Low RPM stutter
 

Lets get this out of the way.

I've also tried a little google and m.net without any real solid feedback.

So on my completely stock 2001 Miata i've been having a bit of a stutter issue.
The stutter occurs between 1000-2000rpm under heavy to heavyish load / acceleration. It's almost always worse after it's warmed up.
As soon as it's 2000rpm + it pulls just as piss ass slow as a stock miata should without any issues. (though i do feel that my 94 stock was quicker than this 01, perhaps weight difference)
Car has 70k miles and the plugs were changed and gaped correctly, new fuel filter, new rear O2 sensor. Oil change, air filter, and other general maintenance.

It seems pretty simple but i'd like to know if anyone else has had issues similar on stock 01's before i go throwing money at it.

I'd like to think one or both of the coils have gone funny, but my logic and knowledge tells me that if a coil were to go bad it would just die. Maybe not? Coils are a bit to expensive for me to just replace without a little more input. I've heard everything from crank sensor to O2 sensor. The car throws no code either.

A miss-fire should throw a CEL, actually a flashing CEL.

What kind of power do you expect a stock miata to make at 1k rpms?;)

just random thoughts:
maybe your vtcs solenoid is janky
maybe your crank position sensor is too far away from the wheel
maybe a bad/weak coil or both

Did you try cleaning the TB and MAF?

Those were my ideas as well.

Yup, i did this too.

I just drove my car to work and was thinking of your "1k-2k rpm" claim.

How the heck do you even keep the car that low? lol
Just curious, cause my commute is all city, and usually 45-50mph, and I still can't get it to stay under 2k aside from a split second in 1st gear, even if I "lug" it.

just another random observation :giggle:

Eh, i kinda drive it like an old man. I'm used to having a torquey american car.

Normally it's just getting up to speed, or if i slow down in gear and don't downshift.

I'll see if i can get a little video of it. It's pretty apparent and embarrassing when leaving a light misfiring.

plug wires

except its got cops

I've heard of the elusive stock cops, but I've never before inspected under the hood of a 2001+ for them.

Why do you always have to be right, 18? go be right somewhere else!

Technically it has both :party:

Bump.

So this seems to be getting a little worse.

Same story, when it's cold in the morning it drives fine. Once i drive my 30 miles home and if i'm driving like an ass, high RPMs, really putting a heavy load on the engine it is the worst.

If i come to a light and do a nice low rpm start without over revving and doing a "jack rabbit" start it will sputter and missfire like crazy. What could get heatsoaked / hot that would cause this, BUT only within 1000-2000rpm? Could be the new O2 sensor i put in, not working properly? MAF? Coils? Maybe something with these crazy butterflys my car has on the intake?

Have you checked the codes even if it doesn't show one or flash?

No code, BUT i do have a stored code for O2 sensor, the one i changed.

How did you go about cleaning the maf?

and an even better question...it's like 8 degrees and snowing, why are you even driving the miata right now? :brain:

MAF cleaner spray stuff in a can...

I drive the NB all year round. Probably why i have stupid little issues like this, it's really not meant for 16 inches of snow.

I tried backing mine out of the garage the other day to make room for a side job, and I got stuck in the driveway after I had already shoveled! It probably doesn't help that I have bf rivals though? You sir are a brave man.

Like someone above already mentioned, have you checked the air gap between the crank sensor and the reluctor wheel on the crank pulley?

I had an issue with my 99 a couple years back where the crank sensor wiring that plugs into the main harness had the insulation rubbed off of it by the little hold down clip that keeps it away from the belts. It left the wiring exposed and every time it rained or I ran over a puddle it would start acting up the way you're describing. I never got a code either because it was so random and I rarely drove in the rain to begin with.

I haven't checked that yet. Seems to be weird that it's related to heavy driving, weather it's 100F out or 3F out.

I drive from allen park to monroe for work too. So it's not like i'm just going down the street. The day we had all that snow a week or two ago i had to back down 3 freeway entrance ramps because of other people being stuck... With enough wheelspin this car can get through just about anything.

I have nothing constructive to add, but if you have a gopro I'd love to see video of fording 18" of snow in a Miata ;)

8 Fast 8 Furious: Detroit Drift

P0420 code now.
Anyone ever take the temperature of their catalytic converter on a stock NB Miata?

So after my 30 minute ride home at 70mph i took the temperature and only got a reading of 350F. After doing some reading, i find that this temperature could mean my cat is no longer operational. It COULD explain my weird stuttering problems at low RPM when the engine is warmed up.

