DIY: AEM Twin-Fire CDI Ignition Install
 

AEM Twin-Fire CDI Ignition Install

As many of us have discovered, the factory coils are prone to burning and failure due to heat, stress and over-voltage when used in conjunction with the Greddy E-Manage or other EMS systems.

The AEM Twin-Fire CDI (Capacitive Discharge Ignition) offers several advantages for the RX-8 over both the OEM coils and other CDI ignitions from other manufacturers.
1) It has two separate capacitors so it is able to fire the leading AND trailing plugs at the same time
2) It is very compact
3) The MSD DIS coils that I used could probably continue to work indefinately even if you set them on fire in a pot of molten lava
4) CDIs fire the plugs with considerably more voltage and longer duration (at lower RPMs) than the OEM igntion which results in a more complete burn of the combustion charge and less potential for plug fouling and a smoother idle

http://www.mazdamaniac.com/images/rx.../AEM/parts.jpg

http://www.mazdamaniac.com/images/rx...ls_removed.jpg

This installation requires a few non-typical skills including an understanding of hobbyist-level electronic circuit building. The output signal from the PCM and/or E-Manage is a positive pulse and the AEM expects to see a signal pulled to ground. This means you have to build a driver circuit. I've included this diagram which shows the schematic for the driver which includes a set of LEDs to indicate the presence of ignition signals:

http://www.mazdamaniac.com/images/rx...ut_circuit.jpg

The OEM coils are removed and a set of brackets are created to support the 4 new coils:

http://www.mazdamaniac.com/images/rx...ew_bracket.jpg

The 4 new coils are mounted to the OEM bracket and grounded with separate wires to ensure a good ground connection. The trigger and source wires (black and orange, respectively) are wired with individual connectors to mate with the AEM harness. The two leading coils have their source wires connected through a common connector to one output of the CDI and the two trailing are wired similarly to their own source.

http://www.mazdamaniac.com/images/rx...ls_mounted.jpg

The new assembly is mounted in the OEM position:

http://www.mazdamaniac.com/images/rx...ted_in_car.jpg

I mounted the AEM module just below my E-Manage in the engine bay. This is probably not an optimum location because of the heat it is exposed to, but I am lazy and I am planning on re-wiring almost all of the aftermarket electronics in the car to eliminate the rat's nest that has resulted from mulit-layer installations and experimentation over the last two years with different electronics in the car.

http://www.mazdamaniac.com/images/rx...it_mounted.jpg

The three DIP switches on the AEM need to be configured to all be off. This sets the multi-strike to active, the firing to trailing edge and the frequency to every crank rev.

I fabricated a new set of plug wires. This is necessary because the OEM wires do not have the correct connector for the DIS coils. I used a Taylor 8mm "universal" kit.

Working backwards:

I don't know if the OEM coils are going to be totally inadequate at any particular power level. It is possible that they are capable of putting out enough energy to keep the flame lit at elevated boost levels. However, the advantages of the CDI setup are manifold and power is but one.

Here are the items I used. Note that this assumed that an igntion harness was already in place. For those that are coming to this with an unmodified ignition/PCM system, you will need to splice the factory coil outputs at either the coil end or the PCM end.

(1) AEM 4 Channel Twin Fire Ignition PN# 30-2821
(4) MSD Blaster DIS Racing Ignition Coils PN# MSD-8230
(1) Taylor Universal Plug Wire Kit PN# TAY-73251
(2) MSD Weathertight Sealed Connectors PN# MSD-8171
(4) PNP Switching transistors (general, 20v min)
(4) 47k ohm, 1/4 watt resistors
(4) LEDs, 3v min (I used yellow for leading and green for trailing)
(1) small project board (Radio Shack)
assorted wire, connectors, solder, etc.

The brackets are cut from aluminum channel stock that is available at Home Depot or Lowe's.

The coils can be mounted in any orientation - they coontain no oil like old-fashion coils and are completely potted and sealed.

I don't know if the heat damage is necessarily arcing - it may simply be extreme heat from a combination of environment and load. But that would have to be a LOT of heat to burn the zinc-coated metal of the bracket.

so how does it run with the twin fire.

nice job, I saw Yaw's writeup on the circuit switch

no progress on mine, just haven't had time t source the connector to fit the OE coil harness yet. It's just not my top priority at the moment. Think I may know where to source the connector though.

Pretty much the same as it did without it, but with a smoother idle and faster starting.
I haven't driven it in boost yet. I posted the DIY 10 minutes after I finished the install. I'll flog it tonight. Its 100° out right now and I don't feel like driving in traffic.

Do you have a link so I can look at it?

from February:

http://forum.aempower.com/forum/inde...91127#msg91127

Interesting. He used field effect transistors instead of common switching transistors. I wonder why?
Same basic principle, though.

I don't have a dual-trace ocilloscope (I just have a single trace scope-meter), but it looks like the AEM with this switching circuit ends up advancing the spark a few degrees, which is bad. I think part of this is because of how quick it loads up and fires - the OEM system is slow and fires in the middle of the pulse. I'll probably have to build a buffer with a 555 timer or something similar to put the trigger a 1/2 wave later to get the timing square to avoid detonation.

