OtherSyde

So my engine has been doing the misfiring-when-warm thing over the last week or two, and rapidly fouling its spark plugs black (fouled its most recent brand-new set in about a month). It doesn't run particularly roughly or stall or fail to start or anything extreme yet, it just slightly chugs and quietly misfires periodically at idle, which I caught onto first by the mild shuddering of the car and from hearing the muffled intermittent misfires while standing behind it while it was running.

I know it's not a clogged/bad cat, since I don't have one (BHR catless midpipe). So initially of course I suspected it was just the ignition system, which was irritating since I have a full BHR kit and it's barely a year old, but nonetheless I took it all apart and examined the coils, wires, etc. and they all look top-notch if a little dusty; no burn marks or corrosion from water leakage or anything like that. I pulled every connector apart and aggressively cleaned them all with electronic contact cleaner spray from O'Reilly Auto before putting it all snugly back together, which did cause it to run a little better.

I relented and ordered a compression tester from rotarycompressiontester.com a week or so ago, and ran some tests with the engine fully warmed up (but not hot from hard driving). I've included 3 tests from the front (forward) rotor and 3 tests from the rear (aft) rotor; the numbers average mostly in the mid-90's, but those ones that are dipping into the low 90's are not looking good.

I've been doing research and seeing several varying rotary compression charts and various conflicting recommendations as far as minimum compression levels - mostly stating the 90+ psi levels are not good (as in, rebuild coming soon) but not yet engine-imploding territory. How accurate is this?

OtherSyde

So, quick update, I called a local Cali place called Rotary Reliability & Racing in Santa Ana after seeing several good reviews involving RX8's getting rebuilds/remans there, and they told me there is no point in rebuilding an engine when it is still scoring in the 90+ psi range unless you just really really want to, and even suggested that I could go ahead and install my supercharger with the 8psi pulley (although obviously it would degrade the engine's remaining life faster). Is this accurate?

Loki

iTrader: (1)

If you have no symptoms, keep driving and saving for a rebuild until you do have symptoms. But 90psi is below Mazda replacement spec.

Low compression doesn't cause fouling, so you have something else going on there. Perhaps a vacuum leak?

NotAPreppie

I agree with Loki. The compression numbers are low but if you don't have any symptoms, just roll with it. My experience with my motor is that low-compression engines that are otherwise healthy just keep slowly deteriorating (rather than suddenly going *bang*). If your engine is anything like mine (which is now low-80's to low-90's), it'll just keep getting more and more lethargic.

9krpmrx8

iTrader: (46)

Rotary Reliability & Racing in Santa Ana doesn't know wtf they are talking about. If you keep driving a low compression engine all you are doing is making potentially reusable parts unusable. Why are 90% of self proclaimed rotary shops so inept?

RotaryMachineRx

iTrader: (1)

Curious what RPM were these numbers recorded at or are those already normalized to 250rpm?

9krpmrx8

iTrader: (46)

I believe on those testers the results are normalized.

9krpmrx8

iTrader: (46)

Yep, from the site "RCTV5.2 Corrects for RPM and Elevation." It's actually one of the only testers I have not used for comparison to mine.

RotaryMachineRx

iTrader: (1)

^ Ah damn, then yup I'd say your numbers are low.

OtherSyde

It seems I do have moderately low compression, but I've figured out my other problem - I ordered one of those little coil spark-testers that looks like a fake spark plug with a little grounding clip on the side (recommended here on the forums) and tested my BHR coils - the front 2 are strong, but he Leading coil for the aft rotor is not firing, and the Trailing coil for the aft rotor is firing very sporadically once it warms up (although I suspect the second/Trailing coil mostly started degrading as a result of the first/Leading one not firing, as I read can happen - cascading failure seems far more likely than two BHR coils failing at once).

I'm talking to Charles at BHR right now and he's sending me a set, and I'm sending back my current set for evaluation and warranty.

So maybe it wasn't the somewhat low compression causing my disconcerting misfires and rapidly-fouling spark plugs in the aft rotor after all (although it's still good to know about and start planning for); weird, and I wouldn't have suspected it since BHR is definitely known for rock-solid ignition setups. Hopefully it was just a fluke. Could leaving the car to sit for 7 months while I was on deployment have caused this..?

