"Why is this engine so damn complicated??" Part 2: Emissions controls
 

If your boss came to you and said, "here, take an engine with some inherent emissions problems and make it meet these new standards. But you can't redesign the basic architecture of the engine, you have to reuse a lot of existing technology, and you can't go over budget." To make things even more complicated, a major foreign market has tougher emissions standards than your country does.

So what would you do? You'd look at the previous emissions control designs, try to simplify or enhance the existing stuff in a few places if possible, and then add whatever extra crap may be needed to meet the standards and stay within budget.

This article how and why Mazda designed some of the complicated and ultimately unreliable emissions control systems. Special attention will be paid to the precat and the airpump, with the airpump's related system called the Air Control Valve (ACV).

Problems and Hurdles

So what emissions problems did the factory engineers have to solve on the FD, either by reusing older designs or developing somewhat new ones?

1. How do we minimize emissions while the catalytic converter warms up?

This is often the trickiest emissions hurdle for many engines, and is the reason why many sports cars of that era had so many restrictive catalytic converters (Vr-4 for example). A 3-way catalytic converter (called 3-way in part because it traps 3 different types of emissions) is employed as the main cat on the FD and the older Rx-7 13B's. That's a pretty common architecture used in a most cars now. But a converter has an effective range of operating temperature.

To illustrate the importance of warming up the cat, here is a page out of the 2nd gen service highlights document which explains the operating range on those older models:

https://www.rx7club.com/attachment.p...1&d=1243260960

Emissions standards are tougher in the US, so Mazda had always needed a cheap way to get the converter up to temperature quickly for only USDM-compliant cars. The Accelerated Warmup System, a valve that brings in extra air to idle the car up to 3000rpm, was employed in older 13B's and carried over to the REW. That system is just a solenoid valve and a simple logic circuit. On a production line, that's not a big deal to implement on some cars and not others. It solved a problem cheaply, but we all know that revving an engine that high when cold can't be good for its longevity.

Still, to keep emissions down while the main cat is still cold, Mazda used two precats on the older engines (both USDM and JDM). They appear to be the same basic design as the main cat, but they are designed to only work as the engine is starting up.

https://www.rx7club.com/attachment.p...1&d=1243262049

The old precats didn't last forever, but they definitely outlasted the FD's single precat. But why is that?

https://www.rx7club.com/attachment.p...1&d=1243262613

Now I'm no expert on catalytic converters, but a quick google search reveals that "monolith" is a standard design for a converter. Whatever "metal" is, it's different that most stuff out there, and it's different than the old precats. But here's the killer: the precat was designed as a filter. And what do filters do? They pick up particles. The more effective they are at picking up particles, the faster they clog up, generally speaking. Get it?

The problem with the stock FD precat is that it worked too well! Here is one of those situations where I think Mazda meant well, and could have chosen a more reliable/durable design but didn't because they felt they wanted to maximize the performance (as in, the emissions reduction capability) of the component. It's the same deal with the interior. They put performance (weight savings in that case) over usable life--and we pay the price.

Many modern diesel engines (like the latest generation of Ford diesel V8's) are dealing with this type of problem with emissions equipment as their particulate filters clog up prematurely.

2. How do we keep the catalytic converter running at optimal efficiency, given the unusual characteristics of the rotary engine?

The peripheral exhaust port rotary (13B-REW and earlier) likes to idle or otherwise run richer than gas piston engines in a lot of the low-load operational range. After that rich mixture combusts it needs to be diluted with fresh air (leaned out) so that the catalytic converter can operate near the 14.7:1 AFR range where it is most efficient.

The air pump usually pumps air right into the exhaust port area ("port air" in Mazda's terminology) and before the factory narrowband oxygen sensor. That oxygen sensor tells the computer if the mixture that is about to enter the cat is richer than 14.7:1 , leaner than 14.7:1, or right at 14.7:1 , but isn't completely precise (the Rx-8 uses a factory wideband before the cat). Under some conditions (usually on the highway with medium throttle position) the air pump will put air directly into the cat to reduce NOx emissions. It's not that important to know how all that works.

3. How do we direct the air form the airpump into the exhaust ports or catalytic converter, while keeping the cat in its proper operational range of temperature and AFR?

That's where the "ACV" or Air Control Valve comes in. It is a series of mechanical valves controlled by solenoids. Some of those solenoids are on the ACV itself and some are located in the rats nets/solenoid rack. The ACV directs air through passageways in the engine to either the exhaust ports or out to the catalytic converter via the split-air pipe.

Here is a diagram of a 2nd gen ACV. It's basic principles are the same as the FD ACV, except the FD ACV does not have the "anti afterburn" valve.

https://www.rx7club.com/attachment.p...1&d=1241820046

The FD's airpump is a little more sophisticated, and that means even more rats' nest crap. The purpose of all these valves is to

1) send air to either the exhaust ports or converter

2) disengage sending air to the exhaust ports or converter, for emissions purposes or to preserve the cat.

https://www.rx7club.com/attachment.p...1&d=1241819160

Note that Mazda drastically simplified the air pump and ACV on the Rx-8, presumably from the relocation of the exhaust ports and through the use of drive-by-wire and other computer controls. They also don't have to send air directly to the cat anymore (no split-air pipe), and the pesky precat has been eliminated.

https://www.rx7club.com/attachment.p...1&d=1243265182

Other emissions systems

These systems are commonly employed on piston engines.