I wonder how well it will perform at higher rpms? It might give better combustion at lower rpms, but at 9K you have a lot more energy to be keeping up with. Will it be able to keep the longer duration (I doubt multiple sparks heh) spark?

you think you'll notice any economy improvements?

Assuming someone made more powerful coils for our car, would that have the same effect as your setup?

Possibly, though not likely.

Possibly, though not likely.

Well, it will maintain a spark for 20° of crank rotation regardless of RPM.
At 9k, it won't be in multi-strike anymore because of time constraints, but it won't loose any energy either.

hows you idle now? you said its better than before, is it better than the stock idle? Do you still get vibration with the a/c on?

The specs for the 8230 are on MSD's site. Being for "race only" I would think might make it more durable rather than less.
Conversely, I can only find a passing reference to the 8232 on MSD's site with regards to a Chrysler DIS ignition. It just looks like the 3230 repackaged with a connector rather than leads.

The zinc plating is pretty thin. I do believe if you get moisture between the plate and the coil it well greatly enhance the the ability to cause a burn like that.

Well, no doubt it will see moisture in that position, though it wouldn't be inundated. I'd think the heat would boil it out way before it could oxidize the plating.
That wouldn't explain the burns on the epoxy potting on the bottom of the coils, however.

I recently encountered a drivability problem, appears that all four OE coils are defective, only 3300 miles on them ...

https://www.rx8club.com/series-i-tech-garage-22/breaking-up-under-part-throttle-88951/

any updates?

I was thinking today about upgraded coils and had a thought, has anyone looked into other Mazda vehicles that might have stronger coils we could use such as the Mazdaspeed6? I wonder if the connectors are the same? Just a random thought, might be worth investigating.

not here, I've been buried at work, no spare time at all

it turned out I didn't have a coil problem afterall, car is running strong so it hasn't been a priority under the circumstances, keeping 6 spd trans from blowing up is higher on the list :Eyecrazy:

please start a thread on your work toward the tranny..

beers :beer:

If i just purchase a set of coils + a set of the weatherpack connectors.. they will work like stock right? I will not need to build a circuit of any sort?


I already have a HKS twin power for the rx-8.. I do not want to cut the connectors ;)

just better ground the factory coils and they will be ok
olddragger

How you do that? As far as I know they are internally grounded.

look at the electrical sematic in the manuel and you will see an indiviual black grounding wire from each coil. people have been spicing into that and running a ground wire from each coil to the negative post on the battery. Read the "grounding kit" thread
olddragger

Thanks. I wasn't sure thats the way ("B" wire). Now I am.

Np
od

well considerin the fact that apparently the rx8's ignition system is now known to be weak........especially in FI applications....wouldnt it make since ur upgrading the coils plugs n wires, to also upgrade the battery preferably to an optima battery, since our battery is known to be weak..........??? just my thoughts......

battery is only there to start the car. thats it. period.

think so, disconnect the battery after you crank it and see

The battery acts as a stabilizer for the electrical system.
Without it, the available current for operating such minor things as your entire EMS and ignition system will be insufficient.

BTW - Why do people feel the need to add things like "that's it. Period." to the end of their posts?
Even if the data presented is of absolute certainty in the situation in which it is applied, its "absolute" nature can always be put asunder and those that don't believe in its certainty will not put any more faith in the presenter just because of his certainty of its absolute nature.
Putting "period" at the end of an assertion only makes you suspect.
Period.

^ End of story.

i apologize in adding ""that's it. Period."" to the end of my post.

as to the statement that the battery acts as a stabilizer for the electrical system, that is partly correct, wherein if you are putting addtional load on the electrical system, ie extra lighting, upgraded audio systems, etc, then yes the battery can act as a supplemental energy source when the available output of the alternator has been surpassed. if the battery was there to provide power to the system to the ems and ignition system, then the battery would be in a constant state of discharge, and would eventually run out of stored energy.

this can be seen in vehicles with larger car audio systems that do not have high output alternators, where the battery initially can have a full charge, but after a while of playing the system at elevated levels, even keeping the engine at cruising rmps, the voltage in the system will drop down, and eventually the vehicle will stall as there is not enough power to keep everything running.

and please dont take this as me trying to bash you MM, i have the utmost respect for you and the knowledge you have. i will freely admit i dont have the accumulated knowledge on rotary engines, let alone motorsports in general that you have, but i have been selling and installing car audio at a specialty retailer for almost 10 years, so i do know a thing or 10 about electrical systems in automobiles.

i have, no problems

The neutral electrical load at idle is about 14 amps. The generator output at idle is about 15 amps. The generator ramps up significantly with RPM.
Turn on your dome light (1.5 amps) or your headlights (about 12 amps) and you will be in an interesting scenario.

Plus, without the battery, any change in load would mean some significant Alzheimer's for the PCM. (Not to mention the car-b-que that would ensue after a while from the melting integral regulator that requires a battery as ballast.)

No disrespect to you, either. However, I have yet to meet a radio installer that could change a light bulb without pictorial instructions, so I don't particularly engage that claim as a credential.

