Ughhh that's a massive bummer about the AC dude, but yeah at least you won't HAVE to do that teardown again until it starts warming up. I watched one of my coworkers replace the entire A/C system on a Crown Vic a few months ago because the origianal compressor grenaded internally... then do the whole thing again because the new compressor locked up and spat debris into the new system. Everything was new, pressures were good, etc, just Ford doesn't make compressors for those cars anymore and the aftermarket one apparently wasn't long for this world. Heartbreaking. At least this time around, you might have some shortcuts you found from the first time...

In reference to the above comments once you get a wideband, I'm really interested to see what AFR's the ECU's got you targeting at WOT. I'm not wholly versed in expected DI AFR's and spark timing but those systems seem to be able to get away with some wildly different parameters at high load compared to port injected engines.

 

Been making progress on a bunch of little things, none of which really deserve their own post.

Exhaust
The biggest annoyance on the Miata was the exhaust - it was just too damn loud (shakes fist at clouds). Fortunately I (and my AI friend) were correct about the resonator - the shop replaced the puny resonator a vibrant ultra-quiet and it's MUCH quieter. It's still plenty loud when you step on it so I'm happy with where it's at.





The second issue with the exhaust was the rattle that, in hindsight, is clearly setting off the knock sensors. I was convinced the flex pipe was the culprit, I could bang on it and hear things moving inside. After the shop replaced it the sound persisted, unfortunately. I once again had violated the first rule of troubleshooting - fix the broken thing first. In this case I knew the header occasionally touches the steering shaft and apparently the sound traveled down the exhaust to the flex pipe. At least I know what the issue is now, I just need to pull the header out and give it a nice dent. Also, kudos to the exhaust shop - they've done all of this labor for free. I stand corrected on my initial assessment and would recommend them.



After taking that picture I've realized I need to keep the brake line away from the header, too.

Gauge cluster
I've been driving the car with my DIY gauge cluster for a few months now and… I love it. It's exactly what I want. I thought I'd want a physical needles instead of a screen but I fixed two things that would drive me nuts: first, the refresh rate is at least 30fps so it's never laggy. Second, the tach is huge so it's still easy to read just by glancing down. I've decided to just run it full time which means I need to clean it up:

• Better mounting / finish around the screen, including adding "normal car" lights like high beams, turn signals, etc.
• Adding a trip meter
• Adding a fuel gauge
• Add an "idiot light" that does not depend on the pi
• Dim the lights / screen with the rest of the interior lights
• Design a PCB to safely shut down the Pi

Adding "normal car" lights is pretty straightforward, I can just buy a set on Amazon and connect them to the factory wiring. I've already added an odometer in software which, due to how SD cars work, was much harder than anticipated. Adding a trip meter is pretty straightforward now, though.

The fuel gauge and idiot lights are going to be more work. Fuel level is an analog signal and because the Pi is basically a PC it doesn't have any analog inputs. The solution isn't super hard, it's just work: wire in a CANbed which does two things: reads the fuel gauge (and bus voltage) and transmits them on the CAN bus, and monitor the CAN traffic for anything alarming. IE, if there's low oil pressure, coolant temp too high, etc., blink an LED so the driver knows something's up. I want this function to be on a µC because they're way more reliable than something running Linux. That, and they boot almost instantly, whereas the Pi takes about 25 seconds.

I could add the voltage scaling, etc. for the CANbed in the harness but… I don't want to. It's ugly and hard to service. Instead I'll design a PCB that does the analog scaling and also includes PWM outputs to drive the stock gauges in case I ever feel like going down that path in the future. More to come on this.

