Mysteries Misfire with no CEL
 

See if anyone has this problem before
The car has 35,000 miles Compression was both good.
The previous owner babies the car a lot (Not good)

So I'm fighting a intermittent Misfire with no code, I notice the hesitation before the catless exhaust but never realized there is an actual misfire now I put the catless exhaust on you can hear the few misfires
so basically at soon as VDI kicks in, (Indicated 8K RPM) (7.5K RPM ECU), AND all the way to redline it was having a few misfires, but no check eng. light at all. It was happening as stock, so I changed a few things
I put, catless exhaust, new BHR Wires, Coilpacks, sparkplugs, and new MAF, Cleaned ESS intake is on its way air filter is a little dirty but should be the deciding factor.

The next step is to pull the intake off and actually check VDI, I'm literally running out of ideas. STFT, and LTFT are fine, no problem, AFR is on point but it does seems like it got a little leaner than targeted when get close to the redline
The fucking thing is no check eng. light it is pissing me off, and doesn't do it ALL the time. Any one has any ideas?

Kevin

Fuel delivery, pump maybe?

Thats what I thought..I mean until you lift off it should also be on the rich side correct?

Kevin

Fuel pump (pressure) might be one, what about oil in the intake? It's possible for oil to be aspirated into the engine via the oil fill neck if the oil is overfull, or if there's excess blowby pressurizing the oil pan, or the PCV isn't working as intended. This tends to show up at high rpm only and in small quantities can feel like a misfire, without actually being a misfire the ECU can detect.

theres a lot of oil on intake before, on the MAF, and air filter. but I dont think PCV recirculate inside the airbox tho no?
Like a lot, I dont know what the previous owner did. .But what annoys me is that when it happens its alaways consistance of hitting 8K RPM IF it happens

Yes so that's blowby pushing/frothing oil up the fill neck and into the intake and then into your engine. This usually shows up at high rpm where there is the most blowby. It's not a great sign unfortunately, it means your side seals are not holding compression like they used to.

Make sure the oil is not overfilled, clean up the intake tube/airbox/filter/accordeon and go for a spin to see if new oil shows up and how much, to make sure it's an ongoing problem and not left over from an earlier time.

If it is ongoing, you can put a catch can in the line that goes to the fill neck to capture the oil, as a bandaid.

Ah, O don’t think that was the case, once I had the oil clean out I have nothing in my intake.

what happened is when I got the car there was oil in the air filter, and also a lot of oil outside on the plastic, what I suspect is that there isn’t anything inside after I clean everything up.I took it to 3 track days already.

Kevin

I see, then it's possible there is oil caked on the intake valves, preventing them from moving smoothly/fully. I'd try to move them by hand where possible to get a feel for the action.

But you are right, I think the seals might not be in the best condition
Front rotor are all 110 front face, the rear rotor is 90 ish all face kind of sucks

Kevin

Unless it's barfing oil (to confirm) that's not the end of the world. By itself, borderline compression on one rotor won't cause the issue you're having. You could try an ATF soak to decarb it. Since the car was babied, it could just be that the seals don't have complete freedom of movement. Track days are also great for self-cleaning the engine.

So can you double-check something for me please?
On the last few 1000 RPM from like 8-9, does your AFR goes from rich to a little lein? Mine is tuned on Versatune but i see the tune was like 11.9 and as it gets from 7750-9000 area it slowly becomes a little lean
Is that on all tunes?

Kevin

Quick summary of my issue
RX8 S2 R3 Sputter/Misfire Issue
2010 R3 with 36,000 miles, tested compression ok, NO CEL at all. Only starting to sputter at excatly 8000RPM indicated (Around 7500ish ECU), and through the red line. It is almost always replicable with half or full throttle it’s like it pauses for a second. It was stock when it happened. Tested ok all rotors have even wear and front rotors are 110+ rear rotors around 95+ hot at 200F. It feels like hitting a rev limiter.
What was done to trying to fix the issue:
1. Decat 3inch full exhaust
2. New Sparkplugs, BHR Spark Wires, and BHR Coil packs
3. New MAF Sensor, Air filter, VDI Valve + VDI + actuator + solenoid, VDI valve looked clean on the inside.
4. Monitored With Logs, AFR Normal, Fuel Trim Normal, throttle Plate degree normal.
5. MAF Reading on OEM Tune about 205g/s maximum.
It has no effect on the issue at all, and by checking the monitors it seems like most of the misfire is on the front rotor, although no check Eng. Light it is taking an awfully long time to get the O2 monitor ready. I am at a loss for such mint car and just ready to set the fire on this car.
Someone suggested APV valve sticking but that shit is stuck on the bottom of the lower intake manifold......

Before you set fire to it, can you confirm if there is oil in the intake?

How did you determine there are misfires on the front rotor if no code is set?

Have you tried the ATF soak? 95 psi is kinda borderline compression, what rpm is that at? Is it similar on all faces of the rotor?

I would think it's the VDI, not the APV. VDI opens at 7250, close to your trouble zone. Yes it is deep in the lower intake manifold, but it's really not that bad, it's right there once you get the UIM off, which is maybe 20 minutes of work with the right tools? Put a vacuum source on the actuator to see if it actuates, or move it by hand to clear it. If the car has been babied that valve may not have moved in a very long time.

Confirmed, after I owned the vehicle there is zero signed of oil in the intake at all even after 2 straight track days, but prior to replacing the filters there was oil spills everywhere LIKE EVERYWHERE, I had to clean it up nicely like in the air filter, on the intake box tray all kind of shit.

Three possibility left.

1. APV Motor/Valve stuck
2. Fuel Pump
3. O2 Sensor Front

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Yes the rotor are even on all surfaces,
I have the app which can access misfire counts from the monitor. I have single digit misfires on both front and rear while driving for a 100miles short trump averaging 60-85MPH, it was like 4 counts in the front and 3 counts in the rear. And then I did a pull from 3rd gear redline and 4th gear redline, The front rotor misfire counts goes to 26 while the rear only at 6. Also with no cat and a full 3 inch exhaust you can hear feel the misfire and unsmoothness.

Kevin

It's not the O2, none of these are symptoms of oxygen sensor failure.
VDI not APV, see my edits above.

VDI is changed, I changed the valve, the actuator and the solenoid no damage to vacuumed line