bvy

Hello! I have an 04 with ~130k miles (fewer on the engine). New plugs/coils/SSV valve. Compression numbers are around 90. No cat, and a spacer on the rear O2 sensor. I have a premix kit and run 93 octane.

I don’t know if I have one problem or two…

Occasionally when approaching redline (almost exactly 6k) the CEL starts flashing, and the revs drop. I have a video of this. It started around Christmas. When it happens, it happens VERY CONSISTENTLY.

Is this “limp mode”? Or could it be a bad APV motor not opening up those auxiliary ports at around 6k? The dealer downplayed it and said that just happens sometimes when traction control is on.

At the time, it was raising a lean code (P2096) and a misfire code (P0302). More recently it’s added some O2 sensor code (P0138/0139).

I took it to the dealer and the plugs were black with unburnt fuel. They were only 2 months old! Dealer said it’s because one or both O2 sensors are raising that lean code and telling the car to dump fuel.

The dealer tech did clean up the O2 sensor in case that was the issue. He also recommended flash tuning the ECU if I wanted to continue without a cat.
Any ideas?

CaymanRotary

When is the last time you replaced ignition components (Coils and wires) You said you plugs were new but did you replace anything else? Could also be those solenoids on the firewall but you usually get a code for those if they are not working. Are the actuators able to move freely on the VDI and SSV? Only the front O2 sensor is important, so that might also be causing you issues. Traction control does not affect the engine misfiring so your dealer isn't right about that.

Misfire is usually due to poor ignition system components. Would look into testing your coils and spark plug wires unless they have been recently replaced with known good components. Flash tune is also not necessary to run a decat. I would suspect its the front O2 sensor coupled with bad ignition system components causing your misfires.

Loki

iTrader: (1)

I would get it away from that dealer, I don't think they know what they're doing.

Did they look at the catalytic converter? High rpm misfires are usually that, the cat gets clogged. Often caused by poor ignition coils and usually causes engine failure if left alone.
Did they check fuel trims or vacuum leaks? You need to see if it's actually running lean due to an air gap somewhere in the intake (open hose, cracked hose, etc). O2 sensors can fail, but finding a vacuum leak is free and replacing the sensor is not free and may not fix the problem.

CaymanRotary

Could be a vacuum leak as well so he could look into that. I believe he said he's running catless but that can also cause issues depending on the reason for running catless. If it was completely trashed, the front O2 sensor would have sustained damage as well from my experience (replaced 2 bad cats and both times had to replace front O2 sensor). If just replacing the cat with a midpipe and there was nothing wrong with it, the O2 sensor can be reused.

NotAPreppie

I second Loki's suggestion to check the catalyst.

If you can get the front of the car up on jack stands, it's only three fasteners to disconnect the front of the cat from the back of the exhaust manifold. Then 4 more fasteners to remove a crossmember for clearance to allow you to tilt the cat down and shine a light into it. You should see a uniform matrix of catalyst material. If it's broken up or in any way irregular, you may have an exhaust clog.

It's possible that you have a bad O2 sensor which caused the engine to run rich. Running rich for an extended period of time can damage the catalyst and lead to it breaking up (which would lead to misfires, bogging at high RPM, and eventually engine death).

Don't drive the car anymore until you've figured out whether your cat is still in good shape.
Seriously. A bad cat will cause heat build-up around the exhaust ports. If that happens long enough, the coolant seals there will fail and the engine will have to be completely disassembled to fix it. So, you're basically looking at a complete rebuild.

jcbrx8

Definitely not limp mode, which limits to 4K rpm IIRC.

Gunked plugs, and misfires sounds ignition related...perhaps initiated by failing or faulty APV operation.

And you said you've no cat. Roger that.

Given that I'd suspect...
- ignition components...though you said plugs & coils were new. Wires? Test each entire path: plugs, wires, and coils using the below...or similar.

https://shop.advanceautoparts.com/p/...xoCQAoQAvD_BwE

- If your SSV was gunked up...requiring change; perhaps your APV is as well and sticking. Check it's operation.

All the best.

bvy

Thanks guys. Again, I'm running with NO CAT. Have a straight pipe, and a spacer on the REAR O2 sensor. Dealer said something about cleaning corrosion off of the front one, which (I believe) is the ONLY one that will influence the air/fuel ratio.

