Hey guys, does anyone know the obvious reason why only cylinder number four is not sparking? I checked one two and three, big arcs there. NA6 Miata, stock everything. I see a lot of questions being answered about pairs of cylinders going out, but I'm not finding anything on a single cylinder. I've tried two separate coil packs, with the same result. I've also tried using a wire from another set.
Does a Mee-otter have two coils and wires going to two cylinders each, or four coils? If two, you must have a dead wire if you've tried more than one coil. If it's four coils, you have a wiring problem or a toasted driver in the ecu.
In reply to Streetwiseguy :
It's waste spark, so 2 coils. Sounds like a dead plug wire.
In reply to codrus (Forum Supporter) :
I tried already with a spare plug wire as well.
Tried another spark plug? I'm guessing yes, but... Is it possible for a wasted spark coil to fail to output on half?
Spare "known good" plug wire? Or spare "rattling around in the shop for a decade" plug wire?
How do you know you have no spark? Have you lifted the wire off the coil with the engine running? Lifted the wire off the plug? You should be able to hear it. If you hear spark going to cylinder one, and none to four, you have a broken coil or wire.
You can usually tell if the coil is arcing internally by grabbing it while the engine is running. Unless you have a heart condition...
In reply to Streetwiseguy :
I put a plug in the wire and flopped it off of the valve cover. Obvious spark on 1-3, no spark on four. Plug is new, wet from gas. The wires on the car were from before and ran before the swap. Swapped in a different coil and different wires - not brand new but not that old. I'm as confused as you are since it's wasted spark.
You can't have spark in three cylinders on an NA6. The electrical path travels through two spark plugs, so you lose two. I'm going to say there's a misdiagnosis of the actual failure.
What are you trying to chase?
Jesse Ransom (patron dork) said:Tried another spark plug? I'm guessing yes, but... Is it possible for a wasted spark coil to fail to output on half?
Dunno, but it's easy to test. Swap the #1 and #4 plug wires on the coil and see if the problem switches to #1.
In reply to Keith Tanner :
That's good to hear - I'll sleep on it and try again. I thought it was the injector not working, but then I checked the plug right after and it was wet. The engine is clearly running on three cylinders (you can pull wire 4 with no change) - I just need to get cylinder 4 playing along.
Thanks everyone! I'll report back.
Check for codes just for fun. All you need is a paperclip.
Or do I have my wires completely crossed? Or are the coils serial in some way?
No Spark:
Tazer Mode (there's spark):
The Miata is waste-spark, meaning that it fires pairs of cylinders at the same time, 1/4 and 2/3. When #1 is fired between the compression & power strokes, #4 is fired between the exhaust & intake strokes. The extra spark in #4 wastes a small amount of spark energy, but it doesn't ignite anything because there's no fuel and no compression on that cylinder. It's built with two identical coils, each coil has two plug wire terminals that are connected to the output side of the internal electrical bits.
The video is fuzzy, so I can't quite tell, but it looks like you're using that wire & plug on one of the terminals (inboard) in the first one with no spark and the other terminal (outboard) in the second video that does have spark. If so then either you don't have the plug wire pushed in far enough (which I assume isn't the case), or the coil has an internal connection breakage between the electronics and the terminal. There is no way for the ECU to send a spark to one of those terminals without also sending a spark to the other. If you look into the terminals on the coil, is there anything visibly different between them?
In reply to codrus (Forum Supporter) :
I know what wasted spark is and how it should work - I'm trying my other coil now. Even swapping the good firing wire to the other cylinder it wasn't firing. I'll check in the other coil as well.
In reply to codrus (Forum Supporter) :
I think you were right, crap in the coil - when I swapped in the other coil and tipped it crap fell out. We've got lightning on cylinder 4!
BUT still not firing. Hurumph. Well, back to the injectors...
Your testing method is fine, but you really should have the spark plug body grounded somewhere, instead of making it try to jump an inch. That is really hard on coils. A second or two, pulled away from the valve cover to see how far it will jump is fine, but that plug needs to be grounded, or all those electrons are going to burn through something, somewhere.
Disable the spark, and record the engine as you crank it over. I want to listen to it cranking/not starting.
