One of those threads Brrraaap was kind enough to linked mentioned that the air pump doesn't produce enough flow to actuate the ports until 3800rpm anyways, so that alleviates one of my concerns. Seems like I don't need to block the outlet after all.

Another problem though, I don't think my ACV is working properly. I made a little sub-harness to connect the solenoids on it up to the ECU, but I started by performing some tests. Here's what the stock vacuum diagram looks like:



The two solenoids that matter in this scenario are the "relief solenoid" and "switching solenoid. If you look at this diagram of the ACV we can see how it works:




Based on this diagram the operation seems simple enough:

- When no valves are actuated, air dumps out the relief port.
- When the relief valve is actuated, air goes out to the passage that feeds the split-air and port-air ports. Which port the air flows through from here is dictated by the switching valve.

- When the switching valve is not actuated, air flows out the split-air (to the stock catalyst)
- When the switching valve is actuated, air flows to the exhaust ports.

Vacuum supplied to the two nipples does the actual work, the solenoids just do the switching. This vacuum pulls on a diaphragm that opens the spring loaded ports inside.

The first problem I encountered is that the solenoids on the ACV don't seem to do anything. At least not on their own. I kind of expected that might happen, since there are actually four solenoids (two on the solenoid rack, two on the ACV). They just don't seem to behave at all as I expected them to.

Here's an excerpt from a spreadsheet I made awhile back:



What's even weirder is that I don't see why you would need more than two solenoids for this job. It seems clear; one solenoid determines whether air is dumped or not. If not, the second solenoid determines where the air goes.

I suspected this choice was due to the limited processing power on the stock ECU. Take a look at how the ACV is supposed to direct the air:




The "water temp switch" listed in that spreadsheet is the two-pronged connector on the bottom of the radiator. It's really simple; no continuity below 59F, continuity above. It's there because the ECU doesn't seem to have enough processing power to do everything Mazda wanted without some trickery. For example we already have a water temp sensor behind the water pump which is used for warmup enrichment, but it's not used for the 3000rpm accelerated warmup. They had to add the radiator switch to do that for some reason.

Similarly, there's an IAT sensor in the MAF and then a second one in the manifold. All the one in the manifold does is increase BAC duty once it's hot enough. Basically there are two full-range sensors but one behaves as a glorified switch. Meanwhile the ECU can do idle regulation with the BAC valve without any issues, but has to rely on the mechanical thermowax system for the accelerated warmup because that's beyond it's abilities.

Confusingly that doesn't seem to be the case for these solenoids though:



The B/W wire from the main relay is powered with 12V and the ECU can switch ground independently on all of the solenoids. So for some reason there are the relief and switching solenoids which control whether the two vacuum nipples above the ACV see vacuum at all, and then two additional solenoids inside the ACV for split-air and port-air. So it doesn't work at all the way I thought it did, and I probably need to restore those additional two solenoids to get everything to work properly.

All of which is moot because A. One of the solenoids in my ACV doesn't click at all, and B. The one that does click doesn't seem to do anything.

Meanwhile when I have both nipples on the ACV connected to vacuum, the port does switch but I get a vacuum leak internally. I can actually feel vacuum at the split-air outlet and I think an internal leak at that membrane is causing it. Ie. Vacuum applied to the diaphragm causes it to open partially, but the diaphragm has a tear and it allows this air to get inhaled by the engine.

I guess disassembling the ACV to see what's happening inside is in my near future. Worst case scenario I just break it further.

 

SendCutSend is great. A friend of mine drew up a part for me - it's a bracket that I mounted my premix reservoir to and will also eventually hold a remote charge point. It came out awesome.

 

They really do make the process easy. I was hoping my local place would do it, but they don't have a laser cutter and none of the places I called would even look at a small order.

Because of the minimum order and shipping cost from Sendcutsend (I'm in Canada) I ended up getting three trigger wheels for the price of one. So if everything works out I'd be happy to send you one of the extras + a printed CAS bracket for the cost of shipping. Assuming it all works as I expect it will, of course.

 

I'm already thinking way too far ahead, but assuming I found the right sensor, that appears to be a Delphi Metri-Pack 150 rear insert sealed connector, yes?

https://www.corsa-technic.com/item.p...category_id=80

And if you don't like buying a sensor for an S10, you can always say it is for a 2000 Cadillac Escalade. Or several other things according to the cross reference list on Rock Auto.

 

It has a ton of different applications. Just to confirm, I'm currently using this guy:


I'll probably buy an OEM sensor but the Amazon special has been working great for two years, regardless of temperature and tested up to about 8000rpm. The bracket needs to be cut down a little but it's a really minor modification. I think it's a Metri-Pack 150, been awhile since I purchased the connector. I'll make sure to get all the information together once I have everything ironed out.

