Sometimes lean, sometimes rich, hesitation/power loss [DATA LOG]
08-14-2018, 06:06 AM
#1
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Sometimes lean, sometimes rich, hesitation/power loss [DATA LOG]
Basic car condition:
- Fresh plugs, fresh OEM type C coils, fresh OEM wires (latest revisions)
- almost brand-new S2 fuel pump
- healthy engine compression, very strong
- cleaned MAS, cleaned ESS, brake stomp
- NO CEL at the moment
- all intake valves functioning
- no detectable vacuum leaks
- fuel injectors cleaned, flow and leak checked
- Fresh plugs, fresh OEM type C coils, fresh OEM wires (latest revisions)
- almost brand-new S2 fuel pump
- healthy engine compression, very strong
- cleaned MAS, cleaned ESS, brake stomp
- NO CEL at the moment
- all intake valves functioning
- no detectable vacuum leaks
- fuel injectors cleaned, flow and leak checked
- all new UIM gaskets, seals, etc
- car is close to stock except AEM intake, RB midpipe, full exhaust
- Grewvin ECU tune via Mazdaedit (more on that later)...
Symptoms:
- Car will lose some power, or almost cut all power, while accelerating. Variable severity and duration of power loss.
- Issue happens at both part load and WOT.
- Issue happens at all RPMs, have felt it happen at 2500 and 8500 rpms.
- No CEL, no misfire code.
- So basically, no consistency with respect to throttle position or RPM.
- Issue tends to happen once the car has been fully warmed for minutes.
Narrative example: At the track last weekend, during the warm-up session, once the car was up to temperature (via my VDO oil and coolant gauges) i started to pick up the speed, and i was getting the rather servere stumbles / hesitations and thought my weekend would be toast. However, very suddenly mid session, the hesitation went away and the car ran like an absolute champion the entire weekend. Super strong, set a class lap record. Then, on the way home during mixed interstate and backroads driving, the problem returned! So the car was driving like garbage, and then suddenly while on track completely cleared up and stayed good all weekend, and then began to lose power on the drive home. Again, the car had excellent power, almost enough to keep pace with S2000s on the straight, at the track, which would make me think NOT plugs, wires, or coils. no misfire, car DOES run strong when it's running right.
Data log attached. There appears to be something wrong with either the Grewvin tune or my car, because it generally runs very lean at WOT, but sometimes runs very rich or very lean. The inconsistency of the STFT astounds me. But overall i'm kinda shocked at the leaness of this tune...
My thoughts? The fact that AFR and STFT are all over at times makes me think there's inconsistency with fuel pressure at the rail, either due to the fuel pump, power to the fuel pump, or a gross malfunction with the fuel pulsation damper (FPD). I don't want to believe that a brand new series 2 FP from mazda motorsports is dead on arrival. Now I've heard from other Subaru and mazda (even RX8) folks that a sticking / failing FPD can cause drivability issues. It's a cheap and somewhat easy test, so given that almost everything else on the car is fresh and sorted, i'm giving that a try and report back. I'm also planning to ditch the Grewvin tune for stock.
In the meantime, i'm happy to entertain thoughts on this nightmarish issue...
- car is close to stock except AEM intake, RB midpipe, full exhaust
- Grewvin ECU tune via Mazdaedit (more on that later)...
Symptoms:
- Car will lose some power, or almost cut all power, while accelerating. Variable severity and duration of power loss.
- Issue happens at both part load and WOT.
- Issue happens at all RPMs, have felt it happen at 2500 and 8500 rpms.
- No CEL, no misfire code.
- So basically, no consistency with respect to throttle position or RPM.
- Issue tends to happen once the car has been fully warmed for minutes.
