I just had an FM turbo, Reverant-built MS3, and Fab9 Coil-on-plug kit installed by Tork Motorsports in Kent, WA on my 1995 with the stock 1.8L engine. John at Tork is a very experienced Megasquirt tuner and he's worked diligently to get everything running.

John sees a couple of issues that would keep us from running anything but wasted spark. I'm hoping somebody with a similar setup can chime in on how to get sequential ignition working.

Issue 1:
Before starting all this, I asked Dimitris (Reverant) about running sequential ignition with his ECU, and especially whether I'd need a crank trigger wheel. He said everything would work fine with only the CAS and I wouldn't need the crank wheel. John believed that you *do* need a crank trigger wheel to run sequential ignition because you need to know exactly what the crank is doing to manage timing. He thinks there's a way you could fake out the CAS signal to make this work but it would be a bit of a hack. Is that correct? Can we do sequential ignition with only the CAS or do we need a crank trigger wheel?

Issue 2:
The Fab9 website says you can run their CoP kit with sequential ignition. John says that the ignition controller included in the kit can only run a wasted spark configuration even if I had a crank trigger wheel. That doesn't add up since I see others on this board running sequential ignition. Can you help me understand how to wire the CoPs for sequential with the MS3?

 

And as an aside, John was seeing spark blowout when tuning the car with the standard .032 gap and the Denso IK22 plugs. I'm running less than 15psi so those plugs should be fine. But John had to knock down the gap to .022 to keep the ignition firing. The car seems to be running OK except for the idle, which is rather rough. John attributes that rough idle to the smaller gap. Does anybody have a thought on this too?

Many thanks in advance...

 

The cas is both a crank and cam trigger, at least on a 1.6. I doubt the early 1.8's are different.

I know this for a fact, because I run sequential injection off a cas alone.

Miata aren't wired for sequential spark, so you will need to modify the stock harness by adding wires. If the cop set was sold as PNP, well, it now needs modifying too. Rev should be able to tell you where the extra two channels are outside your box, then you extend those to the cop kit.

Normally 1-4 and 2-3 are wired together on the coils, you'll need to split those and wire in the extra wires you just ran, new spark triggers. Keep them in order, Rev can tell you how.

Your megasquirt tuner don't sound so good to me.

 

Yes, you can do sequential ignition on the CAS alone. I've done it on more cars than I can remember.

 

Do your FAB9 coils have the upgrade module?

 

Rev, can you share some instructions for running sequential ignition running only with a CAS? My tuner says he doesn't know how to do that.

Braineack, do I need a different (upgraded) module to run sequential ignition with the Fab9 kit? I see on their website that an AEM twin-fire module could be required if running more than 19psi. I'm not doing that so I figured the standard module would work for me.

Is the issue that the standard module can't be wired for sequential ignition or that it's not strong enough to keep the spark from blowing out? I saw another thread about spark blowout on this site. It appeared to be happening because that module wasn't adequately heat sinked, which was causing it to overheat. My module is connected to the body of the car so I'd expect heat control to be OK.

 

The wire for ignition on cylinders 1 + 4, becomes cylinder 1.
The wire for ignition on cylinders 2 + 3, becomes cylinder 3.
Connect cylinder 4 to the DB-37, pin 6 (Ign C).
Connect cylinder 2 to the DB-37, pin 7 (Ign D).

 

Oh, so it's just a matter of wiring up the ignition and then switching to sequential ignition? The ECU figures out the rest of it?

 

Correct.

 

I talked with John and he's extremely hesitant to run sequential ignition without a crank sensor. He says that OEM applications always run their ignition signal off the crank since you need to know exactly where the crank is to accurately fire the plug. He also says that firing off a CAS is asking for trouble because the timing belt could break, stretch, or skip a tooth and cause a catastrophic engine failure.

From my perspective, I'm thinking that all pre-1996 Miatas ran without crank sensors and the ignition timing had to come from *somewhere*. That somewhere has to be the CAS, which means it has to be good enough, right? That's unless sequential ignition fundamentally changes something about engine timing.

As I understand things, the difference between batch and sequential ignition is that you're not firing one of the cylinders when it's not needed. That is to say, you're only firing the cylinder that's ready for its power stroke. That extra efficiency seems like it would tax the ignition module less, which could lessen the possibility for blowout.

What do you guys think?

 

Your tuner is a ******* moron. Find someone else.

Seq. Ignition is a diminishing returns gains. Typically, the reason you want sequential spark is so you can let your coil packs charge up for longer times. If they fire in batch, they've got half the total charge time available, plus they heat up double.

It's not much a problem with good coils and stock redlines, running wasted spark that is.

 

The timing belt will stretch, and your ignition will become less precise. This is inherent to the cam-angle-sensor-only based approach, and is one of the reasons why you can't run as much timing on those motors (because you need to leave a larger safety margin before detonation). It can also break or jump a tooth, yes.

None of these things is likely to cause a catastrophic engine failure, and even if they were, there's nothing magical about running waste-spark that makes it safer than sequential. The only difference is that you're firing the cylinders in pairs, and the other one that gets fired is on the exhaust stroke, so that spark does nothing.