I don't want to spend a ton of money to fix this issue, but i may have to.
I'm thinking a test pipe, but i'm not sure if would solve my issue. I don't have emissions or any of that BS to follow, i just kinda want the missfire and now code to go away.

Flaky coil leading to failed (melted) cat and extreme backpressure? This is tragically common on the NB1 with the shitty coils and precat, but its a mode of failure to explore.

Unbolt the 2 bolt flange before the cat and peer in with a flashlight. Damage will be immediately visible if the above is the case.

I'd measure my NB1 midpipe cat (without the precat) for you except that I don't have an infrared thermometer to do it with. :sad2:

Oh, so the precat (the one before the O2 sensor) is also a catalytic converter? I don't know why i thought that was just a resonator. I'll have to take a temperature of both, before and after the O2.
Not that i'm doubting they're both bad.

I felt like it was worse yesterday when it was -8F outside too.

Man, i don't want to buy $200 in coils and $300 in exhaust for a daily beater.

You said 2001 so NB2 and no precat. The main (and only) cat is built into the midpipe on the NB2.

NB2 flow diagram looks like: head -> manifold -> front o2 sensor -> cat -> rear o2 sensor -> resonator -> muffler.

Okay, so the bulge behind the rear O2 is a resonator...
Seriously, it looks more like a cat than the bulge before the rear O2. So the temp i took was actually on the cat. I guess it wouldn't make any sense to put a catalytic converter behind an O2 sensor. haha
Thanks for clearing that up.

Gonna go rip it apart right now and look for apparent damage.

Here is a pic

https://www.miataturbo.net/attachmen...ine=1424209643

Its taken from the rear, the resonator is closest to the camera, cat is the thing further upstream with swiss cheese heatshield on it. Not shown is the rear o2 sensor as its around the top of the pipe, but it would be after the cat, so between the cat and the resonator in the above pic.

Glad I could help! :bigtu:

Welp, no apparent damage.
I did find my slave cylinder is leaking though. Awesome.
I want to complain, but the amount of hell this Miata goes through on a daily basis says i really have no right to.

I guess either suck it up, or replace the midpipe back with something. I really don't want to mod this car though.

So... This morning on my commute to work the CEL is no longer on.
I didn't do anything except unbolt the exhaust then bolt it back up.
Still missfires pretty badly below 2000rpm.

Just because i didn't see damage on the Cat might not mean something is wrong with it right?

Correct. When it does not look like a screen door anymore then you know you have problems. Visual check is just the easy way to do it, infared thermometer is probably the "right way" but again, I don't have the baseline operating temp for you :(

How do your plugs look? I'm running out of ideas :dunno:

Plugs are bran new within the last 3k miles. The ones they replaced only had like 10k on them.

I don't get it. Oh well.

Do you have another set of ignition coils you could try with it? I'm trying to think of what else might be that affected by warming up.

Nope. I may purchase another set just to try it out. RockAuto has an "ultrapower" for $30. Seems like it could be worth a shot to try.

I've got a set of stock ones I can mail you to try out. Provided I get them back of course ;)

Nothing solid to contribute, but it could be many different things. Bad coil/wire, vaccum leak, etc.

Check to see how much vaccum you have at idle. A semi-large leak could cause it to misfire right when load is applied from being lean, but be massaged out due to the stock computer being rich everywhere else.

Do you have the factory repair manual? If not, I can look into it for you if I get a chance. I would probably start by checking some sensors according to the manual. Just because a sensor is messed up, that doesn't mean it will throw a CEL, especially if it's borderline.

I could have a vacuum leak. That should be pretty easy to verify.

I'll just buy some, thanks though.

Also, when I get home from work, I'll run inside and grab my super awesome Amprobe IR-730 thermometer.

I'm going to guess your converter should be much hotter than 350. Should be closer to 1000F. If your IR thermometer has a low spot:distance ratio, you were probably getting an average temperature with other junk under there. Also, the heat shielding will be alot cooler than the converter itself.

Edit: On a side note, I would take E02K up on his coil offer if I were you. A set of used stock coils will most likely be much better than some generic chinese replacement coils. I have literally seen parts store coils, TPS sensor, MAF sensors not work right out of the box. Shoot, I tried 3 different parts store alternators when my stock one went out, all failed in less than a month. I bought a used stock alt, been good for over a year now. Just my :2cents:

Cat no longer has any heat shielding on it.

I have a Fluke VT04 at work i can try it with. My multimeter even has temperature probes i can use to check it.
I'll get a couple different readings from different instruments. All i have at the crib is a cheapo $40 unit.

When I had wrong sized injectors (too small) in my Civic it also gave a particular bad experience with low-RPM and high load. So your problem could also be fuel related and not spark related.

