Misfiring mystery is getting me seriously irritated.
10-19-2019, 10:44 PM
#1
Misfiring mystery is getting me seriously irritated.
Recently replaced the engine in my 2005 Rx8 with a reman from a totaled Rx8 that has 37k on it now.
Compression tested with a rotary compression tester showed front rotor in the 90's and rear rotor in the 100's.
Started out with dealing with misfires above 7000 rpm no matter if i was WOT in whatever gear or if i was parked in neutral. LTFT's were always in the negatives, at idle typically around -5% to -9%.
I replaced plugs, wires, coils, all 6 injectors, MAF; cleaned ESS. 20 brake pedal stomp done.
Misfiring now occuring just above 4000 RPM. P0300 P0301. I was looking at the logs from that drive and I noticed that above 4000 rpm the commanded air fuel ratio is about 14.5 but the measured air fuel ratio dips down into the 12s and even down into the 11s at some points. This is honestly driving me crazy at this point.
Front O2 possibly giving crap readings possibly? SSV being stupid despite moving freely maybe? I honestly don't know what else to inspect at this point.
Compression tested with a rotary compression tester showed front rotor in the 90's and rear rotor in the 100's.
Started out with dealing with misfires above 7000 rpm no matter if i was WOT in whatever gear or if i was parked in neutral. LTFT's were always in the negatives, at idle typically around -5% to -9%.
I replaced plugs, wires, coils, all 6 injectors, MAF; cleaned ESS. 20 brake pedal stomp done.
Misfiring now occuring just above 4000 RPM. P0300 P0301. I was looking at the logs from that drive and I noticed that above 4000 rpm the commanded air fuel ratio is about 14.5 but the measured air fuel ratio dips down into the 12s and even down into the 11s at some points. This is honestly driving me crazy at this point.
Front O2 possibly giving crap readings possibly? SSV being stupid despite moving freely maybe? I honestly don't know what else to inspect at this point.
10-20-2019, 05:58 PM
#2
During WOT the car should be in open loop, the front O2 sensor's data won't impact that.
Looked at your data log, in roll 100, commanded afr was 13, but measured was 20??? If you are deaccelerating that make some sense, but if you are not, it's worth looking at.
I also see this happen at roll 300-307
Looked at your data log, in roll 100, commanded afr was 13, but measured was 20??? If you are deaccelerating that make some sense, but if you are not, it's worth looking at.
I also see this happen at roll 300-307
10-25-2019, 05:16 PM
#4
Okay time for the update...:
I waited a few days worth of driving before i confidently confirm the problem is resolved... **** a ****** ****** named front o2 sensor. The problem came down to a very idiotic shortcoming of my own doing. A messed up front O2 sensor.
When moving all my components over from the worn out block to the replacement block, I neglected to remember that when I was removing the engine from the vehicle that the wire for the O2 sensor got caught on the bellhousing. Im sure that damaged the wires internally just enough that it still functioned and provided readings however still enough damage to affect the readings that my pcm was seeing by about 1-1.5 on my AFR. Just enough to throw the system off without causing a CEL for the front O2 sensor, resulting in misfires and alike. Really gave me a run for my money. Running excellently now!
I waited a few days worth of driving before i confidently confirm the problem is resolved... **** a ****** ****** named front o2 sensor. The problem came down to a very idiotic shortcoming of my own doing. A messed up front O2 sensor.
When moving all my components over from the worn out block to the replacement block, I neglected to remember that when I was removing the engine from the vehicle that the wire for the O2 sensor got caught on the bellhousing. Im sure that damaged the wires internally just enough that it still functioned and provided readings however still enough damage to affect the readings that my pcm was seeing by about 1-1.5 on my AFR. Just enough to throw the system off without causing a CEL for the front O2 sensor, resulting in misfires and alike. Really gave me a run for my money. Running excellently now!
Last edited by Ricky SE3P; 10-30-2019 at 01:21 PM.
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yapakanichi (10-28-2019),
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. I understand how frustrating things can be at times.
10-30-2019, 02:00 PM
#8
Yes, it definitely can be frustrating at times. Especially when there are individuals who are downers or negative about certain parts of my build or other factors of my vehicle rather than trying to be helpful and attempt to assist with any troubleshooting. I feel like I've made it pretty known by this point that I work on a DIY + budget mentality to show others that it CAN be done (and done well) if you do it right and take your time.
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Red line envy (10-31-2019)
10-31-2019, 07:22 AM
#9
Registered
I agree with the frustration lvls that come with these cars lol just gotta take it I guess.
Take my 8 for example. I believe I have to pull my engine again in the spring to pull the LIM and check it over. I have a few codes that say. Tuning valve stuck open, and runner control stuck open. But when I get to 6500 rpm you can feel the car start pulling hard like it just opened. So is it stuck open? My idle is a bit shaky and it has its little dips in it. Either way I must address these codes.
Take my 8 for example. I believe I have to pull my engine again in the spring to pull the LIM and check it over. I have a few codes that say. Tuning valve stuck open, and runner control stuck open. But when I get to 6500 rpm you can feel the car start pulling hard like it just opened. So is it stuck open? My idle is a bit shaky and it has its little dips in it. Either way I must address these codes.
11-05-2019, 12:44 PM
#13
Registered
Correct me if I'm wrong here but a misfire is usually caused by only a few things.
1. Ignition system (plugs wires coils)
2. Plugged cat
3. Compression
4. Fuel system (injectors pump regulator)
5. Weak or slow signal from ess at higher rpm.
Just a few I could think of. I'm sure there could be more or I could be wrong on some of these points.
1. Ignition system (plugs wires coils)
2. Plugged cat
3. Compression
4. Fuel system (injectors pump regulator)
5. Weak or slow signal from ess at higher rpm.
Just a few I could think of. I'm sure there could be more or I could be wrong on some of these points.
11-05-2019, 08:42 PM
#15
Registered
Good point that would make for some interference in the signal.
11-05-2019, 08:56 PM
#16
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I also forgot to mention that my car hits a fuel cut off at 5k and won’t let me rev past. Even if I try to downshift to get past 5k the rpm gauge will drop to zero until it is below 5k then it will go back to normal.
11-14-2019, 12:06 PM
#17
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rx8
I've read so many posts about miss fire, poor performance, my head spins with all the "possible" fixes.
The real fix, would be for Mazda to buy back all rx8's, and acknowledge the engineering was/is crap!
No reason for ALL these issues with a car, of any manufacture.
I purchased an 8, with less than 19k on it, thinking with that low mileage, I should get many thousand miles trouble free, within 200 miles, the engine is running on one rotor!! The rear is just spinning around dragging the front one down so the car is not drivable at all.
It will be a very attractive anchor for that boat parked in the yard.
The real fix, would be for Mazda to buy back all rx8's, and acknowledge the engineering was/is crap!
No reason for ALL these issues with a car, of any manufacture.
I purchased an 8, with less than 19k on it, thinking with that low mileage, I should get many thousand miles trouble free, within 200 miles, the engine is running on one rotor!! The rear is just spinning around dragging the front one down so the car is not drivable at all.
It will be a very attractive anchor for that boat parked in the yard.
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