Hey guys! I don't often post here, so I may not know a lot of the ins-and-outs of being a good forum user on rx8club, but I have an issue that is driving me crazy. Yes, I tried google and searching through these forums, but anyone that stops and thinks a little can draw the conclusion that no 2 issues or scenarios are identical. They may lead to same resolution, but their starting points may not be the same.

So I have a 2005 Mazda RX-8 (6-port, 6-speed manual) with 134k miles on the body. I have swapped in a used motor, probably from a 2004, with ~63k miles on it now. I've driven the car for 13k miles since I owned it, and I can not be any happier (when she works properly lol). I've done several modifications to the car already: BHR Ignition kit, AEM cold air intake, full aftermarket exhaust (headers, midpipe, and cat-back), a DW fuel pump, and a few other bits and pieces here and there. I have once decarbed the engine (about 5k miles ago), and it helped a lot, brought my compression numbers to 90 PSI even on all rotors (it used to be all over the place). As we speak, I am running on new spark plugs as well, recently changed.

So the problem is, my car is having trouble hitting the red line. It seems to be worse in colder weather, but I cannot guarantee it. By cold weather, I mean Chicago weather . We've seen -20C these past few weeks, then it climbed back up to about 10C, and now we're in the negatives again. When i try to hit redline, at around 6-7k RPM, the car feels like it's hitting a rev limiter, and there's a really loud gurgling noise in my header, as if it's clogged. Sometimes this results in smoke coming out the back, and most of the time it results in a flashing CEL (or misfire). From what I could gather, I believe these symptoms are of a bad to serious blow-by issue. There was oil on the plugs in the rear rotor, and the plugs were crusty like no tomorrow of carbon deposits.

The car starts fine, and it still shoots flames and hits redline when it wants to. I just want a second opinion on the matter. A rebuild is somewhere in the lines planned for the car (I mean, blow-by means rebuild, basically), but I want to know if maybe this cutoff I am experiencing is due to the PCM messing up the fuel trims, or maybe something else. I would greatly appreciate any input on the matter, and I will give more relevant information if requested. I've had some great time w/ the car up until now, and parting ways is not on the list lol

P.S. No, it's not my CAT, I don't have a CAT as I mentioned before. ESS is as clean as a whistle, and I have new plugs.

 

Bingo !

 

Check if there is oil in your intake. That will confirm the blowby theory. If you have the updated oil fill neck (you said the engine is off a 2004, so it probably doesn't), then you may have to look deeper into the LIM, but if you find oil, you have your anwer.

Fuel trims are easy to verify, get an OBD reader and look at them while this is happening.

 

If it’s blowby this will show itself it at idle with combustion gas flow out the oil fill cap and then also by revving it up (be sure to plug the sump venting hose to the intake so there’s not air bypassing the MAF when you check this because the sump is sealed to send those combustion gases back into the intake). However if this were the case I’d expect it to show itself in other ways that you haven’t listed here. So I’m thinking it’s something else, though there likely is blowby with only 90 psig compression.

What comes to mind for me; have you checked the APV assembly by removing the drive motor and making sure it opens/closes smoothly by rotaing the drive gear by hand? You’d also need to check the APV drive motor to make sure it works properly. The only fault code on the APV is if it’s stuck open. So if it’s either stuck closed or the drive motor failed closed then there’s no indication other than it won’t open at ~6400 rpm like it should to extend engine intake breathing to redline other than it just runs out of zoom-zoom. Kind of sounds like what’s happening to me? The 2004-2005 4-port Standard motor has slightly different port timing and a 7500 rpm redline because of this limitation.

Here are some links that will help you with this

https://www.rx8club.com/series-i-do-...valves-174009/

https://www.rx8club.com/series-i-tro...0/#post4431127

Also on the AEM intake you might check to make sure that one of those lousy screens didn’t come loose or is misaligned inside the tube somehow. This is a common problem that gets many users of that particular intake if they aren’t installed and tightened just right. Even had one crazy thing happen to someone where the throttle was going all crazy revving up and surging. A screen assy had come loose and was partially wedged in under the throttle body butterfly plate. Took us a while to figure out what the heck was going on with that one ... strange stuff happens ...

