380,000 mile NA6 Miata smog check saga

[S21FOLGORE]

Here’s the old, original thread, titles as
“300, 000 mile NA6 smog check saga”

http://www.ducatimonsterforum.org/index.php?topic=63479.0

It was posted on 2013.
Posted again two years later, 2015.
Since then, I haven’t posted, but the car always passed in the following
2017, 2019.

This year, however …

I took a car for 45 - 50 min freeway drive Saturday morning.
(For those who are local (San Francisco Bay Area, north of Golden Gate Bridge) From Novato to Cotati on 101, then turned around, heading back south, San Rafael.)

Traffic was flowing smoothly in both directions.
So, I could keep going at 65 to 85 mph all the way.

Got off 101 at San Rafael, went to my regular STAR smog station which is right off the freeway exit.

Waiting was less than 10 min, and I kept my engine running.

And, here’s the result.

15 mph = 1821 RPM
25 mph = 2089 PRM

HC (ppm)
15 mph … Max allowed 94, Measured 8
25 mph … Max allowed 76, Measured 6

CO (%)
15 mph … Max allowed 0.58, Measured 0.001
25 mph … Max allowed 0.49, Measured 0

NOx (ppm)
15 mph … Max allowed 847, Measured 1
25 mph … Max allowed 786, Measured 809

CO2 (%)
15 mph … Measured 15.3
25 mph … Measured 15.2

O2 (%)
15 mph … Measured 0
25 mph … Measured 0.2

So, the problem is only one part,
NOx at 25mph test.

For those who didn’t read the original thread / not familiar with NA6 Miata.

The cat is practically brand new (only gets used for smog), so it’s not a cat.

There’s no EGR on 1.6 NA6.

It's an OBD1 car.

I know high NOx is most likely the result of high temp of combustion chamber.

I did the usual thing, not by myself this time, but by a local shop.
(Due to the serious lack of free time.)

Oil & filter
A set of new spark plugs
Air filter

Checked ignition timing (stock 10 degree)

What is different this time from the past …

I normally run premium gas on this car, all the time.
BUT, this particular time, I took the test with regular gas.
I don’t know if the octane rating makes such a big difference.

Did I make combustion chamber temp too high, for not running premium?
(But it doesn’t make logical sense NOx reading jumped up from 1 ppm to 809 ppm, by just increasing 268 rpm.)

I no longer run Iridium plugs.
I now use V-power.


A few other things I can think of …


The O2 sensor might be responsible for this.
I don’t remember / can’t find the invoice right now, to confirm how many miles on this O2 sensor.
But, this O2 sensor is on the car since Rick (original founder of PR motorsports) installed Jackson Racing Header, which was … pretty long time ago.

With the JR header, you have to remove the header in order to replace O2 sensor. Not the most convenient, but this was the only CARB legal header for NA6 at that time. (I needed a new header because the stock manifold developed the leak.)

Also, it is possible that there’s vacuum leak. But, then, how it does not affect 15mph test?

Anyhow, That’s all I can think of right now.

In case anyone is interested, here are the test result from 2013 and 2015.

2013
HC

15MPH 40(ppm) (Max allowed 94)
25MPH 12(ppm) (Max allowed 76)

CO
15MPH 0,02% (Max allowed 0.58%)
25MPH 0.01% (Max allowed 0.49%)

NOx
15MPH 0 ppm (Max allowed 847ppm)
25MPH 0 ppm (Max allowed 786 ppm)


2015

HC at 15MPH 34ppm (max allowed 94), at 25MPH 10 ppm (max allowed 78)
CO at 15MPH 0.06% (max allowed 0.58 ), at 25MPH 0.01% (max allowed 0.49)
NO at 15MPH 0 ppm (max allowed 847), at 25MPH 0 ppm (max allowed 786)



I’ll wake up early Monday, and go to Hayward right away.

Friday afternoon, I called PR motors on a whim.
Telling them that I may need to bring my car on Monday, because
I’m not 100% sure if the car would pass the test.

