Phu5ion

So I'm failing emissions with high carbon monoxide, and it keeps coming up as being air control valve related. I was able to get an emissions exemption from the state 2 years ago and they thought it was the ACV as well, so that winter I tore into the engine, pulled out the ACV and bench tested the unit. All the valves and solenoids on the ACV checked out, and I also retested the secondary air switching and bypass solenoids, and they all operate within spec, triple checked my vacuum hose diagram, and put it back together.

I can see the clutch engaging on the airpump, but the only thing I haven't been able to verify is that the airpump is putting out pressure. I've asked my mechanic to check that first before disassembling the intake system. Is there anything else I could have missed?

Gen2n3

iTrader: (1)

Could your cat be getting clogged? Do you pre-mix? There could also be a small leak. What about the bypass air tube coming off your cat?

Phu5ion

* Clogged cat - The main cat was replaced two years ago, and the emissions numbers are near identical now as they were then.
* pre-mix - I run a very small amount of pre-mix (~4oz per tank), but that was something I started doing last year, and the numbers haven't changed for better or worse. Good point though, I will top it off to dilute as much of the oil as possible.
* air leak - After I got home I did find one of my silcone lines had split, so i'll replace and retest.
* split air - it's hooked up.

arghx

iTrader: (3)

First of all, this is an IM240 test. It's stricter than constant mph tests, although it is still done on a warm engine.


Since it is passing NOX and HC, you should get a new O2 sensor. They degrade to the rich or lean side over the years. An OBD I car isn't smart enough to detect a bad one. It's probably reading leaner than the mixture really is, so you get CO emission breaking through the catalyst. On an OBD 2 car the front and rear sensors cross che like each other and diagnose the cat as well.

Make sure they thoroughly warm up the engine before the test.

arghx

iTrader: (3)

Ok, let me continue with this line of thinking. You've checked the ACV many times, so I'm going to assume it's ok. You haven't replaced the o2 sensor or you replaced it and forgot to mention it.

Let's review each emission and the factors that contribute to it.

HC emission: HC emission is related to unburned fuel, besides just having a dead cat. It's especially high during cold start where the fuel doesn't vaporize in the intake ports very well. It also occurs during misfire from unstable combustion. This test is a hot test, so assuming the engine was warmed up correctly, the wall wetting is minimized (at least for purposes of this test) and you don't have to worry about HC from bad atomization.

Misfire from unstable combustion can be caused by bad tip in fuel, like a tip in hesitation. That's TPS related, or a bad tip in tuning if it's not a stock ECU. A pre-Rx-8 rotary needs the air pump to stabilize the combustion and reduce misfire at idle and low load because the port timing creates a strong overlap in addition to the gas leakage through the older sealing system. So if you don't have a working air pump you're going to have higher HC.

NOx emission: NOx emission is caused by high combustion temperatures and lean mixtures, or just a cold/dead cat. It's usually highest when oxygen (due to lean mixture) passes through the cat without being reduced into less harmful compounds. It can also be produced at medium loads, when the throttle is open enough to accelerate but not enough for the mixture to richen up. That's what the 150 to 230 second portion of the IM 240 test is supposed to test. It's at a higher vehicle speed than a typical steady mph test in order to load the engine down into the high NOx producing operation area.

CO emission: the number 1 contributor to high CO is rich mixture. For an Rx-7, it's either a non functioning air pump or a bad O2 sensor, OR on this type of emission test the driver being very aggressive on the tip in and the ECU starts to richen up due to boost. Typically a non functioning air pump will also result in increased misfire, so you get high HC with your high CO, but low NOx because the mixture is rich. In your case, the HC is higher than it should be, but it still passes. On a steady mph test the driver doesn't matter, but on a transient test like this see if the driver will be kind enough to drive easy on the acceleration portion of the test. See if he will be easy on the gas pedal and lag behind the target mph trace a little bit. The EPA doesn't like that on official tests but this is just some guy at an inspection station driving your car.

this chart from the 2nd generation FAQ can help guide you:



TL;DR replace the o2 sensor and ask the driver to accelerate as gradually as he can get away with so it doesn't boost much and therefore doesn't richen up.

j9fd3s

iTrader: (3)

i haven't gotten an Rx7 to fail with high CO, so congrats! um the bad o2 sensors i've seen have so far all had high NOX, but i agree with Arghx, try an O2 sensor.