1. Crankcase ventilation--During combustion, there is always going to be some kind of blowby gas or oil. This builds up in the oil pan etc. That gas has to be vented somehow or there will be smoke out the back, especially under load.

There are two ways that these crankcase vapors can leave the engine (through a vent which must be open). They can be drawn out by an external force (manifold vacuum) or they can be pushed out by the internal pressure of the blowby vapors, which will happen by itself under boost/load.

Drawing vapors out under low-load is basically an emissions function. Applying a vacuum to the crankcase is not really "necessary" as long as a vent is open, but in this case Mazda had to apply a vacuum to meet emissions targets. The vapors are drawn out under low load by hooking the crankcase vent to a source of manifold vacuum, and then installing a type of check valve in-line. This check-valve is called a PCV Valve. When the engine is producing a lot of vacuum, especially during deceleration, the PCV valve is open and draws blowby gas back in to the manifold. As manifold vacuum decreases (engine goes into boost/load), the PCV valve will progressively close until it is completely shut.

When the engine is under load then the internal crankcase pressure will force oil and vapors out. This is then routed to before the turbos.

https://www.rx7club.com/attachment.p...1&d=1243266382

EGR System

EGR, or Exhaust Gas Recirculation, sends air from the exhaust ports back into the intake manifold. The point is to cool the combustion and reduce NOx emissions. Hypothetically it reduces the chance of knock as well, but I'm not sure how much that applies here. Mazda managed to eliminate EGR in the series 5 Rx-7's but they brought it back on the FD. Maybe emissions standards tightened? The peripheral exhaust port rotary (13B-REW and earlier) already recycles exhaust when some of the exhaust gases mix back in with the intake charge as the ports overlap.

https://www.rx7club.com/attachment.p...1&d=1243266653

Fuel evaporative emissions control system

On modern cars, this is the system that makes you throw a check engine light when your gas cap is loose. Current cars have very elaborate ways of making sure that no fuel vapors from the tank are escaping. On the FD, fuel vapors from the tank are trapped in the charcoal canister. They are then sent into the engine to be burned up. The purge control solenoid valve is operated by the ECU to send these vapors into the engine at time when it would not affect driveability. Previous rotaries had no solenoid valve for this and not have the ECU controlling it precisely.

https://www.rx7club.com/attachment.p...1&d=1243267038

Conclusion

While Mazda made a huge mistake in their choice of precat design, the rest of the complex system of emissions to me seems unavoidable at the time. They didn't have the budget to redesign the basic dimensions of the rotary engine as they are doing now with the 16X. They didn't have the affordable technology to implement a mechanically simpler ACV, or to use a drive-by-wire system which could simplify some of these emissions functions.

All of these inherent problems I just listed have been eliminated or significantly alleviated in the Rx-8's, and hopefully should be further simplified with the new 16X engine which will be designed to burn the mixture more completely with less emissions. Look at the vacuum routing diagram for the 2009 Rx-8 that I have in my previous post. I don't see any indication of an EGR or PCV valve at all in the 2009 Service Highlights document. Few of those lines are even for emissions functions, but are rather for the sophisticated intake system. Even though the Rx-8 does not really perform like the FD, the Renesis is far more advanced in many ways.

Great post man,

It's nice to see people spending time analyzing rotaries like that.

Diesel particulate filters normally trigger regeneration events as soon as they start to clogged. In modern diesel engines you can have many injections per cycle (1 or 2 pre injections to bring the chamber to adequate pressure and temperature and for NVH too, 1 or 2 main injections - the ones for torque and 1 or 2 post injections), during regeneration events, post injection(s) are activated, they literally burn in the exhaust to heat up the particulate filter to make that one active and burn all of the particulate (or soot). This strategies take about 30% of all the ECU c code, so to say the least, they are complicated... And cost fuel too.

This is true. Clearly something went wrong on the latest generation of Ford diesels then. I have a friend (who is actually on this forum) who is a tech for Ford and sees this problem all the time.

Thanks for taking the time to explain it all for us!

are there any cats out there that can take the abuse of not having an air pump?

Thanks for the articles. Even though alot of it goes above my head its pretty interesting. Thank you for taking the time.

is there any interest in another article that goes deeper into some of the other systems? Like the idle control system, or more about the ACV?

Good stuff.

I think a good explanation of the IAC system would be of great use. (An explanation of the ACV system would probably send everyone to sleep.)

ARGHX - great breakdown on the emissions systems; many do not appreciate what the integrated system really does / works.