So they said they’d keep a slot first in Monday morning for me.
If the car fails to pass, I’ll e-mail Sunday (so that they will know first in the morning that I’ll come in.

(In case you are wondering about this (sort of) strange arrangement.

I really don’t want to reveal too much personal info, but … let me just explain.
I work in a crazy busy restaurant.
I’m most of the time working six days a week, have very little free time.
Since 2020 March, because of Pandemic thing, we have been operating with skeletonized crew, and I have even less free time.
Now, Marin county is open for indoor and outdoor dining, the business is picking up, getting progressively busier, but with the same minimum amount of workers.)

Anyhow, it’s not the end of the world.
I’m pretty sure it can be fixed to pass.

And if it doesn’t, I’ll just start looking for a replacement engine, or another NA6.

[Howie]

I doubt you have a vacuum leak with those numbers.  Since I don't live in California I have no idea of how many times you can go through the smog test or what it costs but premium could cool things enough to get you through or if you could figure out a way to get a little more fuel in, like add a little bit of resistance to the coolant sensor.

[S21FOLGORE]

Thanks.

I had very hard Sunday & Monday.

Sunday was Mother’s Day, one of the busiest day for the restaurant business.

Went to work extra early.

First, I walked into the laundry room, to pick up the towels, finding the floor was all wet.
There was a huge pool of water.
The washer started leaking water.

Then, I found out the dishwasher is not working.
(It was working until the end of Saturday night.)

Called Auto-Chlor, the office told me the tech would come in around 2PM.
(At this point, it was around 12:30.)

Then, I plugged in a meat grinder, into the same AC outlet as the dishwasher, finding there’s no power.
Ran to the circuit breaker board panel #1 & 2. No, not in there.
Ran upstairs, open the door of the 3rd circuit breaker panel.
Yep, the breaker tripped overnight, somehow.

Way too many stuff, even before I start …

…. I came back home around  12:00 midnight.

Monday morning.
Woke up early, left the home at around 7:15AM, heading to Hayward.
Got to PR Motors just around 8:30AM. (They open at 8:30)

This time, they weren’t that much of a help.
(Not complaining or anything. That’s just how it was, this time.)

Basically, they pointed out spark plug wires were connected to the coils incorrectly.
(Basically, #1 & #4 were switched, #2 & 3 were switched)
(But, NA6 has wasted spark system, so it shouldn’t matter…)

And they suggested just fill the car with premium, and take another test.
If it still doesn’t pass, the car may need a set of new injectors, or O2 sensor, …

Anyhow, I drove back to San Rafael, took a test again, at the same place.

… and it didn’t pass.

The same thing happened.

Nox reading went up really hight at 25mph.

(15 mph- 4ppm, 25mph -997ppm.)

……

Went to Easy Automotive (in San Rafael), asking their opinion about this.
(NOx reading suddenly shoots up when tested at 25mph). they told me to go
to MSI Auto, which is located nearby, who is also STAR certified smog station.

Went there, explained what’s happening.
Left a car for half a day.

Nearly 5PM. they finished.

And here’s the result.

Smog passed

It passed, WITHOUT changing any single part that was suspected / mentioned here.

The same car, same O2 sensor, same everything.
Just a different smog station, different operator.

And Nox reading went down to 5ppm, from over 900ppm…

[koko64]

Faulty equipment at first smog station? Equipment out of calibration? Operator error? Operator being a douche bag?
If so, you deserve a refund.

[S21FOLGORE]

I'm pretty sure somewhere on the paperwork, there's a very fine print saying there would be no refund, etc, etc ,...

Anyhow, my first reaction when I was told about this unbelievably high NOx number at 25mph test was ...

"Really? Can it (NOx reading) can jump up like this???"

(IF, both 15mph and 25mph # were high, I wouldn't have doubted.
BUT, 15mph reading was 1ppm,
and 25mph reading was 809ppm.)

I tried twice, at this station, and pretty much the same thing happened.

It is possible that I have some sort of flapper type vacuum leak, that randomly open and close ...



...See you space cowboy...