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Turbo Lag mostly as... Transmission Lag!

supermike

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which engine you got? And if you are used to have Porsche PDK transmission than the Jeep ZF is just a slow dog. Perspective and what you used to drive is key here.

Throttle commander won’t help at all, if you already quickly floor it.
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jmccorm

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which engine you got?
Throttle commander won’t help at all, if you already quickly floor it.
It's a 2021 JLUR 2.0L Turbo, No eTorque, Automatic [WHEW!]. But I suspect the issue is related to the automatic transmission

I probably should be prepared for similar objections from the dealer. I'd like to take it out on the road and come up with an enhanced set of instructions so that nobody can confuse this for a throttle response or turbo lag issue.

What I'm going to test is this (new step 1a added in bold):

1. Go 41 MPH on flat terrain (cruise control if needed) until it puts you into 7th gear.​
1a. Mildly accelerate (accelerate as much as you can) without causing the transmission to downshift.
2. Do not let speed build up (still need to be able to downshift to 3rd). Very quickly FLOOR the accelerator (like it's an emergency). Stomp it to the ground.​
3. Wait. No more acceleration, no sound, no nothing. Wait. Wait.​
4. The vehicle completes the shift into 3rd gear and you start to accelerate over a full second after you commanded it.​
NOTE: Enabling the EVIC setting which displays current gear (while in Drive) is beneficial to performing this test.​

I think the key in these revised instructions would be that someone could feel and see the mild acceleration in 7th gear at 41 MPH Then, when they floor it, they actually feel deceleration because the automatic engages its clutch. Over a second later, the transmission releases the clutch (hopefully) into third gear (and not fourth) and the vehicle accelerates nicely from there.

Under those revised instructions, I think it would be able to negate the idea that it is throttle response issue (because the vehicle actually stops accelerating) and it could negate the idea of it being turbo lag (because turbo lag could not explain existing acceleration suddenly going to zero).

As an aside, I need to do more work on my Jeep JL CAN bus decoders. I can record gas pedal position, engine RPM, vehicle speed, and gear selection in real time and with timestamps. I'm still looking for manifold pressure, engine load, and accelerometer values. I think those last three values would nail any question about what's going on. I also need to go back and do that 75% throttle test (instead of full throttle) and see what happens. I would expect: a downshift to 4th or 5th, ,probably happening in half the time.

But again, hopefully I won't have to go to extremes in data recording to find a fix for this. I can see why this problem may have existed for years.
 

Jebiruph

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There isn't any throttle lag with my JL 3.6 ESS manual, but there's very noticeable lag with my JT 3.6 ESS auto. Recalibrating the throttle on the JT helped - key on run with the engine off and 2 slow cycles of the throttle pedal.
 

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It's a 2021 JLUR 2.0L Turbo, No eTorque, Automatic [WHEW!]. But I suspect the issue is related to the automatic transmission

I probably should be prepared for similar objections from the dealer. I'd like to take it out on the road and come up with an enhanced set of instructions so that nobody can confuse this for a throttle response or turbo lag issue.

What I'm going to test is this (new step 1a added in bold):

1. Go 41 MPH on flat terrain (cruise control if needed) until it puts you into 7th gear.​
1a. Mildly accelerate (accelerate as much as you can) without causing the transmission to downshift.
2. Do not let speed build up (still need to be able to downshift to 3rd). Very quickly FLOOR the accelerator (like it's an emergency). Stomp it to the ground.​
3. Wait. No more acceleration, no sound, no nothing. Wait. Wait.​
4. The vehicle completes the shift into 3rd gear and you start to accelerate over a full second after you commanded it.​
NOTE: Enabling the EVIC setting which displays current gear (while in Drive) is beneficial to performing this test.​

I think the key in these revised instructions would be that someone could feel and see the mild acceleration in 7th gear at 41 MPH Then, when they floor it, they actually feel deceleration because the automatic engages its clutch. Over a second later, the transmission releases the clutch (hopefully) into third gear (and not fourth) and the vehicle accelerates nicely from there.

