I am going to resurrect this thread since I had my car smogged last week. We haven't had a rash of people failing smog as far as I know, but there have been questions about ignition timing for emissions and this thread is as good a place as any to post real results.

94 Miata, n/a, stock motor and exhaust with original cat, MAF is not hooked up so I believe this renders the EGR inoperative, MS3/X running sequential fuel, COPs in wasted spark mode, RX-7 550cc injectors, LC-1 WBO2, 93 octane. Datalog of the smog test and my MSQ are attached.

This is my usual AFR table:
https://www.miataturbo.net/attachmen...1&d=1314850949

Because I was worried about possible high NOx from running over 15:1 in cruise, I changed those cells to target 14.7:1 in all the low load/rpm areas:
https://www.miataturbo.net/attachmen...1&d=1314851399

I loaded up this table and ran VEAlive in TS for the 30 minutes it took me to drive from work to the dealership for the smog test. Our local club was having a tech session that night and I knew the mechanics would be cool with me having the laptop hooked up during the test.

Here's my ignition table. I believe it's basically the DIYPNP base timing map, and some of the weird decimal values probably got there when I upgraded to MS3 and it extrapolated the values for 16x16 instead of 12x12, and I never bothered with the timing except for the idle cells. Anyway, I did not bother to take out any timing before running the test. It was running around 23-25* in the cells hit during the 15 and 25 mph tests.
https://www.miataturbo.net/attachmen...1&d=1314851656

The 25 mph test was done first. This is a screen shot of the datalog during that portion. This was a pretty steady 2100 rpm and 53 kPa. You can see EGO hunting around a bit because I didn't have much tuning time on the all-14.7:1 target map before running the test.
https://www.miataturbo.net/attachmen...1&d=1314851656

And here's a shot of the 15 mph test. In the 1750-1800 rpm range and about 57 kPa.
https://www.miataturbo.net/attachmen...1&d=1314851656


And here's the final passing report:
https://www.miataturbo.net/attachmen...1&d=1314851656

CO and NO are miniscule, but you can see I was close to the HC limit for the 25 mph portion. This means unburned fuel out the tailpipe. The car runs smooth as silk so I'm certain there are no misfires. I think I could have gotten away with leaving my AFR targets alone at 15.x:1 instead of richening them up to 14.7. It's also possible that the original cat could be a bit tired.

FYI, you would have failed in CA. The limit for my '94 is ~92ppm at 15 and 25mph.

In every MS installation I'v seen, the ECU is ALWAYS reading leaner than it actually is. So if you are at 14.7 for realz, it will read 14.9-15.2. Compare the differences in various RPM ranges, and readjust your target AFR table. I have 15.1 on mine when I want to hit 14.7.

I guess I can add my car to the list of items I own that are Not California Approved™. But yeah, it came really close to the VA limits and I would like to see cleaner numbers out of this thing.

Yep, I was going to comment more on this in my earlier post, but decided I should go to sleep instead. This does seem to be the case with my car, about a .3 to .5 discrepancy. MS was doing a pretty good job at targeting what it thought was 14.7, but the gauge in the car was reading mid-to-low-14s during the test. Also, I'm not an expert at reading smog reports but I can only ASS-ume that "dilution factor" is related to AFR and it was 14.5-6 post-cat so the mixture running through the engine was undoubtedly richer (again, ASS-uming that's what dilution factor means).

I'm also not entirely confident in the efficiency of the cat. It's seen nearly 30 track days running 12.8:1 at WOT (almost all the time in a n/a Miata) and spiking richer every time I upshift. Worse than that is the one time when my passenger's foot dislodged the MAP line to the MS, causing MS to see 100 kPa all the time. I drove about 30 highway cruising miles while dumping a lot of unburned fuel into the cat (sub-10:1 AFR) before I figured out what the hell was going on and stopped the convoy to fix it. I doubt these things are good for the cat.

I passed and don't have to worry about it for another 2 years, but "next time" I'll leave the AFR targets untouched (I reverted to my usual settings right after the test) and with the turbo exhaust it will have a new cat. Hopefully that will have it running cleaner.

numbers were better than mine, but I did nothing to my tune to try to pass, plus I'm only on a 200 cell metal core cat.

I will be doing this soon... but i will be using AEM EMS.


I will also be fucking slammed for this so i can do 2 step idle. where they hold the car at idle and say 3000rpm with no load since the car cant make it onto the rollers to do 25mph. this is what they have to do with AWD cars.

I just passed again a few days ago. Set my AFR target to 16.0 and ran VE Analyze Live during the test. I failed about two weeks ago with 1200 HC with an allowed 220, and 12.xxx CO with an allowed 1. AFR then was 13.x

Passed this time with 0 CO and 36 HC, idling at 16.x AFR. We only do an idle test here, although if you fail, they have you rev it to 2500 for 15 seconds to try and heat up the cat, then let you try again, I didn't even need the 2500 test this time, last time I failed so bad he didn't even let me.

