Hello everyone. New guy here!

I bought my first RX-8 a few days ago and have spent the last couple days searching for an answer to some problems but couldn't find them.

Long story short... Bought the car used from someone who said it got harder and harder to start over time and when it finally wouldn't start he took it to a dealer who said it had low compression and sold him another car. After deflooding and TB cleaning it's running and driving. It has the starter upgrade already, header, Borla exhaust, highflow cat, yadda yadda.

What I'd like to know is the transition environments for various actuators and functions. Things like... "aux ports open >5000rpm" "Decel fuel cut at <2% throttle >1500rpm" ect ect. This info will help me diagnose a problem faster then explaining it and reading through 100 opinions it could be.

Finally, does this version of the rotary have any modes of operation where it shuts off a rotor? On decel for example it sounds like it cuts one rotor from running before complete fuel cut. I seem to remember the FCs doing the same.

 

Foxed.ca - Mazda RX-7 Manuals

check out the service highlights book, it does talk about most of the stuff you're asking about.

the Rx8 is like a BMW E30*, the engine can be bad, but the car still runs ok and nobody notices.


*those things have the rings so far down on the piston that in normal street use they carbon up and don't seal, the engine runs rough and is missing power, but since its a 6, its still pretty smooth.

 

Hopefully you got a hell of a deal on the car since you bought it knowing it was going to need an engine.

 

Thanks for the link.


Paid $3k plus a $180 tow. It's in fairly good shape. I see a few rust bubbles starting on the rear lip of the wheel well but otherwise it's clean. Interior is nice. Not sure what packages this car has (sunroof, 18s, bose, hid) but I didn't get the nav.

The car runs smooth over 3~4k rpm. Below that it -sounds- like a light steady misfire from 1000-3000rpm and torque is down. When rolling to a stop idle is steady at about 1000rpm. Once stopped the idle drops to 800rpm and the misfire is "heavier" for lack of a better word. Unplugging both coils to the front rotor has no effect on the idle so it's idling off the rear rotor. Could be dirty injectors, could be bad apex seals. Cold start is fine and cold idle is fine. No codes. Did seafoam treatment already.

Car has new coils, plugs, wires, new 2k starter, battery, tires, brakes, Borla exhaust, header, highflow cat.

If it winds up being severe engine failure I'll drop a v6 in it. That was sort of the intention when I bought it. I just happened to get it running. Since it's running I figure I'd fiddle with it and see if it's something stupid.

 

Well that is a reasonable price at least. The guy you bought it from got the compression tested and it came out as bad right? Any idea what the numbers were or did he never tell you? If it tested badly there is really no getting away from it. You might try and find an rx8 at a dealership near you and test drive it so you can get an idea of how the power compares to yours if that one is healthy.

 

The story on the car was that it got harder and harder to start until it didn't start anymore. A dealer told him it had low compression. I don't know what the numbers were. It was heavily flodded with months old gas when I got it home. Just had to dry it out and new plugs to get it running but it wouldn't idle at all. Turns out the throttle body was plugged so badly with carbon it wasn't getting any minimum air.

The interesting thing to me (while cranking during it's no-start episodes) is the engine starts "running" at the same rpm it's cranking. You can hear the starter just skipping along at ~500rpm or so. Pressing the throttle I can hear the intake change note as the butterfly opens but there's no change to the exhaust note or increase in rpm. I would think opening the throttle would help get it going. On the days it does start, it will quickly transition from crank firing to idle fairly quickly. Leads me to believe it's fuel or ignition related.

It's likely I'll part this engine out and do the v6 swap. Haven't decided on an engine yet. As far as RX-8s go. I love the car, hate the engines. I've owned enough rotaries to know when to quit.

 

Oh no...not another one...

How many Rotaries have you owned that have OBD II, CAN installed??
How many Rotaries have you owned with OBD II where you have successfully changed over to an entirely different engine and actually can drive/use said car?

How much of the cars original features do you actually want to work?

ABS, DSC, Electric Power Steering, Air Bags, Speedo, even able to remotely lock the car doors, and Instrument Cluster which actually works....just to name a few.