You're right. I forgot about all that. But then, If you left the car running at idle, with the lights turned on and the stereo turned up, then the battery should die after a period of time.

No disrespect taken.

As you load the system down, the drain causes drag on the generator which the PCM compensates for by opening the throttle to keep the idle speed up.

ahhh, yes, now i see the light.

and even though the throttle opens up a little, there will be a momentary drop in available current. i shoulda thought of that earlier, but that is the nature of my mania, i sometimes miss the little details.

i knew about the drag, its one of the reasons why you cant build a perpetual motion machine from a generator driven by an electric motor powered by the generator.

thanks mm.

Yeah, a car would be a perpetual motion machine - if it weren't for those pesky hydrocarbons!

Actually, I haven't really thought about why Mazda went with a generator instead of an alternator on the '8. I'm sure there is a good reason.

I don't know, but looking at the electrical schematic, it is referred to as a generator, but it is generating AC current as seen by all the diodes referenced in the schematic.

Yeah. It is an interesting device.
Instead of having a commutator setup like a normal generator, it has a bridge rectifier like an alternator.
In fact, it has a stator and a wound armature, so I don't know what the hell is going on there.

The RX-8 uses an 'Alternator' not a 'Generator'. At least that is what it is called in this part of the world. Why Mazda call the alternator a generator I do not know, although it could be called an AC generator. But it certainly is an alternator in my RX-8. Looking at the wiring diagrams for the car it shows a star wound stator and full wave bridge rectifier. This alternator outputs 3 phase AC power and is converted to +/- 12VDC by the rectifier.

"battery is only there to start the car. thats it. period."

I dont think that is correct. My understanding of the battery and alternator is that the power for the car is run from the battery as well as starting the engine. The alternator/generator is used to charge the battery. Obviously the battery cant be removed, because it would be very difficult to start the engine without it :) , but once started the electrics will work OK, just. Without the battery the voltage would not be stable and would fluctuate with revs and load. The battery can deliver a very high current instantly without relying on the engine revs. If the total current drawn from the battery exceeds the alternators maximum charging capacity the battery will eventually go flat.

Oh,I forgot to say, I like this mod, nice job

The main defining difference between the "alternator" and the "generator" are the internal method for generating current.
A generator uses a fixed magnetic field with a rotating coil (armature). An alternator is the opposite (the coil is stationary).
On the '8 there is a rotating coil even though there is a bridge rectifier.
I need to take one apart to see what is going on.

The whole subject of alternators and their use in the automotive industry is a vast subject and somewhat off topic here. An alternator can have a rotor made using a magnet or more usually a wound rotor. This wound rotor is connected to the cars electrical circuit through a slip ring and carbon brushes. The usual reason for using a wound rotor is so that a varying magnetic field can be achieved and consequently a varying voltage output from the alternator's stator coils. This varying voltage is needed as the cars current/load varies according to demand.

k sorry we all got off topic from this DIY...........however wouldnt it make sense.........if ur goin FI........ there was a TSB about our weak batteries...........n now more recently more of us r startin to realize how insufficient our ignition coils on it are.......so my point was like the creator of this thread upgraded his coils.........to twin fire ones..........wouldnt it make sense to upgrade to a battery with higher cold cranking amps, higher cranking amps, and a faster recharge time...........??? im no electronics genius but i got the generality down......n im not tryin to diss anyone im just sayin wouldnt it make sense..........????

Batterys suffer from a problem.....as the CCA capacity goes up...they get larger and heavier.

The usual compromise is choosing a battery that fulfills the needs....and doesn't sink the ship so to speak :D:

I wish it was in the RR corner of the car...like a lot of the BMW's...it would help to offset some of the L side weight bias...esp with my large ASS in the drivers seat ;)

hahaha dannobre well from what i remember besides the optima battery for as far as cca capacity to weight ratio..........there was a battery i believe its called the braille racing battery, supposed to weigh like 10-15 lbs or so.........n supposed to have high cranking capacity, now i dont know the longevity on it so dont quote me, but its supposed to be up there on battery life with optimas.........have u heard of them???

Ya...TeamRX-8 has one in his car. There are exceptions to every rule :D:

cool cool........he would be the one to ask about how much it costs...........im takin my car to riverside mazda for before it was an intermitten misfire.........now it happens at WOT im sure the coils r fried.........n im gonna replace the battery soon n wanna reliable one but also wanna save some weight.

and i just did a google search from stuff copied from you post..

http://www.google.com/search?q=brail...ient=firefox-a

like this is hard!!!

get out of this thread.

good luck.

beers :beer:

thanx swoope good lookin out........

MM, I would guess that the RX-8 has an alternator. i have seen Japanese manuals refer to them as generators before, and I think that they use that as an inexact term, like the Renesis is a 'engine' (don't know why I think that way).

The automotive generators I am familiar with (now I date myself) would not charge at idle. I understand that was the primary reason for a change to alternators in the early to mid 60s.

As to whether the battery is needed and how it is used, may be a design point. That 60 Chevy I had needed to survive on the battery at idle to support the car. Lights would dim, radio would sag etc. Today's cars start even if you have the headlights on. I would not consider doing that on that old Chevy.