Under those revised instructions, I think it would be able to negate the idea that it is throttle response issue (because the vehicle actually stops accelerating) and it could negate the idea of it being turbo lag (because turbo lag could not explain existing acceleration suddenly going to zero).

As an aside, I need to do more work on my Jeep JL CAN bus decoders. I can record gas pedal position, engine RPM, vehicle speed, and gear selection in real time and with timestamps. I'm still looking for manifold pressure, engine load, and accelerometer values. I think those last three values would nail any question about what's going on. I also need to go back and do that 75% throttle test (instead of full throttle) and see what happens. I would expect: a downshift to 4th or 5th, ,probably happening in half the time.

But again, hopefully I won't have to go to extremes in data recording to find a fix for this. I can see why this problem may have existed for years.
Throttle position vs. accelerator position may give you a good indication of when the ECM is actually commanding the throttle vs transmission gear.

The data logger (MHD) on my N54 also had Boost (manifold) PSI and Target Boost as data sets. Which will show you actual lag.
 

supermike

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It's a 2021 JLUR 2.0L Turbo, No eTorque, Automatic [WHEW!]. But I suspect the issue is related to the automatic transmission

I probably should be prepared for similar objections from the dealer. I'd like to take it out on the road and come up with an enhanced set of instructions so that nobody can confuse this for a throttle response or turbo lag issue.

What I'm going to test is this (new step 1a added in bold):

1. Go 41 MPH on flat terrain (cruise control if needed) until it puts you into 7th gear.​
1a. Mildly accelerate (accelerate as much as you can) without causing the transmission to downshift.
2. Do not let speed build up (still need to be able to downshift to 3rd). Very quickly FLOOR the accelerator (like it's an emergency). Stomp it to the ground.​
3. Wait. No more acceleration, no sound, no nothing. Wait. Wait.​
4. The vehicle completes the shift into 3rd gear and you start to accelerate over a full second after you commanded it.​
NOTE: Enabling the EVIC setting which displays current gear (while in Drive) is beneficial to performing this test.​

I think the key in these revised instructions would be that someone could feel and see the mild acceleration in 7th gear at 41 MPH Then, when they floor it, they actually feel deceleration because the automatic engages its clutch. Over a second later, the transmission releases the clutch (hopefully) into third gear (and not fourth) and the vehicle accelerates nicely from there.

Under those revised instructions, I think it would be able to negate the idea that it is throttle response issue (because the vehicle actually stops accelerating) and it could negate the idea of it being turbo lag (because turbo lag could not explain existing acceleration suddenly going to zero).

As an aside, I need to do more work on my Jeep JL CAN bus decoders. I can record gas pedal position, engine RPM, vehicle speed, and gear selection in real time and with timestamps. I'm still looking for manifold pressure, engine load, and accelerometer values. I think those last three values would nail any question about what's going on. I also need to go back and do that 75% throttle test (instead of full throttle) and see what happens. I would expect: a downshift to 4th or 5th, ,probably happening in half the time.

But again, hopefully I won't have to go to extremes in data recording to find a fix for this. I can see why this problem may have existed for years.

may be you have a bad Throttle position sensor? Get a cheap obd2 scanner and check when floored, it’s reading at 100%.
 

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jmccorm

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may be you have a bad Throttle position sensor? Get a cheap obd2 scanner and check when floored, it’s reading at 100%.
I just got back from testing with JScan... values check out. But otherwise, you know, that wasn't a bad idea!
 

rickinAZ

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I went for a drive to get more info. The delay between floor the pedal and actually accelerating are MORE than a second! That's DANGEROUS.

Steps to reproduce (2021 JLUR 2.0L Turbo No eTorque Automatic):
1. Go 41MPH on flat terrain (cruise control if needed) until it puts you into 7th gear.
2. Very quickly FLOOR the accelerator (like it's an emergency).
3. Wait. No acceleration, no sound, no nothing. Wait. Wait.
4. The vehicle completes the shift into 3rd gear and you start to accelerate over a full second after you needed it.