Narrative example: At the track last weekend, during the warm-up session, once the car was up to temperature (via my VDO oil and coolant gauges) i started to pick up the speed, and i was getting the rather servere stumbles / hesitations and thought my weekend would be toast. However, very suddenly mid session, the hesitation went away and the car ran like an absolute champion the entire weekend. Super strong, set a class lap record. Then, on the way home during mixed interstate and backroads driving, the problem returned! So the car was driving like garbage, and then suddenly while on track completely cleared up and stayed good all weekend, and then began to lose power on the drive home. Again, the car had excellent power, almost enough to keep pace with S2000s on the straight, at the track, which would make me think NOT plugs, wires, or coils. no misfire, car DOES run strong when it's running right.
Data log attached. There appears to be something wrong with either the Grewvin tune or my car, because it generally runs very lean at WOT, but sometimes runs very rich or very lean. The inconsistency of the STFT astounds me. But overall i'm kinda shocked at the leaness of this tune...
My thoughts? The fact that AFR and STFT are all over at times makes me think there's inconsistency with fuel pressure at the rail, either due to the fuel pump, power to the fuel pump, or a gross malfunction with the fuel pulsation damper (FPD). I don't want to believe that a brand new series 2 FP from mazda motorsports is dead on arrival. Now I've heard from other Subaru and mazda (even RX8) folks that a sticking / failing FPD can cause drivability issues. It's a cheap and somewhat easy test, so given that almost everything else on the car is fresh and sorted, i'm giving that a try and report back. I'm also planning to ditch the Grewvin tune for stock.
In the meantime, i'm happy to entertain thoughts on this nightmarish issue...
Last edited by hufflepuff; 08-15-2018 at 05:02 AM.
08-14-2018, 07:03 AM
#2
A couple of things come to mind: it could be heat related. Depending on track and cooling setup, let's say when you start going faster, you're actually cooling the car down more than warm up laps and traffic. I know it sounds backwards, but it would be interesting to see coolant and intake air temp in the logs. Given the tune is lean, it could be getting into knock with a bit more intake heat.
To eliminate the tune being the culprit, can you roll it back to stock and see if issue returns?
The other thing you could try is octane booster or higher octane gas
To eliminate the tune being the culprit, can you roll it back to stock and see if issue returns?
The other thing you could try is octane booster or higher octane gas
Last edited by Loki; 08-14-2018 at 07:25 AM.
08-14-2018, 07:29 AM
#3
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Running 93 octane. No issues later in the weekend when it was much hotter. And I get more issues street driving with lower oil and coolant temperature. Now, it could be that some other electrical or other mechanical component is being effected by heat, maybe... But again, car ran super strong in mid day heat at the track. I'm reproducing this issue doing street driving at cooler temperature.
08-14-2018, 08:15 AM
#4
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I wonder about your front O2 sensor or the front O2 sensor wiring.
Try monitoring AFR and STFT while wiggling the wire where it connects behind the UIM.
Try monitoring AFR and STFT while wiggling the wire where it connects behind the UIM.
08-14-2018, 09:35 AM
#5
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this could play a role in my data, and certainly cause issues at part throttle... but does the RX8 use the front O2 sensor information during open loop / WOT? If not, that wouldn't cause my WOT issue. The data is also very close to 14.7:1 at idle and cruise too. it's really only during roll in/out or WOT that AFR goes screwy
08-15-2018, 05:32 AM
#6
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just to make sure i'm interpreting the data correctly:
Absolute throttle position % is a measurement of where the throttle plate actual is
Commanded throttle actuator control % is a scaled signal sent to command the throttle body actuator
Fuel/Air commanded equivalence ratio is the ratio the ECU is targeting (if it's targeting 1, it's targeting 14.7:1 AFR)
Absolute throttle position % is a measurement of where the throttle plate actual is
Commanded throttle actuator control % is a scaled signal sent to command the throttle body actuator
Fuel/Air commanded equivalence ratio is the ratio the ECU is targeting (if it's targeting 1, it's targeting 14.7:1 AFR)
08-18-2018, 09:16 PM
#8
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fuel pump is brand new.\ mazda OEM.
has anyone had a MAS start to go a bit wonky but not throw a code?
from what i can tell, o2 sensors don't cause issues at WOT / open loop.
has anyone had a MAS start to go a bit wonky but not throw a code?
from what i can tell, o2 sensors don't cause issues at WOT / open loop.
