Interesting crossed ECM Outputs...
Posted: Thu Oct 18, 2018 3:14 am
Well, interesting to me, and maybe a few other geeks on here anyway... So, with my '95 Z-26 LQ1 (3.4 Quad-Cam) swap, I have fully integrated the W-Body ECM and wiring harness, including the ALDL. The donor, for those who have not looked over my thread on that car, was also a '95 Chevy Z (Z-34 Lumina). Interestingly, even the 3.1 'L82' 'M-Code' option on the Base Lumina ran a completely different ECM than our Berettas used. The Lumina even retained the old-style PROM chip, unlike the Berettas.
So, while scanning my ECM (old Snap-On MT2500 'Brick') I noticed a PID for 'Weak Cylinder', which it was showing 'none'. That of course is good. But, I didn't recall ever seeing that PID on other similar-era GMs before, so I wanted to check to see if the Beretta ECM had the same PID list. I should have just moved over to my other, more stockish '95 Z-26, but oh well. So, I reset the scan-tool to think it was talking to the L-Body ECM (which it cannot find in that car, since the ALDL is currently wired to the W-Body ECM, NOT the L-Body ECM). I did not check the PID list for the 'Weak Cylinder', as I shut it all down as soon as I noticed that the Coolant Temperature PID altered with throttle position. (!) Although the 'Brick' should be ECM-safe even when incorrectly identifying an ECM, I admit I got worried for a second -I'll just plug in to the other Z sometime to look for the 'Weak Cylinder' PID.
What is interesting to me is that the inputs as identified to the scan-tool through the ALDL link are clearly not correct. I thought it was odd that the 'Brick' apparently does not know what inputs the ECM is sending back out via the ALDL by name, just as A B C... etc. Also quite surprising that GM didn't maintain 'A' as one specific PID across their entire product line, and 'B' as a specific PID, etc.
So, while scanning my ECM (old Snap-On MT2500 'Brick') I noticed a PID for 'Weak Cylinder', which it was showing 'none'. That of course is good. But, I didn't recall ever seeing that PID on other similar-era GMs before, so I wanted to check to see if the Beretta ECM had the same PID list. I should have just moved over to my other, more stockish '95 Z-26, but oh well. So, I reset the scan-tool to think it was talking to the L-Body ECM (which it cannot find in that car, since the ALDL is currently wired to the W-Body ECM, NOT the L-Body ECM). I did not check the PID list for the 'Weak Cylinder', as I shut it all down as soon as I noticed that the Coolant Temperature PID altered with throttle position. (!) Although the 'Brick' should be ECM-safe even when incorrectly identifying an ECM, I admit I got worried for a second -I'll just plug in to the other Z sometime to look for the 'Weak Cylinder' PID.
What is interesting to me is that the inputs as identified to the scan-tool through the ALDL link are clearly not correct. I thought it was odd that the 'Brick' apparently does not know what inputs the ECM is sending back out via the ALDL by name, just as A B C... etc. Also quite surprising that GM didn't maintain 'A' as one specific PID across their entire product line, and 'B' as a specific PID, etc.