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  1. #1
    Fuel Injected! Willys43's Avatar
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    Last edited by Willys43; 03-04-2016 at 08:33 PM.

  2. #2
    Super Moderator dave w's Avatar
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    I wonder about the IAC controls? I'm thinking only one ECM needs to control the IAC.

    I wonder about reference voltages, like the 5 volts to the TPS. I wonder what each computer sees for a TPS voltage when the ECM's are tied together?

    Do you plan to bench test this setup?

    For the bench testing I've done with a 7747, I use an electric drill for spinning the distributor to send a reference pulse to the ECM. When bench testing, I use TunerPro RT to data log so I can play-back the test.


    dave w

  3. #3
    Fuel Injected! Willys43's Avatar
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    Quote Originally Posted by dave w View Post
    I wonder about the IAC controls? I'm thinking only one ECM needs to control the IAC.

    I wonder about reference voltages, like the 5 volts to the TPS. I wonder what each computer sees for a TPS voltage when the ECM's are tied together?

    Do you plan to bench test this setup?

    For the bench testing I've done with a 7747, I use an electric drill for spinning the distributor to send a reference pulse to the ECM. When bench testing, I use TunerPro RT to data log so I can play-back the test.


    dave w
    Dave I have the same thoughts about the IAC receiving conflicting instructions from both ECMs, I just hadn't made any decisions. I thought possibly about having separate IAC pigtails coming out of the harness at the IAC. I think bench testing will be a good think to do.

  4. #4
    Fuel Injected! Willys43's Avatar
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    Quote Originally Posted by Willys43 View Post
    Dave I have the same thoughts about the IAC receiving conflicting instructions from both ECMs, I just hadn't made any decisions. I thought possibly about having separate IAC pigtails coming out of the harness at the IAC. I think bench testing will be a good think to do.
    Dave I will bench test a TPS and a MAP by putting a single reference voltage on it with a meter on the return "b" and see what the computer sees, then with two meters, then I'll do the same with 2 voltage reference voltage and see what the difference might be.
    Craig

  5. #5
    Fuel Injected! Willys43's Avatar
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    Quote Originally Posted by dave w View Post
    I wonder about the IAC controls? I'm thinking only one ECM needs to control the IAC.

    I wonder about reference voltages, like the 5 volts to the TPS. I wonder what each computer sees for a TPS voltage when the ECM's are tied together?

    Do you plan to bench test this setup?

    For the bench testing I've done with a 7747, I use an electric drill for spinning the distributor to send a reference pulse to the ECM. When bench testing, I use TunerPro RT to data log so I can play-back the test.


    dave w
    Dave, if I understand the 5 volt reference correctly, it is actually an output signal sent to the sensors, that signal is modified by a variable resistor in the sensor, then that modified signal is what the computer reads and bases it output to the other output devices. IOW the ECM reads the "B" terminal on the MAP and the TPS, then it uses the info from the sensors and the programming in the ECM to calculate how long of an injector pulse is needed in order to supply correct amount of fuel.

  6. #6
    Fuel Injected! Willys43's Avatar
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    After thinking about how the IAC actually works I think that it could be possible to leave both ECMs hooked up to the IAC and have it work. At best it would be an assumption and trying to bench test it would be close to impossible, also it would be less complicated using one ECM controlling the idle. I'll change the IAC control to the primary ECM.

  7. #7
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    Yes, do it that way. The ECM keeps track of the IAC position so having 2 ECMs on the same IAC will unsync the IAC from the position each ECM thinks it is at. That is assuming both ECM's can move it at the same time. Drive both coils at the same time and it won't even move.

  8. #8
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    Actually, only one ECM should control the IAC. ECM gets no feedback about IAC position. It only knows what it has commanded for counts. A sticking or unresponsive IAC or in this case, and ecm sending opposite commands, will cause the IAC to move out of synchronization with the ECM's expected position.

    I do not believe I would use only one 5V line. However, the resistance type sensors are part of a resistor network with a terminating resistor in the ecm. Adding a second terminating resistor can alter the total current through the sensor and therefor the voltage reading at the ecm. There are a few people that have published the results of trying to use dual pcm's. I can remember one individual using a 7749 for engine control and a 7427 for trans control in a Syclone and I seem to remember some sensor had to be duplicated. I'll have to see if I can find the information he posted.

    The stock dual plane manifold is divided left and right bank. Each side should have it's own injector. I would expect no trouble with individual bank fuel trim. What would be interesting to me is, after enough time tuning, if VE and/or spark tables end up slightly different between L and R banks.

  9. #9
    Fuel Injected! Willys43's Avatar
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    Quote Originally Posted by dave w View Post
    I wonder about the IAC controls? I'm thinking only one ECM needs to control the IAC.

    I wonder about reference voltages, like the 5 volts to the TPS. I wonder what each computer sees for a TPS voltage when the ECM's are tied together?

    Do you plan to bench test this setup?

