87 N/A Emissions
 

Hi,
I just failed emissions on a 87 Rebuild.
I bought the car and overhauled it as a winter project. I am trying to put everything in in stock configuration.
Yesterday I failed the Virginia emissions inspection on

15 MPH DYNO
High HC - 248 Limit 140
CO% .43, Limit .79
NOx ppm 238, Limit 1097

25 MPH DYNO
HC 261 limit 135
CO% .35 limit .83
NOx ppm 179 limit 179

The car itself seems to run smooth and has plenty of power but it does give off an odor of exhaust fumes even whilie idling.

I have seen other posts regarding strong exhaust fume odors. What is the most likely cause? (I have dialed down the pot on the pass side strut tower but it doesnt seem to have helped that much.

I have started to go through the procedures in the FSM and have not found anything broken or too far out of wack. Although the idle speed screw seems like it has to be bottomed out to bring the idle to 750 rpm.

Also I wired up the two 12v LEDs for ecu diagnostics and they show no error codes.

On the dyno, (steady state crusing under load) what is the ACV doing? Is all the air supposed to be going into the thermal reactor or is some of it diverted back to the cat?

Is there a post anywhere containing a comprehensive write up on the emissions system detailing both functionality and diagnostics? (In my opinion the FSM works on the component level does not explain system functionality very well.)

I don't want to sound rude but rather than pulling a fast one to get around the inspection, I'd rather fix root cause. Please no alcohol or piping right to the cat suggestions I have seen them posted here before.

I do believe the cat only gets its share of the ACV air in 5th gear, activated by the switching solenoid on said ACV. Most of the remainder of the time, the ACV is dumping air in the exhaust port air system, or is dumping it overboard via the hose/ air silencer setup. I don't remember exactly what does what when, though, and I don't have the books here with me...

piping right to the cat? well thats where the smog pump goes if thats what you mean.
how old is your cat?
the NOx limit is a whole lot lower for 25mph, eh.
well, youre close to passing. the numbers are hard for me to come up with a conclusion. i dont have quite the knowhow or understanding of the full emissions system.
one thing i can say, for the 25mph test, is that running leaner causes NOx to go up. that makes me think you're not running excessively rich, but that something else is amiss. wish i could help more. good luck.

Sorry I had fat fingers the NOx level limit at 25MPH is 999 ppm. My problem is the high HC.

If the problem was bad injection I would expect the nox to be way up.

haha, there you go. the only thing that i know (i stress I KNOW) that causes NOx is heat. heat comes from running leaner. the more HC, the less NOx; less HC, more NOx.
i would rather you know the problem, if there is one, than correct it via an S-AFC (or whatever fuel controller). do you happen to know the gear/rpm these tests were done at? (i'm not sure what the standard is if there is one.) two things that i think of is 1. mazdaspeed7 explained low speed bucking as a factory tuning error which leads me to believe a bit of excess fuel (from improper tuning) could be involved, naturally (though, as always, i could be wrong.); and 2. when i showed my auto professor my failed emissions scores, he said that the numbers looked off. again, makes me think there's strange tuning error where the car likes to run rich. i really dont know, those things just come to mind.

Having said all we have so far, I do know of a couple of guys on this forum that have passed because they "rigged" the ACV to dump continuous split air to the cat- something to keep in mind if all else fails. Gotta remember, these ain't the most efficient engines in the world...

That is a good question about the speed/gear ratio. I was going to ask what they are supposed to be myself but didn't want to start rambling. From reading these posts different things are supposed to be happening at various rpms and gears.

My problem appears to be odor at idle and during tests at steady state, high hc.

I suspect that I am not putting air to where it should be to burn up the unused hydrocarbons.

and yet, some still pass with flying colors.
what is the most efficient engine? i mean high power, not honda hx (avoiding hybrids/fuel cells/etc).

There are several ACV-related checks in the Haynes & FSM, have you tried these yet? In fact, IIRC, just doing the checks step-by-step will clue you in on what happens when...

I am working through the checks in the FSM. Also, Hailers posts on this site to be very good. I also have a chiltons but no haynes.

the air is pumped into the cat which uses it to create more pleasant chemical structures. it oxidizes the particals (as many as it can) before they leave your cat. first is oxidizing reduction, then oxidizing (you may have read this in another thread). thats what "burns up" the HCs. they're not actually being burnt, but made into another compound. HC would ideally be H2O and CO2, but in reality you'll still get HCs and probably a bit of CO.

as always, if i say something wrong and someone notices, please correct me. i just know very few people chime into emissions discussions.

Ya know, that's another good question---How old is the cat? If it's OEM, it can't possibly be doing much in the way of chemically converting anything anymore...Probably the root cause of the problem at hand, if the ACV's doin its thing...

also depends on the mileage (which is probably still way overdue; i dont know their year lifespan). my cat, at ~150K, failed me in all 6 tests, whereas the new one itself passed me in 4/6.
his readings are awesome. low CO and fairly low NOx, its just those HCs. thats what makes me think he could take some fuel out. in fact, its pretty much a known fact you can take fuel out from the factory tuning. how much may be debateable.

I don't know the history on the car. The exhaust system including the cat does look like it has been replaced recently.

Do the guys that block off their ACV have problems with an exhaust fume smell?

Is the air to the cat and thermal reactor proportioned or is it all or nothing to either the cat or the thermal reactor?

It's not an "all-or-nothing" setup, there are different internal passageways and solenoids in the ACV, so yeh, I guess you could call it "proportioned...

When I installed my completely open exhaust system, I couldn't stand the smell, and I would get on my kids about getting too close to it for fear they're inhaling nasty noxious fumes. I decided to rig the ACV (via direct vac line to the relief valve, since the relief solenoid is no longer with us) to dump non-stop into the port air system, and that has helped a little. My split-air system is no longer with us either :)

Cool, hearing that others have fume problems shows I am on the right track (or at least not on a wild goose chase.)

Any other thoughts please let me know.