MS3X NA6 - "Misfire" at high rpm related to Timing Error?
09-27-2015, 11:13 PM
#21
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UPDATE 25SEP2015
I've been in contact w/ DIYAutotune for some help on this issue. I've confirmed the following:
I continued to play w/ dwell settings as a part of troubleshooting. Reduced dwell duration to 2.5 ms, keeping spark duration between 1.0 and 1.5 ms, and added fuel between 2.5-4.5k where it appeared slightly lean before. These settings seem to be closer to how the engine was running before removing the MS3X to measure and adjust the VR circuits (14SEP update post)...but it's still misfiring...
Tach behavior during "misfire"
(Dropbox link)
While confirming base timing, w/ TunerStudio still in Fixed Timing = 10 deg, I slowly rotated the throttle plate w/ the timing light still on the crank pulley to determine if timing was retarding. I was expecting a gradual change if it truly was retarding as rpm increased, though what I saw was a sudden step-change. The crank pulley TDC mark suddenly ADVANCES from 10-deg BTDC w/ Fixed Timing (900-2600 rpm) to 0-deg TDC between 2700-3300 rpm. I checked this last night and also saw that the mark went back to 10-deg BTDC from 3300-4100 rpm then started retarding ~5-deg at ~4100 rpm (spark hardware latency = 20 usec).
Crank pulley
(Dropbox link)
The .msq's spark map doesn't have any sudden changes that would retard suddenly through the powerband. If this retardation of spark timing is occurring when the spark map is being used, that would explain the loss of torque I've noticed along w/ the misfires. Trouble is TunerStudio only logs what spark timing is commanded vs. actual, otherwise it could be useful to log spark timing through these occurrences.
VR Circuits
I haven't ruled out the Cam and Crank inputs yet. Testing (can share measurements if needed) showed the output pins of the U7s on each input NOT providing the voltages DIY cites (mentioned in the 14SEP update). Is this worth investigating??
- Igniter is good
- Coils are good
- Spark plugs gapped at .035" or .039" make no difference; not fresh but hardly worn
- Two sets of plug wires confirmed good
- TDC mark on pulley aligns w/ piston 1 TDC using socket extension
- Base timing checked again, confirmed at 10-deg BTDC
- Dwell of 2.5-3.5 ms appears to move torque loss/misfires above 4k rpm
- 1.4.0 firmware made no difference (was 1.3.4)
I continued to play w/ dwell settings as a part of troubleshooting. Reduced dwell duration to 2.5 ms, keeping spark duration between 1.0 and 1.5 ms, and added fuel between 2.5-4.5k where it appeared slightly lean before. These settings seem to be closer to how the engine was running before removing the MS3X to measure and adjust the VR circuits (14SEP update post)...but it's still misfiring...
Tach behavior during "misfire"
(Dropbox link)
While confirming base timing, w/ TunerStudio still in Fixed Timing = 10 deg, I slowly rotated the throttle plate w/ the timing light still on the crank pulley to determine if timing was retarding. I was expecting a gradual change if it truly was retarding as rpm increased, though what I saw was a sudden step-change. The crank pulley TDC mark suddenly ADVANCES from 10-deg BTDC w/ Fixed Timing (900-2600 rpm) to 0-deg TDC between 2700-3300 rpm. I checked this last night and also saw that the mark went back to 10-deg BTDC from 3300-4100 rpm then started retarding ~5-deg at ~4100 rpm (spark hardware latency = 20 usec).
Crank pulley
(Dropbox link)
The .msq's spark map doesn't have any sudden changes that would retard suddenly through the powerband. If this retardation of spark timing is occurring when the spark map is being used, that would explain the loss of torque I've noticed along w/ the misfires. Trouble is TunerStudio only logs what spark timing is commanded vs. actual, otherwise it could be useful to log spark timing through these occurrences.
VR Circuits
I haven't ruled out the Cam and Crank inputs yet. Testing (can share measurements if needed) showed the output pins of the U7s on each input NOT providing the voltages DIY cites (mentioned in the 14SEP update). Is this worth investigating??
Last edited by mkrazit; 09-27-2015 at 11:24 PM. Reason: Added confirmed items
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01-03-2016, 04:30 PM
#22
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UPDATE 03JAN2016 (The FIX!)