 

Yup, that's the one. I suspected V6 S10, and that's the bracket that was included on all of those.

 

So I made some progress on both the ACV situation and the crank sensor. First off, I realized I had a source for the non functional solenoid. There is an identical one on the S5 TII engine:



Then I put the old one in it's place to keep dirt out:



Then I found out that it actually doesn't matter. The functionality that I need is controlled entirely by the external solenoids. I still don't exactly know what the internal ones do, but I've determined I don't really need them. This passage controls whether air goes out the relief port or to the split-air/port-air:



And this upper one opens the passage for the port-air:



So knowing that all I actually need is one solenoid and a tee to control when these see vacuum. Either they see no vacuum and air goes out the relief port, or they see vacuum and air goes to the ports.

It turns out I don't even need that functionality. I was able to successfully test with the air going to the exhaust ports and it has literally zero impact on my idle. It doesn's seem to idle smoother, or leaner, or let me retard the timing further like Mazda did originally, or really anything else. I can see the air is getting to the ports because my wideband reads out of range, but it doesn't seem to do much for me. Kind of underwhelming. For now I just did this:



I drilled a hole in a little plug to allow some air to escape the relief tube, but not all of it. This lets me actuate the auxiliary ports at around 2500 rpm. That's earlier than the factory does it, but it lets me add a solenoid later and use the ECU to control it like a boost controller. This is important because the air pump flows proportional to RPM only and doesn't take load into account. From the factory it uses exhaust flow, so Mazda will have calculated the opening point based on some amount of exhaust flow (which in turn means equivalent intake flow, or load). So if you rev to 4k but under really light load the ports won't move. With the air pump driving them they only correlate to RPM, so at high RPM light load the ports will open. The solenoid lets the ECU determine how much to open the ports based on whatever I want. In this case I'll do a few runs with the port open at various positions, compare the chart so I see where it wants to flow the most air, and then draw a line and use that to make a simple map. Not as scientific as using a dyno, but I do what's within my means.

For now though I tested going down the street with the ports driven directly from the air pump and found it works fine. There's some area under the curve to be had by tuning it properly, but for now it idles and launches smoothly and then the ports open and it has all the top-end power I want.

As far as the crank sensor, I've made some progress but I've also stretched my goals a bit. The trigger wheel that need-a-t2 kindly designed arrived from SendCutSend, and it's exactly what I needed:



It would work, but would still require some clearancing of the water pump pulley. Making the wheel any thinner might make it harder for the sensor to pick it up, so I decided to look at it again and decided on a slightly more elaborate solution.

I played around with the drawing and then extruded it a bit in Fusion 360 (I should have learned this software years ago...) to try and get the maximum tooth height and thickness that would fit:



Tooth height is good. Tooth thickness:



Also good. But this design is a bit more elaborate because it needs to be machined. Instead of a flat piece of steel being cut with a laser, this piece has a step to push the teeth forward and clear the water pump pulley. The alternative is to keep the trigger wheel flat and machine the pulley for the extra clearance, but either of these solutions still requires tools I don't have. So I decided to just see what I could do and came up with this:




Fusion 360 has a bit of a learning curve, but it's super powerful once you get the hang of it. I was able to take measurements and sketch a cross-section of the pulley, then rotate it into a 3D design and add a modified version of need-a-t2s trigger wheel before extruding it.

This solution is a bit more elaborate, and as long as the old design works I will still make the file available for people who want to modify the original pulley. But once I did the math on ordering more wheels from SendCutSend and getting my stock pulley modified it might make more sense to just get a new pulley machined from mild-steel by PCBWay. The cost of the old design approaches the cost of the new design, and still requires welding.

Here's a prototype I 3d printed and installed:



The plastic isn't rigid enough to actually tension the belt without it deforming, but you can see the teeth clear the front of the water pump pulley both front-back and from the end of the tooth to the nose:



In my experience the Chevy sensor isn't very picky about gap. But I still want everything as optimal as possible. The sensor behaves sort of like a switch. Either it doesn't see a tooth and there is no power on the output wire, or it does see a tooth and there is power on the output wire. Obviously we want it to be as unambiguous for the sensor as possible whether it sees a tooth or not. If the wheel is too thin, then there isn't enough metal to trigger the sensor. If the tooth is too short then the sensor might "see" a tooth even between the teeth. So we want the wheel as thick as possible (within reason) and the teeth as tall as possible.

