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Discussion Starter · #1 ·
Guy on the N54 site is experiencing surges in power running high boost on his JB4. He's running straight Map 1 and 2 and said the surging issue is new and used to run those maps fine. While I did advise that most RS owners run a tapered map 6 instead of the stock, flatter boost maps, I don't see huge concerns in his timing numbers. The surging appears to be the ECU boost jumping up and down (from about 12 - 13 PSI to 10-11 PSI) as it moves through the middle of the RPM range. Could that be the spin limit sensors kicking in and out? Maybe warmer weather is requiring a higher spin rate to achieve his same boost targets which is why it has just recently popped up?
 

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Not super familiar with the finer points of JB4 tuning but I recall boost spikes being a very common with JB4 during shifts in the earlier days of tuning on this platform, if I'm remembering
my facts correctly its one of the reasons for the tapper boost profile (the other being the turbos well off the efficiency island).

Are these the spikes your seeing perhaps?

If its during WOT and the car isn't shifting then the ECU is obviously pulling boost for some reason, sadly there
is too many sensors that could cause this to happen though so without actually seeing any logs I at least
couldn't make any guesses.
 

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Not super familiar with the finer points of JB4 tuning but I recall boost spikes being a very common with JB4 during shifts in the earlier days of tuning on this platform, if I'm remembering
my facts correctly its one of the reasons for the tapper boost profile (the other being the turbos well off the efficiency island).

Are these the spikes your seeing perhaps?

If its during WOT and the car isn't shifting then the ECU is obviously pulling boost for some reason, sadly there
is too many sensors that could cause this to happen though so without actually seeing any logs I at least
couldn't make any guesses.
thanks for the info, I'm the guy op is referencing lol. it is during WOT and the car isn't shifting. i have some logs, one on map 1 and one on map 2; ill link to this. these longer logs don't really show the issue but ill add a really short log to give an idea of what it looks like.

link to surging example : Surging
link to map 1 and map 2: Map 1 and Map 2
 

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2018 Q50 Red Sport 400 AWD
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I too have wondered how exactly the OEM sensors work.
 

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I too have wondered how exactly the OEM sensors work.
The ECM controls the electric wastegate control actuator to achieve a target boost pressure based on engine speed, accelerator pedal position, and throttle valve position and calculates the suction pressure near the entrance of the compressor according to the amount of intake air and intake air pressure. The ECM judges the wastegate valve opening angle to satisfy the target boost pressure. The turbocharger speed sensors transmit their signal to the ECM. This allows the ECM to more accurately control boost pressure and reduce potential damage to the turbochargers caused by an excess rise in revolutions.
 

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2018 Q50 Red Sport 400 AWD
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The ECM controls the electric wastegate control actuator to achieve a target boost pressure based on engine speed, accelerator pedal position, and throttle valve position and calculates the suction pressure near the entrance of the compressor according to the amount of intake air and intake air pressure. The ECM judges the wastegate valve opening angle to satisfy the target boost pressure. The turbocharger speed sensors transmit their signal to the ECM. This allows the ECM to more accurately control boost pressure and reduce potential damage to the turbochargers caused by an excess rise in revolutions.
I guess my question wasn't clear. How does the sensor itself work? I know how a wheel speed sensor works, but I doubt the same technology can be applied to something that spins as fast as a turbo shaft.
 

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I guess my question wasn't clear. How does the sensor itself work? I know how a wheel speed sensor works, but I doubt the same technology can be applied to something that spins as fast as a turbo shaft.
I think they are optical type sensors.
 

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I guess my question wasn't clear. How does the sensor itself work? I know how a wheel speed sensor works, but I doubt the same technology can be applied to something that spins as fast as a turbo shaft.
Infiniti's marketing calls it an Optical speed sensor buuut given the RPM's that turbo wheels operate at that seems unlikely.
It probably measuring some type of change in the magnetic field to calculate the speeds.

Found the below website and it seems they sell Turbo Speed sensors that operate either by measuring
the Eddy current or Magnetic Reluctance. But if your looking for a more technical summary that is beyond me!

 

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The turbocharger speed sensors are eddy current sensors.
 
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thanks for the info, I'm the guy op is referencing lol. it is during WOT and the car isn't shifting. i have some logs, one on map 1 and one on map 2; ill link to this. these longer logs don't really show the issue but ill add a really short log to give an idea of what it looks like.

link to surging example : Surging
link to map 1 and map 2: Map 1 and Map 2
I'm am by no means an expect buuut looking at your logs the Engine ignition changes dramatically at two points during you're 3rd gear pull just
as you are hitting peak boost.

Maybe try running a 100 Octane and see if you get the same behavior.

101464
 
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2018 Q50 Red Sport 400 AWD
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Infiniti's marketing calls it an Optical speed sensor buuut given the RPM's that turbo wheels operate at that seems unlikely.
It probably measuring some type of change in the magnetic field to calculate the speeds.

Found the below website and it seems they sell Turbo Speed sensors that operate either by measuring
the Eddy current or Magnetic Reluctance. But if your looking for a more technical summary that is beyond me!