It usually pukes engine oil into the intake if there’s bad blowby, so opening it up is also recommended to check for that too.


Let us know what you find out



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Thank you all for your kind replies, here's some more relevant information.

This phenomenon seems to be worse when I free-rev in neutral, as opposed to being in gear, which is strange. One would think that while in gear, the crankcase pressure would be higher, therefore causing worse blow-by and oil in the intake. If I try to hit redline in neutral, and persist at it, my car might shut off. On the other hand, while in gear, it will sometimes gurgle, but the hesitation lasts only slightly, and I can reach redline in 2nd and/or 3rd gears.

I have planned a fancy oil catch can to be installed on my car on Monday. It was already on the to-do list, so this will aid greatly in figuring out what is going on.

Here's my story on the AEM CAI. I have taken it apart a few months ago to clean it up (along w/ MAF cleanup) because I had an oil spillage. That one was my fault, I overfilled, but since then I've had an oil change. Upon taking apart my intake to clean it, I saw that one of the mesh filters was broken slightly on one side. The mesh itself, not the rubber that holds the mesh in the intake.

I hardly doubt the mesh is the problem, and here's why: when I had my engine decarbed, and the intake was put back, my car would stall after a minute or 2 of running. I was like, "What in the world is going on!? More compression and ECU doesn't know what to do w/ it?" I also got the system too lean CEL. What ended up happening, a mesh from the intake wasn't placed properly, it was almost sideways, so the MAF had trouble reading the airflow. Popped the mesh back in properly, and no issues whatsoever.

That scenario does not apply here. There are no CELs that go along w/ this, and based on the scenario I said above, a misplaced mesh would cause system to run too lean and shut off engine even at idle. I will check up on my VDI, SSV, and APV to make sure they're actuating properly. Please stay tuned for updates with the first chance I get to troubleshoot. I DO have an OBD reader and the Torque Pro app on my phone. I've tried monitoring A/F ratios, and nothing seems out of whack. I've seen it go between 13 and 21 (21 being when engine braking). Under load, it runs slightly richer than 14, which is regular.

 

Well it’s hard to diagnose over the internet rather than be there. We only know what you post, whether it’s the whole story, accurate information, or written up properly is always the issue. Don’t take that personal because that’s just how it usually goes on here. We’re all basicly e-guessing. Frankly when it comes to afrs, trims, etc. the usual RX8 owner that posts these kind of please help me really has no idea what they’re actually doing or in understanding between what’s normal or not. I see that all the time here and based on what you posted above you don’t sound any different to me.



.

 

Ok, sorry it took so long, but I finally have some more info.

I got a chance to install an oil catch can. I also had my valves checked (VDi, SSV, APV) with a scanner, and they check out apparently. Unfortunately, the problem persists... Just today actually, I was driving, trying to redline in neutral and I couldn't get past 6k-ish RPM. I tried further down the road and at around 7k I got stuck again, but then a split second later it felt as if something unclogged and my car revved to infinity and beyond in 1st and 2nd gear.

I'm a bit skeptical that the APV is working properly though. As mentioned above, there's no error codes if it's stuck closed or motor failing... I have 4 more options to run through before pulling my hairs out for good and just driving her like an old lady until I get a rebuild.

1. Fuel Injectors
2. Ignition System (maybe coils are failing at a certain RPM, but come on, it's BHR >_>)
3. APV motor
4. ECU itself...

I'm gonna try again to unplug battery, and do the 20-brake stomp, maybe by some miracle it will get fixed lol...

 

Have you checked the AEM screens again since you started having this issue? Just because your broken screen caused certain symptoms once in the past doesn't mean its going to replicate it again... especially since you are openly admitting that the screen is busted already...

Also 90psi is low compression assuming it is normalized to 250rpm and sea level.

 

According to Mazda specs, yes, 90 PSI is low, but these engines can run at 70 PSI no problems. You obviously won't have the same pep from the engine, and starts might suffer considerably, but no one said it's not drive-able.

I actually bought a new AEM screen and installed it w/ the catch can, and it hasn't fixed my issue, BUT I have now some new information which might have pinpointed to the root of the source.

