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.