One thing that Mazda had a hard time dealing with is the additional oil being burned during combustion as a result of the OMP and it's related components. The pre-cat and port air injection were integral to the solution. From what I understand the renesis has resolved much of the oil in the combustion issue.

the Renesis solved the "oil in the combustion issue" by reducing the oil pressure and not having a center oil injector lubricating the apex seal. Which is why 2004-2008 Renesis engines typically last as long as REW's unless you premix. Series II Rx-8's (09+)have six oil injectors (2 for the side seals, one for the middle of the apex seal), an oil metering pump that functions a bit like a returnless fuel system, and oil pressures back to REW levels.

thanks for the interesting post. Do you know what emission numbers each stock model has? specially the 99spec? i really need to find that out.

You could try looking up on these forums what kind of standards people have had to meet in various US states (especially California). That might give you some ballpark.

Now, the emissions output of stock car depends whether it is USDM California spec, USDM Federal spec, or JDM spec.

-- USDM Cali Spec -- EGR, EGR switch, ECU optimized for Cali emissions, Accelerated Warmup System, precat

-- USDM Fed Spec -- Accelerated Warmup System, precat, EGR

-- J spec -- none of the above... I'm pretty sure JDM cars don't even have EGR.


The USDM series 6 cars were in the emissions stone age, and the JDM cars were worse. "Tier 1" USDM emission were introduced in 1996, along with OBD II. The FD couldn't meet them and Mazda stop exporting the car here. The manual tranny Supra couldn't meet the standards in 96, so only automatics were imported for that year. The 300zx Twin Turbo passed the standards but it was detuned from 300 to 280 horse. Tier 2 standards began in 1999, and over time they have tightened progressively to lower and lower "bins." The lower the "bin" number the less emissions, and you get a different designation like "Super low emissions" and "ultra low emissions." You've probably seen stickers for those designations on newer cars.

https://www.rx7club.com/attachment.p...1&d=1257008839

is it possible to add all the missing parts from an us model to a jdm model? how much work is it?

So in all we need the acv system to help clean out the exhuast fumes?

The precat and accelerated warmup system are for cold start emissions. No emissions inspector checks that. The only other thing that's really different is EGR, and I would only consider installing that as last resort if you are failing NOx levels on a dyno test with the vehicle moving.

Here's something from the 2nd gen section FAQ. I think the chart is kind of generic, not rotary specific.


J-rats Recipe for cheating emissions if its ABSOLUTELY necessary

1. Turn variable resistor to full lean, or as lean as you can get and still run.
2. Trick ACV into pumping air to the cat all the time by removing the FORWARD UPPER vac hose, and capping it.
3. Run 87 octane
4. Run your tank down till your almost empty.
5. 2-3 bottles of alcohol in the tank. Drive VERY GINGERLY to the emissions station.
6. Once you pass go, DIRECTLY to a gas station and fill up with regular unleaded.

That's for a 2nd gen. The variable resistor he is referring to is a screw that sets the idle mixture on series 4 cars. On an FD you can lean out the idle with whatever engine management you have if necessary. For those of you with a PFC who do not have O2 feedback enabled, you can go into the settings-->INJ map and reduce the values in the idle area, which is approximately N2-N3 , P3-P6 .

What he's referring to is the vacuum hose for the switching actuator. The switching actuator closes the passageway in the ACV that leads to the split air pipe (which goes to the cat). If no vacuum is applied to the switching actuator, air will always flow to the cat.

https://www.rx7club.com/attachment.p...1&d=1257025334

https://www.rx7club.com/attachment.p...1&d=1257025334

On a series 5 non turbo the switching valve vacuum line is here, in the red box:

https://www.rx7club.com/attachment.p...1&d=1257024762

That's the "forward upper" hose on the FC ACV that was originally listed. I posted that diagram because the s5 diagram is a lot less overwhelming than the s6. On the s6, it is here:

https://www.rx7club.com/attachment.p...1&d=1257025862

How the ACV Vacuum Lines and Solenoids work

As I started describing earlier, the switching and relief valves are operated by vacuum actuators. The switching valve directs air to either the exhaust ports (port air) or the cat (split air). With no vacuum applied to the actuator, the passage for port air is closed and the split air passage is open. When vacuum is applied to the switching actuator, the split air passageway closes and air flows to the exhaust ports.

The switching solenoid is, functionally speaking, an NO valve (Normally Open). When the switching solenoid is disengaged, vacuum flows to the switching actuator, and air is directed to the exhaust ports. When the switching valve is engaged (ECU applies ground to the coil), vacuum to the switching actuator is cut. With no vacuum applied to the switching actuator, air pump air is directed to the split air pipe and out to the cat.

The relief valve is just like a blowoff valve for the air pump. It relieves air injection pressure right before the air pump is de-clutched. The air pump is de-clutched for how speed operation and when the exhaust overheat warning comes on. The relief solenoid is an NC (Normally Closed) solenoid functionally equivalent to the charge control solenoid. When air injection pressure needs to be relieved (before de-clutching the air pump), the ECU switches a ground on the relief solenoid which allows engine vacuum to work on the relief valve actuator.

https://www.rx7club.com/attachment.p...1&d=1241819160

The split air bypass, port air bypass, and relief 2 solenoids are built into the ACV and require no vacuum lines. They are like recirculated blowoff valves (or the charge control valve) and are used to crudely control air injection pressure and volume. After looking over it, the ACV architecture is mostly unchanged from the older rotaries. The only thing that's different is the anti afterburn function, which in the FD is performed by ISC valve instead of the ACV like on the 2nd gen cars.

