Talk to me about multiplexing please...

[debrucer]

First, I keep reading the terms Multiplex, MUX, batch, wasted spark, semi-sequential and factory ECU. Am I correct in saying these are the same thing? My Supra hasn't run since 2006 and it had a blown head gasket then, so I've never experienced any problem with multiplexing. I have read all the threads about how to remove it, whether $2 or $200, I have to know why? My car is not getting the traditional MS installation, or any of the systems popular here in these forums. We are building in a Speeduino, based on the Mega 2560 microcontroller. Sequential isn't supported on a 6-cylinder. The only possible negative that I see is having that extra, i.e., the wasted part, spark dispersed on closed values... and sent into the car as potential interference. I'm guessing not really something to worry about, or others would be screaming.

Sequential seems to be the way that Supra owners go. Why? Exactly, why do I want to remove multiplexing?

 

[Jeff Lange]

Multiplexing isn't supported by most aftermarket ECU's, it's not a common design. Most ECU's will send the trigger signal to each coil/ignition channel that they want to fire (be that in single coil, batch/wasted spark or sequential), however the way the 7M-GTE ignition system works is there is a single trigger channel and separate coil selection channels. So the trigger signal tells the igniter when to fire, and the selection signal tells the igniter which coil to fire.

IGt Only = Trigger Coil 2
IGt and IGDa = Trigger Coil 3
IGt and IGDb = Trigger Coil 1

I believe that is right. It's not common (even on Toyotas it is only used on the 4A-GZE and 7M-GTE).

If you are running an aftermarket ECU, even if you want to run wasted spark with the stock coils, I would say get a different igniter and ditch the multiplexing, it will save some headaches.

Jeff

 

[plaaya69]

I been doing a lot of research on this myself last summer and for me it seems running sequential has way more advantages when you are running a standalone. I am also making a brand new engine harness myself so it is also easier to wire everything up this way from the start.

For me I am doing:

Removing the OEM igniter and going to wire in a DH61 igniter from a 98-05 Lexus gs300 or 01-05 Lexus is300 to run the 2jz coils.

The fuel injectors I want to stay low independence so I am going to wire in a fuel injector resistor box from a early 90's Acura Legend. It is a 6 cylinder engine with 6 separate channels for each fuel injector.

 

[Jeff Lange]

I been doing a lot of research on this myself last summer and for me it seems running sequential has way more advantages when you are running a standalone. I am also making a brand new engine harness myself so it is also easier to wire everything up this way from the start.

For me I am doing:

Removing the OEM igniter and going to wire in a DH61 igniter from a 98-05 Lexus gs300 or 01-05 Lexus is300 to run the 2jz coils.

For what it's worth, the VVT-i 2JZ ran wasted spark (not sequential) ignition and the igniter from the 98+ GS/IS is only a 3-channel. If you are sticking with the factory 7M-GTE coils, this is a perfect non-multiplexed option, but if you want full sequential ignition, you'll need a 6-channel igniter and coil setup (or coils with built-in igniters).

Jeff

 

[debrucer]

For what it's worth, the VVT-i 2JZ ran wasted spark (not sequential) ignition and the igniter from the 98+ GS/IS is only a 3-channel. If you are sticking with the factory 7M-GTE coils, this is a perfect non-multiplexed option, but if you want full sequential ignition, you'll need a 6-channel igniter and coil setup (or coils with built-in igniters).

Jeff

What I believe I am learning, at least being told, is that even though the C code behind the four-channel Speeduino setup does not support sequential on any 6-cylinder, that with the addition of a six-channel igniter, it will be sequential. I will have to absorb that for a while. Thanks!

 

[debrucer]

I been doing a lot of research on this myself last summer and for me it seems running sequential has way more advantages when you are running a standalone. I am also making a brand new engine harness myself so it is also easier to wire everything up this way from the start.

For me I am doing:

Removing the OEM igniter and going to wire in a DH61 igniter from a 98-05 Lexus gs300 or 01-05 Lexus is300 to run the 2jz coils.

The fuel injectors I want to stay low independence so I am going to wire in a fuel injector resistor box from a early 90's Acura Legend. It is a 6 cylinder engine with 6 separate channels for each fuel injector.

My car is a perpetual project that really needs to be completed in the next year or two. It hasn't been on the road since 2006, and that was hobbling to my place with a blown head gasket. My wiring harness has been worked on many hours, many times, and it's still "complete", although, it's clearly going to get hacked soon. With no ECU, and a stand-alone Speeduino, I end up making my harness, too. I still don't understand the "why", I mean, I can understand when you're hacking, that you hack, but, I don't see the down-side to multiplexing, a wasted spark system. Everybody takes it off isn't really a good answer. Thanks! And good luck with your project. I might post a picture or two tonight of mine, too

 

[Jeff Lange]

You can't really run a six-channel igniter sequentially with only 4 channels on the ECU, you could still run 6 individual coils, but they would need to be fired in wasted-spark batch fire mode. Without six channels, it just cannot be done.

