any help would be 
| appreciated.

Good question -- This topic was raised on the vettenet a month or so ago, and 
the consensus was that GM isn't telling, at least not without a non-disclosure 
agreement.  A fellow on the buick gn/t-type list decoded the data stream for 
the GN, but it is a different type (about 100 baud, not an even rate, the ECM 
just sends a bit whenever it gets some time).  He did it the hard way, a scope 
to determine the baud rate, watch the frames, decipher what the stuff is.  He 
had a tech-1 diagnostic computer or whatever also, which aided the job some.  
I have tried calling GM/Chevrolet to get the info, to no avail, but I only 
spent one afternoon doing it.  You are correct about the baud rate, but it is 
TTL level, not RS-232.  This will drive most serial ports, however, if you use 
a very short cable.  I experimented with this a little with my car ('89 
corvette), but then I wrecked it, so I haven't done much since then.  There 
are aftermarket diagnostic computers, though, so the information must be 
available somewhere.

--steve


| 
|    Next question-- 
|    This isn't really a fuel-injection question, but I am sure 
| some of you 
| know the answer to this one:
| 
|    Kawasaki and Yamaha just announced their 1995 jet-skii lineup. 
| In the 
| spotlight are their new 3-cylinder motors. They range from 900 to 
| 1100 cc's 
| in displacement. After I stoped drooling at the pictures, I read 
| a little 
| about the motors. 2-cycle water-cooled, tripple carbs. No black 
| magic... 
| Until you read abot the compression ratio. The Kaw motor has a 
| compression 
| ratio of 5.5 to 1 !! the Yamaha motor runs 5.1 to 1 !!  This is 
| very low in 
| contrast to their 750cc motors, which run typical stock ratios of 
| 8-ish to 
| 1. Aftermarkit kits for compression ratios of 10 to 1 are very 
| popular for 
| the 750 motors, and have proven to be a powerful and reliable 
| combination. 
| So my question is, why would ANYONE design a motor to run at 
| 5-ish to one 
| compression? I heard once that in-line 6-cylinder 4-cycle motors 
| have 
| problems spinning at high rpm's. I dont recall why. Is a 
| 3-cylinder 2-cycle 
| motor subject to the same problems? Are these problems for real?  
|  Any help 
| would be appreciated.
| 
|                                                ----- Lou Faustini
| 
|