The warmer and not-so-snowy weather has been a treat and allowed for additional troubleshooting of this misfire issue I've documented here.
Discussions w/ Joe Perez and DIYAutotune left me w/ the symptom of a poor CKP signal causing a loss of spark at above 4.5k. If the signal was bad from the stock CAS, then it needed to be filtered. I'm not into making circuits, so I arranged a Dual VR v2.1 from JBPerf (Jean Belanger). It arrived last week, so this past weekend, I reviewed the latest (2015-10-12) MS3X V3.57 hardware manual as Jean's instructions detailed needing a pull-up resistor for the input, which sounded similar to what I had read in the MS3X setup documentation (https://www.diyautotune.com/tech_art...azda_miata.htm).
I determined that my DIYAutotune MS3X did not have the internal 1k pull-up at R57 on the main board, so I installed one early December since Jean's instructions also called for it.
I reinstalled the MS3X w/o adjusting the VR pots and logged this:
Since I was losing sync above 5k, I was fairly certain I wasn't meeting the voltage threshold required to create a CKP pulse to fire the coils. Adjusted Main and Expander pots to get 2.5V w/ 5V applied (at top of R54 and ZC test point, respectively), I got the following (log was huge, so just a screenshot):
Nothing crazy, just shows pulls to 7000 rpm…but after months of not being able to do this and not being able to figure out why, it feels like a small win!
This allowed me to continue tuning the VE Table (as you can see, I had conservatively WAY too much fuel above 5.5k) and start exploring closed-loop idle tuning and AE for throttle tip-in.
I appreciate the help along the way in troubleshooting this issue. The solution forced a much deeper understanding of the MS3 and how it triggers the Miata’s coils via the CAS, but in the end, the idea was to better understand engine management…so another win!
Key words: MS3, MS3X, high-rpm misfire, no tach signal, no rpm signal, no sync loss, R57, pull-up resistor, VR circuit, crank input, CKP
Discussions w/ Joe Perez and DIYAutotune left me w/ the symptom of a poor CKP signal causing a loss of spark at above 4.5k. If the signal was bad from the stock CAS, then it needed to be filtered. I'm not into making circuits, so I arranged a Dual VR v2.1 from JBPerf (Jean Belanger). It arrived last week, so this past weekend, I reviewed the latest (2015-10-12) MS3X V3.57 hardware manual as Jean's instructions detailed needing a pull-up resistor for the input, which sounded similar to what I had read in the MS3X setup documentation (https://www.diyautotune.com/tech_art...azda_miata.htm).
I determined that my DIYAutotune MS3X did not have the internal 1k pull-up at R57 on the main board, so I installed one early December since Jean's instructions also called for it.
I reinstalled the MS3X w/o adjusting the VR pots and logged this:
Since I was losing sync above 5k, I was fairly certain I wasn't meeting the voltage threshold required to create a CKP pulse to fire the coils. Adjusted Main and Expander pots to get 2.5V w/ 5V applied (at top of R54 and ZC test point, respectively), I got the following (log was huge, so just a screenshot):
Nothing crazy, just shows pulls to 7000 rpm…but after months of not being able to do this and not being able to figure out why, it feels like a small win!
This allowed me to continue tuning the VE Table (as you can see, I had conservatively WAY too much fuel above 5.5k) and start exploring closed-loop idle tuning and AE for throttle tip-in.
I appreciate the help along the way in troubleshooting this issue. The solution forced a much deeper understanding of the MS3 and how it triggers the Miata’s coils via the CAS, but in the end, the idea was to better understand engine management…so another win!
Key words: MS3, MS3X, high-rpm misfire, no tach signal, no rpm signal, no sync loss, R57, pull-up resistor, VR circuit, crank input, CKP
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01-04-2016, 07:13 PM
#24
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I definitely had sync loss from the 1st screenshot in yesterday's post. This was w/ previously set crank and cam VR pots set to what gave me the most rpm range before the "misfire" and w/ only adding the R57 pull-up. Once I reset the pots per the MS3X hardware manual, I no longer had sync loss and could increase rpm to rev limit (2nd screenshot is R57 pull-up w/ pots set per hardware manual).