09-11-2018, 05:25 AM
#9
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UPDATE:
- OEM ECU flash reinstalled
- Changed the plugs
- Changed the MAS
I haven't had a chance to log yet, but the car has been strong at WOT, and idles nicely. I'll need to do more pulls and datalog to see if any issues return.
QUESTION: is it typical for the RX8 to be "surge-y" in the 1000-2000 rpm range transitioning from closed-to-open throttle? mine tends to buck and surge a bit as i roll from no throttle to very light throttle. it also might be my imagination, but sometimes the car seems to surge (slightly accelerate or decelerate) while i'm holding a steady throttle position cruising on the highway (say 60-75MPH, 6th gear)
- OEM ECU flash reinstalled
- Changed the plugs
- Changed the MAS
I haven't had a chance to log yet, but the car has been strong at WOT, and idles nicely. I'll need to do more pulls and datalog to see if any issues return.
QUESTION: is it typical for the RX8 to be "surge-y" in the 1000-2000 rpm range transitioning from closed-to-open throttle? mine tends to buck and surge a bit as i roll from no throttle to very light throttle. it also might be my imagination, but sometimes the car seems to surge (slightly accelerate or decelerate) while i'm holding a steady throttle position cruising on the highway (say 60-75MPH, 6th gear)
09-25-2018, 01:04 PM
#10
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Thread Starter
UPDATE: The issue was still there and still ugly even with the OEM ECU flash reinstalled, Changed the plugs, Changed the MAS.
I was at the track and felt that the clutch pedal was grabbing a little too low (even though i tried to match mazda recommendations). I adjusted the clutch pedal higher, giving it more stroke, and voila, as a side-effect, it seems that the misfire issue has gone away. my thought is that the clutch petal up-switch may not have been getting fully pressed, or intermittently pressed, and this resulted in a harmful logic signal being sent to the RX8 ECU.
Just a theory... but i'm happy the car is running strong at the moment. i'll report back if the issue returns.
In other news, my Series 2 fuel pump let's me run to 1/4 or even a hair below and I've had no fuel starvation even at left-turn heavy tracks. very satisfied. i used all quick-disconnect fittings (no hose with clamps business).
I was at the track and felt that the clutch pedal was grabbing a little too low (even though i tried to match mazda recommendations). I adjusted the clutch pedal higher, giving it more stroke, and voila, as a side-effect, it seems that the misfire issue has gone away. my thought is that the clutch petal up-switch may not have been getting fully pressed, or intermittently pressed, and this resulted in a harmful logic signal being sent to the RX8 ECU.
Just a theory... but i'm happy the car is running strong at the moment. i'll report back if the issue returns.
In other news, my Series 2 fuel pump let's me run to 1/4 or even a hair below and I've had no fuel starvation even at left-turn heavy tracks. very satisfied. i used all quick-disconnect fittings (no hose with clamps business).
09-25-2018, 02:02 PM
#11
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When you say MAS, do you mean Mass Air-Flow Sensor?
I just went through a similar refresh of my car with a Mazda Reman (Normalized compression after break-in: R1=131/134/136 R2=126/127/130). All valves and solenoids were cleaned and tested, all gaskets replaced with OEM, and injectors were cleaned and tested. Engine starts immediately, power delivery is fantastic and consistent with the only notable dip happening at ~7300RPM for less than a second, which I attribute to the VDI valve engagement. My car is completely stock except for a midpipe (My cat was damaged). While I cleaned the MAF, I didn't replace it, nor did I replace the forward oxygen sensor.
