I purchased my 1985 RX-7 from a county that required a dyno smog test, at 25 and 40 mph two years ago, and it passed. In my county, we go by the "less stringent" two-speed idle test, which doesn't measure NOx, only HC and CO. But it measures it at idle and at 2500 rpm with no load.

At 2500 rpm my car passes with flying colors, 1/6th the legal limit of HC and CO. Thus, I think my air injection system and catalytic converters are working. However, at idle, it seems to be running rich, nearly 6x the legal limit of HC and CO.

My fuel pump failed several months ago, and I installed an aftermarket fuel pump. I read that it can cause the float bowls to overfill if there is too much pressure, so I just installed a fuel pressure regulator and a gauge. I am able to regulate the pressure down below 3 psi. I also followed Sterling's method for setting my idle speed and idle mixture. If I lean out any more on the mixture screw, my engine stumbles. Wires & plugs are roughly 1 month old.

I just had them re-check the emissions at idle, and it's made no difference whatsoever. I'm still producing 6x the legal limit of CO and HC at idle. Is this because my car is running too rich at idle? Is that normal? Is it just impossible for a 12A RX-7 to pass a two-speed idle test? Can anybody help me? I only have a month before my registration expires.

I'm going to try going to a shop that has a tailpipe oxygen sensor, and see how it changes when I adjust the mixture. At the moment, there is NO oxygen in the exhaust at idle. HELP?!?!?!

 

i think the pressure needs to be 1 PSI.

 

start with the factory way of adjusting idle mixture, and then try your shop.

when you go too lean, HC's can go up, you get misfires, and sometimes the cats like to be richer and not leaner

 

Ya i would set idle the way the manual says to do it. If your float level is in the middle of the window when its running. Then fuel pressure is not a problem. I always had a problem passing when it came back down to idle from 2500rpm. Most if not all of your air injection works on decel. My problem was the anti after burn valve #1or2 was bad. You sure the leading and trailing are in time. 0 leading 20 trailing set at idle with both vacuum advance disconnected and hoses plugged up.

 

They perform this test at the smog shop (checking the timing and the timing advance) as part of the normal CA smog check procedures, and it passed. When I was buying my RX-7, the first one I tried to buy failed this test. The timing was set improperly and the advance system wasn't working, so it failed before they even stuck a probe up the exhaust pipe. The seller told me he'd get it fixed but then he told me he wanted to raise the price we negotiated, even though I said that was for a car that passed smog, so I looked elsewhere.

My car passed every test they threw at it except visual (because the EO number on the Cat got scraped off by the exhaust bottoming out on pavement, so I have to show them a new one with the EO number on it so they can confirm it is the right part) and emissions at idle.


Holdfast, I'm curious what your symptoms were with a bad afterburner valve. I've read about it and it seems like a bad afterburner valve would produce noticeable drivability issue, which my car has none (besides no 2nd gear synchro). I have noticed that one of my afterburner valves seems to be missing a hose (not a vacuum line, bigger). Can you take a picture of yours so I can see where it's supposed to be connected to? I hesitate to conclude that's the problem, as the car passed the dyno test at 25mph and 40 mph 2 years ago in the same condition (no hose). What problem did the bad afterburner valve cause you, specifically?

Zenobia, every other source on the internet regarding the 12A and the nikki carb suggests 2.5 to 3 psi. In any case, that's irrelevant, as I've found the sight glass and the fuel level is right on the money (in the front one anyway, I haven't been able to disassemble enough stuff to see the rear one). So I know it isn't excessive fuel pressure.

j9fd3s can you please elaborate on your comment about HC's going up with leaner mixtures? I thought that HC was unburnt fuel, and CO is not enough oxygen. I thought lean conditions produced NOx. Also, at idle the emissions test recorded no measurable oxygen content in the exhaust. If my emissions were caused by a too lean condition, wouldn't I be getting a nonzero oxygen reading?



A mechanic gave me the following advice: There should be a switch on the carb that indicates when the throttle is at idle position. This lets the emissions control unit know that the vehicle is at idle. If this switch isn't working, it may cause improper fueling at idle, check the function of this switch.

Does anybody know where this switch is, if nikki carbs have one?

 

So if the afterburner valve is the same mechanism as the shutter valve, then according to figure 4-64 of "Rotary Engine" by Kenchi Yamamoto, that means the disconnected side is just supposed to pull air from the air cleaner. So again, I don't think that's the issue.

 

the 81-85 cars have a throttle position sensor, and it does run the air injection system , its on the front of the carb, plunger style, with a 3 pin electrical plug.

for HC's, if you are too rich the HC will be high, and as you lean it out, they go down to a point and then come back up. that point happens at a richer mixture with these engines than it does on a normal piston engine, so often they do better if they are slightly rich rather than slightly lean.