I checked my catch can, and yes, there is blowby. I didn't find any oil in there, mostly condensation and fuel. The fuel is a clear sign of blowby. I have completely reset the ECU maps (disconnected battery, held brake pedal pressed, reconnected battery, 20 brake stomp), and I even cleaned my MAF and throttle body again. These have not fixed my symptoms, but ever since I mentioned a post above that it felt as if something unclogged, it led towards something.

I have figured out the behavior of my car now, and it's probably due to an APV not operating properly. My conclusion is so due to the fact that when the car is in gear, and engine under load, I can now redline properly. As soon as I shift gears, and the engine loses that power/pressure/vacuum whatever u want to call it, pop it into the next gear, it will hesitate and gurgle for a second, and then I can hit redline again.

So either fuel pressure issues, possibly an injector problem, or the APV having some carbon deposits, not letting it to actuate properly unless there is enough vacuum to overcome it being stuck. My money is on the second one right now. I have done a smoke test, and there aren't any leaks in the vacuum system.

 

Why not hook up an OBD reader and get fuel trim, airflow and pressure data to diagnose properly?
It could be one of those 2 things, it could also be something completely unrelated.

The fuel in the catch-can, misfire, smoke and gurgling all point to you running rich. What you need to figure out is if computer is commanding it to be rich for some reason, or you're not burning fuel effectively, or something else. OBD data will help.

 

"run at 70psi no problems"

 

I am willing to look into that, could you give me any specific number range I should be in? What kind of pressure data? Fuel Pressure?

Sorry to revive a thread that seemed to have died, but these ladies are just weird. One day they'll run PERFECTLY fine, and the next won't. Keeping in mind all the issues I described above, it's mind-boggling how one day I can do a full power run (1st gear to 4th gear redlines) and nothing will be wrong, no misfires, no hesitations, just a serious pull as if the car is brand new from factory, and then on some other days I can't even redline w/out some gurgle or hesitation. Since I got my catch can (and boy am I glad I did), I had some serious oil burps. The rebuild is inevitable now, I know that for a fact, however, I want to make sure that nothing else is wrong w/ the car, because if I get a rebuild, and find out something else was the issue, I might be driving and damaging a rebuilt engine because of misfires, and I definitely don't want that.

I have replaced my plugs again 2 weeks ago (have to do it more often now, they looked hideous... all had some carbon deposits on them and they r only like 5-6 months old... one of them actually had copper oxidation on the igniter tip of the plug, which is scary), and haven't misfired since... until today... I also haven't had many gurgles or fuel cutoff symptoms, but it's definitely not running properly some days. I have replaced my MAF, completely new one, to rule out that possibility.

Here's a question though... an engine that has a failing oil control ring and low compression... does it run richer? Is it a direct correlation between low compression and running rich? Last time I checked my AFR w/ my Torque Pro app, I didn't notice anything out of the ordinary, but again, please let me know what range of values I should be looking for in terms of AFR, pressure, etc.

 

So are you still getting misfires?

 

There is no correlation between running rich and oil control or compression. Mixture is managed by the computer based on AFR, airflow and short and long term fuel trims. Those are the numbers we need to get from OBD on a warm idle, then we can diagnose.

fuel trims nees to be near zero, AFR around 14.7 and airflow around 5g/sec.

It will probably be easier to get next steps if you post the actual numbers, we can draw collective conclusions from there.

 

Are you sure the oil isn't still overfilled? Even if the oil was changed again, it can still happen. Make sure when you check the oil level that you warm the engine up, stop it, then wait for 5 minutes before pulling the dipstick.

I overfilled mine but caught it and drained what I thought was enough. Drove it around with no issues. A month later, attended my first autocross since the oil change and discovered the fun way that I hadn't drained enough oil. About 3/4 way through the first run and it looked like Spy Hunter.

 

No, that's not the issue here anymore, I know what my problems are in terms of failed ring and rebuild. I have a catch can, so oil getting into the intake and fouling the MAF or combustion in the chamber is not the problem anymore. Right now, I'm just trying to diagnose these misfires and what seems to be like a fuel cutoff or something that makes the car hesitate for either fractions of seconds or whole seconds before revving higher.

Yes, it still happens, Cajun.

