When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Is it 'normal' for the inside of the ACV to be 'dirty'?
Thanks.
yes, if you're worried the big check valve to the port air port 1480-13-730 could be replaced. you should put vacuum on the ACV valves and make sure they work before you put it back. the FD ones are really good, but you should check it while its off
I suspect there is some kind of spec for leakage between the port air system (and maybe split air too) and the actual ACV and they eventually get gummed up no matter what. There's always going to be some rough combustion at times (especially at idle on these engines) due to overlap between intake and exhaust.
Remember that back when all this stuff was designed (basically 70s and 80s), emission warranties were not very long. Nowadays emission components have to last 120k-150k miles to comply with modern regulations. So significant carbon buildup isn't surprising. It's the same thing you see on EGR valves etc (and the FD did have EGR in '93).
I'm bringing this thread back and also re-read this thread. (Good thread, by the way) I was going to private message you, but other people in the future can benefit from this too. (If they buy expensive emission parts and want to keep them for a while.)
I'll get straight to the point, I bought an expensive catalytic converter from FEED and want to keep it healthy. My previous bonez cat blew out; it was old, the car is running rich, and the air pump is not connected, but I will get it tuned and run the air pump with the new cat. Here is the list of mods and new parts that are on my car (or going on my car shortly) before I ask my questions and bounce ideas around:
Greddy V-mount
New OEM fuel injectors Water Injection, AEM
99-spec twins with all-new hoses and all-new solenoids in the rat's nest
New Air pump out of the box
Fujita Engineering twin catalytic converter
EGR delete, along with deleted solenoid in the rat's nest
Power FC, (removed wires "AWS Solenoid," "EGR Switch," and "EGR Solenoid," but going to put back the "Split air bypass".)
I read the Power FC can run the air pump if I have the wire "Split air bypass" connected in the harness to the ECU and not cut like everyone else says to do. (Correct me if I'm wrong that the Power FC can't run the air pump) Also, I read that water injection can help with carbon buildup, which is the only reason I have it. My theory so far is to have the air pump installed with the Power FC and ensure the ACV is working while the system is getting water injection to fight carbon buildup.
Basically, I have 2 goals, keep my catalytic converter healthy as long as possible and minimize exhaust smell as much as possible. (I'm not trying to pass emissions btw since there is none in my state) If there is anything that you recommend, I would be happy to listen.
Last edited by CREEPENJEEPEN; 11-04-22 at 10:46 PM.
Power FC, (removed wires "AWS Solenoid," "EGR Switch," and "EGR Solenoid," but going to put back the "Split air bypass"
there is no need to put the split air bypass back, the JDM FD does not have one, and that pin goes nowhere
the Red arrow is the split air bypass, its an add on for the US. the actual work is done by the big diaphragms which both markets have and the PFC runs. we cut the 4 wires because they have different functions between US and Japan
the Green arrow is the Relief, it chooses if the air pump air is relieved to the air cleaner, or keeps going in the valve.
the other diaphragm is the Switching Valve, it Switches the air pump air from "Port Air" to "Split Air"
as far as keeping the cat happy, the stock cat wants to be kept under about 650c, over that it starts melting. i would assume FEED is using a metal converter, and those typically have a higher temp limit, i think the SARD ones are 1100c, which is higher that you can hit with a rotary, which is nice. the JDM setup has a temp sensor in the cat, so there is a provision for EGT there
for best performance, i'd think if you tuned the thing so it hit the AFR targets in the base map you'd be really in the ball park, best performance in a converter is when its in closed loop dithering around 14.7:1 afr, which is what the stock, and PFC maps do until the EGT gets high enough that they start adding fuel to keep temps down. if you did have a test, you'd tune it so it hit the values on the base map, under the same conditions as the test, and make adjustments from there. for example the California test is 15mph in 2nd gear and then 25mph in 3rd gear, so i'd log data for that, and if it tested high for something, its easy to tweak the AFR/timing.
i don't think water injection will make any difference here at all
Thank you for that informative response; I'm still learning something new every day and recently jumped into learning about emissions because of this expensive cat, lol. Yeah, I'll have my tuner adjust for the optimum AFR for health of the engine and the components attached to it. Not chasing the edge of tuning to make crazy HP. My theory is that water injection is mainly for carbon build up; it's always steam cleaning the engine.
You're right, I should have thought that those pins go nowhere, I remember now, (de pinned them 3 years ago). Here are my 3 questions after reading your response:
1. First, will having an air pump with a PFC do anything on a USDM rx7 since one diaphragm is completely disabled with the PFC?