--Ian

 

John is correct in saying that proper sequential isn't possible on the 95, but yes it can technically work as "sequential" with the CAS. You can run it with the CAS if you run 2 extra wires, unless the igniter on the FAB9 cops are only in wasted spark. If it has an individual output for each coil, then you can do it, but personally I wouldn't

If you want a real way to add sequential spark, you can always grab a:
crank pulley and timing wheel
crank sensor
intake cam wheel
cam sensor
valve cover
associated connectors for the sensors

off a 99-00 miata and wire those in. Then just wire up the crank and cam sensors into the CAS wiring, run the 2 extra wires to the igniter/coils and choose 99-00 miata settings in megasquirt. Not hard, but it's more work than just using the CAS

also, running in wasted spark is just fine. It might help extend your coil life, but it won't give you better performance

 

What do you mean "true sequential?" It's either sequential ignition or it's wasted spark, no sortof partially sequential. As stated, it's not as precise, but running sequential with just the CAS is still sequential. And doing it that way really is not practically different than what the factory did with the wasted spark configuration as far as I understand it.

 

yes, it's sequential, but it's more of a bandaid. Full sequential fuel and spark needs a crank and cam signal. The CAS gives both the cam and crank signal, but both signals are going off the exhaust cam, and not the actual crank. I think when I took a datalog and looked at timing error when going through only the CAS, I had around 15% timing error. With a proper crank sensor and timing wheel, along with a cam sensor, my timing error went down to 3%

the whole point of doing full sequential is to get fuel and spark to happen exactly when it's supposed to right? so if you're using a sensor with that much error, what's the point if it's off by so much?

maybe I shouldn't have used the word TRUE, but the word proper

 

I think John's a *****.


Running sequential off the CAS is not a bandaid.

It's not "fake sequential".

It's not "untrue sequential".

It's simply "not-quite-as-precise-sequential as with a crank sensor".


If you're not upgrading to a crank sensor, you're still using a sensor that has that much error, regardless. There's still plenty of benefits going TRUE sequential over batch fueling -- even with the erroneous CAS as your CMP/CMK signals.

Timing Error % in MS logs is the "% off from expected" -- and unless they've reworked the code it's not even that useful a log.

 

Thanks for the feedback, guys. The main reasons I want sequential injection are:
1) I got the CoP to avoid spark blowout as I switched from supercharger to turbo. But to my surprise I'm still getting it. It seems like the spark blowout in the Fab9 CoP kit could be caused because the module is firing two plugs instead of one. I'm figuring if one plug is being fired as in a sequential setup then there will be more energy, which means a bigger spark and less blowout.
2) The precision of sequential appeals to the engineer in me.
3) The computer supports it so I figure I might as well take advantage.

The Fab9 kit has outputs for each cylinder and the website has a sequential option for the wiring harness, which basically means it doesn't come with a PnP connection. That strongly implies the kit supports full sequential ignition and I believe I've seen others on this site who are running it that way.

FWIW, I don't think John's a *****. He just hasn't run sequential ignition with a Megasquirt this way before and he wants to make sure it works. As my tuner, he feels (justifiably) responsible to ensure my car runs well and does it safely. Since neither of us have done this before, I'm happy he's challenging my requests instead of simply following my potentially stupid instructions.

John's objection is the CAS's diminished accuracy relative to the crank angle sensor, just as you all note. He made a similar argument to bmxfuel007 that the timing variability could be large enough to cause problems. I made the point that we're already running off the CAS, which ipso facto must be sufficiently accurate to run, even with the timing variability we know about. As I see it, sequential ignition wouldn't affect - or be affected by - timing accuracy from the CAS since it would be exactly the same as the current batch fire setup. The only difference would be that we're firing one plug instead of two, which provides the benefits I mentioned above.

I'm hearing very clearly that a crank sensor would be better than running exclusively off the CAS, not least because that adds the accuracy that appeals to my engineer's mind. Let's say I run off the CAS now and add a crank sensor later as bmxfuel007 suggested. Would I really see a difference? What would that be? And why would I need a new intake cam wheel and cam sensor (which is a CAS, right?) to replace the CAS I've already got?

 

Define "A difference." If you plug in the computer and log **** then yeah, you'll probably see a difference in the logs. Will you see a difference in drivability? I don't know. Will you see a difference on the dyno? possibly, if you tune at the higher accuracy as mentioned -- you can tune more on the edge since you can control things more precisely.

^All this? It's all regurgitated from reading other people's posts. Just saying.

 

JOHN (the tuner) is NOT a $%!^** moron. What he is suggesting the OP is to rewire the ECU with an engine that has a crank sensor and crank wheel capabilities in order for the MS3 ECU to read the most accurate timing available which will yield the most power when the car is tuned. Pre-95 engines do not have this feature which most of you know is not a good thing due to the fact factory 89-94 OEM crank pulley design is defective in first place.

The addition of 2 wires to run sequential ignition in the MS3 sounds like piece of cake.

 

Nope, He's a moron.

I understand entirely why he thinks a crank wheel is necessary, but it's not a requirement, and the car won't spontaneously explode because of whatever slight error might be introduced.

Same tuner also let this guy leave his shop with his tune in batch fuel injection still megasquirt and car all pre-wired for that, the tuner is a ******* idiot.

Is "bandaid untrue" sequential fuel injection off a CAS going to cause an engine to explode off a bit of timing belt stretch? According to this tuner, probably.