I also want the teeth to be as tall as possible because it makes the bracket more compact. The more compact the bracket the more rigid it will be. I need to revise the bracket for the new wheel but it looks like I might need something stiffer than polycarbonate for it. I've been rebuilding it from scratch in Fusion with tighter tolerances to minimize flex on the end that fits in the CAS bore. If I can't get it to be rigid enough in PC I'll have to look into aluminum (CNC might be cost prohibitive due to the size of the block required, so maybe SLS printed).

Lastly, I'm probably going to pick up one of these sensors from DIYAutoTune and test with it. The Chevy sensor works great in my testing, but the little bracket needs to be trimmed to avoid interfering with the front cover. The DIYAutoTune sensor is compact, cheap, tested up to 19,200 rpm, and actually has a datasheet. It also has a longer nose which will make it easier to change belts. I might still end up using the Chevy sensor but it's worth testing with both. I'm also tracking what the cost will be for someone to order these parts and make their own kit, and (no promises) it looks like it might actually come in cheaper than the FFE kit when all is said and done.

Until next time

 

Just throwing the idea out, could you get some sort of metal tube that tracked farther down in the CAS bore and is a tight fit, then attach the 3d printed bracket to it?

 

Great minds think alike! I should have mentioned this in my earlier post, but I'm actually doing something similar albeit still in plastic. This is the redesigned CAS plug (which is the basis for the bracket, of course):




It improves on my prior design in a few ways:

1. The hole for the bolt (stud from the factory, but removing it and replacing with a bolt makes installation a lot easier) is tighter so there's no side to side rotation.
2. The ridge above and below the o-ring groove are widened by 1mm for a snug fit
3. The ridge above the o-ring in this photo (below when installed) is lengthened a bit to fill as much space as possible.
4. Similar to what you're suggesting, there is an extension above that fits further down in the bore. The CAS bore steps down slightly so this extension also gets a bit narrower.

The problem with making it longer is that returns diminish. If I continue to extend the top part in this photo to nestle further down in the bore, the length also makes it less strong. So a 1cm extension from here might reduce flex by say 5% (an arbitrary number, I don't actually know the figure) but an additional 1cm on top of that might only reduce flex by 2%. Lengthening that extension also makes it tougher to install. Normally I wouldn't care about that but if it isn't providing any benefit for rigidity then I don't want to complicate install for no gain. The same issue occurs if I use a metal extension because then there is flex introduced at the place where it joins the plastic bracket.

The other problem is just the distance from the CAS bore to the sensor. It basically just drops straight down a couple inches. This forms a lever that makes any fore-aft movement at the sensor side flex the area where the vertical meets the CAS plug. Sort of like a see-saw. If you put the pivot of the see-saw way at one end and put a weight on the short side, a small push at the long side can lift the heavy weight due to the mechanical advantage. Fortunately this is minimized a bit since the engine only really vibrates side to side (in the direction where the bracket is strong), but the sensor does want to wobble a bit fore/aft which is what concerns me. I can triangulate the bottom but the limiting factor at the top of the bracket is the thickness of the CAS plug itself, so unless I make it absurdly thick plastic might just not work.

To be clear, this might not even be an issue in practice. I just want to make the bracket the best it can possibly be, especially if others want to make use of the design. I don't want to install this on the turbo engine only to blow a seal due to sync loss at high rpm.

Also, as a disclaimer, I'm not an engineer. So if any of the terms in the paragraph I just wrote are incorrect and someone reading this knows better than me, please feel free to correct me

 

Alright, this idea might be a bit far but…


maybe tie the bracket to or around the oil cooler line? For some reason I feel like there’s threaded holes down there, that would give you the best rigidity.

 

I don't think there's a way to tie it around the line that wouldn't just rotate when the sensors moved fore/aft. Plus it suffers from the same problem which is that it's several inches away lengthwise.

The best thing would be if there was a free fastener just below the sensor. Then the bracket would be in tension/ compression whenever the sensor tries to move and it wouldn't budge at all.

Unfortunately Mazda didn't leave any excess fasteners in the area. There's one front cover bolt, and then there's the studs for the accessory bracket which would require that bracket to be modified or spaced out.

 

I certainly like where this is headed. Just thinking out loud, but why continue with the current laser cut part and just put a thin shim behind the AC pulley to get the clearance you need on the water pump pulley? I'd think bolt clearances between the AC bracket to engine, and AC to AC bracket there would be enough "slop" to move the AC unit enough to line up sufficiently. Worst case you slot bolt holes in the AC bracket a bit so you have some front to back alignment capabilities.

Also for the trigger mounting bracket you should design something up that's nice and ridged. Between welding and machining, I'm sure we could get you a stiff bracket for a reasonable material cost.

 

could you use the front cover bolt? maybe add a second leg?
it looks like its right there, but maybe not

 

I'd like to avoid messing with the belt alignment. I'm not 100% against it, but I made my alternator bracket custom a few years ago and the alignment needs to be a lot more precise than it seems. I think I measured it was 1mm out and it was already scrubbing the sides of the v-belt. It adds some complication that I'd prefer to avoid if possible.