BEFORE, you decide to transplant your RENESIS RX-8 with another engine (V6 or V8 or I4), take a look at a few transplants being done here and the issues these 'owners' are having first.

All end in an abortion of a disaster....let alone the financial one.

I am doing you a favour.....Don't go there!

 

do the v6 swap

...but I've no clue which V6.

That's funny, right there.

 

Why's that? As ASH8 mentioned, it'll need to be OBDII. Other things required will be an engine from a rwd application, dohc, closed deck with forged internals (boost later?), and fit the 8's engine bay. As far as piston engines go, an engine is an engine is an engine. So long as I have the ECU for the engine, things like the cas trigger pules train and maf can be used. If I have to make an intake and it starts screwing with VE curves, I'll get an FIC to compensate. FYI I'm the guy who came up with the COP conversion using Toyota COPs on the Miata. I ran the AEM EMS in mine on DIY maps, 15psi, sequential ignition, and passed emissions. Wiring is not hard. Not to me anyways. I had a sandrail for awhile that I swapped a KL into. THAT was some good power to weight. :D

As far as the instrument panel goes, the gauges themselfs are analog. I don't have to drive the 8's canbus systems. I can retro another vehicles systems into the 8 and invert/level-shift another vehicles instrument panel electronics to drive the 8's gauges.

EDIT: ASH8. The other rotaries I've own were an '85 RX-7, 89 RX-7, 91 RX-7, and a Johnson Golden Ghost. I have yet to find a Grasscat.

EDIT: Various engines I've been researching are the Mazda K-series, Taurus SHO, Nissan VG30 or VQ30, and Honda's C27. The SHO engine would look nice in the engine bay with it's plentiful intake runners. There are also bolt-on transmission options that wouldn't require an adaptor plate.

 

moonroof+HID+bose = grand touring. nav was an option, but no nav is a there have been some advances in navigation systems since 2003...

step one is a compression test, chances are its low compression on the front rotor, the side seals wear quickly in these, so compression starts fine, and then gradually drops off.

if it passed a compression test then, maybe you'd look at something else...

 

One thing I tried last night was sucking in a capfull of ATF into each vacuum port, on the intake runners, one at a time while it was running. No change. I also gave it a sprinkle of carb cleaner through the same ports and it seems to load up rich. So fuel seems ok but I think the atf should at least cause a slight raise in compression which would lead to a raise in idle rpm.

I think I've decided on an engine if I do a swap. I'd go with the VW VR6 engine and boost it. It's cheap, has a great exhaust note, large selection of aftermarket parts, strong internals, OBD-II ECU, peak torque in the upper rpm range 5000~6000 and 7000 redline. Should cooperate well with the 8's gearing but requires an adaptor plate. It's also a narrow engine compaired to V engines, plus the exhaust ports would all be on the right side of the engine bay which makes exhaust plumbing easier. I've seen 8's online with inline 6s in them so there should easily be enough length in the engine bay for the VR6 engine.

The engine bay is pretty big in this car but I forsee the steering rack location being the biggest issue for an engine swap. There's only ~15" between it and the cowl and ~19" to the firewall. The back of the head on most engines would hit the cowl for sure unless the crank pully was above the steering rack. From the steering rack to the top of the strut bar is ~18.5". The VR6, I've read, is 27" tall so the crank pully would have to be behind the steering rack in order to drop the engine low enough but that puts the back of the head into the cowl. I may have to go back to the v6 search. Suzuki H25/27A engines are pretty small but expensive.

 

Between the leading and trailing plugs, is one or the other more responsible for starting/idling then the other?

EDIT - It idles on either the trailing or leading plugs so all 4 coils are firing anyways. I did the poor mans compression test by rolling the car in 2nd gear and I can clearly feel a compression stroke every 180deg of rotation by watching the crank pully. Rolling the car I feel it tug-tug-tug-tug-tug-tug constantly vs. tug-tug------tug-tug------tug-tug if it had a blown apex seal. I'll get a real test done soon.