The important thing to note is that multiplexing isn't the same thing as wasted-spark. You can have a multiplexed sequential ignition system or a non-multiplexed wasted-spark system.

I would not recommend a multiplexed system if you aren't running the stock ECU. Anything standalone will be easier and simpler to run non-multiplexed. Whether that is wasted-spark or sequential (in your case, it sounds like a non-multiplexed wasted-spark setup is what you should be doing).

Jeff

 

[debrucer]

You can't really run a six-channel igniter sequentially with only 4 channels on the ECU, you could still run 6 individual coils, but they would need to be fired in wasted-spark batch fire mode. Without six channels, it just cannot be done.

The important thing to note is that multiplexing isn't the same thing as wasted-spark. You can have a multiplexed sequential ignition system or a non-multiplexed wasted-spark system.

I would not recommend a multiplexed system if you aren't running the stock ECU. Anything standalone will be easier and simpler to run non-multiplexed. Whether that is wasted-spark or sequential (in your case, it sounds like a non-multiplexed wasted-spark setup is what you should be doing).

Jeff

Once again I am going to have to absorb this info. I believe the original question in this thread was along the lines of "are these the same thing....". What you've just said here is, they aren't. Thank you so much. This will help. (I'll be back!).

 

[Jeff Lange]

Gotcha, yes they are definitely not the same thing. :thumbup:

Jeff

 

[debrucer]

Thanks again for responding. I'm going back now and re-reading the thread and making sure I understand everything I learned here. Here are some posts you made, and my thoughts later.

I been doing a lot of research on this myself last summer and for me it seems running sequential has way more advantages when you are running a standalone.

Like what? Advantages is just too vague to design to... and that's all I hear. The simple 36-1 wheel is a clear example of why sequential on a four cylinder since it fires every ninth tooth, i.e., four time per rotation of the crank. I don't know if it can be achieved on a six-cylinder with two sensors, or a different wheel configuration. As the Speeduino project stands today, it is not supported, so I'm grasping, and asking as clearly as I can ask, WHY?

I am also making a brand new engine harness myself so it is also easier to wire everything up this way from the start.

For sure I have an intimate relationship with my wiring harness, but I don't want to eliminate circuits, and therefore, the functionality of those circuits, without knowing why. Why the circuit existed, and what is being used to replace it, or not. If the answer is "or not", then, again, I want to know "why?". The stand-alone I'm installing isn't to be just a patch, it's a replacement system. Functionality of the original system needs to be preserved, and supplemented where support is missing. For the Speeduino, there is no OBD II or CAN bus, and my '88 had something, OBD 0, perhaps, or M-OBD, don't know, or care, but, since I'm putting several components in the car that talk, I am attempting to include a new CAN bus.

Removing the OEM igniter and going to wire in a DH61 igniter from a 98-05 Lexus gs300 or 01-05 Lexus is300 to run the 2jz coils.

The fuel injectors I want to stay low independence so I am going to wire in a fuel injector resistor box from a early 90's Acura Legend. It is a 6 cylinder engine with 6 separate channels for each fuel injector.

For some reason, I thought the igniter on mine was a DH61, might have been a DH60, not sure. But, again, I don't have a reason as to why make the change from what was on the car. I believe the igniter is on the left wheel arch, and still mounted in my car. The injectors I bought are the same impedance that I had, so I wouldn't have to change. The "why?" for you is? You want 6 separate channels, one for each injector. I get that. The Speeduino only has four channels. Well, it's DIY project... you can build it out with one, two, three or four channels, but you still need an igniter I get that as a reason. I sort of like the stock look and location, and unless I find something objectionable, I don't want to change it.

 

[3p141592654]

Multiplex or sequential really only matters to the person integrating the system, as it requires different interfaces between ignition and ECU. Its a don't care as far as performance goes. The only reason it matters is that there are far more production cars running sequential than multiplexed, and so the selection of sequential candidate ignition systems in the junk yard is larger.

Waste fire was used as a cost savings measure as it was slightly less complicated to build. Waste fire's only disadvantage is that the coil dwell time is half that of a non waste fire system. But, that's also a non-issue for any application where your redline is below 10000 rpm. Again, the trend in industry is coil-on-plug non-waste-fire ignitions. That's what you can find on most cars in the junkyard and the systems are now quite inexpensive.

Since you have a 4 channel ECU and a six cylinder, its all moot. You have to go waste-fire, no other option.

 

[plaaya69]

Like what? Advantages is just too vague to design to... and that's all I hear. The simple 36-1 wheel is a clear example of why sequential on a four cylinder since it fires every ninth tooth, i.e., four time per rotation of the crank. I don't know if it can be achieved on a six-cylinder with two sensors, or a different wheel configuration. As the Speeduino project stands today, it is not supported, so I'm grasping, and asking as clearly as I can ask, WHY?

Some advantages of sequential injection is more accurate fuel metering, individual cylinder tuning (could drive up tuning costs as well), better throttle response, slightly better fuel economy/emissions at lower speeds. You might be better off making a custom crank trigger wheel and mount it on a cam gear or the crank pulley for a alternative to the CPS.