One other thing I'm thinking is to make the sensor mount bracket a multi-piece part. One piece would require a large block of material to CNC, despite not actually being that large. One option is SLS aluminum printing, the other would be breaking the bracket into three small parts. This way each part requires a much smaller block of aluminum to produce. One for the CAS plug, one for the vertical, one for the sensor mount. Then tap some threads and use counter-sunk hardware to try and keep everything as aligned as possible. It's unclear whether the added complexity would offset the reduction in materials price, since I haven't even tried designing it yet. Just an idea I'm toying with.

It's possible, but the picture is deceptive. The bolt is only slightly below the CAS mount itself. It would definitely provide some rigidity by effectively shortening the length of material in the vertical section, but it suffers from the same problem as the CAS plug in that it's just a bit too far away. I'm going to try my best with plastic (keeps costs down significantly) but I'm thinking I might just be near the limits of the material.

 

oh i was thinking you could add an ear to your existing bracket or something

 

Okay, so this update has some mixed news. There were some complications with the pulley, but the bracket rigidity problem might be solved for good.

PCBWay's initial quote for the CNC'd pulley was way under their formal quote. Once I made a few alterations to pass their engineering requirements, the approved design would cost $350 USD for one unit. Apparently a design this complicated requires a lot of extra machine-time, which is entirely understandable. This does mean I had to find a lower-cost solution though.

The prior trigger-wheel designs I created each had a downside. The flat trigger-wheel could be laser cut and kept costs down, but would require machining of the AC pulley for it to fit (or clearancing of the water-pump pulley, but that's the same work for a less clean outcome). Ordering some of these would be the cheapest option. But I don't have the tools to machine the AC pulley, and while need-a-t2 offered to help, shipping it to him and back would become costly compared to my other trigger-wheel design.

The other design had a step in it that allowed it to fit over the AC pulley and be welded on at the back. This has the advantage of saving time and machine work on the pulley, but does mean the cost of the initial part is increased due to needing it CNC'd rather than laser cut. Once I did the math it still came in under the cost of trying to modify my pulley. So one is ordered, and as soon as it arrives I'll get to welding it to the pulley.

In the meantime though, I had already glued a plastic version of the CNC'd design to my AC pulley. This let me make a new bracket in Fusion 360, and I printed it in PLA as a test:



The sensor is pretty light, so I just used a small gusset to triangulate it and prevent it wobbling.



There's still a good amount of clearance on the inside from the back of the pulley to the bracket.



Most of the rigidity gains are from making the clearance on the CAS bore as tight as possible. I'm not sure if the extra step really adds anything, but it's a small amount of material so it's worth it.



On the inside I added these gussets. I had some on my previous design, but these ones are a bit more optimized. Less material, just as strong. I might also extend the rearmost gusset down the back of the sensor bracket for a bit less flex, but it's already rigid enough I don't expect any issues. Once it's printed in a material that will tolerate oil and high temperatures, of course.



And this camera angle is crappy, but this just goes to show that it still clears the AC tensioner pulley even at the bottom of the adjustment range.

At the end of this I'll be sharing three files, possibly four:

- Trigger wheel intended for use on a machined AC pulley (can be laser cut)
- Trigger wheel intended for use on a stock pulley (must be CNC'd)
(wheels should end up functionally identical, and in the same place)
- Bracket for S10 sensor with either of the above wheels. Requires trimming of S10 sensor hold down.
- Bracket for Honeywell style sensor that DIYAutotune sells. More expensive than S10 sensor, but comes with an impressive datasheet and works out of box with no modifications.

Both bracket designs will require removal to install new alt / air pump belts, but hey, you can't have it all. It's a minor inconvenience.

All in all, I'm happy with how things are shaping up. Updates as soon as I have them

EDIT: Oh, and I'll release the file for the full pulley as well. In case someone feels it's worth the expense

 

I did this last fall, but had yet to actually sit down and write about it. But recently J9 had a few questions about it and my answers constitute most of a post anyways. So here goes.

Last summer I came to the conclusion that speed-density based tuning just wasn't for me. A lot of people seem happy with it but I could never really get it to adapt to changing variables properly. I would tune it in the summer and it would be great, then fall would come and even at the same coolant and intake air temps the car would be lean. Or it would always stumble a bit on a hot-restart, and after-start enrichment was unable to tune it out. Or the required warmup enrichment curve would vary a bit and I would have to run the car extra-rich as a precaution during warmup. I was relying on the closed-loop system to get the idle to smooth out in that sort of situation. That's never a good sign. I'll explain some of the tuning process as well so people can see how the MAF assists with this.