RotaryMachineRx

iTrader: (1)

Not likely anything from the car sitting for that long, I park mine for 5 months every year.

Agreed, BHR is a rock solid company, but he doesn't build the D585 himself and they (like any product) have a certain percentage that are prone to failure. The best part about dealing with Charles is that he's going to back his product as you mentioned before and make it right for you. You're not the first person to have a set of BHR coils fail on them, you won't be the last.

I'd definitely give you car some good hard pulls when you get the replacement set, help clean that rotor our that hasn't been firing properly and try the compression test again. You may see improved numbers but when you do the compression test the ignition system isn't firing anyways, it's just the starter spinning the engine so it's hard to say.

OtherSyde

Will do.

Today I pulled out the air box and accordion hose, removed the old coils, and dismantled the rack they were sitting in so I can swap in the new ones when they arrive in a day or two. I labeled the Leading:Rear and Trailing:Rear coils as well, so when I send them back he can test them and maybe see what went wrong. Also, I put in four brand new spark plugs in preparation for the new coils, so hopefully everything will be running super-smooth once I get them installed!

I also installed my Ryan Rotary Performance alternator pulley and fitted my strut tower brace spacers/long bolts for when I finally get around to getting my supercharger installed, but I'm gonna post the pics of that in the Pettit Supercharger Owner's thread.

neit_jnf

min compression for all previous Mazda rotaries per respective shop manuals:

79-85 12A NA (9.4:1), 13B NA (9.4:1)
86-88 13B NA (9.4:1), 13BT (8.5:1)
89-91 13B NA (9.7:1), 13BT (9.0:1)
92-02 13BREW (9.0:1)

85psi @ 250rpm

max permissible difference between chambers: 21psi

Only the 13BMSP has a higher limit and the compression of 10:1 is not that much higher than the last NA 13B at 9.7:1.

As long as the compression between chambers and rotors are close the engine will run fine.

RotaryMachineRx

iTrader: (1)

Not arguing it won't run fine. But the fact is 90psi is defintely on the low end.

9krpmrx8

iTrader: (46)

Yeah "fine" as in in makes 100WHP fine. RX-7 Logic.

OtherSyde

Well I put the new ignition kit in from BHR (apparently they have a new/updated model now, the coils look slightly different and are labeled differently), and the car is just humming - and with noticeably more power, which I guess is to be expected after driving around with a sputtering/dying coil for 2-3 weeks.

Since I've still got my rental car for 2-3 more days, I took my 8 down the street to a local well-reviewed body shop, to get the hood painted to match the car - the clear coat on the carbon fiber started getting all those ugly white spots under the surface (UV damage?) just like the CF hood I had on my last car did, and it was almost more white than CF at this point. So screw it, I didn't really like having a two-tone car anyway, I've wanted a cleaner look for a while now.

For an engine swap, I was looking at buying an upgraded unit from Rotary Resurrection, they're about $3k or so. Anyone have any experience/opinions regarding them? Are they legit or should I avoid?

RotaryMachineRx

iTrader: (1)

I believe Rotary Resurrection has a good reputation of building quality engines. Before you pull the trigger you still plan to re-test your current engine with the new plugs tho right? I'd do a few hard pulls with these new coils before testing to help clean out any carbon first; but I'm curious to see just how much the compression numbers will change.

Loki

iTrader: (1)

I had a comp test in 2014 that showed less than 90psi. In 2015 it showed 120psi. This year its around 112. Same engine, different testers (real rotary ones, but not the specific one you're using). . Don't rush into a rebuild until the other stuff is sorted and you have symptoms of low compression.

neit_jnf

Rotary Resurrection is well known and reputable in the RX-7 world, quality builds.

With the new coils I'd do a de-carbon procedure, either with water, seafoam, atf whichever you prefer. Then run it hard and redline a few times and re-do the comp test.

I'd also add premix to the gas if not done already to extend the engine's life.

BigCajun

iTrader: (1)

https://www.rx8club.com/rx-8-discuss...ilders-265177/