motorheaddown

Well, it's the New Year, and I'm at home waiting for some new goodies for the project. In the mean time, I thought I'd bore you with some ignition facts that I've learned over the last couple of months.

Angel and I were one of the first AEM owners to get the EMS working with the sc300. In Angel's case, he stuck with the distributor; In my case, I opted to go wasted spark (i.e. no distributor). Upon getting the wasted spark working, I realized that my tach stopped working. Hmm... that's odd. I don't remember Angel having a problem with his tach. Additionally, the TT guys didn't have a problem with their tach when using the AEM either. Urgh... more investigation. My tach problems must be related to by-passing the OEM distributor and igniter.

After some digging and signal measurement, I learned that the sc300 *and* sc400 tach signals are generated by the pull-to-ground signal of the primary side of the coil. You can see on the NA Supra how the igniter, coil, and tach signal are related. Notice that the tach signal comes from the igniter (actually it comes from the coil, but I'll get to that later): http://www.mkiv.com/manual/1995_elec...95elec_065.JPG I actually put the OEM tach signal on an o-scope and was very discouraged to see the waveform. Unfortunately, It's a very messy 45volt pulse with a bunch of ringing, etc, etc. I'm thinking... how the heck am I going to synthesize that thing when I don't have a distributor-based ignition and the OEM igniter? Well, I know the Stealth/3000GT uses wasted spark (i.e. 1 coil supports 2 cylinders); so maybe there's some insight to be gained by learning about its ignition and tacho signal.

Fortunately, someone on the Stealth forums was savy enough to capture the pull-to-ground signal to a Stealth coil on an O-scope. Note the upper trace: http://www.3si.org/forum/attachment....chmentid=28243 Turns out, this signal is *identical* to what I measured when investigating the sc300 NA tach signal. It makes perfect sense now. The pull-to-ground of the coil *is* the tach signal. In fact, you can see for the Stealth igniter how the 3 pull-to-grounds are "OR'd" together (actually NOR'd) to generate the tach. Note the simple igniter schematic at the bottom of this link: http://www.stealth316.com/images/stim/tim_14-10.gif This explains why the NA tach signal is so messy; it's actually the coil pull-to-ground. In the TT case, however, the signal is generated differently due to the ignition setup to run coil-on-plug and direct fire.

Now for an off-topic discussion. I looked into the Stealth igntion because it could solve all my problems when using the AEM. The Stealth has a 6-cylinder motor and runs wasted spark. It also has the added benefit of providing a tach signal that is based on all 3 coils. Consequently, it looks like it will work *perfectly* with the AEM *and* give me the tach signal that no other solution can provide.

BTW, I highly suggest this web site for good info: http://www.stealth316.com It's obviously slanted toward the Stealth/3000GT, but the information can be applied to any car. In fact, I found the discussion of the Stealth ignition quite informative: http://www.stealth316.com/2-ignitionsystem.htm

-scott

awj

I'm beginning to think you are a genious. Let me know if you need any more coils. I have access to the new generation 4 GM coils and also the new 6 cylinder wasted spark brick (3 coils w/ 2 towers each potted in one case). (It's a secret though. ) I can also get plugs, harnesses and brackets. Possibly schematics and proprietary info if someone is really nice to me.

motorheaddown

Thanks for the kind words. Actually, I might take you up on the 3-coil brick. Is it the one for the buick (Accel P/N 110-140016)? Can you get it for less than $85 shipped? I thought about using the 3-coil brick, but it doesn't provide the voltage output of the Accel dual post (110-140017). I have one Accel coil and 4 LS1 coils rigged up right now. So, I know the dual post arrangement will work. I'm just waiting on a Stealth igniter and pigtail I found on the web.

-scott

aliga

iTrader: (147)

Scott,

What is your education background/profession, you come up with a lot good stuff.

motorheaddown

Thanks again for the encouragement. I like to contribute info that the group can benefit from in addition to dispelling myths. Plus, I like digging for information; probably comes from my research background in academia.

I have an advanced degree in engineering and currently manage sensor simulation development (IR and radar) using real-time computer graphics in the military visual simulation market. I'd give it up, though, if I could make a good living boosting cars!

-scott

P.S. Although I'm relatively new to forced induction, I'm probably one of the "Old Farts" of the forum. (I'm even older than DaveH)

awj

1 accel twin coil and 4 ls1 coils - that's like frankenstein, and You are gonna try an ignitor from a dodge Stealth? I might like a picture of that. How much voltage you need? I'll check the specs. on the brick. I can meet the other requirements. I'll shoot ya a pm on the brick.

motorheaddown

Yeah... it's not pretty looking right now, but I had to test the dual-post first before going with an all remote coil setup. In fact, I actually got the Accel coil firing using the OEM igniter. The LS1 coils fire directly off the EMS. I also have a voltage booster wired in to both ignition setups

Once I knew the dual post would work, it's just a matter of collecting the parts. The 3-coil brick (or 3, dual-post coils) and Stealth igniter (plus voltage booster) will replace everything.

-scott

motorheaddown

O.k., I might have found a problem with using the Stealth igniter with regards to the tach signal. Looking at the igniter schematic again, it appears that the ECU uses a 5v pullup resistor to synthesize the clean looking square wave that's shown at the bottom right of this link: http://www.stealth316.com/images/stim/tim_14-10.gif That explains why the tach signal doesn't match the pull-to-ground signals for the coils shown just above. Hmm... it might be possible to "T" the tach signal off the ground wire, but I'm not sure if that will affect the operation of the coils. Oh well, at least I have a wasted-spark igniter; more work ahead.

-scott

awj

Scott,
I did some government work this morning. Got some real good info I think. Basically, the ignitor is integrated on the brick . I need a voltage requirement from you though. Are you going to run over 45,000V? Probably so are we talkin 60kV or up to 100kv? My guy says it could work but doesn't know how at this point depending on your amplification. I have a few questions. Technically, this thing should handle it. I have some things you should see though. Basically, I want to learn a little more about this and getting this to you and seeing it work will do just that. We should talk.
Later,
AJ

siniquezu

Can someone post the 3si.org attachment?

motorheaddown

Hmm... I tested the link, and it seems to work. I also got your pm, but I don't understand your question.

-scott

siniquezu

I'm just too lazy to register. PM sent.

motorheaddown

Woohoo... I got the Stealth igniter to work with the AEM: http://forum.aempower.com/bbs/viewto...?p=37125#37125

Awj, sorry man I was premature about the igniter not working. The pigtail I bought with the unit has bad connectors.

-scott

awj

You are the man. In my opinion, that is quite an accomplishment. That is some real good detective work, intuition, and electrical know how at work there. I'll have to get more involved with that aem forum if not just as lurks - to do a little more learning on the subject. I'm having problems with my computer at the house. I tried to send the info I have out but having trouble. I got your last message and I'll try that address but I'm not sure I'll be able to do anything until I can get the home computer straitened out (the old lady dl'ed something that has screwed up my OS ). Lots of luck. Keep up the good work man.