With that knowledge I started to look at my MAF options. There are a ton of them out there but I decided on the MAF from a Z32 300ZX. This was for two reasons: The flow curve is known and available online, the outlet is the same size as the stock intake tubing, and the inlet looked suspiciously like the stock Rx7 flange. Turns out none of these panned out the way I wanted, so I'll make it short and say that you are probably better off with an R35 MAF in a custom housing. I'll explain more about that later on.

Stock Rx7 MAFs were not an option for me. S4 has the flapper door style which adds restriction (probably not a ton, but enough that I noticed when I removed my old one) and S5 is marginally better with the sliding cone but still not as good as a hot-wire style MAF.

I ordered a used OEM Z32 MAF on eBay (don't buy the knockoff ones that are of dubious quality):





The mesh is a little wonky, but that doesn't really matter. You can see the hot wire in the center in that little plastic housing. However, I did notice a couple of things. The first was that the bolt pattern didn't match up at all with the stock airbox, and the second was that even if it did the MAF would be too short to reach the intake tubing. This meant an adapter would be required:





The one side is adapted from an existing model on Thingiverse that I had been using to replace the MAF with a tube. The other side has the bolt-pattern necessary to adapt to the Z32 inlet flange. There's also a small mounting boss for my IAT sensor, since I find putting it here is more accurate than the manifolds due to heat-soak.

If you're wondering what's up with the honeycomb shape, that's a simple air-straightener I made. One thing I learned in the early testing stages was that airflow is super important with this style of MAF. The air should be in a straight tube the same diameter as the MAF for several inches before reaching the wire to ensure consistent even flow throughout the tube. If the airflow is swirling around, all one one side of the tube, or reverting back in the tube, these will cause the MAF to be way out of whack. The honeycomb shape was an attempt on my part to mitigate the challenge presented by the shape of the intake in this area. Take a look at what I mean:




That's actually an earlier revision of the adapter (and it required the MAF to be upside down), but it still illustrates my next point. The air in the airbox passes through the filter, then makes a sharp 90-degree turn through the outlet. Then it has about 7-8" of space to straighten out before reaching the MAF. This is obviously less than ideal in terms of ensuring even flow. Hence why the honeycomb was a necessary addition. I should also note that there are commercially available honeycombs for this purpose, usually with a much tighter diameter for the honeycomb cells. I couldn't fit one without making the adapter tube inside exactly cylindrical (resulting in a more abrupt transition), so I was limited by the 3d filament in terms of how thin I could make the walls of each cell in the honeycomb.

I think the only reason Mazda got away with their stock MAFs is that the design of the flapper-door and sliding-cone don't really care whether airflow is even. The amount of air passing by exerts some known amount of force on the door / cone, and this translates to the MAF reading. Done. Meanwhile with the hot-wire it can read low if the pipe is flowing a lot more air on one side, or bounce around if air is swirling a bit.

Speaking of Mazda's stock design, I also noticed something weird. The outlet of the airbox had this rectangular piece in it, reducing the surface area of the opening at the top of the outlet. I can only assume they wanted to use off-the-shelf Denso MAFs and decided the opening didn't need to be any bigger than the rectangular MAF inlet, which makes some sense. But now that I am not using the Denso MAF that restriction can go:



And the rectangular piece also covered this side near the filter:



I found this picture that shows the original lip thing (left) as well as a comparison with the S5 airbox. The S5 has a much larger valley where it transitions from airbox to filter, and it's located more central to the filter as well. I kind of wonder if there are any more gains to be had here, but if there are I doubt it's anything substantial.



With that, everything gets bolted up and put into the car. The wiring was very simple, I just made a little sub-harness and ran it down to the ECU. +12V, signal ground, power ground, signal.

Then I needed to make the relevant ECU changes:




This might look confusing because I'm still using speed-density on it, but hear me out:

- Primary Fuel Load (the way the MS3X calculates how much fuel to inject at any given time) is changed to MAF. I'll discuss how this affects tuning shortly.

- Primary Ignition Load and AFR Table Load are still speed-density. This lets me use my old tables as-is, without having to rescale the y-axis. If I changed these to MAF then I would have to find out the relationship between manifold pressure and air flow and scale the y-axis appropriately for my old values to work. I should note that I DO intend to do this in the near future once everything else is 100% worked out. It's just that for now it was much easier to start with known good ignition timing and AFR values.

Then I had to set the MAF settings:



- The Z32 is a voltage type sensor. Many modern sensors are frequency type, so look into that if you are doing a similar conversion.