Understanding that is above my pay grade. Thanks.
 

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Here i thought the speed sensor worked like that arrow thing on the big price is right wheel.
 

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eddy current sensors have a coil of wire wrapped around an iron core inside them. alternating current is sent through that coil which then induces a magnetic field. whenever an impeller blade passes by the sensor, a small opposing magnetic field is created inside the impeller (because its metal) and eddy currents are produced. the sensor sees the feedback (eddy currents) the impeller blade creates as a pulse and the ecm calculates impeller speed based on the frequency of pulses.

this information in this paragraph is in the service manual. the q50's sensors are operated with a 5V signa. with key on engine off, its 5V, and it's 0.1V to 0.9V at engine idle. if you have a consult tool, you can actually see the sensor speed data. On consult screen, select “ENGINE” >> “Data monitor” >> “TC/SC SPEED B1” for bank 1. the manual also gives a speed to check for diagnosing the sensor: Check that the values displayed on “TC/SC SPEED B1” is 14,000 – 26,000 rpm when maintaining 3,000 rpm with no load condition.

not sure what the problem is, but im fairly certain the speed sensors are not a part of it. to put it a better way, i dont think impeller speed is the problem. the sensor can sense things quickly but i highly doubt the signal can be sent, processed, compared to other parameters, then a corresponding signal sent to the wastegate for adjustment in a quick enough manner to matter unless its a sustained overspeed.
 

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thanks for the info, I'm the guy op is referencing lol. it is during WOT and the car isn't shifting. i have some logs, one on map 1 and one on map 2; ill link to this. these longer logs don't really show the issue but ill add a really short log to give an idea of what it looks like.

link to surging example : Surging
link to map 1 and map 2: Map 1 and Map 2
Avg ign is a learned value over time the higher it is the worse, you really don’t want to see over 6 ideally 4 or less. The is learned ignition retard value. You don’t have the octane to support the boost you are running. The reason you don’t see or notice the “surge” at first (not really surge) is because it hasn’t learned this value and adapted over time yet, but now it has. The more timing you have at an rpm the more boost the stock ecu will target, the less timing (like from avg ign value dropping it) the less boost you’ll have.

if you ran no jb4 map you probably wouldn’t have this issue, or if you ran higher octane you wouldn’t have this issue. A custom map 6 could be tailored to your octane to also prevent this.

the points in that log with “high” boost is when avg ign is lower, but most of that log you have “low” boost because avg ign is so high for most of it.
 

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Discussion Starter · #15 ·
What I see that looks like the surging is in timestamp 23 - 33 range below where the ECU and total boost jump up and down in a very short period of time. I believe the ECU should just be calling for smooth boost at that RPM probably in that 12.5-13 range and taper down smoothly at higher RPMs (over 5000). Timing should be judged by the Ign_1 field which is the real time value. Not sure what the Avg_Ign measures exactly (don't hear references to it in log reviews). The log is very short, but not unusual to see the drop below when you 1st get into a pull. His longer logs show the classic curve of teens at low RPM, lower into single digits mid RPM and then back up to double digit range as he approaches redline.
EDIT - 17awdQ50P posted at same time and explained the Avg_ign value right before my post.


timestamprpmecu_psitargetboostwgdcthrottleign_1
0​
2600​
0.5​
4.1​
0.5​
50​
6​
49.5​
7.5​
2612​
0.5​
4.1​
0.5​
50​
6​
49.5​
14.25​
2837​
0.2​
4.1​
0.2​
50​
99​
19​
17.5​
2937​
1.6​
4.4​
2.5​
50​
100​
16​
19.25​
3087​
2.6​
4.4​
5​
99​
100​
16​
21.25​
3250​
4​
4.6​
8.5​
99​
100​
12​
23.25​
3400​
7.6​
4.9​
13.5​
98​
100​
8​
25.5​
3575​
12.4​
5.1​
18.3​
83​
100​
6​
27​
3681​
10.5​
5.1​
15.3​
89​
100​
6​
29.25​
3962​
12.3​
5.1​
17.8​
85​
100​
6​
31.25​
4000​
11.3​
5​
16.1​
83​
100​
6​
33.25​
4237​
12.7​
5​
18.1​
81​
100​
6​
35​
4362​
12.6​
5​
17.5​
77​
100​
6​
37​
4462​
12.2​
5​
17.1​
81​
100​
6.5​
39​
4662​
13.4​
5​
18.7​
76​
100​
6​
41​
4775​
13.4​
5.1​
18.4​
20​
100​
6​
 

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eddy current sensors have a coil of wire wrapped around an iron core inside them. alternating current is sent through that coil which then induces a magnetic field. whenever an impeller blade passes by the sensor, a small opposing magnetic field is created inside the impeller (because its metal) and eddy currents are produced. the sensor sees the feedback (eddy currents) the impeller blade creates as a pulse and the ecm calculates impeller speed based on the frequency of pulses.

this information in this paragraph is in the service manual. the q50's sensors are operated with a 5V signa. with key on engine off, its 5V, and it's 0.1V to 0.9V at engine idle. if you have a consult tool, you can actually see the sensor speed data. On consult screen, select “ENGINE” >> “Data monitor” >> “TC/SC SPEED B1” for bank 1. the manual also gives a speed to check for diagnosing the sensor: Check that the values displayed on “TC/SC SPEED B1” is 14,000 – 26,000 rpm when maintaining 3,000 rpm with no load condition.

not sure what the problem is, but im fairly certain the speed sensors are not a part of it. to put it a better way, i dont think impeller speed is the problem. the sensor can sense things quickly but i highly doubt the signal can be sent, processed, compared to other parameters, then a corresponding signal sent to the wastegate for adjustment in a quick enough manner to matter unless its a sustained overspeed.
Very succinct thank you!
 

