3rd Gen - What is that hole above the spark plugs?
 

Hi all. Long time 1st gen owner and racer, now I have this beat-up 3rd gen in my collection (actually, she's got a nice body, but everything else is questionable). The car runs and drives, but I don't want to get crazy with it until I've done a full tune up. When looking to replace the spark plugs I noticed some sort of hole above the front plugs. What is that? In my uneducated guess, I would say a sensor goes there?

Welcome to the board. :)

It's for a knock sensor

Thanks for the reply! So, if said sensor is missing, what should I do?

Since you specified the front plugs, let me ask: Is there a sensor on the rear?

As far as I know, there should be just one and I think Mazda originally had them on the front. That said, if the car is otherwise stock, then I suppose it would be wise to get one if it's missing. If you plan to modify (or it's already modified), then I will defer to someone else because I don;t know if they are upgrade-able or used in non-stock setups at all.

The car has one knock sensor. The same hole should exist on the rear rotor housing and should have the sensor in it, if it does then you have nothing to worry about.

Thanks, I'll check. It's kind of tight down there, even with the elbow off, but I'll look. Even if it does have a sensor back there, shouldn't I plug this hole with something?

No need to plug it since nothing can leak out of it. It's just a threaded recession in the side of the housing.

Also, the glue inside the knock sensors usually melt over time and drop on top of your spark plugs.

That would explain why I thought I might need to plug it, as it looked like it leaked something (I assumed oil) on the spark plug wires. That also means I have an empty hole where maybe I shouldn't. I tried to get a picture, but I had some difficulties with lighting.

I also found two other things that probably need addresses. It looks like these two vacuum tubes should have a hose connecting them? Also, anyone know what (I assume) sensor connector this is and where it goes?
https://cimg1.ibsrv.net/gimg/www.rx7...de78251c2f.jpg
Disconnected vacuum line?
https://cimg2.ibsrv.net/gimg/www.rx7...60cf263c46.jpg
Sensor lead to...?

Believe that’s just the “empty pipe” as labeled here...
https://i1126.photobucket.com/albums...psbxez2ujc.jpg

Not certain on the plug either. Maybe for the Windshield washer pump....that’s the only thing I can think of in that area.

Sidenote....you do have a belly pan, right?
Looks like this....
http://i1126.photobucket.com/albums/...ps4ac8a6c2.jpg

Thanks for the info. I do not have the undershield. Stay tuned as I find more questions about this crazy beast. I've been reading through the threads posted in the main 3rd gen forum, but feel free to impart any wisdom I should know upfront. I'm very familiar with 1st gens, but there's not a ton of translation between the two, other than they're both rotaries and have 4 wheels.

You’ll need an undertray/belly-pan. It’ll run hot and likely overheat without one.

First thing I recommend (if you haven’t already) is downloading or getting a copy of the Factory Service Manual.

http://wright-here.net/cars/rx7/manuals.html

Fritz Flynn should have one in Charlottesville.

Thanks, I PM'd Fritz. I have the service manual, but reading a Mazda service manual is it's own art. I wish they had a Haynes manual for this car.

You don't need to plug them as they are not holes, just recesses. It's the knock sensor itself that melts

The FSM is not that hard to understand. There's a workshop manual and a service highlights manual (for 93). The service highlights manual explains how a lot of the systems work

Reach out if you have any questions. There's several FD owners in the area

I'm in Fairfax Station now - I should update my profile. I have a lift in my garage with high ceilings, so if anyone wants to change their oil or work on their FD, and would like to come share some of their expertise with me, just let me know (hint: I;m trying to bribe you to come over and inspect this car!)

From what you've told me, this looks like the knock sensor.
https://cimg8.ibsrv.net/gimg/www.rx7...941a1a2b1d.jpg

But what is this for?
https://cimg7.ibsrv.net/gimg/www.rx7...9cb1148acc.jpg

I also have 4 BUR9 plugs, and as far as I know this car is pretty stock. Can I run BUR9s in T&L for now or will it be bad for the car?

Yep, that’s your toasted knock sensor.
Second pic is the pressure switch for the power steering. .
No harm in running 9’s L and T but they might foul a little quicker on the stock car.

So I take it I should replace said sensor? Does the whole thing screw out? Can I get a new one at a parts store, or is this going to be an adventure?

Google answered my question on where to get it, but $250 from autozone?

Sorry, I’m old, without my cheaters and on my phone and didn’t look close. If it’s not leaking it’s probably fine. Maybe clean the connection and make sure it’s snug.

What signs will the car give if it's not fine? Will I get a dash light or something?

Another question a search didn't answer: How tight should the plugs be (wrench feel)? I can't see the 1/2-2/3 turn I normally do on my 1st gen because I can't get my eyes and hand on the plug at the same time. I basically went with "good resistance but not put some muscle in it tight"

Yes, on the stock ECU a bad knock sensor will generate a CEL.
Depends on how long your wrench handle is, but good snug is enough. I sort of feel for the new washer to crush and seat.
Be sure to use low temp anti-seize on the plug threads.

Ok, another topic. What screw is this and how do I replace it (does it just screw out with pliers?)? Hopefully I can get one at Autozone.

https://cimg3.ibsrv.net/gimg/www.rx7...ba388ac69a.jpg

Use the double nut method to remove them and go to the closest ACE hardware or fastenal to get replacement studs

Took a video for diagnostic purposes. This car hasn't been run but about 1/2 mile from the drop off to my house in I don't know how long. Needed to change oil, belts (one broke), and plugs before I wanted to run it and diagnose it. It seems pretty good to me, the idle calmed down a lot once it warmed up. I want to know what you all think. It sounds (idle, revs, etc) a lot more like my 1st gen car setup for racing than it does a daily driver. Maybe the previous owner tuned it for track driving...? It definitely shows indications of a track car (but not enough that I think the person was a serious track driver).