For sure I have an intimate relationship with my wiring harness, but I don't want to eliminate circuits, and therefore, the functionality of those circuits, without knowing why. Why the circuit existed, and what is being used to replace it, or not. If the answer is "or not", then, again, I want to know "why?". The stand-alone I'm installing isn't to be just a patch, it's a replacement system. Functionality of the original system needs to be preserved, and supplemented where support is missing. For the Speeduino, there is no OBD II or CAN bus, and my '88 had something, OBD 0, perhaps, or M-OBD, don't know, or care, but, since I'm putting several components in the car that talk, I am attempting to include a new CAN bus.

Personally I want to keep everything in place as it would be oem but with a standalone a lot of features are added such as fail safes or extra sensors and some are no longer needed depending on the application. For a example I made a wiring pinout of the plug-n-play pigtail that comes with the ECU Masters standalone. With the oem ecu and using the factory engine harness and I have pinned out what wires are needed which is only about half of them for my ECU Masters standalone.

For some reason, I thought the igniter on mine was a DH61, might have been a DH60, not sure. But, again, I don't have a reason as to why make the change from what was on the car. I believe the igniter is on the left wheel arch, and still mounted in my car. The injectors I bought are the same impedance that I had, so I wouldn't have to change. The "why?" for you is? You want 6 separate channels, one for each injector. I get that. The Speeduino only has four channels. Well, it's DIY project... you can build it out with one, two, three or four channels, but you still need an igniter I get that as a reason. I sort of like the stock look and location, and unless I find something objectionable, I don't want to change it.

Different standalones will offer different features and some standalones will even drive the ignition coils without a igniter. Some older AEM standalones did not play nice with the factory 7m electronics so people looked into alternatives at the time such as installing the DH61 igniter. With the low Independence fuel injectors, I am running the 6 channel resistor box so I do not have to tap into the stock 3 channel resistor box since I am wiring up everything from scratch.

I am not familiar with Speeduino but it sounds better to keep it waste fired with 3 channels if you can not go past 4. I am not a multiplex expert but just sharing what I have learned from others and how I am going about my set up.

 

[debrucer]

Multiplex or sequential really only matters to the person integrating the system, as it requires different interfaces between ignition and ECU. Its a don't care as far as performance goes. The only reason it matters is that there are far more production cars running sequential than multiplexed, and so the selection of sequential candidate ignition systems in the junk yard is larger.

Waste fire was used as a cost savings measure as it was slightly less complicated to build. Waste fire's only disadvantage is that the coil dwell time is half that of a non waste fire system. But, that's also a non-issue for any application where your redline is below 10000 rpm. Again, the trend in industry is coil-on-plug non-waste-fire ignitions. That's what you can find on most cars in the junkyard and the systems are now quite inexpensive.

Since you have a 4 channel ECU and a six cylinder, its all moot. You have to go waste-fire, no other option.

In this case, the person integrating the system is me. I'm a long way out, too. Thanks for the response, I appreciate your information. My 4-channel ECU isn't cast in stone. If there's a valid reason to change it, I will. I simply did not want to go with MS. There are a lot of people building new boards, perhaps a 6 or 8 channel isn't so far away. I don't have much to base things on operationally, but, I don't dis-like the stock coil look.

 

[debrucer]

Different standalones will offer different features and some standalones will even drive the ignition coils without a igniter. Some older AEM standalones did not play nice with the factory 7m electronics so people looked into alternatives at the time such as installing the DH61 igniter. With the low Independence fuel injectors, I am running the 6 channel resistor box so I do not have to tap into the stock 3 channel resistor box since I am wiring up everything from scratch.

I am not familiar with Speeduino but it sounds better to keep it waste fired with 3 channels if you can not go past 4. I am not a multiplex expert but just sharing what I have learned from others and how I am going about my set up.

Thank you. All very helpful and I will re-visit a few times, I', sure. That "people looked into alternatives at the time" is exactly why I'm doing it my way. Speedy may not be the answer, but a spin-off, perhaps. MS was done 20 years ago, and yes, it's good, full-featured, apparently some plug-n-play, all the good stuff... but, it was still done 20 years ago. I'm not saying anything bad about it or anything else. It's just been done. For some that's a good thing. Thanks again.

 

[figgie]

you are really not multiplexing

you are speaking of the waste-fire config.

I come from the airplane world where multiplexing meant,

1 wire, multiple signals based on either a digital parameter (canbus, flexray etc) or analog (not used but before it was).

the stock ignition was three wire, three signals in a very elementary binary configuration (ie 1-0, 0-1, 1-1). The timing of that is what essentially initiated the ignition process (oh boy, my memory is faltering on the tech).

At one point in time i had the dwell factors of the OEM 7m-GTE ignition coils and they were pretty stout (so stout, that the Buick Grand National folks that decided to not keep their cars OEM, used them).