Band saw
When the exhaust got built I had about a week without a car and, well, I got bored. A while back I'd bought a second 4x6 band saw to convert to vertical-only use - there's really no cheap metal cutting vertical bandsaws on the market. Even the portaband + swag offroad stand is around $500 all in. I bought the HF bandsaw for $125 on marketplace and decided to build a stand for it like this or this or this or this. $60 at the scrapyard got me some steel plate, a segment of angle iron, and this nice aluminum base. A few hours of cutting and welding and I had this:





Definitely worth the $200 I have into it. It's a little top heavy (hence the sandbags and I-beam) but overall it's way better than using the saw in stock form. I do plan on making a better table at some point, the stock table is pretty flimsy. Some people rotate the guides such that the band is parallel with the wheels but that significantly limits how wide of a piece you can cut - by leaving it as-is I can always rotate the guides to trade off depth of cut for more width and vice versa.

Wall takedown
I should have knocked out a bunch of work on the car over Christmas but… it was cold (for NC) and I needed to work on not-a-car for a few days. When we moved into our house the garage was finished in (hence the crown molding) and one of the first things I did was to turn it back into a garage. I tore out everything (carpet, wall in front of the garage door, etc.) except for the utility closet on the left side:



That remained because there were 7 switches in the two walls and I didn't feel like dealing with the electrical at the time. My Miata did fit sideways but just barely, the bumper had to be removed. Because I'd like to store the Miata there again without removing the bumper (and because I need space for a chassis table eventually) I decide it was time to tackle the job. It took …way longer than I was expecting but I'm very happy with the results, I've gained a lot of room and the space is much more usable.





Pictures don’t really do justice to how much additional space there is now. I also installed 33,000 lumens of harbor freight shop light while I was at it and, well, I might get a tan if I spend enough time out there. If I screw something up it won't be because I can't see what I'm doing.

The electrical work wasn't terribly difficult, just time consuming. I got lucky in that I only really had to run wire for one switch, the romex exited the drywall at the top back of the garage and the switch needed to be next to the door to the house. The rest of the work was really just converting the wiring back to how the house was when it was built. Mounting and pulling wires through the wiremold took most of the time but I'm pretty happy with how it turned out.

 

That's a nice looking garage you got. Jealous.

"Exhaust
The biggest annoyance on the Miata was the exhaust - it was just too damn loud (shakes fist at clouds). Fortunately I (and my AI friend) were correct about the resonator - the shop replaced the puny resonator a vibrant ultra-quiet and it's MUCH quieter. It's still plenty loud when you step on it so I'm happy with where it's at."

Did you replace the resonator with a Vibrant, or replace the Vibrant? My Ecotec side exhaust is also too loud, I was looking at the Vibrant. Thanks.

 

Thanks! I spent a long time working in driveways \ parking lots so I feel like I've earned a place to work

For the exhaust I replaced the tiny resonator the shop had installed (it looked like it came stock on some Mercades) with the vibrant and the vibrant really quieted it down a lot. Not sure what sort of muffler you're running but if it's a reactive type (no internal packing) adding a resonator will probably help out a lot. I was surprised by how much of a change there was.

 

Back to some actual Miata content. I'd put ~800 miles on it since I got it on the road (I don’t know the real number since I didn't have an odometer) and identified all the teething issues, so it was time to do the (hopefully) final teardown and fix all the little issues.

Sound deadening
The car was pretty loud on the highway without any of the carpet installed. Not surprising, but while it was apart I went ahead and added some boom mat and then a sound deadening kit from FM. It's probably overkill for a convertible, but it wasn't all that expensive or heavy so I figured it was worth a shot.





Wiring
The interior wiring was pretty rough - nothing was really combined into a harness, most of the connections in the glove box were done with wire nuts, etc. That was all pretty straightforward to clean up. Before I finished, though, I wanted to add the clutch position sensor from the Camaro. This would hopefully fix the rev hang I was experiencing between gears with the engine warmed up. I picked up the sensor and connector from Rockauto and with those in hand I had to figure out how to mount it. The factory the position sensor (a potentiometer) directly engages with a pin on the pedal.