Secondary air injection control strategy:

https://www.rx7club.com/attachment.p...1&d=1257028329

great info, thanks !

Few additions for ya -

- The '95 US FD's don't have EGR. Not sure how Mazda got rid of it there. Funny thing is the '86-88 FC's had EGR, the '89-91 cars didn't. JDM FD's didn't have EGR at all, I've verified that first hand.

- The EGR system on the FD is a joke. If you look at the gasket between the EGR valve and the LIM, there is literally a PINHOLE for the exhaust gasses to travel through to the engine. Anyone who has scraped carbon off motor internals knows that passage would clog in record time. I think the Mazda engineers had to put an EGR valve on not for the effect it had on emissions but to check off some box in the federal emissions standards.

- The '96+ JDM ACV's were redesigned. They only had the vacuum lines going to them, the 3 solenoids that are electronically controlled were totally eliminated. You can see the spot in the casting where they were supposed to go - same casting, just less finishing work. Not sure how the ACV works without those built-in solenoids.

- The PCV system was also re-designed on the '95 US FD. The hose going from the oil fill neck to the PCV valve and then to the upper intake manifold was removed and both ports were capped. This left just one hose on the oil fill neck going to the primary turbo inlet duct. This is really all that's needed, not sure if it was just over-engineered originally or they had to check a box that said the car had a PCV valve. I *think* the JDM cars followed the same design, early cars had PCV, later ones didn't. The '95 system works fine - the turbo inlet duct is at atmospheric pressure, and the gasses can vent there to be burned by the engine and scrubbed by the cats, which is how all evaporative emissions must be handled.

Dale

Great post as always, arghx. Nice to see the history of how Mazda did things before the FD.

DaleClark, awesome info as well. Always good to hear about small details and updates like that.

Peripheral exhaust rotary engines (all rotaries up to the Renesis) have a natural EGR effect. There is always some exhaust gas escaping back into the intake charge. It makes sense that EGR isn't really necessary. The Renesis is just a much cleaner burning engine on so many levels, it doesn't need EGR. Very few gas piston engines have EGR systems now. Variable valve timing systems create EGR effects by increasing the amount of overlap between intake and exhaust strokes.

https://www.rx7club.com/attachment.p...1&d=1257109946

I will speculate that the switching and relief valves were controlled by vacuum duty solenoids, like a boost control solenoid. That makes sense given that they went to a 16 bit ECU for the series 7. That would allow for quicker response and more precise control over the switching and relief passageways in the ACV, without crudely turning those bypass valves on and off.

There is precedent for this. The series 3 GSL-SE engines did not have a duty controlled ISC valve. It had a mechanical ISC valve with a vacuum solenoid and a vacuum vent solenoid that were alternately switched on and off to adjust bypass air.

https://www.rx7club.com/attachment.p...1&d=1257110476

https://www.rx7club.com/attachment.p...1&d=1257110476

The series 4 FC switched to a duty operated plunger valve that evolved up through series 8. ISC valve design is probably why the FB had a base idle speed of 800, the FC had a base idle speed of 750, and the FD had a base idle speed of 720. Improved ISC design and ignition control allowed the engines to idle stably at a lower base speed.

Yes is this like the Rx-8's. I think your "check box" theory of Mazda piling on emissions control components has merit. The FC had two ventilation ports. One came right off the oil filler and went to a 3 port PCV valve, the other came from the middle iron and tee'd in with the evaporative emissions system (charcoal canister).

https://www.rx7club.com/attachment.p...1&d=1257111007

That's for the 2nd gen turbo cars. The FC did not have an EVAP purge solenoid to precisely meter fuel vapor emissions like the FD. The Rx-8 has an EVAP purge solenoid but also adjusts the drive-by-wire throttle position so that introducing fuel vapors has even less effect on driveability

Back to the ACV, so if i was to put back the air pump and ACV all i would need is just 2 solenoids right? Valve relief and valve switching? this on a FD BTW.

Do you plan to run the cat for a long time or are you just trying to pass an emissions test so you can pull it back off? Do you have the stock ECU? I see you are in Japan, is this a series 6?

Nah i guess you could say its a series 1? its a efini 92. i went to get the land transportation office LTO inspection and it failed for no air pump. i just put it on and the acv , but got vacuum to both of the acv ports, it passed but i just want to put it on the right way. took out the solenoid rack. I got a sard sports catalyzer.

That's interesting that you applied straight vacuum to both the relief valve and the switching valve and still passed. According to the diagrams, that would send your airpump air right to the exhaust ports (port air) but also bleed air out of the ACV through the relief valve.