The curve colors are washed out on those screenshots, but I have not logged any sync loss since the R57 + setting pots. I simply wanted to document what happened to me here for anyone in the future.
The curve colors are washed out on those screenshots, but I have not logged any sync loss since the R57 + setting pots. I simply wanted to document what happened to me here for anyone in the future.
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01-08-2016, 06:02 PM
#25
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I've been in contact w/ DIYAutotune for some help on this issue. I've confirmed the following:
I continued to play w/ dwell settings as a part of troubleshooting. Reduced dwell duration to 2.5 ms, keeping spark duration between 1.0 and 1.5 ms, and added fuel between 2.5-4.5k where it appeared slightly lean before. These settings seem to be closer to how the engine was running before removing the MS3X to measure and adjust the VR circuits (14SEP update post)...but it's still misfiring...
Tach behavior during "misfire"
(Dropbox link)
While confirming base timing, w/ TunerStudio still in Fixed Timing = 10 deg, I slowly rotated the throttle plate w/ the timing light still on the crank pulley to determine if timing was retarding. I was expecting a gradual change if it truly was retarding as rpm increased, though what I saw was a sudden step-change. The crank pulley TDC mark suddenly ADVANCES from 10-deg BTDC w/ Fixed Timing (900-2600 rpm) to 0-deg TDC between 2700-3300 rpm. I checked this last night and also saw that the mark went back to 10-deg BTDC from 3300-4100 rpm then started retarding ~5-deg at ~4100 rpm (spark hardware latency = 20 usec).
Crank pulley
(Dropbox link)
The .msq's spark map doesn't have any sudden changes that would retard suddenly through the powerband. If this retardation of spark timing is occurring when the spark map is being used, that would explain the loss of torque I've noticed along w/ the misfires. Trouble is TunerStudio only logs what spark timing is commanded vs. actual, otherwise it could be useful to log spark timing through these occurrences.
VR Circuits
I haven't ruled out the Cam and Crank inputs yet. Testing (can share measurements if needed) showed the output pins of the U7s on each input NOT providing the voltages DIY cites (mentioned in the 14SEP update). Is this worth investigating??
- Igniter is good
- Coils are good
- Spark plugs gapped at .035" or .039" make no difference; not fresh but hardly worn
- Two sets of plug wires confirmed good
- TDC mark on pulley aligns w/ piston 1 TDC using socket extension
- Base timing checked again, confirmed at 10-deg BTDC
- Dwell of 2.5-3.5 ms appears to move torque loss/misfires above 4k rpm
- 1.4.0 firmware made no difference (was 1.3.4)
I continued to play w/ dwell settings as a part of troubleshooting. Reduced dwell duration to 2.5 ms, keeping spark duration between 1.0 and 1.5 ms, and added fuel between 2.5-4.5k where it appeared slightly lean before. These settings seem to be closer to how the engine was running before removing the MS3X to measure and adjust the VR circuits (14SEP update post)...but it's still misfiring...
Tach behavior during "misfire"
(Dropbox link)
While confirming base timing, w/ TunerStudio still in Fixed Timing = 10 deg, I slowly rotated the throttle plate w/ the timing light still on the crank pulley to determine if timing was retarding. I was expecting a gradual change if it truly was retarding as rpm increased, though what I saw was a sudden step-change. The crank pulley TDC mark suddenly ADVANCES from 10-deg BTDC w/ Fixed Timing (900-2600 rpm) to 0-deg TDC between 2700-3300 rpm. I checked this last night and also saw that the mark went back to 10-deg BTDC from 3300-4100 rpm then started retarding ~5-deg at ~4100 rpm (spark hardware latency = 20 usec).
Crank pulley
(Dropbox link)
The .msq's spark map doesn't have any sudden changes that would retard suddenly through the powerband. If this retardation of spark timing is occurring when the spark map is being used, that would explain the loss of torque I've noticed along w/ the misfires. Trouble is TunerStudio only logs what spark timing is commanded vs. actual, otherwise it could be useful to log spark timing through these occurrences.
VR Circuits
I haven't ruled out the Cam and Crank inputs yet. Testing (can share measurements if needed) showed the output pins of the U7s on each input NOT providing the voltages DIY cites (mentioned in the 14SEP update). Is this worth investigating??
I had a similar issue, turned out to be a slack timing belt
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