Denso 234-1040

arghx

iTrader: (3)

does that Denso part number plug right in?

all your tests are idle and steady mph aren't they? In that case there's no risk of the driver giving it too much throttle. Experienced emission certification technicians can drive the mph trace on a transient cycle almost perfectly. The EPA actually has a formula to calculate how aggressive the driver was on the test because it is so important for CO emissions on acceleration. Expensive emission labs can give you a datalog showing the emission on a second by second basis. That's how you find out where in the test you failed.

Gen2n3

iTrader: (1)

Good to know!

If you are looking for an exact replacement O2 sensor, consider this website: Oxygen Sensor Depot
They have the sensor with OEM connector at reasonable prices. I also understand that Rock Auto has it available.
A recent thread of mine that discussed O2 sensor replacement: https://www.rx7club.com/3rd-generati...ement-1104560/

Side note: what the hell did IB do to the reply box? Damn it, why fix something that wasn't broken!

Phu5ion

Arghx is correct, Colorado uses a IM240 rolling test. Also, I did forget to mention, when I had the cat replaced two years ago, the O2 sensor was also replaced, and the spark plugs and air filter were replaced this spring. Now that doesn't mean the O2 sensor was put in correctly, and my shop is checking that out too. They did buy a "universal" unit, so I don't know if the stock connector is still in there, I'll check that out as well.

The tech who drove the car during the test was a little too aggressive with the accelerator and was repeatedly out pacing the dyno, and I do try and go during low wait times so the engine is good and warm when the test begins, but that's not always in my control.

If it helps, I've included the measurements taken during the test.

EDIT: As I'm looking at these graphs more, as Arghx mentions, the HC seem to spike under deceleration, like the fuel injectors are still firing (stock ECU). Is that normal, or also a byproduct of a misbehaving O2 sensor?

j9fd3s

iTrader: (3)

yep, the universal one is a different number (234-1000).

in CA we have three different tests depending on where you live, either none, the IM240 test, or third the stationary idle and stationary 2500rpm tests.

by far the hardest one to pass is the third one. the idle test is really really hard, stock FDs won't pass this pretty much no matter what.

the IM240 test is really easy, its a high enough rpm ~1800, where its in closed loop, but its still in port air so its right were all the emissions equipment is working.

just as a note the split air pipe isn't used during the test, and it can be removed, its kind of a red herring anyways.

j9fd3s

iTrader: (3)

wow thats cool, we don't get anything helpful like that here....

so far O2 sensors do two things, they get lazy, and/or just completely fail.

my friends FC had a failed one, and it was too lean, NOX was really high, everything else was low
my miata had a lazy one, and it was also lean, NOX was too high, but just by a bit.

i haven't seen one that failed in a way where the car was too rich, but i'm sure its been done

j9fd3s

iTrader: (3)

also it could be a bad/failing water temp sensor, it has a rather large impact on the mixture, and i have seen it where its broken and alternates between, fully rich, fully lean, and reading correctly.

if its open or short it will throw a code, but if its just slow/lazy the ecu may not figure it out.

jza80

iTrader: (32)

Just throwing this out there, but along the lines of the ECT failing if the coolant temp is too low due to an aftermarket or stuck open thermostat, the OE Mazda ECM may keep the engine in a partial cold start enrichment mode causing elevated CO. Not sure if this applies to a hot running car like the FD, but I found this exact thing on a customers car we had procured for IUVP testing - ran the car on the FTP test and it failed miserably for CO. Did some checking and found that the owner had installed a 160° thermostat and the car never fully exited cold start enrichment.

mdp

You said that you replaced the catalytic converter and the O2 sensor two years ago and you got a two year test exemption. So, two years ago the car did not pass with a new cat and new O2 sensor?

johnchabin

iTrader: (2)

Stock cat?

I went through YEARS of this, gave up, but came back and passed in Colorado. With a Bonez high flow!

I "heard" a bit of denatured alcohol in the mix doesn't hurt.

if you go new O2, you might consider wideband with both 0-1 and 0-5 v outputs, you can kill 2 birds that way... good luck. It sucks.

arghx

iTrader: (3)

Keep in mind that there is a delay in the second by second graphs due to the time it takes for the gases to travel.