If you want to do it "properly" you need to plug in the 3 plugs on the ACV (relief 2, split air bypass, port air bypass), then hook up the switching and relief solenoids to their respective actuators. When the switching solenoid is engaged by the ECU, vacuum is cut from the switching actuator. With vacuum cut, air pump air is directed to the cat instead of to the exhaust ports. When the relief solenoid is engaged, vacuum is supplied to the relief actuator. The relief actuator is like a blowoff valve for the ACV--it usually engages right around the time the airpump is declutched.

Now I haven't examined the switching and relief solenoids closely. Do they have just two ports on them? That's what I would expect.

they didnt smog check it, they just checked to see if the pump was there. it wont pass smog its running rich with the stock pfc map. i just got rid of all the vacuum lines not needed since i went single turbo.i guess ill get rid of the pcv and double throttle also. maybe the AWS and the heater hose for the butterflies too.

you are asking slightly the wrong question, each agency be it the EPA, or the CARB or the local smog check guy, all have DIFFERENT tests and DIFFERENT standards.

a stock JDM car will pass any of the local smog check tailpipe tests, but it fails the visual because it doesnt have a check engine light.

the 96+ FD's are not OBD2, so they will also fail, there is no ecu to plug into the smog test machine too...

and also the VIN number is weird....

if you are trying to bring the car into the US the DOT and EPA have easy to find and follow rules...

i don't want to know the different standards of EPA CARB or any other smog test agency i just want to find out the C0 NoX and HC Values on different rpms for the 99spec jdm stock model ... i don't really care if this model fails some us smog tests because i need those infos to legalize my car in germany ...

Definitely! I'd like to learn more about the idle control system. You have helped me in this area in other posts but who knows what else there is to learn.

I'm still trying to figure out how I would do an article on the idle control system. I could address Rx-7 stuff specifically but I'd also like to explain comparable systems on other cars, like plunger style coolant controlled fast idle and bimetal fast idle, stepper motors, etc. I'd also like to discuss some of the simplifications/modernizations Mazda did on the FD compared especially to the series 3 FB (which I've already briefly mentioned--the FB was VERY crude). And that's just the mechanical side. On the control side there is all the basic control parameters for different loads but then there is idle ignition control logic, cold start idle ignition advance blah blah blah... it could be a very sprawling type of deal. Sometimes it's hard to explain one system without explaining the context of what other cars were doing at the time. And the FD's idle and TB control systems are pretty much exactly what most of the other manufacturers of that time were using, there's nothing really unique about it.

Air/Fuel Ratios and Emissions Chemisty

There are four major types of emissons produced by an automotive engine (rotary or piston). They are HC, CO, NOx, and CO2. Due to the nature of the combustion process, something undesireable is going to come out of the tailpipe even if it is in small quantities.

Reducing emissions of one type of gas increases emissions of another. At lean mixtures, NOx is produced. At rich mixtures, NOx is minimized but HC and CO are produced. At the ideal stoichiometric air/fuel ratio, CO2 emissions are maximized. Very few people understand this!

The first type of emission is HC, basically unburnt fuel. Besides the air/fuel ratio, the geometry of the engine plays a big role. When the flame front collides with something, it is extinguished and HC emissions can result.

https://www.rx7club.com/attachment.p...1&d=1258681811

The 13B-REW and 13B-MSP Renesis have a geometry such that the leading and trailing flame fronts collide before they fully reach the side housings (think 3 dimensionally). The experimental 16X Renesis engine has a relatively "thinner" combustion chamber. The leading and trailing plugs are farther apart, so that their individual flames will reach the side housings before they collide with each other, resulting in less "quenching" and unburned fuel. See http://www.rotarynews.com/?q=node/view/1050 and the 16X patent literature http://www.worldcarfans.com/10905261...-rotary-engine

Carbon Monoxide is mostly the result of mixtures richer than 14.7:1

https://www.rx7club.com/attachment.p...1&d=1258681811

NOx emissions occur when the mixture is too lean or combustion temperatures are too high. That's why manufacturers can't run engines as lean as possible to reduce fuel consumption.

https://www.rx7club.com/attachment.p...1&d=1258681811

Carbon Dioxide (CO2), the leading greenhouse gas emission, is actually maximized when the catalytic converter is working most efficiently. As counter intuitive as it sounds, the cleanest engines at a particular level of fuel economy actually produce the most greenhouse gas. This explains just how difficult and complicated it can be to control emissions.

https://www.rx7club.com/attachment.p...1&d=1258681811

these images are sourced from Toyota technician training documents

Catalytic Converter Efficiency

Some of us here may have had narrowband air fuel gauges, or have read O2 sensor readings before. They are not that precise, and they always oscillate from "lean" to "rich." Few realize that catalytic converters are actually designed for this oscillation. In closed loop O2 sensor controlled operation, air/fuel ratios intentionally oscillate around the 14.7:1 AFR. Because lean mixtures produce one type of emission and rich mixtures produce another, two alternating processes are required for clean combustion. Rich mixtures supply gases to catalyze NOx emissions (reduction) while lean mixtures supply gases to catalyze HC and CO emissions (oxidation).Thus it is necessary to alternate between the two conditions.


https://www.rx7club.com/attachment.p...1&d=1258684615

Rear O2 sensors (which are always narrowbands) are used on OBD II vehicles to make sure that the converter is still working. Widebands signals are not depicted here, but on vehicles equipped with factory widebands (Rx-8's, WRX's), the AFR will still oscillate around 14.7:1 but won't deviate as far from that switch point. Wideband O2s allow stock cars to control fuel more precisely during closed loop operation.

https://www.rx7club.com/attachment.p...1&d=1258684615

You rock!