I have logged some data, I have a spreadsheet, not sure where I should upload. Maybe a shared dropbox link would work? I wasn't able to fully hit red line, and I was mostly in stop and go traffic on the expressway, until about 10-15 minutes from the end of the log where I finally got on streets. When I revved once to about 5k or 6k RPM, I saw my AFR drop in the low 11s.

 

When you get misfires, are you getting CELs or codes?
Have you checked to see if any are stored in the Torque app?

 

When you rev up your car, it runs in an open loop, which means the car just runs on the built-in map.

When you are idling or going at a constant RPM, the car will run in a closed loop, so the input from the AFR sensor will be read and used to adjust the amount of fuel injected.

I have read that if your car is having trouble burning the fuel, AFR will try to make your car run richer since it detects excessive oxygen in the exhaust.

 

Warm idle. Revving it out is meaningless for diagnostic purposes. I know you don't have problems at idle, but that's not important at this point. We need a baseline.

Dropbox is fine, or you can just quote the averages here. At warm idle the numbers should be stable.

 

Wow this thread is like self diagnosing a stroke with out going to see a doctor for seven months.

Your very determined to find the needle in the hay stack ten fields over.

You haven't actually swapped out any parts or spent any money to try and diagnose this properly but you are convinced it is something else more complicated than it really is.

Well 7 months later we are still here.

Its really not that hard to check the easy and most common things first already documented on this site.

No need to do logs to determine what you already know that you have a Misfire , lean burn blah blah due to the ECU doing it job for safety reasons or something that has failed and isn't quite right.

1. You already know you have a shot engine but still think there is something else to the problem.
low compression on these things is a gimme. So the motor will still run but not as smoothly.
low compression symptoms are longer start times,hot start issues, sudden stalling for no reason but is not an intermittent issue.

Blow By is a term related to boost. Air being pushed under pressure past any of the seals on the rotors bleeding air into the next chamber or into the oiling system. You don't have boost you are NA you don't have blow by. Any vigorous driving will cause these things to puke into the intake healthy or not. Congrats your driving it the way Mazda intended it to be.

The gurgling noise you are hearing when you get your symptoms is your motor loosing ignition but it still has to ingest air through the engine.
The smoke is what ever fuel or oil that is left in the engine due to failed ignition so its pushed out the exhaust.

so forget the motor unless your going to replace or rebuild it.

Happened to me low compression starting issues still drove the snot out of it. Now been on my second keg for a while now eek guaranteed low comp oh well fingers crossed. Carry on next!

2. Your aftermarket air intake can cause this. Dodgy MAF screens ie missing, damaged, miss aligned or poorly installed so just reinstall the stock air box and see if it fixes the problem.

Happened to me working on a buddys boosted 8 and Brettus Was correct on the call of miss aligned MAF screens in the AEM intake.Hmm I was pretty sure I had them all straight anyhoos.

Did it fix it? no carry on next!

3. Your aftermarket BHR coils can cause this to happen out of the blue.

Re install the stock coils and wires if problem goes away then box them up and send them to Charles. His customer service is actually pretty impeccable regardless in or out of warranty as he stands by his product.

Happened to me started the car up to warm it up cause it was -20C and a coil would crap out intermittently for no reason. BHR awesome service thanks Charles.

Did it fix it no? carry on next!

4. Your aftermarket deatchworks fuel pump can cause this issue ie it maybe be an intermittently defective fuel pump, stuffing a high flow fuel pump into a stock high mileage fuel pump assembly that it is not designed to flow the higher amounts of fuel errr not really a good idea, fuel pump assembly orientation/ not pointing in the correct direction causing bad fuel pickup check your arrows.

Reinstall a new Oem assembly if problem goes away bin the aftermarket fuel pumps they are a bandaid solution anyways you don't need it your NA. I would pretty much bet my life on a brand new Oem assembly will out flow a high mileage assembly with an aftermarket pump stuffed in it any day.

Happened to me DW200 Failed, Walbro Failed, Aeromotive Failed been back on brand new OEM for a long time now and never looked back. oh I track too with no issues.

Again shout out Charles at BHR for the only person in the states to bend over backwards to get me a replacement DW200 to the middle of no where at DGRR in a few days to replace a failed walbro. His customer support is wow just really wow.

Did it fix it? no carry on next!