2. Is "Port Air" to "Split Air' important for cat health and smell?
3. Do I need to modify anything so the air pump can work correctly with the PFC?
(Example would be removing vacuum lines or unplugging anything on the ACV)
1. First, will having an air pump with a PFC do anything on a USDM rx7 since one diaphragm is completely disabled with the PFC?
both diaphragms work as they should. the part that the US cars have that is added is a little solenoid.
2. Is "Port Air" to "Split Air' important for cat health and smell?
yes. there are charts in the service manuals, but basically the air injection to "port air" at low rpm and low throttle openings. on decel and some transitions it goes to "split air", and then at high rpm and big throttle openings it just gets turned off
basically what happens is that the engine is tuned to run as lean as it can without misfires, but due to the way its constructed this is like 12:1 or so, but the converter needs to see 14:7:1, so they add the air pump air.
3. Do I need to modify anything so the air pump can work correctly with the PFC?
(Example would be removing vacuum lines or unplugging anything on the ACV)
nope, plug it in and it works. kind of why the PFC is/was so good
So getting the air pump working is all about getting the AFR inside the cat lean enough so it's actually oxidizing. Otherwise it's can clog up with unburnt fuel, and (speculating here without elaborate equipment) occasional deceleration fuel cuts basically throw a bunch of hot air from the engine into a bunch of unburnt fuel in the cat and cause a lot of reactions inside heating it up.
You need to keep your EGT's down under boost as well. WIthout having a fast action EGT probe in the inlet of the cat it's hard to know what's going on. Usually 900-950C inside the catalyst is about the most they can take without accelerated wear, so it's best to keep the temperature coming out of the manifold below that if you can. Generally speaking though, I'd keep AFR's between about 10.5:1 and 11.0:1 , with occasionally going slightly leaner. I know that's on the rich side, and possibly costing power, but there's a reason why stock tunes run so rich. I'm not going to tell you to advance timing to keep EGT down because a Bonez cat is a lot cheaper than rebuilding a motor, so a good safety margin on spark timing is preferred for reliability.
So getting the air pump working is all about getting the AFR inside the cat lean enough so it's actually oxidizing. Otherwise it's can clog up with unburnt fuel, and (speculating here without elaborate equipment) occasional deceleration fuel cuts basically throw a bunch of hot air from the engine into a bunch of unburnt fuel in the cat and cause a lot of reactions inside heating it up.
You need to keep your EGT's down under boost as well. WIthout having a fast action EGT probe in the inlet of the cat it's hard to know what's going on. Usually 900-950C inside the catalyst is about the most they can take without accelerated wear, so it's best to keep the temperature coming out of the manifold below that if you can. Generally speaking though, I'd keep AFR's between about 10.5:1 and 11.0:1 , with occasionally going slightly leaner. I know that's on the rich side, and possibly costing power, but there's a reason why stock tunes run so rich. I'm not going to tell you to advance timing to keep EGT down because a Bonez cat is a lot cheaper than rebuilding a motor, so a good safety margin on spark timing is preferred for reliability.
Thank you for that information; I'll keep this in mind. I have duel EGTs from Defi (one in each runner, pre-turbo) on my stock manifold. Can I use those for a healthy reading to the cat? I'm guessing the temperature doesn't change much going past the downpipe.
Normally under WOT or heavy acceleration your hottest temperatures are going to be pre turbo. When you start talking about an air pump being involved, and deceleration fuel cuts (backfires etc), then you'd literally need to drill into the cat. Measuring pre turbo is a useful indicator, although it won't tell you if there are some reactions going on inside the cat causing it to get significantly hotter. You probably won't get a fast enough reading just eyeballing a gauge. We have to look at it from the perspective of a hobbyist driving an old car around a few thousand miles a year. From that point of view it starts becoming cheaper to just replace cats than to do the work to keep them going a long time.
Here's a diagram from a paper studying emissions that shows how various EGT sensors are placed in a downpipe (in this case no turbo, just a nonturbo 4 cylinder exhaust manifold). UEGO indicates a wideband and HEGO are narrowbands. These various sensors were used in this study to measure the impact of the reactions throughout the exhaust system, and each "TC" (K-type thermocouple, found on most EGT gauges) measures temperatures through the exhaust stream. There was an air pump as well, just not pictured. In your case you basically have temperatures on the upstream portion of the exhaust system (left side of the picture) but not inside the actual cat.
We have to look at it from the perspective of a hobbyist driving an old car around a few thousand miles a year. From that point of view it starts becoming cheaper to just replace cats than to do the work to keep them going a long time.