Question on the catalyst - does it matter whether its a metal core or a ceramic core? Does the above info change at all depending on core material?

That's a good question.

Ceramic vs Metallic Substrate Catalytic Converters

The two questions people usually ask are

1) which flows more?
2) will metallic substrate cats pass emissions tests?

First, remember that what is changing is the substrate (ceramic vs metal), not the catalysts themselves. The substrate is almost like the work bench for the catalyzing process; the process takes place on top of the substrate. The catalysts are still platinum, palladium, and Rhodium with cerium for oxygen storage during the lean portion of the closed loop cycle.

https://www.rx7club.com/attachment.p...1&d=1258753158

https://www.rx7club.com/attachment.p...1&d=1258753158

If you take two cats of the same basic dimensions but one of them has a metallic substrate, the one with the metallic substrate will typically flow more and will heat up faster. Note that the factory FD precat has a metallic substrate.

https://www.rx7club.com/attachment.p...1&d=1258753158

There are a lot of factors that go into the efficiency of the converter, but I'll make it simple. We'll discuss this hypothetically first, to isolate the results from changing only the substrate. If you compare two converters of very similar dimensions and physical shapes on the same engine,

1. the metallic substrate cat may be marginally more efficient at idle for HC, CO, and NOx, at least on paper. But exhaust temperatures, idle AFR, and a lot of different factors really come into play here.

2. the ceramic substrate cat will be more efficient at HC and CO conversion for lower to medium loads and rpm ranges. These are the kind of conditions you may have on an emissions dyno test.

3. the metallic substrate will convert HC and CO better under higher loads and rpms, but these are not likely to be tested at an emissions station.

4. NOx numbers probably won't change much between either type of converter, except perhaps at idle.

Now that's examining the substrate material only. The fact of the matter is, physically smaller converters with less volume will not burn as clean. Conversion efficiency is measured by comparing how much gas is converted vs the amount of exhaust gas per a unit of volume in the cat. This is what's called space velocity:

Space velocity = a constant * [exhaust gas flow / (exhaust molecular weight * catalytic converter volume)]

That's the formula, roughly. And here are some comparison charts:

https://www.rx7club.com/attachment.p...1&d=1258753158

So in conclusion, for aftermarket performance applications a metallic substrate converter will yield at least some improvement in performance compared to a ceramic substrate cat of similar dimensions. This improvement can't be easily quantified because it depends on a number of factors. On OBD 1 cars that need sniffer tests, it may be more difficult to pass with a metallic cat. Rotary engines have enough problems with HC and CO emissions, and metallic cats exacerbate the problem under most driving conditions. This is especially true with performance cats because they are physically a lot smaller (less volume) than OEM units and thus don't work as well to clean up the exhaust. On OBD 2 cars where no actual sniffer tests are involved, there really isn't a downside to using a high quality metallic substrate cat if you are a performance enthusiast.

some images taken from: Santos, "Evaluation of the conversion efficiency of ceramic and metallic three way catalytic converters," Energy Conversion and Management Vol 49 Issue 2, 2008.

my brain s fried

+1

To arghx: I just want to take a moment to acknowledge your efforts and contribution to the board. I know how time consuming it is to research and write technical posts that are factual, meaningful and accurate. Your FC notwithstanding, presenting such posts is sufficient to assure that you have no life.

Thanks.

For reference, here are two emissions test from the same FD, the first with the stock cat and the second with an SMB metallic. The tests were performed a few weeks apart and, apart from the cats, the car was identical. The results pretty much concur with what you were saying.

Test________CO2%__O2%______HC(PPM)________CO%_____ ____NO(PPM)______
______RPM_MEAS__MEAS__MAX_AVE_MEAS__MAX__AVE__MEAS _MAX__AVE__MEAS
15mph_1768_14.30__0.80_|_88__21___22__|_0.52__0.06__0.01_|_704__150__167
25mph_2922_14.40__0.50_|_53__13____6__|_0.50__0.05__0.24_|_738__136___87

Test________CO2%__O2%______HC(PPM)________CO%_____ ____NO(PPM)_____
_______RPM_MEAS__MEAS__MAX_AVE_MEAS__MAX__AVE__MEA S_MAX__AVE__MEAS
15mph_1771_14.69__0.16_|_88__21__120__|_0.52__0.06__0.57_|_704__150__245
25mph_2034_14.70__0.11_|_53__13__106__|_0.50__0.05__0.65_|_738__136__201

This was with the stock ECU. I am pretty sure with a little tweaking, it would be possible to pass with a PFC and a metallic cat. Though the PFC turns off the air pump at 2500rpm (the stock ECU turns it off at 3000rpm) so the 25mph part of the test would have to be done in third gear.