New plugs and wires, ignition coils, and solenoid valves (December).

I've since gotten it back from the dealer. No CEL codes and it's running smooth. But I'm not comfortable that the issue of it dropping revs at 6K is fixed. Nor am I totally convinced that it's running any less rich.

NotAPreppie

Get an HEI coil tester for $20 and test your coils. Bad coil can lead to misfires. Also, make sure that the right plugs are installed in the right holes and that the coils are connected to the right plugs. The car will run with the leading/trailing plugs swapped but not well.

Also, put a pressure gauge on the fuel line that comes up between the brake booster and the UIM. It may be that the pump isn't able to supply enough fuel.

CaymanRotary

Pretty typical to run rich catless. Not being able to rev past 6k RPM isn't normal however. This could be an SSV problem so make sure the actuators move freely and are not binding up. I'm skeptical that cleaning up that front O2 sensor actually did anything. But if it's not throwing a code maybe it's good in the short term. Better off just changing it out really and save yourself headaches down the line.

bvy

Right. But that's only happened a few times. I have a video of it happening (of the instrument panel) if I can figure out how to post it...

CaymanRotary

Upload to YouTube and link it.

bvy

Approaching redline in first and second. Revs consistently start sinking when it hits about 6k. Ignore the horn...

NotAPreppie

CaymanRotary

Both my cars catless, both run a bit rich. Figured it to be a normal consequence from running without a cat.

CaymanRotary

your traction control is kicking in due to your tires spinning. They in good condition? Traction control drops revs in the event the tires slip. You'll get the same effect from launching in first gear. Traction control goes on and drops your revs even with your foot on the accelerator. You could always just disable it. There is a button called "DSC off" to the left and down from the steering wheel. Just hold it down for a bit and you'll notice that light is solid yellow. I keep mine off at all times unless the roads are wet.

Loki

iTrader: (1)

How are you determining that it's rich? It will smell richer, obviously, but the cat and the post-cat O2 plays zero role in determining mixture.

DSC will cut power if it senses you're doing something silly, which could be exactly what's happening. In the video I see the DSC light blinking, I don't see the check engine light. You're barely pushing the car, on a dry road, so the DSC should not be acting up. +1 to how are your tires.

CaymanRotary

Black spark plugs. Before taking off the cat they would be more brown, now they are black.

NotAPreppie

Post hoc ergo propter hoc.

Agreed. No CEL there. That just looks like TC/DSC killing the fun keeping you out of a ditch.

CaymanRotary

Well, this happened to two RX8's I've owned. Brown plugs before decat, black plugs after. It's nothing I really worry about as I get no CEL aside from P0420 from running catless. Ignition system nearly new (Mazda Rev C coils with NGK plugs and wires) and works great with compression 7.5-7.7 across all rotor faces. I dunno why it's running rich but it does. I run the car pretty hard and commonly get it over 7k RPM and once a day to 8.5k RPM. Power is good so I dunno...

jcbrx8

I'm not convinced traction control has anything to do with your symptoms. But test it. Disable your TC and go for a spirited drive (somewhere safe). My bet is you'll still see your 6k rpm rev constraint.

bvy

Well actually we haven't seen the constraint except a few times since. The night of the video, the roads were wet as I recall.

The tires were purchased new in November.

So traction control is pretty anticlimactic, but if that's all it is, I'm okay with that.

jcbrx8

I understood you experience the issues on dry roads.

You do know what TC does, right? So, if you're revving in excess of 6k rpm in 1st and 2nd gear on wet pavement or loose gravel you might expect TC to activate, right? Nothing to bring to the forum.

What am I missing?

bvy

I don't know what you mean by nothing to bring to the forum. Is it traction control kicking in or not?

CaymanRotary

I think he means that it's normal for TCS to kick in if the wheels start slipping. It is kicking in but that's a safety feature so you dont crash. Always good to have on wet roads. Dry roads I turn that off every time.

bvy

Ah, got it. Truly I didn't pay much attention to what was flashing, but now I see it's not the CEL at all. Also, I didn't make the connection to wet roads until tonight. Tires should be good though.

My "rotary guy" diagnosed it as the APV motor which, now, I think was a grave misdiagnosis. I spent a lot of time trying to connect that to everything else going on (running rich for example) so I'm glad I got some fresh input here.