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Thread: ECM elimination

  1. #1

    Cool ECM elimination

    Hey gang, I've got an 89 Chevy Crew cab that's legal for historic tags and no more emissions testing. I've blown a head gasket
    and decided to pull the engine (5.7L) 350 and tranny and overhaul everything. I'd really like to get rid of the ECM and run a straight
    classic/clean set-up under the hood. What kind of peril is getting rid of the ECM? Do I need a different Wiring Harness? Can it just
    be unplugged, but what other components might be affected (a/c, radio, etc?) Your ideas/help would be GREATLY appreciated!

  2. #2


    Most likely the ECM controls the automatic transmission. I've never done this but I talked with a guy at a show and he got a seperate transmission contoller from GM Performance to run his 700R. He had installed a 383 with dual carbs.

    2005 Chevy Silverado Z71 Crew Cab
    6" Skyjacker lift w/Edlebrock dual front remote resoviour shocks, single rear remote. Rancho skid-plate.
    17" x 9" M/T Classic Lock Wheels, 35" BFG A/T or M/T tires
    4.10 PercisionGears w/factory locker, T/A Performance rear-end cover
    Banks CAI intake, ported throttlebody, JBA coated headers, over-sized Magnaflow cats, Magnaflow cat back exhaust, Diablo tuned
    B&M aluminum deep transmission pan
    Warn brush guard w/Warn 9.5 XP winch, PIAA bulbs, Line-X bedliner, AWS Black tool chest, Extang tonneau cover
    Weather Tech floor mats
    Cover-Craft seat covers
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    One black Lab in rear seat.

  3. #3

    Default ECM removal

    I've got the stock TH400, and intend to keep it. I wonder if ECM affects it as well. I might start looking
    at trouble codes and pin info to help sort that out. I'd love a clean break if at all possible.

  4. #4


    I doubt the TH400 is run by the ECM. The ECM may control some of the gauges, but I'm not sure.

    ---------- Post added at 12:57 PM ---------- Previous post was at 12:22 PM ----------

    The ECM does control the ignition timing/distributor.

  5. #5
    Caddiac's Avatar
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    There is a difference in the cam shaft on the older 350's and the more modern 5.7L Vortec engine. What year the change was made I do not know. Fuel system differences, come to mind as being a major obstacle. Not insurmountable but certainly an important consideration.
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  6. #6


    Instead of a total ECM elimination, what can I do to just go with an aftermarket intake/carb/distributor, into headers that allow an O2 sensor?
    I cannot find what functions the ECM would allow or miss, and would the engine operate properly, with a nagging "check engine" light?
    There's gotta be an easier way to step up this engine mildly after all the rebuild work I'm putting in, rather than piece it all together stock--Help!

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