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Old 07-26-2008, 12:19 AM   #1
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Default Can a miata run on two cylinders? COP problems

So I thought nothing was wrong with my car, just needed to get my timing set. Finally I got a timing light, hooked it up, and no strobe light. After a little more investigation I figured out that cylinder #1 isn't sparking. So thats why my engine is running so rough! Black smoke is coming puff puff puff out my exhaust. I haven't checked cylinder #4 to see if it gets spark too, but surely the engine can't just run on the middle two cylinders, can it? I mean, it looks like its running fine, it just shakes a little. I'm running toyota COP's and I bench tested the #1 coil already and it works. I get a primer spark on all the cylinders. I cranked the car with the #1 plug and coil out and the car actually started! Even then It didn't spark, so it doesn't spark on crank or running. I suspected my 4700uF capacitor I've got on coils 1 and 4, but if you have problems with that it should just be on crank and cold start, right? I get a primer spark so I feel like its all wired correctly. I'm totally stumped, any ideas at all? Any insight would be greatly appreciated! Could my ignitor circuit in my megasquirt be fried? What do you guys think would happen if I switched my trigger wires for each pair of coils?
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Old 07-26-2008, 12:42 AM   #2
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It'll run fine without the capacitors, actually.

You can bench-test a coil by installing a plug, grounding the threaded portion, applying +12 and GND to the coil, and tapping +5 onto the trigger wire very briefly. If it's working, it'll be obvious.

The engine can run on two cylinders. In fact, my motorcycle does so quite happily. The Miata engine does not like it quite as much, but it's possible.


Understand that the "primer" spark isn't something that the CPU is doing intentionally, it's actually a design defect in the way we do the spark output mods. But if you're getting it on all four, then your coils are probably ok, and I'd start by critically analyzing the output mods on the MS and the software settings related to SparkA and SparkB.
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Old 07-26-2008, 01:13 AM   #3
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It'll run fine without the capacitors if you make your dwell 5ms.
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Old 07-26-2008, 02:19 AM   #4
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a seemingly unrelated problem is that my stim doesnt work correctly after I've loaded my msExtra firmware. the rpm gauge doesn't work, and the lights don't respond properly. all the other sensors seem to work though. Everything works on megatune when its plugged into the car though. Could this be an issue?

Edit: cranking or running dwell 5ms? Then why did someone tell me to run capacitors? What do they benefit?

Edit 2: is there some way to blow your ignitor circuit in the megasquirt? is this within any realm of likelihood?

Last edited by N3v; 07-26-2008 at 02:50 AM.
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Old 07-26-2008, 12:22 PM   #5
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Quote:
Originally Posted by Joe Perez View Post
Understand that the "primer" spark isn't something that the CPU is doing intentionally, it's actually a design defect in the way we do the spark output mods.
Some OEMs do this intentionally though. The ECU grounds the ignitor repeatedly to produce multiple sparks, either on engine shut off or key-on. Helps keep the spark gap clean of gunk.
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Old 07-26-2008, 01:01 PM   #6
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Quote:
Originally Posted by N3v View Post
a seemingly unrelated problem is that my stim doesnt work correctly after I've loaded my msExtra firmware. the rpm gauge doesn't work, and the lights don't respond properly. all the other sensors seem to work though. Everything works on megatune when its plugged into the car though. Could this be an issue?
Yes, it very well could.

Refresh my memory- are you the dude who has a regular Stim, not a JimStim? If that's the case, then the stim won't produce an RPM signal the MS can read once you've configured the MS software to look for a Miata CAS. More importantly I assume you do see RPM when cranking?

Quote:
Edit: cranking or running dwell 5ms? Then why did someone tell me to run capacitors? What do they benefit?
They are beneficial, but not 100% necessary. My point was that if one of the caps is bad, it won't prevent the engine from starting. The caps are there to prevent misfires under high load, by helping the coils charge faster. You can accomodate for the lack of caps by increasing the running and cranking dwell, however this can be detrimental to the coils in the long run.

Quote:
Edit 2: is there some way to blow your ignitor circuit in the megasquirt? is this within any realm of likelihood?
It is possible, under certain conditions, to blow any circuit.

The "igniter" circuit as you put it is just a couple of low-current TTL outputs. An NPN transistor with a pullup on the collector and a grounded emitter. It's a classic open-collector configuration, but with the pullup inside rather than outside.

