DIY Wasted Spark for 84-89 Carrera

[scarceller]

I'm starting on a new project to attempt to build a Wasted Spark Ignition setup that will simply plug (add on) to the stock Motronic DME.

I'm in very early research stage and am looking for anyone with technical background of the Flywheel ref sensors. Also technical background of Ignition Coil Dwell times across the RPM range in the 3.2L.

At this time I'm just starting to look at the relationship between the TDC sensor signal and the Ignition Coil signal from the DME. I may also use the Speed Sensor signal but am hoping it's not needed.

The basic idea is to build a controller, simple set of circuits to convert the existing coil signal which fires 3 times per rev into 3 new signals to fire the 3 Wasted Spark coils.

I also think I'll control coil Dwell times from the new circuit as well.

But, I plan to fully honor the Ignition Maps in the stock DME. I have researched some other aftermarket systems but these want to take control of the timing tables away from the DME and I simply do not wish to do this. I only wish to remove the distributor and goto 3 double-ended coils. I also wish to control Dwell to optimize Dwell for the coils choicen.

Here is a timing diagram of the signals, the top 2 are existing signals available from the DME and the bottom 3 are the new generated signals.



At this time I'm only working on the Digital side of the controller to produce the new signals. Then later I need to design the hi-power section to drive the new coils but this should be easy, I plan to simply copy/follow the stock DME output stage for driving the stock coil, I'll replicate this output stage 3 times. The hard part is the early research for knowing how the 'TDC Ref signal', 'Stock Coil Signal' and possible the 'Speed Ref Signal' are all related. Also understanding how the Stock ignition dwell works would be helpful. Few things I don't know about Dwell is how long is the stock dwell in milliseconds (I can scope to get this) but more importantly does the stock system reduce dwell time at very hi-RPM? like above 5000RPMs. At hi-RPM it is often dificult to find enough time for optimal coil charge and some systems simply must comprimise and reduce dwell at hi-RPM. Does the Motronic system do this? Any help here would be great.

I'm a Electronic Engineer so I feel good about building the controller but I need to learn a bit more about the Stock Ignition and the signals that drive it. Any info here would be very helpful.

Lastly, this should not be a very expensive project. Parts for the controller should come in under $100.00, then you need the coils and wires.

[Porsche_monkey]

I think the Ford unit is the one that the Megasquirt guys modify and use for this. I'd look in that direction.

[cgarr]

Don't you ever sleep! I'm still trying to find a good rpm signal to tap for my LM-1?

[scarceller]

Originally Posted by Porsche_monkey

I think the Ford unit is the one that the Megasquirt guys modify and use for this. I'd look in that direction.

If you decide to replace the entire DME with something like megasquirt then this is easy as most of these modern EFI systems have full support for wasted spark.

But, I wish to keep the stock DME but install Wasted Spark. In my oppionion installing an entirely new DME is way to much work, you need to build all new Fuel, Ignition and startup tables. I like the stock motronic system but simply wish to improve the ignition section.

[Bart_dood]

http://www.arduino.cc/

These little arduino microcontrollers are cheap and easy to use, you can get add-on boards to drive higher current devices such as ignition coils. They only cost $30 or so.

You'd only need 2 digital inputs to sense the pulses coming in, and then 3 digital outputs to deliver the sparks, a little code and you'd be done. They are easy to program and they are all open source with lots of support and examples online etc.

:O)

[scarceller]

Originally Posted by cgarr

Don't you ever sleep! I'm still trying to find a good rpm signal to tap for my LM-1?

The coil '-' signal should work perfectly for RPM. I use this in my TechEdge install. Many folks try to use the coil '+' side but that won't work. Have you tried the coil '-' signal? You can get this at the DME Harness from pin #1 you may also need to put a diode in series into the line. Put the striped side of the diode toward pin DME #1 then wire the other side to the LM-1. The diode prevents negative going spikes (less than ground) from being seen by the LM-1. These spikes often occur in hi-voltage ignition coils and could confuse the LM-1. The diode may or may not be needed but it's a good idea to put one in. Get a 1N4001 diode from RadioShack for this.

Good luck

[scarceller]

Originally Posted by Bart_dood

http://www.arduino.cc/

These little arduino microcontrollers are cheap and easy to use, you can get add-on boards to drive higher current devices such as ignition coils. They only cost $30 or so.

You'd only need 2 digital inputs to sense the pulses coming in, and then 3 digital outputs to deliver the sparks, a little code and you'd be done. They are easy to program and they are all open source with lots of support and examples online etc.

:O)

This is great! $30.00 sounds good, I'll research these controllers. THanks

[scarceller]

One of the main reasons I started to think about Wasted Spark for the 3.2L was because I suspected that the Ignition Coil suffers at hi-RPM (above 5500RPM). Meaning there may not be enough time to fully charge the coil. One of the main objectives was to provide better spark across the entire RPM range.

