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  • March 28, 2024, 02:48:29 PM

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Author Topic: GM 4-pin HEI Ignition Module vs newer higher current 7-pin???  (Read 1934 times)

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Offline Canoe

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    I've been seeing posts around the internet about using GM's 7-pin IG modules instead of the usual GM 4-pin HEI modules, but details aren't given (that I've found).
    Now I've found a resource on the modules that provides info that seems to back this up.

http://gpzweb.s3-website-us-east-1.amazonaws.com/Ignition/HeiModules/HeiModules.html
http://gpzweb.s3-website-us-east-1.amazonaws.com/Ignition/HeiModules/Hei7pinDR124moduleNotes.txt

It appears that we could use the more modern higher current 7-pin module in place of the 4-pin module by:
  • +: Positive power ~12 VDC
  • C: Coil; connects to negative terminal of coil (module uses low-side current sensing to limit current when necessary)
  • P: Positive of distributor pickup
  • N: Negative of distributor pickup
  • E: not connected / not used
  • R: not connected / not used
  • B: not connected: module uses the pickup inputs to drive the module's Dwell circuit, hence the coil
  • ground the module through the hole

And we might be able to use the B/Bypass tab to control between running in the mode above (Bypass) or in Run mode to use the MCU to control the timing & dwell. Using the MCU would allow it to control for Ping from the knock-sensor. This is speculation on how it might work:
  • +: Positive power ~12 VDC
  • C: Coil; connects to negative terminal of coil
  • P: Positive of distributor pickup
  • N: Negative of distributor pickup
  • E: ECM input returned from ECM, drives coil using ECM timing & dwell. Return from Eagle MCU may be compatible to control timing & dwell???
  • R: Reference signal: DC generated from distributor pickup to ECM. May be accepted by Eagle MCU in place of the distributor pickup signal???
  • B: Bypass:
    • 0/not connected: Bypass ignores any E signal and uses the pickup to drive the module's Dwell circuit, hence the coil
    • +5 VDC voltage (higher?): module uses the E signal to drive the coil
  • ground the module through the hole
NOTE: if I understand corectly, you have to turn off and restart to change Bypass modes. Which seems odd, as Bypass is also referred to as Start mode. I suspect the module wouldn't get confused and would be happy to start in Start mode and then switch to Run mode when the B tab changed.

Too bad we don't have a map of when the Eagle MCU changes timing/dwell. Or is dwell controled in the stock IGM?[/list]
« Last Edit: July 05, 2020, 02:54:15 PM by Canoe »

Offline Canoe

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Re: GM 4-pin HEI Ignition Module vs newer higher current 7-pin???
« Reply #1 on: July 05, 2020, 08:47:44 AM »
I suspect the module wouldn't get confused and would be happy to start in Start mode and then switch to Run mode when the B tab changed.
Found out that is exactly how it works in normal operation, 0 VDC provided to the module Bypass tab by the ECM when starting, and 5 VDC provided by the ECM once started and in Run mode.

And the 7-pin has been used to replace the 4-pin using

It appears that we could use the more modern higher current 7-pin module in place of the 4-pin module by:
  • +: Positive power ~12 VDC
  • C: Coil; connects to negative terminal of coil (module uses low-side current sensing to limit current when necessary)
  • P: Positive of distributor pickup
  • N: Negative of distributor pickup
  • E: not connected / not used
  • R: not connected / not used
  • B: not connected: module uses the pickup inputs to drive the module's Dwell circuit, hence the coil
  • ground the module through the hole

Unclear is compatibility with our distributor pickup output.
« Last Edit: July 05, 2020, 02:53:48 PM by Canoe »

 

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