5. Your stability control will kick in for a split second and can cause this without even blinking a lamp on your dash yup it does, El cheepo junk no name tires, varying tire wear on all four corners causing different wheel speed rotation, aftermarket suspension system components miss matched or incorrect corner balancing, worn suspension components.

6. Do you buy cheap gas from no name gas stations including Costco?
if I remember right Olddragger lost a motor due to Costco garbage gas.

Are you filling up using premium?

Just because you have replaced Oem parts that probably had nothing wrong with them in the first place with aftermarket doesn't mean they are 100% better than Oem in fact its the opposite. Most aftermarket performance parts have short life spans and don't meet Oem factory standards hence most parts will say for off road use only.

I have had all the above issues through the 14 years I have owned my 8 and loved every second of these stupid cars and all there problems.

I have covered the most common and most very likely causes and will be very surprised if its not any of them listed above.

Happy hunting hope to hear back from you when you fix your issue if not let it die or pay some one to fix it thanks.

 

Most of the above is incorrect. Blowby is not related to boost and diagnosing by throwing parts is an expensive way to find out what all isn't the root cause.

The intake screen thing is a definite possibility though. Again, the computer can tell you exactly what you need to know via OBD.

 

scottish, I've already been through more than 3/4 of that list...

I replaced a broken air intake mesh, didn't fix the problem... Charles already sent me 2 coils, and then a BRAND NEW FULL coil set with his latest module, so no, that's not the problem... So I've had coils replaced twice now. No, it's not traction control, I have learned how that feels like when it kicks in w/out need to look at my dash to see the little skid mark show up. I know the DSC system the car comes with and have felt it like u said w/out it showing up on dash.

Car isn't boosted, has only full bolt-ons, and the DW fuel pump has the potential to pump more fuel, but it isn't actually pumping more than the car needed from the stock pump in the first place, so what u're saying doesn't make sense... I've had some issues w/ fuel pressure when the pump was first installed, but now everything is fine in that area.

I was able to log a short "power run" today, and there was a very short period (we're talking 1-2 seconds) of hesitation when I shifted from 2nd to 3rd... I'll upload both logs. Loki, the idle numbers seem to be fine, from what I checked, I'm above 14, but under 14.7 most of the time. I'm wondering if it could be front O2 sensor, but I don't see it being the case, unless I'm not fully aware how they work.

https://www.dropbox.com/s/4n8c67lvnm....csv.xlsx?dl=0

https://www.dropbox.com/s/xf24bppb9q....csv.xlsx?dl=0

First link is my drive home from work, lots of stop and go, few times I got to 5-6k RPM and towards the end I pushed first gear to about 8-9k RPM... was able to idle a lot, especially at the very end of the log, I let it idle a few seconds before shutting it down.

Second link has a first to 3rd and 4th power run, but I pushed to redline only first and second gear, then let go, then 3rd I believe hit red line but not sure.

 

Also torque doesn't seem to be rotary friendly, as RPMs reach a cap on the sensors before we can reach redline :

 

Oh, I forgot... When this hesitation/gurgling happens, I don't always get a blinking CEL, but if I insist at it, I'll get a blinking one. Sometimes it will start blinking w/out any gurgling or "fuel cutoff" feeling. Upon checking the codes, at first, it was rear rotor misfire, and now for the past few months it seems to have switched to front rotor misfire. No other CEL codes stored, except a very frequent O2 slow response for the rear O2 sensor (I'm using an O2 spacer so that I can trick my emissions, and believe it or not, I'm one of the few unicorns where it actually works LOL... passed my emissions here in Illinois while the exhaust was smelling like no tomorrow... dude plugs in OBD... I pass all monitors... go home pass lol)

 

I don't know, I'm not as knowledgeable as a lot of the members here, so I'm spitballing now and offering suggestions that don't require parts changing.
I would try to figure out what's causing the misfires.
(duh)
I think instead of the gurgling causing misfires, it may be the misfires causing the gurgling.

Smoke test or vac pump check might be a good idea.
I've seen a bunch of discussion about intake issues causing a lot of problems.

Be sure your wires are in good shape, snapped on tight and not bundled together or arcing on the engine.
Inspect your plugs for cracked or loose insulators.

That's all I got.