In reply to Streetwiseguy :
1 swapped in fuel rail from the other motor and we're firing on all four cylinders! Looks like it was a compounding of errors. Something is messed up with the fuel rail around injector 4, I swap the good ignitors off and put on the ignitor that has crap in it - same symptoms so I leave the "bad" ignotor on and try some things. Cleaning the inside of the ignotor "fixed" the 4 not sparking, swapping the rail fixed the original problem. Now just to work out the other 30 things and maybe I'll have a driving car again.
Hint - when you're testing for spark, you have to ground the plug.
An injector that's weak will still wet the plug but may not provide enough fuel for ignition.
They say the biggest impediment to learning is 'knowing' things. The way wasted spark works, which you may already 'know', is that each coil's secondary circuit is hooked to two spark plugs, two plug wires, and the engine itself (between the threads of the two plugs) . The circuit goes out one plug wire, across one plug gap, through that plugs threads into the head, across the head to the other plugs threads, across that plug gap, and back up the wire to the coil. Spark plugs 'ground' through their threads (although technically, the threads of both plugs are 'power' in a waste spark circuit, but ignore that if it's confusing) . If you take them out of the cylinder head but don't hold the threads or metal body of the spark plug to a ground, you have added a crazy amount of resistance to the circuit because now the ground path includes air! As you saw, depending on a bunch of factors you may still be able to jump a certain air gap and get spark without holding the spark plug to ground, but it isn't a good idea and isn't representative of what the ignition system actually has to do anyway. The reason why someone mentioned it isn't a good idea is because the ignition coil can make enough 'open circuit voltage' to burn a new path right through some insulation somewhere and make it's own new ground path that's better than the crappy one you gave it by having a plug hanging un-grounded. Normally the coil voltage will only rise to the level necessary to initiate the spark across the plug gap and the insulation is designed to handle that voltage. If you add a bunch of resistance to the circuit the coil's voltage can go up high enough to burn through the insulation somewhere in the spark circuit.
This is related to the other scenario which noone specifically mentioned: Your coil can have a short to ground inside its housing. This is a fairly common scenario and on a regular COP setup you just lose spark from that coil. However, in a regular COP system one end of the secondary winding (the spark circuit) is tied to engine ground and can complete the full loop that is required for current to flow. In a waste spark setup the secondary winding doesn't have any connection to anything except through those two plug wires. What that means is when you have a short inside the coil, you will not lose all spark, because you need TWO connections from the secondary winding to anything else to have a full loop/complete circuit. The odds of that are extremely low, so what you have instead is the circuit going out one spark plug wire, sparking across that one plug, going into the cylinder head, and then finding its way from the head to the coil bracket and back through the coil housing to the secondary winding again. Which wire you get spark from is just going to depend on where the internal short 'lands' on the secondary winding. You could even make it spark on one or the other by increasing resistance on one side. Hold one wire too far off the plug and you might find the other one starts sparking because it's now the path of least resistance.
It's tough to 'prove' this other than by process of elimination. You could just take the coil off its mounts and by interrupting that path from the engine back into the coil it might start sparking both plugs again. But, the coil also has a primary winding in it and if the open circuit voltage is enough to burn through the insulation to the grounded mounting bracket, it can also burn through the insulation until it connects with the primary winding which would have it doing basically the same thing with nothing gained from the test.
Anyway, replace the coil!
In reply to Vigo (Forum Supporter) :
I did suggest he could check for a leak in the coil by grabbing it...
Streetwiseguy said:In reply to Vigo (Forum Supporter) :
I did suggest he could check for a leak in the coil by grabbing it...
And if it leaks, you'll know shortly after you grab it.
Lol - thanks for the help hive collective. I'll have another dumb set of questions for you guys shortly I'm sure.
All seems ok on the western front - I **hopefully** will get to beat on it at NCM tomorrow if all goes well. Nothing like shaking down a car you just literally touched EVERY FACET of on track! Shake down drive ~2 hours went well, a few touch ups here and there and she's feeling REALLY good right now.
This story will eventually make it's way on to my awful thread of miata failures:
https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/miata/170843/page1/
The little Miata gave a poorly driven corvette major heart burn today! Right up until I spun it trying to keep pace, lolololol.
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