My car seems to run very rich at times, I've seen +20% on STFT logs, particularly in the low-RPM and idle conditions; and fuel economy is bad even for a rotary. Due to the midpipe the smell is unpleasant, but seems more-so than I recall with de-catted RX-7's, another possible hint to running richer than it should be. I'm suspect of the oxygen sensor in my car though there have been no codes to confirm it, so I'm either off on my diagnosis or the sensor is marginally passing ECU expectations. This car is very twitchy off-idle, every RX-8 I've driven has been, again worse than RX-7's I'm familiar with. I'm not sure why that is but can presume it relates to the low torque/air velocity of the engine below 2,000RPM.
I just went through a similar refresh of my car with a Mazda Reman (Normalized compression after break-in: R1=131/134/136 R2=126/127/130). All valves and solenoids were cleaned and tested, all gaskets replaced with OEM, and injectors were cleaned and tested. Engine starts immediately, power delivery is fantastic and consistent with the only notable dip happening at ~7300RPM for less than a second, which I attribute to the VDI valve engagement. My car is completely stock except for a midpipe (My cat was damaged). While I cleaned the MAF, I didn't replace it, nor did I replace the forward oxygen sensor.
My car seems to run very rich at times, I've seen +20% on STFT logs, particularly in the low-RPM and idle conditions; and fuel economy is bad even for a rotary. Due to the midpipe the smell is unpleasant, but seems more-so than I recall with de-catted RX-7's, another possible hint to running richer than it should be. I'm suspect of the oxygen sensor in my car though there have been no codes to confirm it, so I'm either off on my diagnosis or the sensor is marginally passing ECU expectations. This car is very twitchy off-idle, every RX-8 I've driven has been, again worse than RX-7's I'm familiar with. I'm not sure why that is but can presume it relates to the low torque/air velocity of the engine below 2,000RPM.
09-26-2018, 05:21 AM
#12
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When you say MAS, do you mean Mass Air-Flow Sensor?
I just went through a similar refresh of my car with a Mazda Reman (Normalized compression after break-in: R1=131/134/136 R2=126/127/130). All valves and solenoids were cleaned and tested, all gaskets replaced with OEM, and injectors were cleaned and tested. Engine starts immediately, power delivery is fantastic and consistent with the only notable dip happening at ~7300RPM for less than a second, which I attribute to the VDI valve engagement. My car is completely stock except for a midpipe (My cat was damaged). While I cleaned the MAF, I didn't replace it, nor did I replace the forward oxygen sensor.
My car seems to run very rich at times, I've seen +20% on STFT logs, particularly in the low-RPM and idle conditions; and fuel economy is bad even for a rotary. Due to the midpipe the smell is unpleasant, but seems more-so than I recall with de-catted RX-7's, another possible hint to running richer than it should be. I'm suspect of the oxygen sensor in my car though there have been no codes to confirm it, so I'm either off on my diagnosis or the sensor is marginally passing ECU expectations. This car is very twitchy off-idle, every RX-8 I've driven has been, again worse than RX-7's I'm familiar with. I'm not sure why that is but can presume it relates to the low torque/air velocity of the engine below 2,000RPM.
I just went through a similar refresh of my car with a Mazda Reman (Normalized compression after break-in: R1=131/134/136 R2=126/127/130). All valves and solenoids were cleaned and tested, all gaskets replaced with OEM, and injectors were cleaned and tested. Engine starts immediately, power delivery is fantastic and consistent with the only notable dip happening at ~7300RPM for less than a second, which I attribute to the VDI valve engagement. My car is completely stock except for a midpipe (My cat was damaged). While I cleaned the MAF, I didn't replace it, nor did I replace the forward oxygen sensor.