- MAT correction curve allows a percentage correction for the MAF based on the intake temp. This can be useful if your MAF becomes inaccurate with heat-soak, but wasn't necessary for me. While the setting is enabled I have that curve zeroed out.

- Use VE1 as trim table is a way to enable the VE table as a multiplicative correction on MAF. I'll explain what this does later, but again, it's enabled in my setup but I am not using it (table is set to 100 across the board).

I don't really know what sensor range does other than possibly affect the visual scale and initial values of the flow curve in settings. You need to manually input the flow curve values for your particular MAF anyways. I selected 650g/s because it was the closest to the values I found.

Speaking of values, I started with an "official" Nissan flow curve I found online. Turns out it was 100% wrong for my setup, needing to be leaned out by at least 25% just to run. So my next post (in a few minutes) will be all about the tuning.

To be continued

 

So as a quick refresher, let's talk briefly about how speed-density tuning works:



This is the VE table in a speed-density setup. You need to try and hit every bin and make sure the car is hitting your target AFR for said bin in open-loop:



So if target AFR at 3100 RPM and 50kPa is 15.2, you want to adjust the equivalent VE cell until the engine is running as close to 15.2 as possible. Tuning for a specific AFR isn't good practice since we actually want to do whatever makes the engine happiest rather than hit an arbitrary number, but assuming the AFR target is correct we can try to get as close as possible by adjusting the VE number. These tables really need to be tuned in tandem, finding the AFR that the engine wants at the same time as you find the VE that achieves this AFR, and then putting that target into the table for the closed-loop.

The complication is that there is no real "link" between those tables other than in closed-loop when the ECU is trimming fuel to try and hit the targets in the AFR table. The other thing is that high load + low rpm is not the same as high rpm + low load in terms of airflow in the VE setup, so you need to try and hit a bunch of awkward bins (go up a hill at 1500rpm in 4th with the pedal flat to hit the top left, or travel at 7000rpm with the throttle cracked open doing 40kph to tune the bottom right). It complicates things a lot without a dyno.

Then once the VE table is as close as we can get it, the closed-loop algo should take care of minor variances.

In comparison, here's what MAF tuning looks like:



With MAF it's entirely different. Instead, I only use one curve and a table. The curve on the left represents the flow rate of the MAF (grams of air / sec) at a given voltage. The ECU doesn't have to take the VE number and do any math with the MAP, it just takes that number (say 1 gram) and then multiplies it by the target AFR for that bin. So at idle the ECU is just taking ~2.8g of air and using the air-fuel ratio to calculate how much fuel is required, then opening the injectors the appropriate amount.

The left axis still shows kPa in that AFR table, but the ECU isn't actually using it for any calculations. All the ECU is using MAP for is to know which AFR to target based on that table, and then otherwise the sensor is basically not used. This means that (assuming the flow curve is correctly calibrated) the AFR table itself dictates how much fuel is injected. If I want to idle at 13, even in open loop, I just drop 13 into the desired cells. Or 14, or 15, etc. I don't need to change the cell values in the VE table and then see what happens on the wideband and tune it in. It just works. If it doesn't, then either the calibration is wrong for that flow rate or there is a vacuum leak / other issue. The reason my curve is choppy above 3.7V is that I can't make it flow more with my current engine. That value is only ever hit when I'm in 4th gear going at a pretty good clip, and I would need to be going very fast to flow more air in an NA car. Turbo car should be able to do it under hard accel.

Closed-loop works the same as in the speed-density setup, it just doesn't need to do as much work.

Now I mentioned before that I had to tune the entire flow curve myself because the ones I found online were way off. I didn't really go into how to do this yet. Take a look at this log:



The right side shows the AFR table, but the important part is on the left. The second box from the top shows AFR and AFR error. So it's targeting 14.1 but it's 0.1 off of target. I can also see the MAF volts and flow at the bottom. So this part of the curve is pretty well tuned, but if not I would open TunerStudio and increase or decrease the g/sec value at 1.769V.

I also have an equation I made to do it for me which is why there's a "Calculated MAF" value. That's a custom field that takes the MAF g/sec reading (red line, 12.510 volts) and multiplies it by (Measured AFR / Target AFR) to make a "corrected" value I can drop into the curve at that point. Users on MSExtra were kind enough to offer some help and also show me that MLV has a histogram function that lets you define the scale:



So basically the scale on the left has the same voltage units as my flow curve, and the histogram on the right shows the average of all Calculated MAF values. This means I don't need to hit an exact voltage value and hold it either, since MLV will do the job of fitting the values to this scale for me. I can just take a nice long drive and then copy / paste these values into the flow curve. The darker the green colour, the more "hits" at that voltage value during the drive and the more accurate the number is likely to be.

