Well, my problem is fixed just by switching to the NGK plugs Faefae, so not certain what you are getting at bro.

Nothing I could have done tune-wise or build-wise could have fixed that issue based on what I'm seeing - the plug was simply way too cold for the engine. And that's from someone who works for the people who make the plugs, so I have no doubt he's right. I am sad in the pants though because that's the best the Miata has ran under hard acceleration yet.

what exact plugs are you running?

Blaen,

Don't feel too bad. There can be a up to 5% variance in a plug's IMEP, (that's a measurement of heat range), in a given part number from any manufacturer. Most of the time this isn't an issue but you could see why only going a step colder could sometimes have little effect. I've seen 7's and 8's in NGK's test almost identical for heat range. That's simply due to production variances. Going two steps colder on any application can sometimes even cause a no start condition in cold climates. Running too hot of a plug can be a REAL disaster though. You usually can't come back from melted parts.

The trick is to find a plug that runs hot enough to burn off carbon deposits at cruise and idle and is still cold enough to handle boost at the top end. For most of my boosted builds I start with as cold of a spark plug I feel I can get away with then inch up if I have to. You can see what a tough time an OE has trying to pass emissions and make boost these days.

I know I'm the Autolite guy saying this but frankly your car should be running fine at the upper rpm range with NGK's, (or about most any plug), if they are in good shape and the gap and heat range are correct. If they are too hot and you are getting some abnormal combustion you may not be able to hear it but you will drop delivered torque.

Personally I'd like to see you get to a point where the car is most stable on average and tune from there. If you don't have stable fuel, ignition, compression, or cam timing you will be chasing a moving target forever and begin to hate your life.

Dave

Autolite XS3922, as per Superdve's recommendation

Well, I've got stable fuel, timing and compression right now. I'm chasing an ignition target at this point, however.

I've used 3922s without any issues. ill use them when the store is out of bkr7es.

Okay, Brainy. Maybe you can help me figure out wtf is going on then.

Car runs great with BKR6E's, no problems.

Runs like crap on the 3922's. The only difference is the plugs. What would you check/do/look for?

Alternatively, is it possible I got a crap plug in my batch?

what are they gapped at, what coils, what dwell?

i watched your video, but didn't hear any sounds. is it possibly running on 3?

0.030, Toyota COPs, 2.5ms

I don't think it's running on three, the feel of it running on three is distinctly different from what it is doing now, but I'll definitely check that at lunch.

i mean its possibly a weak coil, but odd it changes with the plugs.

maybe post your msq and log idle and post that.

I just so happen to have a spare COP. I can swap it in on all cylinders to see if it changes anything?

I've posted numerous idle logs in this thread, and my msq is posted in the OP Brainy. Changes are dead time and req_fuel now.

im not good at reading. i just looked for the video :)

Post with tune: https://www.miataturbo.net/showpost....40&postcount=1
Changes to the above are req_fuel and deadtime

Post with NGK datalog at idle: https://www.miataturbo.net/showpost....5&postcount=44

Post with Autolite datalog at idle, both normal and super-rich: https://www.miataturbo.net/showpost....2&postcount=46

You guys may be on to something with the coil(s). Have you done a cylinder balance test to isolate an individual cylinder by yanking injector leads or coils noting RPM drop? It would be nice to know if any cylinder is contributing less.

FWIW, I took my Miata apart today after work and put my oscilloscope to work on your behalf since my car is also a 1.8. I did a transducer based cam timing measurement, running and static compression test with and a pressure fluctuation test at the exhaust pipe to measure any appreciable misfires. Not sure of the mileage of my car but it's over 100K for sure. No misfires, compression was 155-158 on all 4 holes, running compression was about 57psi, (seemed a bit low buts runs great) and snapped throttle compression was over 215. I've read 180 psi is what a new 1.8 is supposed to hit but mine has miles.

1) There should be NO puffing at the tail pipe on a 4 cylinder. Meaning you can hold paper to it and it wont go in and out. Anything else and you have a misfire.

2) Have you looked at your crankshaft and camshaft sensor signals in Megatune? I can't remember if you said you did.

Looking at your logs I didn't see any crank trigger dropouts. Hmm.

I'll be happy to send you some more plugs to try if I have them here. Maybe we got a bad or dropped one. Stuff happens once in a while. PM me your snail mail.

Swapped my spare COP on all cylinders, it exhibits the same behavior regardless of what cylinder my spare COP is on :(

Compression on all cylinders is 189-192.

It acts the same regardless of what injectors or fuel harness I use.

havent a chance to check logs, will today.

Check your plug harness wiring.

Other than obscure MS fukkery, This is one of a few things:

Fuel map
injector
spark plugs
coils

Also, try unplugging your IAC valve and see what happens. Just curious. While you're at at look at the tension on the throttle cable.

i find log 2012-04-24_20.31.19 to be odd.


GVE is stuck at 62% (thats your fuel table cell number)


but the pw is all over the place and map is very upset cycling up and down, but you idle valve is also locked at 62.5%...which is like fully open and it's flat as well.

same with timing, flat at 18°. very odd behavior that the min things that would effect idle quality (fuel, idle valve, amnd timing) are all locked flat, yet the motor is oscillating like crazy.



does your AFR always sit at 15.0:1 as it warms up? cause the thing stablizes the instant it drops to 9.4:1 from 15.0:1

also, what's controling idle, cause your idle valve isn't doing ---- and you're idling way too slow.

Ya i did not look at logs but i was guessing idle valve too cus of the afr wierdness