If you don’t have any luck there you might try at McMaster-Carr.

https://www.mcmaster.com/

Looked at that video a couple of times now. I'm a little worried about the smoke, but it seems to be lessening the more I run the car (still have only warmed it up twice then shut it down). It's not overly white or blue, in fact it looks more grey black, which might just be due to the highly efficient engine we have that has sat for a few months (at least) and had crappy spark plugs before now. It does seem less each time, and my first gen spits actual fire out the back, so I don't know if this is a point to be worried about.

BTW, I see in my searches a lot of people shifting at 5k or so, and recommendations to not redline the engine. I don't drive my first gen Under 6k, ever, as the engine bogs. I've always seen rotories run at high rpms, so I don't understand taking it easy on these engines. I heard that will actually carb them up. Just curious if there's a complete change from 12a to 13b in how you treat the engine. I know I drove a 20b for a while like I drive my 12a (never below 6k) and it never performed better. Thoughts?

Turns out this RX7 is an R1 model that originally was competition yellow (J9 code on VIN and I can find spots inside the panels). I put eyes on the dual oil coolers and I believe it's the original suede seats too. The seats are actually in really good shape.

Awesome. I was going to speculate on that when I saw your earlier pic in this thread of the mystery plug. I thought I saw hints of yellow. Somewhere there is a VIN decoding thread if you want more confirmation.

Regarding the idle, it sounds like it might be ported. Is the compression good. That's should be the first thing to check

Also as a quick fix, you can replace the TB elbow stud with a nut. If there's not much clearance, you'll probably need a small head nut or an allen screw with a washer. Contact Ray Crowe to see if there's an OEM replacement or as mentioned McMaster Carr

And for the life of me, i don't understand why people do the things they do (e.g. paint a CYM white and hack the interior). And all CYMs were R1s BTW

And that's why we have people who restore cars out there, to return them to glory.

A CYM painted white? That paint is SOOOO expensive!!

Anyways, welcome!! Regarding your knock sensor issue, as well as many of the other sensors and little issues you are sure to come across in the near future....if you have to question it, replace it. Atkinsrotary is your friend.

I also recommend you get a compression test so you know what you're up against, because that will be the basis of everything else regarding the life of the engine. I suspect the car sat for a significant amount of time so I couldn't be too concerned with the smoke (seems to be condensation, but I could be wrong), but I wouldn't spend another penny on it until you get a compression test.

Welcome!! I look forward to seeing this car returned to former glory (AND COLOR!!)

I agree, I need to run a compression test. I did a test drive for 10 mins just to check out the turbos and such and... wow... this car pulls like a madman. I didn't realize it was this insane. It's going to make my gen 1 race car feel lame. In fact, I've run Ferraris (430, 458) around the track and this is more thrilling. You feel so much in this car. Even though the Ferrari is faster, it's a modern car where a lot is dampened. This thing is fast, and raw. I feel like I could easily terrify any passenger.

Radiator Fans
 

Ok, neither radiator fan is kicking on. I let the car idle and get up to temp, and I have a infrared thermo sensor so I was checking temps at various spots (radiator, fill cap, thermostat, etc) and while the car got up to operating temps (101-108c) I didn't see the fans kick on. I've been checking connections and stuff, but everything seems to be where it should be. So, what are my likely problems that the fans aren't kicking on? This is a pretty complex fan system (I read up on it) and I don't know if I should replace relays, sensors, etc. I would think they should engage at least at low speed at some point, so something has to be interuppting the whole system.

Also, my car has an OBD2 port. Did 93's come with those? I thought they had original OBDs.

The stock fan thermoswitch initiates at 105 C. It’s located on the back side of the thermostat housing. Are you certain you let it get hot enough?
It was OBD1 as a new 93. So somethings not right. Can you post a picture?

So, I don't know what the box of (relays?) are that the fans seem to be connected too. I didn't see it in the FSM. Here's pics.
https://cimg3.ibsrv.net/gimg/www.rx7...ad02f0d4d2.jpg

https://cimg2.ibsrv.net/gimg/www.rx7...1cf8ab7e6c.jpg

https://cimg5.ibsrv.net/gimg/www.rx7...2111256b1f.jpg

https://cimg8.ibsrv.net/gimg/www.rx7...b666c22fb0.jpg

This is interesting.

The 2nd photo has me holding the cover to the "diagnosis" port open. Borrowed my friend's OBD2 reader and it's clearly NOT an OBD2 port. Reading up on the fuel system it appears those relays in the front where the stock airbox would be are for the fuel pump (or at least one is), but I swear the fans are connected to that box (maybe the 4 fan relays route through there).

Any help?

Re: 2nd pic, that’s the OBD 1 diagnostic box.
Re: the 4th pic, not sure what the rectangular box and connector are for on the the relay bracket. Although the bracket has a provision for ‘something’ to be attached there, my car only has the 4 square fan relay boxes.
You might want to have a read thru these threads if you haven’t already....

https://www.rx7club.com/3rd-generati...system-906142/

https://www.rx7club.com/3rd-generati...ntrols-876767/