Serious Blowby, or Other Issues? - RX8Club.com



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Old 01-12-2018, 11:26 PM   #1
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Unhappy Serious Blowby, or Other Issues?

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.
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Old 01-13-2018, 12:21 AM   #2
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Quote:
Originally Posted by Eirulisse View Post

AEM cold air intake

maybe this cutoff I am experiencing is due to the PCM messing up the fuel trims, .
Bingo !
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Old 01-13-2018, 02:41 AM   #3
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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.
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Old 01-13-2018, 09:00 AM   #4
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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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Last edited by TeamRX8; 01-13-2018 at 09:13 AM.
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Old 01-13-2018, 10:45 AM   #5
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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.

Last edited by Eirulisse; 01-13-2018 at 10:49 AM.
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Old 01-13-2018, 02:54 PM   #6
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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.



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Last edited by TeamRX8; 01-13-2018 at 02:59 PM.
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