kenneth_ugalde

Hi,

I have failed emissions test twice in a month.
The car is an 86 N/A with no major mods.
It has a single cat( brand new Magnaflow) , air pump and ACV. Rats nest is intact except for EGR valve (block off plate in place of valve). I just installed a Crane Hi-6 that I had bought a while ago and made no difference emission-wise.
It is only measured at idle and I get CO5.4%, HC 1490 ppm CO2 10%

The weird thing is that the idle mixture screw its to full lean and the car still runs well. It measures within spec with a multimeter. It seems that it´s running rich at idle. when I move the Idle mixture screw to rich it gets worse. I remember that some time ago, I could make the car almost stall if the screw was too lean.

I suspect a few items:
Old fuel Injectors that might be allowing to much fuel in
Bad fuel pressure regulator. I have buy a guage to see what the pressure @ idle is now.
Bad air pump. Not enough flow of air to the ACV
or bad Air control Valve.
On this last item I just recently took it down, cleaned it and tested all diaphragms. They all work.

It really baffles me why the Air mixture screw does not make the car run bad at full lean.

Any ideas what might be wrong?

lduley

iTrader: (1)

I'm not 100% on how a EGR works, but i know they are vital to passing emmisions

IIRC, with the egr removed, isn't the computer dumping more fuel because it isn't using exhaust gas to burn instead of using less air?

kenneth_ugalde

Not really. EGR valve is only allowing gases back into the intake during deceleration in specific conditions where it doesn´t affect engine operation.

jjwalker

Not true.

The EGR is there to reduce combustion temps and lower NOx emissions. EGR will actually cause more HC because there is less 02 in the intake stream. EGR doesn't even operate at idle, only under engine load.

Since you are failing the HC test, It's the cat you have. If it doesn't have a split air tube like factory, it isn't going to work. If it does have the split air tube, then I would suspect the ACV.

If you still have an air pump, you can hook it to the split air tube and bypass the ACV, just need some plugs and a hose.

kenneth_ugalde

The Cat does have an air tube.
To make the pumped air go directly to the cat all that´s needed is to disconnect the switching solenoid valve and air will be sent to the cat.
That didn´t help. I need to figure why so much fuel is being dumped at idle. I´ll get a gauge tomorrow to measure the presure in the fuel lines and rule out a high fuel pressure condition.

MjhRotor

iTrader: (1)

Having high hc and co looks like a possible slight misfire. High co alone leads more towards rich. Without seeing the car in person though it's hard to say.

Egr shouldn't affect either of those in any significant way and certainly not at idle.

I would suspect the cat or that you really are misfiring. If it is to lean this can cause small intermittent misfires that can cause these numbers. Normal afr for rotaries at idle is pretty rich. As previously mentioned the air pump properly diverting air is needed. Also I have not seen anyone mention timing yet be sure it's on the money.

j9fd3s

iTrader: (3)

on these cars the EGR does nothing.

high HC and CO on these cars is an indicator that your first stop is to check the ACV, and then the TPS, as the TPS controls the ACV. the ACV must be in what Mazda calls "port air" which is fancy talk for the air pump air to be going to the exhaust ports. the split air pipe is not used during an emissions test.

step 2 is to check the o2 sensor, its really simple to build a little LED tester to see if the O2 voltage is switching when the car is in closed loop, over ~1500rpm

DeaconBlue

iTrader: (31)

If the car does not have the pre-cat, it is highly unlikely that it will pass the HC and CO limits, even if everything else is present and functioning correctly.

RotaryEvolution

iTrader: (30)

step 3 is to drill out the AFM blind plug and count the turns to full clockwise stop, turn it back out to the original position and then continue backing the screw out and see if the engine begins to hunt for idle indicating a lean condition. you may need to jumper the fuel pump test connector as bypassing too much air through the AFM will cause the pump switch to close. this is a hack, not a proper fix and only to bandaid the AFM being faulty or another slightly more complex issue.

only other reason besides a faulty AFM i can think of is a restriction in the fuel system return, causing high fuel pressure and a rich condition.

a large discrepancy in rotor compression can also cause it, say 15% or larger variance in compression from one rotor to the other.


those numbers are far too high for the ACV to clean up anyways folks, it would have to be in the 500HC/2%CO for the smog pump to be able to take over the rest. the test is indicating the engine isn't burning all the fuel that is going through it and that is either an engine issue or engine control issue.

kenneth_ugalde

To reply to previous comments:

TPS is properly adjusted.

EGR does not affect idle emissions.

Ignition timing is properly set.

Misfire is not a concern since a Crane Hi-6 is fitted and is set for multi spark @

kenneth_ugalde

I wrote an elaborate answer and this F...... thing only posted the first few lines.

Bottom line is that all settings are good(TPS, Timing, Etc.) ACV was checked and seems to be working fine, No misfire since the Crane HI-6 gives multiple sparks below 3000K RPM. Fuel pressure was tested this morning and matches the specs in the workshop manual. Only things that have changed are a used ECU and AFM that were bought from a low millage car since the previous ECU's (4) were damaged by a refurbished AFM bought from Rockauto.