Unfortunately the catalytic converter that I bought from FEED was almost 2,900USD. (Twin Cat, same air flor as a midpipe) Trying everything I can to keep it healthy, and this thread is helping out a lot. I came across an excellent program for the Power FC, called "FC tweak" and I believe it has everything I need to help keep the correct ratio of air to fuel for the cat. Installing a bunch of sensors in the cat seems more of a learning curve. I'd rather have the AI built into FC tweak take over than have someone like me, that's not an engineer or tuner, take over. You seem like you went to school for this subject or taught it; you're very knowledgeable.
Unfortunately the catalytic converter that I bought from FEED was almost 2,900USD. (Twin Cat, same air flor as a midpipe) Trying everything I can to keep it healthy, and this thread is helping out a lot. I came across an excellent program for the Power FC, called "FC tweak" and I believe it has everything I need to help keep the correct ratio of air to fuel for the cat. Installing a bunch of sensors in the cat seems more of a learning curve. I'd rather have the AI built into FC tweak take over than have someone like me, that's not an engineer or tuner, take over. You seem like you went to school for this subject or taught it; you're very knowledgeable.
when i got my PFC i wanted to tune it like i've seen Arghx tune for years, but the FC Tweak is so much faster its amazing. in theory one tweak, and about 4-5 drives and you could be done to the point where you're fine tuning the idle, and the temp corrections. its amazing.
The FC Tweak software automates stuff that a lot of tuners are doing in their head or in Excel. (Full disclosure: I was given a free copy of it, but have not done an extensive evaluation).
That being said... there are inputs and there are outputs. The output is the catalyst bed temperature, which is directly related to the life of the cat. The input is air, fuel, and spark. We can make certain assumptions about what spark timing and AFR for example will do inside the cat, but without direct measurement it's all estimation. That being said, direct measurement is not an easy thing for a home hobbyist, so you do the best you can with rules of thumb and good tuning.
So having good tuning helps, but you can't reduce cat temps under load without giving something up. You can't add fuel to lower cat temps without reducing power/fuel economy relative to not caring about exhaust temps. You can't advance spark to reduce cat temps without increasing the risk of knocking, etc. Also,the airpump affects cat temps, but its control is mostly hard coded into the PFC and the stock ECU.
The FC Tweak software automates stuff that a lot of tuners are doing in their head or in Excel. (Full disclosure: I was given a free copy of it, but have not done an extensive evaluation).
Xavier, recently added an OMP update that automatically adjusts the OMP, depending on coolant temp, instead of its default settings. That said, an Air pump update can be available with your help. I don't know if that's possible or necessary to control the Airpump with FC tweak, I'm not an engineer, but it's an idea. That would be awesome if you did an extensive evaluation. It's already good, but your input would help a lot.
but it works fine as is, so you don't need to do anything
I don't have a good feel of how well the air pump cycling on and off during tip in and tip out is affecting cat temps as it relates to a stock setup vs a modded one (changed exhaust system, different fuel or spark tuning etc). It doesn't matter much though, because we can't change it.
it doesn’t just come on for initial cold startup only like on an RX8?
I always thought it was only used to get the cat up to temp for that reason, weird.
.
essentially its the reason for going side port in the first place, the pre MSP exhaust ports carry too much exhaust gasses into the next intake stroke (internal EGR), so to get the engine to run without misfiring the mixture needs to be rich, and then they need the air pump air to make it work for the converter. the data Mazda has published is pretty incredible. if you put your emissions probe in the INTAKE port of an REW its about 2% CO... with the air pump and cat the HC on an FD is under 100ppm (the 99spec was right there with the Rx8, about 11ppm HC), but remove the cat and it jumps to ~1900ppm. remove the air pump and its around 5000ppm HC.
i live in California, my couch has an emissions sticker on it.
Mazda figured out that they needed the side ports really early, like before the FD was on sale, so the test bed was an NA miata with an early 13B-MSP, which is a neat idea for a fun car
Can I use the newer ACV from the later 4, 5, and 6 series FD's in my 94 USDM FD?
From what I've read:
The JDM ACV has a spot for the split air bypass solenoid valve, but it's not being used.
Once more, we're skipping a solenoid valve. Right here is where the 'Relief 2' solenoid valve would fit.The newer ACV versions ditch two valves: the split air bypass and the Relief 2. The only valve they keep from the old to the new ACV is the port air bypass.
So, why can't I fit the newer ACV into my '94 USDM FD? It seems like the relief actuator, which is vacuum-controlled, should already be relieving the air pump, why do we need a separate "Relief 2 solenoid valve"? Also, we might not even need the split air bypass valve if it's supposed to work off the switching actuator, which is also vacuum-controlled.
The later ACV models are still available new, so it would be convenient if I could use them.
06-06-21, 09:53 AM