But, I now realize this objective could simply be met with a Capacitive Discharge Ignition (CDI). So how much better would a Wasted Spark system be over a CDI system in a 3.2L Motronic car? I suspect that a CDI system, like a multi-spark system would be a good improvement over the stock Inductive Coil wich has lengthy coil charge times. The CDI charge time are down in the 1millisecond range for full spark, while traditional inductive coil systems can't get much better that 2.5ms and many in the 5ms range.

Now I'm wondering what's the best use of money and time if trying to improve the stock ignition? May well be a simple to install out-of-box CDI system like the ones from MSD like the 'MSD 6'. Has anyone used these on P-Cars?

Thanks.

[RWebb]

my bet is that the stock system is good for redline on the cs model - was that at 6200?

[911st]

I think red line for the CS was 6840.

I would love to see some economical way to get to dual plug w/o having to buy an Andial Spliter or better yet even a C2 distributor.

If successfully, could this be used as a base for an economical dual plug system?

[scarceller]

Originally Posted by RWebb

my bet is that the stock system is good for redline on the cs model - was that at 6200?

Redline is 6520RPM in the Carrera cars. I already know that the spark is at a reduced intensity above 6000RPM. So yes the stock config has enough spark but I'd like a little more.

[scarceller]

Originally Posted by 911st

I think red line for the CS was 6840.

I would love to see some economical way to get to dual plug w/o having to buy an Andial Spliter or better yet even a C2 distributor.

If successfully, could this be used as a base for an economical dual plug system?

I did not think about dual plug, but for a dual plug setup you'd be firing 4 plugs at sametime in a wasted spark configuration. You'd need more final drive circuitry to drive the extra plugs. Wasted spark fires 3 times per rev and each firing will need to fire 4 plugs in dual plug configuration.

I think it might help a dual plug setup, but I really have not given this thought yet.

[stlrj]

Originally Posted by scarceller

...I suspected that the Ignition Coil suffers at hi-RPM (above 5500RPM). Meaning there may not be enough time to fully charge the coil. One of the main objectives was to provide better spark across the entire RPM range.

Now I'm wondering what's the best use of money and time if trying to improve the stock ignition? May well be a simple to install out-of-box CDI system like the ones from MSD like the 'MSD 6'. Has anyone used these on P-Cars?

Thanks.

Hi Sal,

I also have been struggling with this idea, to convert to a more modern wasted spark system or MSD for the same reasons you have. I have come to the conclusion that such a conversion would be too complicated and too much trouble in light of the fact that the stock DME ignition is more than capable of firing at all rpms but is limited by the ignition cables, cap and rotor which are not high energy capable.

Since the weak link in the Carrera ignition is in the secondary side, it would be much easier and most cost effective to concentrate your efforts there so your engine would be able to take full advantage of the DME ignition potential which is not limited in any way by the coil not having sufficient time to charge. This would mean converting to HEI ignition cables, cap and rotor that would enable your system to fire your spark plugs gapped at 0.060" consistently from idle to redline and never having to worry about it again.

All I can say is that converting to a complete HEI system on my secondary side was probably the best bang for my buck from a performance upgrade perspective that has enhanced driveablity in all rpms. If you took this route I seriously doubt that you would feel the need to pursue more exotic solutions.

By the way, the wasted spark or coilpack ignition system also requires the use of HEI ignition cables (and so does MSD) but eliminates the need of the HEI cap and rotor.


Cheers,

Joe

[sjf911]

I think the real advantage of a wasted spark system is when converting to a twin-plugged setup although high RPM needs can be met as well. The problem you would face converting your DME system is getting the appropriate advance and dwell computations from the OEM DME. You would still need a separate controller to manage to coil pack itself. This is easily done very inexpensively concurrently with megasquirt by using a Ford EDIS system salvaged from the junk yard (< $100). However, this would require the addition of a crank-pulley toothed wheel and sensor as well as a MS controller. It doesn't appear that the DME coil output would be useful without some sort of custom electronic logic interface and the Porsche system uses 2 different sensors on the flywheel for its logic calculations. I am not aware of any aftermarket controller that would be compatible with this. The ones that I have reviewed used a single sensor system (missing tooth wheels).

Here is the MS documentation on ignition control and EDIS:

http://www.megamanual.com/ms2/Ignition.htm
http://www.megamanual.com/ms2/EDIS.htm

A look at CNP function including an excellent video on dwell:

http://www.megamanual.com/seq/coils.htm
http://video.google.com/videoplay?docid=-6218245369765754251&hl=en

[RWebb]

Originally Posted by scarceller

I already know that the spark is at a reduced intensity above 6000RPM. So yes the stock config has enough spark but I'd like a little more.

first, how much time does your motor spend above 6,000?

