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  1. #1

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    Possible easy solution for 7x ignition woes with megasquirt.

    Hi 'ya folks, I'm a noob here so cut me some slack if this has been covered already.

    Anyway, I've been known to fool around with Megasquirt and ignition systems are sort of my specialty,

    To begin with, the 1.9 Saturn uses a version of the GM 7x DIS. Both the Gen-1 and Gen-2 systems require modifying the Megasquirt to work properly.

    The good news is there is an early version of the GM 7x DIS used on J cars and S10 trucks with the 2.2 pushrod engine. This version of the GM 7x DIS should work on the Saturn engine without modifying the Megasquirt. I have used this early version of the DIS on other project cars with the addition of a fabricated crank wheel. Since the Saturn 1.9 already has a the 7x crank trigger this might be the holy grail of simplified ignition with Megasquirt.

    Keep in mind, I have not tested this on a Saturn.


    The early version of the 7x DIS that was used on the 2.2 pushrod engine is electronically identical to a conventional distributor. In other words, it sends a single reference signal to the Megasquirt and the Megasquirt sends a single EST signal back to the DIS. The DIS module sorts out which coil pack to fire. No need to modify the Megasquirt because all the synchronizing sequences are done by the ignition module. This means that in the tuner studio setup you configure the ignition as a distributor ignition and not a 7x system.

    Given that Tuner Studio is always evolving, it may have evolved to have a setting for this 7x system, however 2 years ago this 7x system was not supported.

    Unfortunately I don't remember the setting I used... rising edge or falling edge bla bla bla. I do know the system worked well for nearly 7K miles on my non-Saturn project car before I changed over to EDIS-4. Also, as I recall the system required a fair amount of offset to be dialed in.

    Since I'm a noob, let's see if I can post some pictures...



    Here is an ignition module from a early 90's S10 truck with the 2.2 pushrod engine




    This module has three connectors going to it. The left connector is power and ground, The middle connector is reference, EST ,bypass. The connector on the right is for the crank position sensor. Since the crank position sensor goes directly to the module all the hard work is done by the module and megasquirt only has to deal with Reference and EST....


    the 1.9 Saturn and the 2.2 pushrod 7x timing appears to be the same ...


    FSM diagram of the electrical connections to the 7x module.


    Here is a picture of a 7x system I built for a Mazda engine. This system worked great with an unmodified Megasquirt.... of course I had to use a custom built crank wheel.

    Like I said at the beginning of the thread, I'm not sure this version of the 7X system has been covered already on a Saturn.

    Jim

  2. #2
    6S Moderator S.Bretz's Avatar
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    The OBD1 saturn ignition system conditions the tach signal too. I had used it for many years as a hall signal input and it worked very well.
    The only thing required to mod would be to install a 1k ohm resisor inline on the EST wire or esle the ignition module starts doing weird things under high load and high rpm.
    -6S Resident Mechanical Forensics member #001.
    1995 SC2 Turbo 3.6L DOHC, 6sp manual, Ford 8.8 rearend running on MS3x.
    1998 F-250 5.4L triton...stock.

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    The Saturn OBD1 and OBD2 ignition systems require the ecm or Megasquirt to read the crank position sensor. On the J-car/S10 2.2 push rod engine ignition module, the crank position sensor goes directly to the module. All of the 7x decoding is done by the module. As a mater of fact the 2.2 push-rod module will work without an ECM or megasquirt when in bypass mode. The module even has a built in ignition curve to provide decent performance while in limp-home mode. The module is pretty mush a stand alone ignition system that will work with power, ground and crank position signal.

    When the weather gets warmer I'll go ahead and do a better write up and install one of these on my roached out 96 wagon.

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  5. #4
    siris's Avatar
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    No, the OBD1 icm functions the same way as your describing. It has a fixed 10* bypass spark advance.

    The OBD2 icm requires the pcm to condition the crank sensor.
    72 Charger: pissed me off, on jackstands.
    95 SW1m: Dohc swap. DD. I can haz boost?

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  7. #5

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    Wow, I guess I should have looked at the OBD1 schematic. LOL Looks like using the OBD1 module should be simple to connect to a megasquirt. I guess disregard all the stuff I posted.

  8. #6
    siris's Avatar
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    No, you may be on to something with the 2.2L stuff. It seems like it might be a good upgrade to the stock turd icms, especially if it plays nice with the cranks in the LLO.
    72 Charger: pissed me off, on jackstands.
    95 SW1m: Dohc swap. DD. I can haz boost?

  9. #7

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    The 2.2 ignition should play nice with the Saturn crank, but it is just a theory at this point. Quick question, on the saturn OBD1, the 6x signal to the ECM... do you ignore this when connecting to a Megasquirt?

  10. #8
    Approved Vendor ZombieSatty's Avatar
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    I'm probably wrong, but i think some use it and some don't.
    It's not my fault, blame the radiation.

  11. #9
    siris's Avatar
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    I think most run off the ref high, from my understanding the Saturn pcm used the 6x line to get a more precise knock window.
    72 Charger: pissed me off, on jackstands.
    95 SW1m: Dohc swap. DD. I can haz boost?

  12. #10

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    OK, I figured the 6x signal wasn't used but at this point I'm not going to assume..lol

  13. #11
    6S Moderator S.Bretz's Avatar
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    One the 95's I think the PCM used the 6x for a tach input too. Something about it be more precise. The 95's still have the "tach out" pin on the ICM but it was not pinned with a wire to the tach like the 91-94's.

    Ref hi for the tach signal to the megasquirt is what I used. It connects in me internally with the sack out & pin dick, so if you have a 91-94 harness either wire will work for a tach signal.
    -6S Resident Mechanical Forensics member #001.
    1995 SC2 Turbo 3.6L DOHC, 6sp manual, Ford 8.8 rearend running on MS3x.
    1998 F-250 5.4L triton...stock.

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