Vacuum leak sounds plausible, this would cause a lean situation in low-RPM situations.
It also would not hurt to check fuel pressure I think.

Do you have a wideband O2 sensor laying around? Sticking it into tailpipe to see if you are running rich/lean in the 'stutter situation' would also be a great help.

If you do not want to fork out a lot of cash to debug the issue, maybe try to find someone with the same car in the area. You could swap out coils / wires / sensors and see if things move along.

Well, I don't think you should be too worried about your cat temps being low. I just checked mine, but mine has heat shielding and I forgot for about 10 minutes, and it was right at 310F. I'm not sure, but I'm guessing it cools down quickly after shutoff.

That worries me even more.

I get right off the highway after 30 minutes and check it with no heat shielding at all. Still 350F.

10 minutes that thing will have cooled off by probably as much as 50%.

Well, with no heat shielding the converter itself will be cooler because all of that radiant heat will be dumped to the surroundings. Mine was after a trip on the highway as well. I'm not sure it was 10 minutes, but it was a small conversation with the wife. Could have been 5 minutes. I got distracted lol. I got my temp from the rear portion of the cat that's exposed, not the heat shielding itself.

Anyways, I'll check it again tonight, right after I stop. I live less than a quarter mile from the highway.

For what it's worth, I have seen cars that had catalytic converters that were completely broken, and they didn't affect the performance of the engine, they just completely failed emissions. Only on my old RX7 did the cat cause problems with the motor. It just didn't have any power, especially at higher RPM. The cat was clogged with ash and partially melted. Car got a lot faster after I swapped it for a pipe. Go figure.

Well from the looks of it, i've completely solved my issue.
No more low 1000-2000rpm stutter missfire when hot.


Put new ignition coils on.

One thing i noticed, my old ignition COPS are longer than the new ones. I may take one back off to snap a picture.
Does anyone have any prints or dimensions of the COPs? Specifically the socket?

Nice! Glorious resolution, comrade! :bigtu:

How long have the coils been in place? I'm curious as to if the fix "holds" and also the quality of the Rockauto coils.

I can measure the set I have, but no drawings.

New on the left, old on the right.
https://www.miataturbo.net/attachmen...ine=1424822853

Markings on the old one.
https://www.miataturbo.net/attachmen...ine=1424822853

I can't imagine they went on TOO far. Either way, the short ones are working now.
They are "ultrapower" brand. No idea how long they will last, we'll see. They were the second or third cheapest on rockauto.
The old ones were on the car when i bought it, so i'm not even positive they're the correct ones.

me too....
 

Ironically enough, I was going to write something very similar to this, but I decided to check out engine performance, and wah-la... here we are. I have an 04 msm , decided to drive it to work one day and was cruising.... all a sudden, it bogs then multiple misfire, it was so bad that it lost speed and gave a flashing CEL . You would think it wouldn't run. But it would idle.... and I say idle but barely. So I pull the car over, pop the hood, start the car then tap on the front coil a few times and bam! back in business... it did this two more times on the way to work and continued on the way home. I had already changed the plugs a week ago thinking that may be it, but wasn't... so I ordered new NGK wires, and then Ordered two new "high performance" coils . The coils came in and when I went to put them in I noticed the boots were shorter than stock, so I changed them out with the stock boots, the stocks looked fine, I cleaned them, checked the springs, and they were good.. no corrosion, or hairline fractures etc. I did this Not even trying the new short boots. I Dielectric greased everything, started it up and it ran... like ran good... at least I thought it did. So no It doesn't misfire anymore, but the rpms spike from 800 up to 2200 back and forth repeatedly when first started and When driving and accelerating under heavy load it's "ok" anything else is questionable. Certain rpms it surges especially coasting to a stop while it's still in hear, you HAVE to depress the clutch, if not it "bucks"... it does this but no CEL, just embarrassing "bucking" or "jolting" . depress the clutch and rpm will fall right under a thousand .. to "normal"... I'll also note that before when it was running as normal as it had since I've owned it, you would have to coast to a stop and have trans engaged until the engine speed was near 1200 rpm before depressing the clutch out it would die, or be close to dying (500rpm or so). I've tried cleaning the maf and the boost solenoid valve. Since then I've replaced the maf and the filter.... just very frustrated. Haven't really had the time with work, then the weather has been crazy too.... just lost my job do to restructuring so I have the "time" now.. any help is most certainly appreciated... thanks in advance!.. also.... I need a new ecu , and want a MS. anyone know how to get help on that? I've responded in the appropriate threads and pm'd Demetrius and Scott both.....I Haven't heard back... =/ again thanks for any constructive, productive input...