I think a lot of this is coming down to the driver. How does the gear shifting work on this test? Does the driver follow a shift schedule or do they decide on their own when to shift?

see if you can get a different driver or go to a different inspection station.

TomU

iTrader: (11)

Has the air pump been ruled out? And do you have a down pipe. Usually you can pass w/o the pre-cat, but not sure in CO

The fuel purge system sometimes messes with emissions also

I would start with a stock 02 sensor then try a different station

arghx

iTrader: (3)

OP can you give us a list of every engine mod you have? I have been assuming it's stock everything except a downpipe. Do you have a stock ecu, stock boost control, all that?

Phu5ion

Ok, a lot of things to reply to here, I'll try and catch them all.

j9fd3s & jza80 - water temp sensor is new, but I decided to go with a lower operating one. I've also been dealing with an overheating issue. The stock temp gauge never hits the upper white hash mark, but it is rising from it's 9-o'clock position under spirited driving. A pressure test revealed a small pinhole leak, which is getting fixed as well. I just don't know if a pinhole leak would be enough pressure lost to effect the cooling system that much or if it's the fact that the Silla radiator I have just doesn't have the cooling capacity. Anyway, I don't want to sidetrack the thread from the emissions failure, unless it's a symptom.

mdp - correct, the car didn't pass two years ago either, the numbers where almost identical to two years ago

johnchabin - yeah, I've heard those things about alcohol too. I'd rather not have to go that route, but we'll see. I'd love to go wideband right away, but I need to read up more about it.

arghx - hard to tell, but he seemed to follow the prompts to shift pretty accurately. With the 3" exhaust, I have been boosting to about 12-8-12 psi

TomU - haven't heard back about the airpump yet. I clamp off the purge lines. I did try a different station last time and readings were higher.

My car is pretty stock, I've mostly focused on reliability mods:
* 3" exhaust with both pre-cat and main cat (long story short, the dealership I bought the car from put a pre-cat in to try and help with emissions)
* Rotary Performance SMIC
* 180 degree thermostat and 185 degree fan switch from Pettit
* aluminum AST

TomU

iTrader: (11)

So the only thing not stock is the SMIC, AST, T-stat, fan switch, and O2 sensor

It should pass (the prior fail rules out a testing anomaly).

Since you've ruled out the control system, my bet is on the O2 sensor and/or the air pump

arghx

iTrader: (3)

Oh. There's your problem. turn the boost down! try turning off your boost controller so it goes back to base pressure at the precontrol actuator. Or go back to stock exhaust and stock boost control system. The stock boost control and stock fuel maps are specifically tuned together for passing emissions tests.

when you add more boost you add more CO, but only during acceleration. It won't ever show up in these constant speed tests that most cars go through, because the engine isn't under enough load in those cases.

also, these transient emissions dynos simulate road load more accurately than a dynojet. The road load calculation, at least in certification tests, is for worst case vehicle test weight. That loads the engine down. So if you have a base model it will actually load the engine down as if you had the slight extra weight of a touring model.

johnchabin

iTrader: (2)

The guys at County Line & Colorado were RX-7 fans and kept it out of boost. It helped.

Guess that’s a bit of a haul for you.

mdp

One other general tip for this type of test is to minimize rolling resistance. Make sure your rear tires are at least at the recommended pressure. It never hurts to pump them up to the maximum psi rated on the side wall for the test. It can make the difference if the car is right on the edge of passing under load.

Phu5ion

Forgive my ignorance on boost controlling with an essentially stock setup, I'm currently reading up on it from Robinette's page, it sounds like for me boost is limited based on the restrictor pills in the wastegate control and turbo precontrol lines. When I did the vacuum lines I did reinstall the pills, but they did not fit as snugly as the stock rubber lines. Could they be rotating in the line, effectively limiting or stopping the actuator from doing it's job? My first thought is a couple of zip ties could help hold them in place, sound reasonable? Or if I decide to go with MBCs, what are some decent, reasonably priced options?

Phu5ion

Thanks, I'll check them out, I heard Precision Imports at W. Hampton and Federal is supposed to be good too.

EDIT: oh you mean the air care station, might be worth a shot. It's definitely out of my way but if I keep having trouble with the golden station I might make the trip.