The AFM I have now is in great condition and stock (original plug for by-pass is still in place). I have thought of many possible culprits for this problem and can only think now of: a faulty ACV although I checked it and seems to be fine, worn/too old injectors that may be allowing more fuel to pass than new ones, a worn Air pump that is not pushing enough air into the system, and finally a cat that's too small for the engine.

If no more suggestions are received, I will try to adjust the AFM by-pass, Although I would really like to keep mine stock as it is.

RotaryEvolution

iTrader: (30)

you can always revert the air bypass screw back to its original setting.

DeaconBlue

iTrader: (31)

You are not running pre-mix, correct?

I have know a few folks that out of shear desperation have resorted to the following method to get a car to pass with high HC and CO readings - I do not recommend this, nor do I condone this and if you do this, you do it at your own risk...

They drain the tank, then in a 5-gallon gas can mix up say a couple gallons of 87 octane with a gallon of E85 (or straight ethanol if you don't have E85 locally) and toss it in the tank. Also if you are pre-mixing - don't add any to that batch. She may run like ****, but drive her to the test station, see if she will pass. If she does then drain the tank again and fill her back up with fresh gasoline.

j9fd3s

iTrader: (3)

not true. i live in CA, and have had to smog 3-8 cars a year for the past 20+ years, and i've smogged Rx7's with and without precats, and the precats seem to make no difference once the car is warmed up

RotaryEvolution

iTrader: (30)

precats no, additional 3 way cats do help though.

ACR_RX-7

iTrader: (1)

Based on your CO2 level of 10%, you have poor combustion. This is supported by the 1400ppm HC you have. HC is raw fuel. You have a misfire. You also are at 5% CO, which means you are rich. Way rich.

Have you checked compression? Low compression will cause poor combustion. I would love to know what the car is doing at 2500 rpm, but I noticed you said that they only test at idle.

The cat is also way too small for the engine. Magnaflow cats are among the worst out there for efficency. The stock FC cat is huge and is dual chambered, plus the 3 precats. A cat will not clean up the output.

You need to check the oxygen sensor for operation. If its reading low at idle, but is reading pig rich on the test, the ECU is trying to add fuel to bring the O2 voltage up. Hopefully it's something that is simple, but don't rule out a misfire just because you have a Crane box installed. That means nothing, especially since it didn't make a difference. You could still have a faulty coil, plugs, wires, injectors, etc.

j9fd3s

iTrader: (3)

i once put a T2 with no cat or air injection on a smog machine, and it was ~3,000ppm of HC's and like 5-6co. with the cat and air pump, HC's were 187, and CO was around 0.

1400ppm HC's can be achieved by just having a bad ACV...

ACR_RX-7

iTrader: (1)

Good to learn. I worked as an emission diagnostic tech at a shop here in Washington and never encountered any rotary vehicles in for emissions failure, so I didn't know that they blew that dirty. When I was in tech school, I did hook up my '85 FB up to the gas analyzer and pulled the probe out once it got over 3k PPM HC. I didn't feel the need to clog the filters in the machine so I aborted. Where I live, we don't have emissions testing, so I didn't care how dirty my FB was.

All of the cars I sniffed were piston engines, so in my experience on a piston engine, the numbers he had listed would indicate poor combustion. It just comes back to the fact that all of my training in emissions failures were on piston engines. I actually brought up rotary engines in one of my recertification classes and the instructor hissed and poo-pooed all Mazda rotary engines as the work of the devil and that they are impossible to keep clean.

RotaryEvolution

iTrader: (30)

difference is, this car has a cat and is putting out 1500/5

not 1 piece of malfunctioning smog equipment would cause that. now if his cat had broken apart and got spit out, then it might be an applicable comparison.

Turbonut

iTrader: (1)

Make certain trailing plugs are firing. S4's are problematic, so disconnect the leading igniter and car should still run. A timing light on the trailing wires cannot detect whether the plugs are actually firing, depending on the light.
I've passed emissions for years with no precat, a Bonez cat and functioning air pump.
Make certain air is going into cat at idle, some use an electric pump from a Vette. In Jersey they do the test when the car is in gear @ 2000 rpm, not at idle.

RotaryEvolution

iTrader: (30)

a 2000 rpm test would be cake, its the idle test that fails most of these.

fidelity101

iTrader: (11)

EGR typically affects NoX emissions anyways.

j9fd3s

iTrader: (3)

yeah the old idle test was HARD, the new dyno test is easy, if the ACV and o2 sensor is working, it'll pass, you don't even need much of a cat

Turbonut

iTrader: (1)

Been away from the statistics for a while so not certain as to what state, if any, does the test at idle,
as even California, after the visual does the test at 15mph and 25mph last I heard.

RotaryEvolution

iTrader: (30)

california has 2 different areas, enhanced and non enhanced. enhanced are in heavily populated areas and is a loaded dyno vehicle speed 15/25 based test. non enhanced is an unloaded stationary idle and 2500 rpm engine speed based test.

las vegas had a similar unloaded test, but the passing figures were about twice as lenient as california. but with rotaries you're either really clean or really dirty, they really don't often have much wiggle room.

the OBDII cars are actually easier, since it is a simple scanner plug in and emissions readiness read which can actually be emulated. it's all just the ignorant heavy hand trying to wipe older cars off the road still. at least vegas gave the option to keep your car and register it as a classic, historic or rod while limiting your usage.