My car seems to run very rich at times, I've seen +20% on STFT logs, particularly in the low-RPM and idle conditions; and fuel economy is bad even for a rotary. Due to the midpipe the smell is unpleasant, but seems more-so than I recall with de-catted RX-7's, another possible hint to running richer than it should be. I'm suspect of the oxygen sensor in my car though there have been no codes to confirm it, so I'm either off on my diagnosis or the sensor is marginally passing ECU expectations. This car is very twitchy off-idle, every RX-8 I've driven has been, again worse than RX-7's I'm familiar with. I'm not sure why that is but can presume it relates to the low torque/air velocity of the engine below 2,000RPM.
O2 sensor sounds like an okay place to start in your case, although most OBD tools can do some basic O2 sensor diagonistics (at least i recall OBDWiz freeware having that feature). i'd monitor your o2 signal and make sure it's cycling correctly most of the time: cruise, idle.
Good to know that a slightly surgy drivability is common with RX8 at very low rpm... guess i'll just keep the RPMs higher and ignore the behavior!!
11-02-2018, 08:35 AM
#13
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Hmm, the problem is back. sudden power loss, and some surging / hesitation. i am thinking maybe ESS, MAP/Baro, or ignition condenser intermittent issues. or perhaps fuel pump or fuel pump circuit... i have a fuel pressure gauge to install to rule out fuel delivery. problem is the problem happens at completely random times and i can't race with a laptop datalogging...
guess i'll do some more logging and troubleshooting and report back. i hate resorting to swapping things... but this issue is so randomly intermittent that i'm rarely in a position to gather data while it happens.
guess i'll do some more logging and troubleshooting and report back. i hate resorting to swapping things... but this issue is so randomly intermittent that i'm rarely in a position to gather data while it happens.
11-05-2018, 12:18 PM
#14
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I wanted to correct an earlier statement I made so it doesn't confuse your diagnostics. The logging software I was using was erroneously holding peak values instead of tracking learned values, so higher percentages were seen in areas of the table where it wasn't actually changing or changing only slightly (2-3%). I'm seeing 19-21MPG depending upon how I drive and only minor trimming in the LTFT tables.
Did you ever get your actual compression numbers and the test RPM/altitude for calculation?
Still seeming like a sensor or wiring issue given the inconsistency of the challenge. Have you measured reference voltage on the TPS or MAF/MAS to see if the input is not a clean 5vdc+? Also check input 12vdc+ on the ECU to see if there is any variance. They are designed to handle some variance, but significant values over 15vdc+ or under 10vdc+ will cause significant miscalculations from the sensor values and ECU reference.
Maybe check the ECU harness for damage or corrosion? Pin connections in the ECU box are well protected, but easy enough to check and rule out visually. Pinch points in the harness include just behind the thermostat housing, the OMP and AUX valve harness (not likely related to this concern), the cooling fan/EPS sub-harness over the fan assembly, and the power sub-harness that goes over the A/C compressor to the starter and oil sensor.
Did you ever get your actual compression numbers and the test RPM/altitude for calculation?
Still seeming like a sensor or wiring issue given the inconsistency of the challenge. Have you measured reference voltage on the TPS or MAF/MAS to see if the input is not a clean 5vdc+? Also check input 12vdc+ on the ECU to see if there is any variance. They are designed to handle some variance, but significant values over 15vdc+ or under 10vdc+ will cause significant miscalculations from the sensor values and ECU reference.
Maybe check the ECU harness for damage or corrosion? Pin connections in the ECU box are well protected, but easy enough to check and rule out visually. Pinch points in the harness include just behind the thermostat housing, the OMP and AUX valve harness (not likely related to this concern), the cooling fan/EPS sub-harness over the fan assembly, and the power sub-harness that goes over the A/C compressor to the starter and oil sensor.
06-06-2023, 10:43 PM
#15
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In the end it ended up being damaged BARO sensor wiring. That would intermittently tell the ecu there was a sudden drop in ambient air pressure, causing driveability issues. Repaired wiring and problem solved.
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06-09-2023, 11:25 AM
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