You know I teach this stuff privately for money right...

FD vs FC precat system

The FD precat had a metallic substrate, which [when the converter is new and not clogged] means better emissions and less backpressure. The USDM-compliant 2nd gen cars used two ceramic substrate precats. During warmup, metallic substrates are better for emissions because it takes less heat to get them to operating temperature (lower specific heat). Once the car reaches operating temperatures, metallic substrates are better for flow but worse for HC and CO emissions.

https://www.rx7club.com/attachment.p...1&d=1258908182

FD:
https://www.rx7club.com/attachment.p...1&d=1258908182

During conditions that produce high levels of HC and CO (idle and warmup), the ACV directs airpump air to the exhaust ports (before the O2 sensor) by using the port air solenoid and actuator. During port air conditions the main converter is used exclusively for oxidation (HC and CO conversion). For whatever reason, the FD metal precat clogged very quickly compared to the FC3S dual ceramic precat design. The Rx-8 Renesis engines are sufficiently cleaner that both the precat and split air pipe were eliminated altogether, although the air pump remains and still supplies port air.

this post is AWESOME!! but i have to be the jerk-off that has to ask the question, would you happen to have the vacuum routing for the rat's nest on the 96 and newer FDs?

minor correction here. On series 6 the ACV delivers air to the exhaust ports by using the switching vacuum solenoid and actuator, with the port air bypass solenoid to control the pressure.

I've got something on my computer at home that I found on these forums a while back. I'll try to post it up later. Are you Japanese? How come there are very few Japanese people on this board, given how many FD's there must still be in Japan? No offense intended, but I honestly would've expected there to be at least a few Japanese guys on here who have extensive knoweldge of the series 7 and 8 cars. And it's not like there is a huge language barrier since a lot of countries teach English in school.

I was dealing with the fast idleing problem today. Thanks for a great post. The fd was idleing at 3k lol

I'm not sure who originally did this, but these pictures and diagrams are supposed to be for series 7 and series 8 cars. I can't really answer any questions on them. I've never even seen a series 7 car in person.
I have no idea if routing changed between series 7 and series 8.

https://www.rx7club.com/attachment.p...1&d=1259032128

https://www.rx7club.com/attachment.p...1&d=1259032128

https://www.rx7club.com/attachment.p...1&d=1259032128

https://www.rx7club.com/attachment.p...1&d=1259032128

no, not japanese, just another american dealing with an FD build in Japan. i've looked around for a japanese manual, but haven't been able to get ahold of one, and besides that, i'm not much for reading Japanese either. always have to find someone to help decifer all the Kanji symbols.

thanks for the pics. that is the same block i have. its just that someone else took this engine apart and now i have to piece it all back together and this is what i've came too.

I originally posted this on the Rx-8 forums, but most of us here are driving an OBD II car every day. 2001+ models have stricter standards for OBD II readiness.

OBD II Inspection Readiness

I think there's a lot of confusion floating around about what inspection "readiness" really means.

Here's how it works. OBD II was designed to make tailpipe testing unnecessary. Therefore the PCM tests the emissions control systems on its own. The ECU can't always take a "snapshot" of sensor data to know whether a system is working right. It takes time and certain types of driving conditions to know for sure.

The most common/important tests that need to be flagged "Ready" are:

-- Catalytic Converter test: the PCM monitors rear O2 sensor voltage over time to see if your cat is working right

-- Evaporative system: the test that makes you throw a code when the gas cap is loose. EVAP systems are actually crazy complicated.

-- Oxygen sensor: the PCM checks for a particular signal curve over time. The exact test depends on the sensor's position (Front or rear) and whether it is a wide or narrowband sensor. There's also tests for the the O2 sensor heater.

-- EGR system: not many newer cars have this, but you will find it on a lot of early OBD II cars (late 90s).

After you disconnect the battery or clear codes, most of the readiness monitors go to "Not ready."

https://www.rx7club.com/attachment.p...1&d=1261277860


It is a myth that you need to drive x miles for the car to be "ready" for inspection. There's no set number of miles. I've passed inspections after less than 50 miles of driving sometimes. It just depends.

The Do-It-Yourself OBD II Inspection

The best way to determine whether your car is ready for inspection is to hook up to a higher end OBD II scanner if you have one. I have one of the big orange Actron scanners (Actron CP9180) that you usually see being used by auto parts store employees. It was maybe $120 new off ebay when I bought it a while ago.

Now I'm going to demonstrate me checking to see if my car will pass inspection. This is my daily driver, a 1997 Infiniti Q45. My 1988 Rx-7 Turbo doesn't even have a check engine light!

https://www.rx7club.com/attachment.p...1&d=1261277860

The first shot here is of the main menu in the Actron CP9180. I have two choices. I can select "State OBD Check" to get a summary of my readiness monitors and DTC's. I can also select "I/M Monitors" to get a breakdown of all the readiness checks in the PCM. So first I select "State OBD Check."

https://www.rx7club.com/attachment.p...1&d=1261277860

From this screen I can see that the check engine light (Malfunction Indicator Light) is not active. I do have one DTC however, but it is a "pending" code that has not yet tripped the MIL. This number could be "3" if I had two active codes and one pending code.