2nd, if the stock ignition is enuff -- then a little more will not benefit you.

3rd - how do you know the spark intensity is reduced above 6,000

i don't understand your problem. if components are worn [stck or street motor], just replace them.

otoh, if you are building a race motor or something, i would toss the dme and use motec

[scarceller]

Yes, the stock ignition may be just fine and possibly can't be improved. I'm simply doing some research to see what could be done and what results may be obtained.

One other thing about MSD CDI system is multiple sparks below 3000RPM, my car currently has a lean mis-fire if I bring the AirFuelRatio to 14.7 at idle. This is most likely because I have non-stock cams. The sweet spot for best idle is AFR at 14.2 and timing advanced 7deg with RPM set to 920RPM, I achieved these settings by altering the Idle Fuel and Ignition maps in the chip.

So, would multiple sparks lasting for 20degress of crank rotation help with this lean mis-fire? not sure but I think I'm going to try the MDS 6 ignition as it is very non-invasive to install. But I do have a few questions to ask MSD Techs. Like will the timing be slightly retarded because of a delay caused by in-lining the MSD 6 between the DME and the stock coil. I think the answer may be no, if the MSD CDI simply fully charges the coil ahead of time and then removes the ground from the coil based of the DME ignition signal. Of course I'll also be testing this with a timing light.

[scarceller]

As for wasted spark I think that I can create the basic circuit to take in the TDC Sensor Signal, Speed Sensor Signal and the stock DME Ignition Coil signal. Then from these 3 signals I can create the new seprate signals to fire the 3 new coils. I'm rather certain creating this controller will not be that hard. If I do this I may then simply use a 'MSD DIS4' CDI box to produce the high energy side to fire the 3 coils. The MSD4 is simply 4 seprate CDI boxes in 1 package, I'll only be using 3 of the 4 inputs and outputs.

Here's the genral idea for processing the signals into 3 new seprate ones:

[304065]

Sal, I've written a lot here about dwell, search under my name for some history. I am working on reverse engineering the old tach circuits for fun and to understand the input signal it's necessary to translate the dwell into a duty cycle.

The reason the automotive world went away from CDI is because even though the charge time is short, the spark duration is also short. Klaus Lattinger (klatinn, inventor of the LM-1) developed a system that would use a capacitor to start the arc then switch to a transformer for a very hot, long burn. This eats the plugs in half the time but a set of plugs is only about $10 for a 911. Anyway, if you have a clean sheet of paper, that is the road I would follow.

Search here and on the Innovate forum for more information.

[scarceller]

Originally Posted by john_cramer

Sal, I've written a lot here about dwell, search under my name for some history. I am working on reverse engineering the old tach circuits for fun and to understand the input signal it's necessary to translate the dwell into a duty cycle.

The reason the automotive world went away from CDI is because even though the charge time is short, the spark duration is also short. Klaus Lattinger (klatinn, inventor of the LM-1) developed a system that would use a capacitor to start the arc then switch to a transformer for a very hot, long burn. This eats the plugs in half the time but a set of plugs is only about $10 for a 911. Anyway, if you have a clean sheet of paper, that is the road I would follow.

Search here and on the Innovate forum for more information.

John,

MSD ignitions say they gaurantee spark for 20deg of crank rotation, that's a lot of spark duration. Below 3000RPMs they generate multiple sparks, as many as needed to fill the 20deg slot. Then above 3000 there better units claim to control the amout of time the single spark lasts. Maybe they have come up with new tricks here. I plan to get my hands on one of there controllers, right now I'm looking for a used MSD DIS-4 unit, this is top of the line 4 CDIs in one unit. I can first use it as single CDI with stock distributor and see how that works. Then I can goto Wasted spark and use 3 of the internal CDIs and simply never use the 4th. The box is designed for 8cyl cars, then they also have a DIS-2 for 4cyl but nothing for 6cyl.

I'm just wondering how much a CDI system such as this might help the 3.2L. Some have said don't bother and leave well enough alone. But I'm always tinkering.

As for Dwell: if you use the MSD products they don't care about the stock dwell, all they care about is a negitive (ground) going pulse 12->0 volts then they simply only look at the positive (rising edge) 0->12v edge, it's this edge that's important this is when in the stock config the Ground is removed from the coil '-' and this in turn causes the spark. So the MSD products simply look for this transition 0-12V and this tells the CDI to fire. They claim it all happens so fast that it does not introduce any timing retard at all. We shall see.

Thanks for the dwell tips.

[RWebb]

msd users often report improved running, driveability....

another idea - twin plug it and compu-map plug #2 to fire at, before or after plug #1` depending on conditions

- that is what mb did in the late 1990s - not sure if they still do it and it surely ain't cheap

but it will keep you busy fer a good long while