Why this is a position sensor and not a switch is beyond me. HPTuners has an option to use a switch, but based on my experience with some of the ancillary ECU features it can control, I'm skeptical it works as advertised. Directly actuating this with the pedal was out of the question as it would have been a total PITA, so I came up with a workaround:


I shaved the fingers off, epoxied on a 3d printed pully, and ran a string between the pully and a hole I tapped in the pedal. I was surprised by how well this worked - the range is spot on and it's dead simple. TBD if this solves the rev hang, but it was a fun project either way. With the carpet installed and wiring cleaned up it was starting to look like a real car again



Passenger Airbag Area
I'd initially removed the airbags in the car because I want to eventually add an aftermarket steering wheel, but one of the unintended benefits is I created an area to mount my Raspberry Pi.

As an aside, after giving it some more thought I'm not super excited that I removed the airbags - turns out the NB2 seatbelts likely have a deformable member inside them that slows your body into the airbag. Without the airbag in place it just slows my face into the steering wheel. Not really sure what to do about this. As Dave Coleman said, "On the one hand, I kinda wish I still had that big, explosive face pillow in the car. On the other hand, if this was a 1970 Miata, would I still be doing this? Hell yes, I would. Time to man up and not crash…"

Anyways, the first step was trimming the airbag cover so I could fit stuff in there



An oscillating tool made quick work of this. I also needed a way to remove it without reaching up behind the dash and pushing it out, so after removing half the clips to make it easier I stuck a piece of duct tape to the back and let it dangle out the front. It's not pretty, but it works for now. I've got a better solution in mind long term but this works for now. Next I needed something flat to mount the Pi to - a few hours with some sheet AL and I and I had a mount



It's attached to the dash with some - if you haven't used it, it's amazing stuff. I have to limit how much I use so that I can actually get stuff apart. Everything is mounted to the plate with dual lock as well. The tube on the left side is from the HVAC vent - I noticed during my initial drives that it got pretty warm under there, so I wanted a way to get at least some fresh air in there. The wiring is …still not done. I plan on designing a board to go on top of the pi to power it and allow it to gracefully shut down. Right now power just gets cut and it can corrupt the file system. In the meantime I've hacked a 12V to USB power supply in and taped it down, hence the wire nut.

The other item of note in that image is the red thing in the back - that's the inertia switch attached to the dash



I welded 2 studs on to the dash bar and attached it with locknuts. When that switch opens (in the event of a crash) it opens the powertrain relay, which then cuts power to the ECU and fuel pump. It's cheap insurance against gasoline spraying everywhere.

Garage AC
It's starting to heat up here in NC so it was time to finish the garage remodel I'd started over Christmas. One of the last items on my list was plumbing in fresh air to the AC unit. For those unfamiliar, most floor units (like mine) take air from the room to cool the hot side, then dump the hot air outside. This sounds fine until you realize that it's taking quite a lot of air from the room and the makeup air has to come from somewhere - in my case it's directly past the garage door. So while the unit is pumping ~12k BTU of heat out of the room, it's drawing probably ~4k BTU of 90° outside air inside, significantly reducing the overall efficiency. I solved this by 3d printing a manifold to go around the air inlet and plumbing it to 2, 4" ducts to the outside





The 2x4" ducts already existed from when the garage was finished in (long story) and I added the 6" dryer duct for the hot air, both vent to outside. It's certainly not the prettiest solution, but it's better than spending ~$2k for a mini split, plus the time and headache to rearrange my breaker box for a 220V circuit, etc. I'll have to wait until it gets hotter to see if it makes a big difference, but it certainly seems like it should. Prior to the fresh air mod it would keep the garage at 80° on a 95° day. I also plan on insulating the garage door, so hopefully between the two I can keep it to ~75° during the summer. I also put a wall-mounted fan up, an excellent $60 purchase. I should have done that years ago.



I've got a few things left to do before I get the Miata back out on the road: replace the entire AC system AGAIN, install a roll bar, wire in wideband, fuel pressure, and clutch position sensors, design a PCB to read the oil temp and fuel pressure sensors, etc. Once it's back on the road, though, it shouldn't need to get taken apart again for a while. If all goes well I'll have it done by MATG and then I can hopefully get it out to VIR before the end of the year.

 

I look forward to seeing this at MATG. Only a few months to go!