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Avg ign is a learned value over time the higher it is the worse, you really don’t want to see over 6 ideally 4 or less. The is learned ignition retard value. You don’t have the octane to support the boost you are running. The reason you don’t see or notice the “surge” at first (not really surge) is because it hasn’t learned this value and adapted over time yet, but now it has. The more timing you have at an rpm the more boost the stock ecu will target, the less timing (like from avg ign value dropping it) the less boost you’ll have.

if you ran no jb4 map you probably wouldn’t have this issue, or if you ran higher octane you wouldn’t have this issue. A custom map 6 could be tailored to your octane to also prevent this.

the points in that log with “high” boost is when avg ign is lower, but most of that log you have “low” boost because avg ign is so high for most of it.
good to know, i haven't seen any documentation of what the avg ign value is. and like jbc said I've been paying attention to the classic curve that is discussed over on N54 site with Terry, avg ign seems like something that he should have brought up but i digress.:unsure: so thank you for help ill try what you suggested.
 

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Avg ign is a learned value over time the higher it is the worse, you really don’t want to see over 6 ideally 4 or less. The is learned ignition retard value. You don’t have the octane to support the boost you are running. The reason you don’t see or notice the “surge” at first (not really surge) is because it hasn’t learned this value and adapted over time yet, but now it has. The more timing you have at an rpm the more boost the stock ecu will target, the less timing (like from avg ign value dropping it) the less boost you’ll have.

if you ran no jb4 map you probably wouldn’t have this issue, or if you ran higher octane you wouldn’t have this issue. A custom map 6 could be tailored to your octane to also prevent this.

the points in that log with “high” boost is when avg ign is lower, but most of that log you have “low” boost because avg ign is so high for most of it.
i just looked at a Map 0 and im seeing a avg ign value of 5.5. reading this params link its saying to expect a value of 5 or higher on pump gas. is this link correct for the VR30 platform?
 

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i just looked at a Map 0 and I'm seeing a avg ign value of 5.5. reading this params link its saying to expect a value of 5 or higher on pump gas. is this link correct for the VR30 platform?
Pretty much accurate. on 91 that is probably the case for stock red sport to be around 5.5 havnt seen enough stock RS logs to say for certain, I would suspect 93 should be a bit better though. like I said before ideally you'd be 4 or lower, but up to 6 is still fine. Not sure what octane you are running. Adding even map 1 to a red sport with 91 octane is really pushing it, not sure your other mods either. I would run a custom map 6 with a red sport especially if not running 93.

AVG IGN is also not applied to every single rpm the exact same, each RPM interval will have its own AVG IGN that is has learned over time, mine fluctuated up and down depending on the RPM and Boost combinations.

Your "surge" issue is the AVG IGN each time it is "surging" (again not really surge) but each time that event happened your AVG IGN dropped much lower at that RPM interval (technically a good thing) and thus the vehicle made more boost but then shortly after the AVG IGN increased again to your "normal" AVG IGN and thus your boost dropped in correlation. Obviously for smoothness, drivability, and predictability you don't want this to happen though. So to resolve higher, octane and or custom map 6.
 

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Pretty much accurate. on 91 that is probably the case for stock red sport to be around 5.5 havnt seen enough stock RS logs to say for certain, I would suspect 93 should be a bit better though. like I said before ideally you'd be 4 or lower, but up to 6 is still fine. Not sure what octane you are running. Adding even map 1 to a red sport with 91 octane is really pushing it, not sure your other mods either. I would run a custom map 6 with a red sport especially if not running 93.

AVG IGN is also not applied to every single rpm the exact same, each RPM interval will have its own AVG IGN that is has learned over time, mine fluctuated up and down depending on the RPM and Boost combinations.

Your "surge" issue is the AVG IGN each time it is "surging" (again not really surge) but each time that event happened your AVG IGN dropped much lower at that RPM interval (technically a good thing) and thus the vehicle made more boost but then shortly after the AVG IGN increased again to your "normal" AVG IGN and thus your boost dropped in correlation. Obviously for smoothness, drivability, and predictability you don't want this to happen though. So to resolve higher, octane and or custom map 6.
thanks, yeah im on 93 octane. ill make map 6 and see how it does. i haven't had this "Surging" in the couple of years ive been running JB4 so could be bad gas. i try to only use gas from "name brand" stations but i dont think one was around the last time i filled up.
 
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