It's not a perfect system. I found it took several attemps because my equation will overshoot slightly. If it's targeting 13 AFR and measuring 12.5, and I take the Calculated MAF value for that and drop it in the curve, next run I'll measure 13.2 under similar conditions. Run it again and put in the new value, I'll get 12.9. It needs to be done again and again until the curve smooths itself out.

This would be a great opportunity for the Tunerstudio developers to create an autotune for it, but they haven't. The VE "correction" table can be autotuned, but that tends to result in some weirdness because it's still trying to use two independent variables (MAP and RPM) to calculate the correction value for something that only has one independent variable (airflow). So it doesn't seem to work very well when used that way, but then the developers didn't seem to intend it to do that in the first place.

And what's the result?

First off I have yet to re-enable closed-loop and the car is almost always within 0.3 of target AFR. Usually 0.1 at steady state conditions. It's super accurate even without correction, and I can probably get it even closer by tuning the curve more. Second, I need almost no acceleration enrichment or after-start enrichment. I also noticed it's much smoother returning from decel fuel cutoff, and throttle response is generally improved. The MAF reacts so quickly to the changes that the speed-density algorithm struggled with. Third, the tune doesn't drift with outside temperature anymore. I thought it did until I got the flow curve dialed in, and now it's rock solid all the time. I don't need the closed-loop algo to help with hot starts anymore.

The only thing I have yet to tune out is that it runs a little lean after warmup ends (at 176 degrees) for 5 minutes or so before running properly and hitting target AFR. Meanwhile if I'm driving the car on a cool day the coolant often drops below 180, so I can't keep the warmup enrichment on longer or it activates when already warmed up. Still haven't figured that one out yet. The closed-loop algo can probably handle this but I'd rather tune it out the proper way if I can.

Overall I'm really happy with how it turned out. It was a bit of an adjustment to how I had learned to tune, but the results were well worth it. Until next time

 

thanks for the write up! um do you have an air temp map? maybe that needs a tweak? my car does the same thing, but i keep changing hardware and retuning so i haven't gotten to that yet.
i guess you could go the other way and do some insulating and make it run less hot, actually the turbo might fix it lol

 

Question! if you changed the entrance/exit to the MAF would that change the MAF calibration?

B i wonder how Mazda did the speed density without having the same issues that you (and i) have. the air pump and main cat work amazingly well, maybe they just let it be rich sometimes?

 

I do have an air-temp compensation map, but I currently have it zeroed out. I did try using it for this purpose but I realized the issue is my relocated sensor lives way up in the MAF adapter and doesn't heat soak much. I'm guessing the fuel vapour from the injectors is hitting the wall of the manifold. Like a cold mirror fogging up when I take a hot shower, the vapour is probably condensing back into droplets. Droplets reduce the surface area of the gasoline molecules and it doesn't burn as completely. Hence the same amount of fuel is being sprayed but I'm getting a lean condition.

This problem doesn't present when the manifolds are all the way warmed up, which is of course the condition for which I tune the car. Corrections come later.

So basically the engine runs fine during WUE. Ends at 176 degrees like the stock ECU does. But the car idles about 0.5 - 1 AFR leaner for about 10 minutes, I think until the manifolds warm up. Then it runs fine. If I were to extend the WUE taper out by a few degrees it fixes the issue, but then I go for a drive and coolant temps dip down below 178 and the WUE starts to kick back in. Then it's running rich.

What I should try is reconnecting the stock sensor Mazda put in the dynamic chamber, observe the manifold temp at which the AFRs become accurate, then apply enrichment at all temps below that. This is sort of how Mazda uses that sensor with the stock ECU, except they use it as a switch for BAC duty. I think it's manifold temps below 70 have a reduced BAC duty, and above 70 have an increased BAC duty? They don't explicitly say it's for fuel corrections but I wouldn't be surprised if they put it there for this purpose as well.

To the first question, almost certainly. I think any changes from the back of the filter to the front of the throttle body has the potential to change the calibration. The intake air runs through the snorkel, hits the filter, swirls around some as it passes through, then goes through the elbow thing into the MAF. Then it goes up the intake duct and into the throttle body.

I doubt (although have not tested) that pre-filter changes would make any difference. Post-filter changes will almost certainly cause a difference in the airflow. The MAF is surprisingly sensitive. I think even rotating it in-place might affect the reading, although this would probably be mitigated if I had a longer run of pipe before the wire. Post-MAF changes probably don't matter as much, but if they affect reversion at all then it could cause something to happen. The stock intake duct has corrugation to make it flexible, so I was wondering if switching to a smooth aluminum tube and silicone joiners would affect the MAF reading. On the one hand it's a really tiny change, but on the other if it causes air to bounce a little bit differently in the intake then anything is possible.

