Interesting crossed ECM Outputs...

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Interesting crossed ECM Outputs...

Postby Rettax3 » 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.

1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26

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Re: Interesting crossed ECM Outputs...

Postby woody90gtz » Thu Oct 18, 2018 11:53 pm

Oh yeah. I've mistakenly tried to read my truck codes via the Beretta definition and vice versa and it's totally off with different masks. The bin file for the actual calibration is actually even 64k for the truck vs 32k for the Beretta.

91 "SS" WOT 3400/5spd - EP, FFP, TCE, SPEC, DSS, S&S, OBD1 GEARHEAD dezign

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