Preamble:
Us three, beer, digging craigslist for cars. 3 hours, 12 pack of NewCastle's, and 450$ later, we have an 86' NA, base model, with a supposedly blown engine.

Aftermath:
The motor turns over fine, and the car starts, but doesn't hold idle unless you give it gas. What's strange is that both rotors are affected - unplugging spark for each makes the engine unstartable, and the spark-out "compression test" doesn't help either - all faces give an equal "thump". Neverthelsess, there's no idle, and above ~2k rpm the car gives the same power regardless of engine speed. Difference between part and full throttle is also minimal.
I could barely drive the damn thing over 40 mph, although it got to 40mph relatively fast. Basically, felt like riding a very big moped.
Exhaust doesn't smoke, but smells like total crap. The most foul-smelling exhaust I've ever dealt with.
Oil pressure gauge shows flat damn zero until the car is warm, then it shows ~15-20psi at 2000rpm "idle" and rises to ~40 at higher rpm. BTW, would a faulty oil metering pump cause these symptoms?
Overflow tank is empty, yet the radiator is full.
I'd think it's an apex seal or two, but for all rotors? Wouldn't that make the engine... err... dead?
Fuel injectors? Vacuum leak? Worn rotor housings? Dirty spark plugs? TPS? MAF? I'm at loss. Will try injector cleaner, two-stroke premix, and clean spark plugs tonight, together with vacuum leak testing. Any other tips?...

 

Get a new engine.

 

Yeah, thanks.
The new owner is broke, so the further this car will go on its current engine, the better of an engine we'll be able to stick in it.
The original plan was to put a junker engine in it right away, but if the current engine holds ground till winter, we'll be able to pull apart a few junkyard engines and build one from best available parts (with new seals and what not). So, tell me how to make this one breathe, if you feel like talking.

 

If it cranks well enough you should do a compression test - a piston compression checker will do fine.

I don't think the engine would build up enough compression to start if it had two blown rotors.

 

Clogged cat?

 

Sounds promising. Will the car run with just the manifold, and the rest of the pipe disconnected (given rotary's exhaust sensitivity)?

 

yeah, disco the exhaust after the manifold for testing - I have a parts car that was written off as "dead apex seal" by the previous owner. come to find out the tank was sugared and after fixing the affected fuel parts, the cat was clogged too giving it no power and hard start.

if the pulses are equal then the apex seals are good enough, especially if you can start it. I'd be concered with the low oil pressure reading. try changing the sending unit...have you done an oil / filter change yet?

why can't you drive it over 40mph? does it matter what gear you're in? ~rich

 

Awright! Couldn't get my hands on a new set of plugs yesterday, so while waiting on these, I let the old ones soak in mineral spirits for a minute. While doing it, I checked the labels... Damn right, (T) plugs were on the front rotor, (L) plugs on the rear So I put the trailing plugs uptop, leading ones on the bottom (where they should go, right?). Here's the question: how do I verify that proper lines are connected to proper coils? I have blue (trailing) and black (leading) lines, going from coils at the firewall and at the right headlight, respectively. Sounds right?

I then proceeded to undo the exhaust...
There are 3 bluges. The one in the middle of the car looks like a conventional cat. The ones between that one and the manifold appear to be made of cast steel. Are these what they call pre-cats? I managed to separate the exhaust between the first and second pre-cat, which gave me a small improvement - together with fresh oil and correctly installed plugs, it now lets me hold "idle" RPM's at 1500, as opposed to 2000+. Still, it shakes violently when you let the idle drop, and eventually stalls.
I couldn't get the last cat off, but I did spray it with penetrating oil, and hammered it pretty hard, should come off today. Now, if that doesn't get it loose, should I just stick a big screwdriver in there and gut it this way? I'll prolly gut it anyway, hopefully when it's off the car.
Oil got changed yesterday, and came out moderately clean. Where's the pressure sending unit? BTW, any tips on pdf's of factory manuals? All I have now is a previous owner's crappy Chilton's manual that covers all mazdas (duh). Worthless crap. Everything else I have to order, nobody stocks Rx-7 books around here
As for 40mph, yes, it doesn't matter what gear, although naturally if you drive it below 2.5k rpm it slows down to 30mph or so. Didn't check it with exhaust off, though, I'm pretty sure it could do 55-60 right now.
How do I check for good fuel flow? Undo the injectors? BTW, plugs were of a good brown color, like the bottoms of well-baked cookies, so I think I don't have a lean condition here.
Spraying carb cleaner all over the car with the engine on didn't induce any changes, so I assume there aren't any significant vacuum leaks.

 

+2 for clogged cat, it will cause ALL of your symtoms. Disconnect the OMP and run pre-mix, get the car running right premixed, then go and investigate the injection system for flow or issues.

 

i melted the cat on my GSLSE and it wouldnt let me go certain speeds.

 

cats cause alot more problems than they fix, they should all be destroyed