Then the scantool separates my readiness monitors into 3 categores: OK, Incomplete, or Not Applicable. Any 2001+ car must have all but 1 supported monitor set as "OK." Only 1 readiness monitor can be set flagged as "incomplete." This car will pass an inspection because the MIL has not been set and all monitors are ready. Now let's take a more detailed look at my list of readiness monitors in the "I/M Monitors" screen.

https://www.rx7club.com/attachment.p...1&d=1261277860

Those top three are my continuous monitors. Those three are always active. Any monitor that is not supported is listed as N/A. This particular car has an EGR readiness monitor but it does not have an EVAP monitor.

https://www.rx7club.com/attachment.p...1&d=1261277860

Any monitor that requires some sort of drive cycle is called a non-continuous monitor. Those are the ones you are waiting on when you visit the inspection station. In my experience the Catalyst monitor and the EVAP monitors take the longest to be set. Here is a drive cycle that may help set the monitors:

https://www.rx7club.com/attachment.p...1&d=1261277860


I hope that clears up some confusion about OBD II inspections and "readiness" tests. Engines don't just arbitrarily become "Ready" after x number of miles or x number of drive cycles. PCM's go through a series of tests to make sure the components are working, and different criteria must be met for every engine. A lot of inspectors really don't understand this system fully. They just do whatever their inspection tool tells them.

93 does not get a signal to keep the air pump on
 

Hi Arghx,

First let me thank you for a great article.

I am praying that you can shed some light on the de-clutching of the air pump itself. I purchased a 93 with no modifications to the emissions system except for the removal of the precat, (it has a downpipe). Currently the air pump will only come on momentarily when the car is first started, and then it immediately is told to shut off. If I short the air pump relay and force it to run, the car will pass smog here in California with no problem. However, I can not for the life of me figure out what is causing it to not get a signal to stay on below 3250 rpm like it is supposed to.

The O2 sensor is fine, the map sensor is fine, the air pump relay is fine, and the air pump itself is fine.
Having read your thread, it sounds like the ACV and its controlled solenoids direct the air, but do not tell the air pump to clutch or de-clutch. Can you tell me what controls the on/off behavior of the air pump itself? And have you already written something about this that I have not seen?

Thanks in advance for any help.

-Coov

The only information I have seen is from the stock ECU pinout, which indicates that it is controlled based on rpm:

https://www.rx7club.com/attachment.p...1&d=1320637339

That's all the documentation I could find on the basic control logic. It's possible that there are undocumented parameters affecting its control. We do know that if an airpump relay fault code is triggered, it will disable the output from the ECU to the relay:

https://www.rx7club.com/attachment.p...1&d=1320637602

The diagnostic procedures mostly relate to checking the air pump relay, the electrical connection, or the ECU itself.

https://www.rx7club.com/attachment.p...8&d=1320637456

https://www.rx7club.com/attachment.p...1&d=1320637602

https://www.rx7club.com/attachment.p...1&d=1320637602

EDIT: After re-reading your post, it looks like I'm not telling you much that you don't already know. If there's any more information available on the air pump clutch control I've certainly never seen it, and I have collected a lot of information on these cars over the years.

Try swapping the ECU at this point, if you're sure everything else is ok. There are a few out there as far as California vs Federal spec ECUs and such. I'm not sure how much it matters.

Hi Arghx,

Thanks. You are right, most of this I have already went through. However, I am getting a ACV code when I take it down to my local mechanic. With the manifold now removed, I can see the the main switching solenoid in the ACV "rat's nest" is not connected, (the one that feeds the downstream solenoids that send to the cat or the exhaust port).

I have to wait for Monday in order to get a manifold gasket to put the whole thing back together. The solenoid seems to check out. I and my local mechanic are both praying that this is the reason the ECU is telling the air pump clutch not to remain on. Everything else from the relays all the way up to the exhaust overheat system all seem to be functioning correctly.

I am hesitant to say that this is the culprit, since where the air goes should not affect the air pump being turned on, but hopefully it is. My only fallback at this point is to swap the ECU, (I have a Power FC coming out later this week.)

-Coov

You could invert the signal to the air pump relay if you really wanted to. You say that it turns on the relay and then turns it off. Wire up a relay that flips the control logic.

If you are installing a Power FC it will probably solve it. The Power FC doesn't have much in the way of self-diagnosis or fault mode.

Hey @arghx and others

I have my ACV off to replace a gasket and just re-read this to better understand how it worked. And also to under why the inside of the ACV is so crusty looking. It looks like it has carbon build up from exhaust.

Reading through this, the ACV gets clean, filtered air from the air pump. The split air to the cat has a check valve so that exhaust theoretically should not be re-introduced to the intake from there.

Is it 'normal' for the inside of the ACV to be 'dirty'?

Thanks.