One conclusion I've drawn from all of this is that airflow is super complicated. I always knew it was complicated, just not how much

To your second question, I don't know. If I had to speculate I would say it's a combination of what you brought up (air pump and catalyst), the other emissions controls, and them having a ton of time and resources to really nail the tune. It's worth noting my car is entirely street tuned because I don't have access to a dyno. I really should go to the dyno one day, but when I look at the cost of a dyno session I always just figure I can spend that money on more parts.

I think the emissions horse is finally dead so I don't want to beat it too much, but all of the "emissions" stuff people throw in the garbage also has drivability functions. You already know this but just to name a few tricks Mazda had in their pocket:

- Ability to pump air into the exhaust ports and mitigate charge dilution
- Ability to pump air into the catalyst to compensate for richer mixtures when needed
- Ability to pump air into the intake ports on decel to control bucking
- Solenoid that switches away fuel pressure regulator's vacuum reference to prevent fuel boiling in the rails on a hot-start
- Vacuum controlled valve to slow rate of secondary throttle-blade opening
- Temperature controlled valve to control operation of above valve

And that's just the FC which had a MAF from the factory. I know the FD has a ton of solenoids too (although they also need to control the twins, so it isn't a fair comparison). Add in an unlimited number of hours on the dyno and the ability to design whatever additional compensation curves they need (since they wrote the firmware themselves for the ECU) and they managed to make it work. It's also worth noting that many people are running speed-density based tunes and are quite happy with their results. I just found that between the tune drifting a bit in different conditions and the "little things" like a hiccup returning from decel or a bog when I floor the pedal, it didn't quite do what I needed. And this is after tons of time spent trying to tune accel-pump based AE, enhanced AE, fuel cutoff taper time, ignition taper during the fuel cutoff, fuel return adder (duration + percentage), etc. I probably spent a cumulative 4 hours on the MAF conversion and maybe another 8 cumulative tuning it (drive time, not just computer time) and it's already way smoother. And I'm not even done yet

I'm considering wrapping this all into a big post (in an instructional format I mean) or maybe a YouTube video, starting with the process of selecting a MAF (R35 is probably more ideal), designing the adapter, installing, wiring, and then the tuning. The number of people running MAFs with a standalone is comparatively small. It makes me wonder how many are happy with their speed-density tune and how many have just learned to tolerate minor hiccups.

 

Oh, and I never actually mentioned why the R35 MAF is a better choice.

The R35 MAF is a newer hot-film style which allegedly reacts a bit faster than the hot-wire type. I don't know if this matters, but theoretically it might provide quicker reactions to throttle input and require fewer compensations (not that the Z32 MAF isn't fast already). It also includes an IAT sensor built-in which is really nice from a packaging standpoint, and has a simple two screw flange that lets it bolt into any number of available housings. If available housings don't work for a given setup, the simple flange will also make it easy to design a custom housing and have it printed. Or buy a flange in aluminum, locate it where you want it on an aluminum tube, and have it welded in.

Add to this the natural advantages of the R35 MAF from a non-technical standpoint (it's newer, similarly priced, they seem to be more plentiful, there are aftermarket versions, etc) and it just makes more sense. The Z32 MAF might be more convenient if they were common or fit without an adapter, but then I needed the air straightener anyways so it is kind of a moot point.

 

yeah if you need to print the housing anyways, it would be better to just use the R35. or maybe the Rx8?

and you're right, except for the turbo control solenoids, the FD only adds a Purge solenoid, and the double throttle system is also on a solenoid. so just two more

 

I hadn't considered the Rx8 MAF. It looks like they also have the integrated IAT sensor. Cheaper than the R35 sensors too (the used OEM R35 sensors I see currently listed are 2x the cost of the last time I checked, so maybe they've gone up).

Rx8 MAF seems like a good candidate as well.

 

I am following your build and have made it to the duckbill replica part.

I bought an OEM one when eBay had parts for rx7s cheap, it was the only one I could find. It arrived bent and box looked like it was in a WWE match. Furthermore, it had a weird deformation on the passenger side, it too kind of twisted upwards to where it's leaving a gap on the body. It also appeared to have "melted" as that is the best way to describe it. Surprisingly, the OEM material is rubber almost, like the T2 spoilers. The heat straightened it out eventually.


Anyways the holes mounted fine, I first mounted originally on my coupe but then I sold it and kept the spoiler. I installed it on my Vert and it was a chore as you have to double drill the frame of the trunk to mount it.

I'm getting off topic here, but I used on the coupe double sided body tap to hold the corner down and it ended up lasting a long time. Unfortunately you can't on a convertible as that would mean no access to your trunk.

Either way, this is a good read and good work so far!