 

Its a carburetor so its control by vacuum. Most if not all emissions on this car work on decel or when the engine is off. Evap. This old mazda guru once told me that look at it like a watered down glass of wiskey. Thats how mazda dealt with the emissions. It the same whiskey in the glass just watered down with the air pump. Its when that air pump comes into play that matters. On decel there is more emissions thats why air pump works on decel. The problem i had with aav2 was high hc and nox on decel only. If u ever open one up u will see there is more than one valve inside . They all looked good. Car ran flawlessly. Newly rebuilt motor. But i bought one new anyway cuz it wouldnt pass and was a gross polluter $600 back inthe day was alot for me at 18yrs old. But it passed . Now i havent try this out myself but the guru mazda guy told me that if u gut the anti after burn valve have the air pump diluting the exhaust all the time it will pass no matter what. On the out side the smog tech cant tell its gutted. But he lived in Oregon where the smog laws aren't like california. Take that with a grain of salt.

 

Do you have any advice as to how to test if the throttle position sensor is working? It's been suggested to me that the emissions controls might be working improperly if they don't think the throttle is in the idle position when it is. I need to confirm that the computer is receiving the correct signal regarding throttle position at idle.

I'm not sure why a lean condition would cause high HC, but I'm sure that a lean condition wouldn't cause CO, and I'm getting excessive amounts of both. Carbon would rather form carbon dioxide than carbon monoxide, and it only forms carbon monoxide when there isn't enough oxygen.


After talking to several sources, it sounds like what I need is to find somewhere with an exhaust gas analyzer to read my exhaust gasses while I play with the mixture screw. I don't suppose anybody knows somewhere in the SF bay area or Santa Cruz where I can use one?

 

not really, the factory test is silly Foxed.ca - Mazda RX-7 Manuals

you can make sure that the Air Control Valve (ACV) is in 'Port Air' for the test. the air pump air should be going to the exhaust ports on the engine, the round port on the intake manifold.


you're thinking too hard about this part, set the mixture so it runs the best, and go about 1/2 turn richer.

i know most smog places can do a pre-test, or just find a guy who will do a free retest.

 

The place I went does a free retest, but just one. It failed my first test (how I knew there was a problem) and then I convinced them to just test the idle and not consider it a retest after I adjusted the idle mixture, and it failed just as badly. The smog place tested the ACV the first time, and said it was functioning correctly. But I think I found the issue:

I went to test the throttle position switch yesterday... and I don't seem to have one. The female connector from the harness with the wire colors listed in the FSM isn't plugged into anything, and there doesn't seem to be any male connectors sitting loose around that side of the carb. Furthermore, what I think i've identified as the linkage that attaches the position switch to the throttle assembly seems to be disconnected. It's hard to tell because the illustrations in the FSM aren't that clear. There is a rod which comes up on the firewall side of the carb from the throttle mechanism, rising up when you press the throttle pedal. I think it's supposed to pull the throttle switch mechanism down when the throttle closes and allow it to move upward when the throttle is opened, but the linkage and the rod are disconnected. I will upload a picture later.

If I understand correctly, the position switch is there to tell the computer when the car is idling, and without it being connected, it never gets the idle signal. That might explain why the ecu isn't controlling the emissions at idle.

Does anyone have a picture of the throttle position switch installed? Also, where can I get one, since it seems like mine is missing?

 

This information conflicts with page 4A-37 of the 1985 FSM. The FSM clearly shows a 2 conductor connector from the car to the throttle sensor.

It doesn't show where the throttle sensor is, so it's possible i'm mistaken about the disconnected linkage. Again, if anyone can take a picture of their throttle sensor installed on their nikki carb, it would be greatly appreciated.

By the way, here is the picture of the smog test report, for reference. Don't worry about the fuel cap or the "modified" catalytic converter, I have a new fuel cap and the only reason he couldn't mark the cat as legal was the EO number was scraped off. I have a new one to show him.

 

the test connector is 2 wire, sensor is 3

sensor looks like this, bolts to the metering block of the carb and literally touches the throttle linkage https://www.atkinsrotary.com/store/8...0-18-910B.html

 

I know this is a stupid solution but can't you somehow modify the carb to force your car to idle at say 1500 RPM? My 2010 Sentra idles at 1200 so unless the shop knows your car idle's at 600 normally, it could theoretically pass

 

Ca. smog is program is one of the strictest there is,If idle rpm was @100 over specification,they'd let that slide. That car by vin# is in their system from previous testing and so are the specs it tested at. Trying to put it thru with twice spec idle speed in attempt to pass won't fly.
Whattsa matter with your Sentra that it has 1200 rpm idle speed,that's not a factory spec either.

 

It varies from 800 - 1200 depending on the temperature. No idea why

 

the Ca smog machine knows the idle speed, and it gives you a little margin, but at 1500rpm it wouldn't even let you start the test

 

Hey all,

Thank you for the input. At this point I got a valid smog cert by registering at my father's house, so they did the dyno/nox test and it passed with flying colors. I'm guessing a throttle position switch would be required to make the idle pass.