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Thread: Schematic for delco ignitin module

  1. #1
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    Schematic for delco ignitin module

    Greetings,
    anyone have a schematic for the delco ignition module?

    I purchased aTbi system from affordable fuel injection to replace the carburetor on my boat. I did this the same time I replaced the engine. All is mostly well with the system but I think the wiring for the new distributer is wrong.

    David

  2. #2
    Super Moderator Six_Shooter's Avatar
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    What makes you think it's wrong?

    Any GM TBI service manual should have the pin out. The Mega Manual also has pinouts for several different GM ignition modules.
    The man who says something is impossible, is usually interrupted by the man doing it.

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    Quote Originally Posted by Six_Shooter View Post
    What makes you think it's wrong?

    The idle is not smooth.

    The B+ line for the distributer is connected to the positive line of the coil. However, the positive line for the coil is still connected to +12 through the resistor wire.

    I am curious if this is an issue for the "refernce" signal from the distributer to the ECM.


    Any GM TBI service manual should have the pin out. The Mega Manual also has pinouts for several different GM ignition modules.
    I would like to get a schematic for the internals of the ignition module. That way I can know what to expect signal wise when I look with a scope.

  4. #4
    Super Moderator dave w's Avatar
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    I hope this helps.

    dave w

  5. #5
    Super Moderator Six_Shooter's Avatar
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    Oh, I don't know of any public domain schematic of the internals.

    If you look in the Mega Manual I believe it has a description of the signals there.
    Also some pinouts for the ECM will have what the the signals should be on those wires. So look at TBI pinouts charts, not the schematic. You shoudl be able to find some of those in the '7747, '7427 and other TBI therads found on this site in the GM hardware forum (a sub forum of this very forum).

    Basically though, The Black/red is ground so there should be near zero volts on it, the tan/black is the bypass and should have 0 volts when off or cranking and 5V when above 400 (or so) RPM, the white and purple/white are signals too and from the ECM and have TTL level pulses IIRC on these. The signals vary based on RPM and commanded timing. The pink is 12V ignition and the white paired with the pink is the coil trigger that will have an AC signal on it, I just don't recall the magnitudes or exact wave form off hand.

    Basically if it's working, then it's wired correctly. Swapping any of the pins on the ICM will cause a no run condition.

    Get rid of the resistor wire, and your idle should smooth out then. The GM ICM and coil needs a full 12V to it, not through a resistor wire.

    The 12V feed to the distributor being connected to the coil is how GM did it, so that is not of concern.
    The man who says something is impossible, is usually interrupted by the man doing it.

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    Thanks,
    the boat has a shift interrupter circuit that momentarily grounds the coil to make the engine "stumble". This circuit requires the coil to be fed with a current limited source. This is the resistor wire. But this is an issue for the new coil and distributer that wants the full 12 volts.

    More study required.

  7. #7
    billygraves
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    Last edited by billygraves; 06-30-2019 at 06:16 PM.

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    Quote Originally Posted by billygraves View Post
    If I remember wright. You can use the REFERENCE incoming to the ECM. This will shut off the Injector pulse width. I just hope I remember correctly. I know there are Delco Ignitions that are for this interrupt.
    I have an interrupter circuit that is designed to interface with a deco efi distributer. This is NOT meant to be connected to a distributer with an ECM. When used with the EFI distributer, the shift interrupter causes the distributer to intermittently go back to base timing thereby removing the timing advance. It does this by pulsing the input on the distributer.

    The input on the deco distributer that comes from the ECM to tell the distributer that the ECM will now control timing is likely the best choose to use in this instance. I just need to create an interface that will allow the interrupter to intermittently cause the timing to go to base timing resulting in the engine "stumbling" during the shift.

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    Quote Originally Posted by davidgoodin View Post
    Thanks,
    the boat has a shift interrupter circuit that momentarily grounds the coil to make the engine "stumble". This circuit requires the coil to be fed with a current limited source. This is the resistor wire. But this is an issue for the new coil and distributer that wants the full 12 volts.

    More study required.
    That circuit will be incompatible with stock type HEI installations. billygraves provides a working suggestion: Ground the REF signal. Although removing power to the injectors might be preferred to ensure the ecm doesn't accidentally utilize anti-stall logic. However, if the interrupter uses a relay I'd switch to a solid state circuit. Relay contacts can bounce which can cause problems.

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    You are correct on the "incompatibility". The company that makes the shift interrupter have another model that is compatible with the delco "EST" troupe distributer. The company I purchased the EFI kit from claims it is good for "marine" applications, but they are a little fuzzy on the details when it comes to shift interrupters.
    So, I am left in limbo doing more R&D.
    My current plan is to use the "EST" type interrupter and build a circuit that will give the correct voltage to the ignition bypass input to the distributer. The circuit will essentially AND the input from the ecm and the input from the shift interrupter.

    Whe the ecm wants to take over timing from the distributer, the new circuit will pass that signal as long as the interrupter is not sensing that the boat is shifting. If the boat is shifting, then the new circuit will pass the pulses from the interrupter circuit making the timing go from what the ecu wants to base timing. This will make the engine "stumble" momentarily uploading the dogs on the transmission and allow the boat to shift.

    This is essentially what that circuit does to the EST type distributer.

    A few resistors, a couple voltage comparators and a transistor should take care of it.

  11. #11
    Super Moderator Six_Shooter's Avatar
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    The circuit could possibly be more simple than that, I would have to see the schematics for the interrupter to know for sure.
    The man who says something is impossible, is usually interrupted by the man doing it.

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    Quote Originally Posted by Six_Shooter View Post
    The circuit could possibly be more simple than that, I would have to see the schematics for the interrupter to know for sure.
    Yes, a, it could be as simple as a couple of transistors as well.

    basically, the ECM sends out a 5 volt signal to the distributer when it wants control of the timing. The shift interrupter sends out 4 volt pulses when it wants to make the timing go back to base timing. The output is low when the circuit is inactive.

    So, a logic inversion, level shift plus an ANDi g function.

    any ideas on the simplest circuit possible are welcome.

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    Fuel Injected! sturgillbd's Avatar
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    What I did was use a relay on the power to the coil on my boat. When the shift interrupter gets tripped, the power to the relay coil is dropped momentarily during the shift. It works well on mine.

    HTH
    Brian
    I don't know if this will set a trouble code on the ecm. My old boat is has a carb and I changed over to an HEI distributor.
    Last edited by sturgillbd; 12-14-2014 at 11:12 PM. Reason: Addendum about setting a trouble code

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    Thanks Brian,
    the current interrupter hold the negative lead of the coil to ground preventing the coil from firing. I am getting error codes on the ECM complaining that the ignition circuit has a problem. Possibly a short. Go figure.

    That is one reason I am trying to move away from that system. Would really be cool if the ECM had an input that would stumble the motor during a shift. But, alas, this is an old '299' from a truck that the guy says is optimized for a boat.

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    Fuel Injected! sturgillbd's Avatar
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    If it is a Mercruiser I/O drive, I have a service manual for them. Does the engine run with it shift interrupter switch disconnected? If is is grounded all of the time, the interrupter may be out of adjustment or stuck. I'll try to find my service manual this eve.

    Brian

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