This is all at a static 10* timing btw.

I failed emissions today.
https://www.miataturbo.net/attachmen...ine=1337033621

Things about my tune that are relevant to this failure:
AFRs were hovering around 14.7 on the high speed test, but kept dipping close to 13 on the low speed test.

Ignition timing is 29-30* at 2500 rpm (high speed) and 26-27* at 2100 RPM.

VVT angle is 0-1.5*, depending on load. Basically no advance.

Injector timing is 385*.

No EGR. Even though I could control an EGR solenoid, my exhaust manifold doesn't have an EGR port.


My current plan is to put on the stock intake, or relocate my current intake to behind the radiator, maybe even with some ducting to bring in more hot air from the exhaust manifold. I need to retard the ignition timing, but I don't know how much. I'll also do a full recalibration of the LC-1. Last but not least, I'll run VEAL while on the dyno.

Do you guys have any other ideas? If I don't pass the free re-test I'm going to call the DPS and see if they offer a waiver for vehicles converted to run on E85. I'm pretty sure my fuel system will handle it.

why bother with all that? fix the high HC (too much fuel) and N0x (too high of EGTs).


sounds like you dont have enough timing....im pretty sure im closer to 35* at the same area, I'd have to check my map...what AFRs are you targeting there?

Those are all the things I can think of that will contribute to the high nox.

The low speed hc failure will be easy to fix, it was running a Tad too rich. I'm mainly worried about the nox.

I'm targeting 14.7. Ego was on. Iirc nox is caused by advanced timing.

This figures... I got a citation for expired sticker yesterday while driving home from the alignment shop. Prior to yesterday, the miata had been sitting for almost a year. Oh Murphy...

I've got 20 days to get this thing to pass. My plan is to run ~10 degrees less spark advance, double-check my Afr reading offsets and correct as necessary, target 14.7 AFR closed loop, and try 5 and (if 5 fails) 10 degrees advance on the intake cam with vvt.

Damn this higher-compression NB motor.

I Passed.

Less spark advance and 5* intake cam advance did the trick.

Relevant info:
MS3X, full sequential fuel and spark with DW800 injectors and LS2 truck coils.
VVT motor with VICS intake
180* thermostat.

20* spark advance. 5* intake cam advance. Actual AFRs according to MTX-L gauge were richer than I wanted due to miscalibration between MS-WBO2 again. They were 14.35 ± .3 for the low speed and 14.5 ± .3 for the high speed. I'm pretty sure I incorrectly grounded my MTX-L at the sensor ground pin because I have wild AFR noise and am running an averaging factor of 25 to compensate. Gonna fix that.

https://www.miataturbo.net/attachmen...ine=1383116783

I'm not sure why there are different standards for this test compared to the last one I posted. I have a report from 2007 that shows the same standards I was tested for today.

Log attached. I actually failed the first low speed test. I think the operator's foot twitch had something to do with it too. CLTs were also higher once the low speed test was revisited. This was done after 15 minutes of hard driving in traffic followed by ~10 minutes of idling. They also pointed a powerful fan at the mouth. See how the CLTs dropped when they turned the fan on? Now time to do more mpg tuning.

Oh how I wish we just had the sniffer like you guys.....So jealous

You wouldn't if you had to deal with it.

We have both, OBD2, and the sniffer for pre-OBD2. I hate the sniffer test. I can never KNOW that I am going to pass before going in. With OBD2, I can hook up my OBD2 scanner and know with 100% certainty that I'll pass the emissions part of the test, on my own time, as many times as I want, for free*.

*Plus cost of scanner. One time fee applies.

Wait, are you running parallel?

Full standalone.

Any cars in major cities and surrounding counties here in TX have to do emissions testing. 1988-1995 cars have to pass the sniffer test on the dyno, and in some areas (or 4WD) a two speed idle test. 96 and newer just need a happy ECU for OBD2 test, no sniffing required. 25 years and older cars are considered antique and are exempt from emissions testing.

I hate the sniffer test because there are so many variables and passing is never a certain thing. The operator couldn't hold his foot still, which literally caused me to fail the low speed test the first time.

When you take into account the fact that there are fewer and fewer pre-OBD2 vehicles on the road these days, there is less financial incentive for owners to keep their dynos functional. Out of the 4 shops I went to, 3 had broken dynos. The owner of the shop where my friend works doesn't plan on fixing the dyno, ever. I don't know if they have any legal requirements to maintain a dyno, but it was much harder finding a working one this year.

how do you pass the obd scanner test with a ms?

You gotta know somebody.

Or:

You'd have to run parallel, and keep the OEM ECU happy so it doesn't throw any codes. A friend did that with his turboed 96 a long time ago, but it did require a little trickery. I'm not aware of anybody with an NB that does this.

MS standalone won't communicate via the OBD2 port as far as I know.

Otherwise, you go back to stock ECU with wastegate wired shut and drive around a couple days so the stock ECU can complete it's readiness tests.