    For the bench testing I've done with a 7747, I use an electric drill for spinning the distributor to send a reference pulse to the ECM. When bench testing, I use TunerPro RT to data log so I can play-back the test.


    dave w
    The bench testing worked slick, Both ECMs "see" the same voltage from the 5v reference and the sensors provided the same out put with one or two ECMs hooked up, except for the ECT which required two sensors.

  10. #10
    Super Moderator Six_Shooter's Avatar
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    There's no real documentation for dual ECMs like you're trying to do. The only dual ECM engines I know of run each half of the engine COMPLETELY independent of one another. The ONLY common part is the crack, which each half of the engine just happens to share. Those ECMs are also designed with this setup in mind. The ECMs you are using are not.

    On the bench is one thing, where signals and conditions are perfect, it's a very different thing on a running engine where syncing of each set of cylinders will a nightmare.

    What you're trying to do is just over complicating the situation simply for the sake of over complicating it.

    I ask again; Why have you not tried to use a single ECM? I think you'll be pleasantly surprised that it will likely work right with the right ignition module that takes into account the odd fire.

    As I have already said the ECMs will not be in sync and when one ECM, sees an out of spec condition it will throw a code, our worse go into LHM. It won't take much for this to happen, a simple command in idle RPM change that it's not seen will cause the ECM to start doing other things, like changing spark timing to further compensate, which will then make the engine fight itself.

    I just think you're over complicating what needs to Hadrian and there are far better ways to put EFI on an odd fire engine.
    The man who says something is impossible, is usually interrupted by the man doing it.

  11. #11
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    The only way a singe even fire ECM could work on an odd fire engine is by not doing timing with the ECM. I this this has been well established.

  12. #12
    Super Moderator Six_Shooter's Avatar
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    Well established by whom? There are (single) ECMs that will run an oddfire engine without issue, definitely in the aftermarket, and I'm sure the same could be done with an OEM ECM as well with the right ICM set-up... If I cared enough about injecting an oddfire engine I think I'd use an 8 cylinder reluctor (or how ever many it would take to get even pulses between firing events), so that the pulses were even and just used the dizzy cap towers that are needed for the engine to run. Boom, one ECM, even pulses for the ECM to read, and odd fire at the ignition with timing control. Yes the RPM will read a bit high, but with a simple edit of the ADX it could be made to show accurate. No sync issues between ECMs, no ECM trying to control something it can't or isn't connected to and throwing a fit.

    I'm sure I could come up with a more elegant way if I really wanted to as well. Actually that more elegant way would be an ECM that will run an oddfire engine natively without any trickery, save the headaches.
    Last edited by Six_Shooter; 04-18-2016 at 07:48 AM.
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    I'm not sure if you want comments, or just posting because or what, but I see a few things that won't work.

    You should use 1 ESC module with the output going to both ECMs. Alternatively, you will need 2 knock sensors if you want to use the 2 ESC modules.

    You can't connect both ECMs to the IAC motor. You'll have to let one of them control it.

    Your IGN relay is wrong, the pink should be on the right terminal.

    You'll need a coolant temp sensor for each ECM.

    I believe the TPS and MAP can be shared but I'm not sure you want to connect the sensor 5V terminals together. I think you'll want to use the 5V from one ECM for the TPS and MAP with the common and outputs going to both ECMs.

    I highly doubt you can run closed loop which makes the O2 sensors rather pointless. The control loops get out of sync and the one ECM will be adding fuel via one injector while the other is trying to remove it via the other injector causing a big fuel imbalance.

  14. #14
    Fuel Injected! Willys43's Avatar
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    All constructive comments are appreciated. I would much rather change the schematic then try and diagnose problems. I originally tied all inputs and most outputs together thinking that if one computer has a problem that the other will continue to operate my limp home mode.

  15. #15
    Fuel Injected! Willys43's Avatar
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    Quote Originally Posted by lionelhutz View Post
    I'm not sure if you want comments, or just posting because or what, but I see a few things that won't work.

    You should use 1 ESC module with the output going to both ECMs. Alternatively, you will need 2 knock sensors if you want to use the 2 ESC modules.

    You can't connect both ECMs to the IAC motor. You'll have to let one of them control it.

    Your IGN relay is wrong, the pink should be on the right terminal.

    You'll need a coolant temp sensor for each ECM.

    I believe the TPS and MAP can be shared but I'm not sure you want to connect the sensor 5V terminals together. I think you'll want to use the 5V from one ECM for the TPS and MAP with the common and outputs going to both ECMs.

    I highly doubt you can run closed loop which makes the O2 sensors rather pointless. The control loops get out of sync and the one ECM will be adding fuel via one injector while the other is trying to remove it via the other injector causing a big fuel imbalance.
    I absolutely want feedback, just be prepared to explain yourself if I don't understand!
    OK I'll buy 1 ESC, 1 Knock, and you're correct about the ignition relay pink.
    I don't understand the need for 2 temp sensors, or what problem the second 5v ref feed. I have some research to do before commenting on the fueling
    Craig

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