It adds up fast but is the only way to utilize its true potential.

The PFC has no knock retard. It displays the knock sensor but doesn't do anything with it. The chipped or piggyback ecu you mentioned you have is a very likely culprit. With these cars you really need to tune the actual car, not a generic flash for xyz mods as each car is a little different. Could also be another issue with the fuel system, ignition, harness etc which is why I strongly suggest going through everything. I'd hate to see anyone replace a motor only to not find the underlying cause of failure and have it happen again. Additionally, when picking an ecu selecting what your tuner is comfortable with is just as if not more important that the ecu itself. For example there are certain ecus that we will not touch.

Welcome to the club that no one wants to be a part of :sad:. If you own a turbo rotary long enough eventually it will happen, so you're in good company here. I've had 5 rebuilds myself: 3 were preventable and the other 2 were by choice. it may sound like a lot but I've had my car since 98' and I've put a shit ton of miles on it soo...

Quoted for awesomeness:

I bought my car with 68,000 miles on it and a Mazda reman in it in 2004. Blew the engine at 78,000 hot dogging with an untuned PFC and intake/downpipe/cat-back. Rebuilt it myself and I now have near 140,000 miles on it with an OK-tuned PFC that I did the tuning myself on, running 14psi with zero problems.

Blew up 2-3 motors back in the FC days - back then the only real options to keep a motor together were a bigger fuel pump and some prayer :)

Dale

Thank you everyone for the very helpful input. Learned a lot and feel well equipped to tackle this car now.
Will update this thread with results when I perform the compression test this weekend.

Prayer is always a part of my FD owning experience, no matter the ECU or tune :biggrin:

Great advice here, especially choosing an ECU your tuner is familiar with. If you don't already have a tuner or ECU preference, I would try to find successful racecars (not just forum guys or youtube guys) and ask about their experience. IMHO I would get a good modern standalone with logging and safety features before even considering a turbo swap. Even if an ECU plus harness and sensors costs $2000, it's money well-spent if it avoids another expensive rebuild. I haven't added all the prices, but I went in this order:
Wideband on mostly stock engine (2007)
AEM standalone ECU (later in 2007)
Fuel Injectors, fuel rail, fuel pressure regulator, and fuel pressure sensor (2009)
Replaced engine with used JDM, after the original coolant seals finally gave up the ghost (2010)
Newer AEM standalone ECU, old one wasn't bad but newer generation is better and I got a deal for helping beta test (2014)
Oil pressure and Oil Temperature sensor (2020)

Went ahead and performed the compression test-- engine has 0psi in both rotors on all faces. Tried spritzing some water in the tester head as a sanity check--nothing came out. Also tried putting my fingers over the plug holes and felt absolutely nothing.
Here's video of rotor 1-- exact same story as rotor 2 so I figure no need to beat a dead horse.
Rotor 1 compression test
Rotor 1 water in the tester head

The results pretty much line up with what my ears heard cranking over the car right after the failure-- absolutely no noises besides starter whine.
Against Dale's advice I stuck a borescope inside and took a few pictures. They aren't great but you can clearly make out gouging in the rotor housings so probably everything in the engine is trashed.
https://cimg0.ibsrv.net/gimg/www.rx7...38ee13939b.jpg
https://cimg1.ibsrv.net/gimg/www.rx7...d6d03c08c4.jpg

Although you’ve tested for compression, if my old school rear end had seen this thread quicker, my first thing would have been to check the MAP sensor hose connections on the fire wall. After friends FD went to the local Mazda dealer back in the 2000s and diagnosed within a blown engine, it was the map sensor they never checked.

The map sensor on my car looks to be brand new and is routed into the intake manifold near the tps. Anything in particular I should check for?
The car has always run extremely rich in all the time I've had it but I just ascribed the issue to the tune.

That compression test doesn't lie, for sure the engine needs to come out and assess the damage.

Dale

This is a really stupid question, and I've never done a compression test on a rotary, but since you're seeing all zeros, I'll ask it. When you did the test, did the plug holes the tester was not screwed into still have the plugs installed? If not, IMO, all zeros would be automatic.

I have never seen or heard of 0 compression so I was kind of wondering myself.

Yes of course
Put the tester in one plug hole and all others were left alone

As I said, it was a stupid question...

FYI, you typically pull both trailing plugs. Disable spark/fuel (pull EGI fuse) and screw the tester into one of the rotor housings. Floor the gas pedal and crank until you get your reading.

If you pulled leading and trailing plugs that would result in zero compression as the compression pulses would head out the other spark plug hole.

You can do a basic test with a piston tester - that can show relative health, show if you have a blown apex seal, but can't give good info on actual health of the engine. For that you need a rotary specific tester, that can give exact PSI numbers for each face so you can see how the motor's health is.

Zero compression isn't unheard of. It does suck because that motor is most likely zero parts good.

Oppai, I would seriously consider getting a Mazda short block with that result. There may be some good hard parts in the engine but that may just be some odds and ends to recoup some money, not a basis for a rebuild.

Dale

Any reason it should specifically be the trailing plugs instead of the leading plugs? I used the leading plugs because they were a tad bit easier to access from above without taking anything off.
Just curious.

It doesn't matter if your just trying to find out if you have any compression.

Leading plug holes have larger openings so the test tends to be more accurate. Sorry about the bad news.

Most likely cause of failure still seems to be bad gas since the car was running great up until the point it gave up on living.
Guess I learned an expensive lesson about old gas, even with fuel stabilizer mixed in.
Note to self next time I let a car sit for that long to not leave it on a full tank so I can at least put in some fresh gas when it goes back on the road. Maybe some octane booster would also be prudent.

A better idea is to keep your tank full for the off season to prevent tank and fuel system corrosion. When the season comes around DONT boost any of the old gas until empty. And don't bother putting any crap in your engine. Instead turn your engine to TDC and call it a day.

No octane boost... waste of money.

What's TDC? Top dead center?..

Yes

Tap-dancing Donkey Channel.

Dale