In normal operation, the outputs are current limited by their pullup resistors, so they will survive a short. There is no protection on the transistor side (between the output pin, the transistor, and ground) so if you applied a non-limited +5 or +12 onto these pins, the transistor (Q6 / Q8) in the MS would probably pop as the current backflowed into the circuit, through the transistor, to ground.


Quote:
Originally Posted by The_Pipefather View Post
Some OEMs do this intentionally though. The ECU grounds the ignitor repeatedly to produce multiple sparks, either on engine shut off or key-on. Helps keep the spark gap clean of gunk.
May very well be true. I can tell you that the MS CPU does not intentionally "prime" the ignition lines at either startup or shutdown. The reason we get a spark at power on is that the two 5v -> 1K pullups on the spark output lines cause those lines to go high before the CPU has a chance to boot up and asset Q6 and Q8 to pull them down.
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Old 07-26-2008, 04:55 PM   #7
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Update:
Well, I finally had time to get to work on this a little more, and I can say that not only will a miata run on two cylinders, mine did, and looked pretty good doing it! 1 and 4 plugs were wet with gasoline, and 2 and 3 were black from my rich pre-tune setup. Now I'm back to figuring out why I get no ignition on that ignition wire. Hopefully I'll have a solution by the end of the day
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Old 07-26-2008, 08:03 PM   #8
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ok I'm totally stumped. I checked the wiring and removed my capacitors just to simplify the equation as much as possible. I've got the primer spark in megasquirt set to do it twice on startup, and all 4 coils pop twice nicely and evenly. So doing it twice totally shows they've got a signal, right? another thing that's weird and I'm sure is related to the problem is this:I have two spark output LEDs, and the one closest to the DB-9 which is wired to IGN just like in braineack's writeup is visibly brighter than the one hooked up to IAC2B, which is the 3rd LED, furthest from the DB9. They're the same brightness when I hook it up to the stim. What determines the brightness of those lights? I think if I figure that out I'll solve this problem.

Edit: I've got all four plugs out plugged into coils resting on my valve cover, currently while I crank it only 2 and 3 spark. all four do a primer spark though.

Last edited by N3v; 07-26-2008 at 09:33 PM.
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Old 07-27-2008, 04:20 PM   #9
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ok this looks like a megasquirt issue as I checked all the wiring and it looks good. The issue has to be with my spark B output. Spark A is the brownish gray wire, right? I'm having all kinds of issues with spark output B. I checked the voltages across the spark output LEDs on the megasquirt and they look the same, 2 volts, so maybe the different brightness is just how it looks to my eyes when its outside. Could be different amps I suppose.

Anyway, spark B's output (the green/white wire) is pushing out 2 volts, the same as that LED. I have checked with a multimeter, and these 2 volts are definitely coming from the megasquirt, not faulty wiring in my coils or something. I tested by unplugging my megasquirt and turning the key to the ready position, and the coils all get power, and both trigger lines read 0v.

I've only tried a couple different things to try to fix this so far because I don't want to blow my coils. The first thing I need to worry about is getting that 2v off of output B right? I went into wheel decoder settings and tried falling trigger instead of rising, nope still 2v. I guess I could try inverting the spark output in spark settings without cranking the car to see if the voltage changes, but I doubt that will do anything. Does this tell anyone anything about a circuit I could have installed incorrectly or blown? Also, I'll have to check this again in a sec, but when I crank it I believe that the LED closest to the DB9 (aka spark A) stays more or less solid, but Spark B (aka LED furthest from the DB9) can be visibly seen blinking, or perhaps just less rapidly where the human eye can see it.

Something is definitely wrong with spark B.
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Old 07-27-2008, 10:53 PM   #10
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UPDATE: problem fixed.

SOLUTION: my mod wire to the LED for spark B was wired to the wrong side of the led *ducks*

Sorry for taking up everyone's time with my stupidity. I caught it on the 4th lookover of my board when i was pretty sure something in that area was causing a problem.

On the bright side, I did a lot of research and diagnostics, and I've learned a lot more about the megasquirt than I would have ever imagined.

So my car's actually running on all four cylinders! yay! set the timing and boy does it sound great. still a couple of things to iron out, but definitely much further on my way now.
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