I wouldn't complain, but two or three times now when I floored it and needed power, it wasn't there. And those were in times which I was avoiding a potentially dangerous situation in traffic. IMHO, stomping the pedal and having a surprise delay > 1 second is unpredictable and dangerous.
Based on your required conditions (especially the very specific 41mph), it sounds like this issue would rarely come about. Do the stars have to align to this degree for the hesitancy to rear its ugly head?
 

The Last Cowboy

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I've found with turbo engines that steady throttle input vs abrupt works a lot better.

The throttle commander will make it fell better, as it removes the factory restrictions and allows the throttle to open at the same input that you are giving the pedal.

Also, if you have changed to a taller tire, adjust the speedometer.
 
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jmccorm

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Based on your required conditions (especially the very specific 41mph), it sounds like this issue would rarely come about. Do the stars have to align to this degree for the hesitancy to rear its ugly head?
Negative. You're reading a simplified series of steps to reproduce the issue, not a full range of speeds (41 MPH) that the problem occurs. The actual range is far wider than that.

You have to give specific instructions which you're instructing others on how to reproduce an issue.
 
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jmccorm

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I did some more driving and spotted something major:

Starting with the instructions on how to reproduce the problem (automatic, 7th gear, ~41mph), I smashed the gas pedal, and this time I concentrated on the tach gauge. It jumped nearly instantly from ~1500rpm to ~2250rpm, took a small pause, and then jumped directly to ~4000rpm. After another pause, the vehicle took off. So that was a major clue.

I reproduced the problem yet again, this time concentrating on the tiny gear numbering (superscript) next to the "D" gear indicator. I had missed it! It was jumping from 7th to 5th to 3rd. I reproduced the problem from a slower speed and a lower gear, and I saw something very similar with it jumping from 6th to 4th to 2nd. Totally never seen that before! (And never suspected it before now because you don't feel anything the first time it shifts gears.)

So I think I have more information on why I'm seeing what would ordinarily be blamed on turbo lag or throttle response. The Wrangler sees a full-throttle situation where it needs to downshift, it drops two gears and (probably) engages again, sees it has another full-throttle situation where it needs to downshift, it drops down two gears and re-engages yet again!

Holy hell, that's bad decision making.

The upside? I totally would have spotted it earlier if the vehicle wasn't so dang smooth with its shifts. It RPM matches perfectly (regardless of what I'm telling it) while switching gears. The only problem is that it's switching into the wrong gear to begin with, so it has to correct it's own mistake!

This can't be the desired behavior... can it?
 
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GATORB8

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I did some more driving and spotted something major:

Starting with the instructions on how to reproduce the problem (automatic, 7th gear, ~41mph), I smashed the gas pedal, and this time I concentrated on the tach gauge. It jumped nearly instantly from ~1500rpm to ~2250rpm, took a small pause, and then jumped directly to ~4000rpm. After another pause, the vehicle took off. So that was a major clue.

I reproduced the problem yet again, this time concentrating on the tiny gear numbering (superscript) next to the "D" gear indicator. I had missed it! It was jumping from 7th to 5th to 3rd. I reproduced the problem from a slower speed and a lower gear, and I saw something very similar with it jumping from 6th to 4th to 2nd. Totally never seen that before! (And never suspected it before now because you don't feel anything the first time it shifts gears.)

So I think I have more information on why I'm seeing what would ordinarily be blamed on turbo lag or throttle response. The Wrangler sees a full-throttle situation where it needs to downshift, it drops two gears and (probably) engages again, sees it has another full-throttle situation where it needs to downshift, it drops down two gears and re-engages yet again!

Holy hell, that's bad decision making.

The upside? I totally would have spotted it earlier if the vehicle wasn't so dang smooth with its shifts. It RPM matches perfectly (regardless of what I'm telling it) while switching gears. The only problem is that it's switching into the wrong gear to begin with, so it has to correct it's own mistake!

This can't be the desired behavior... can it?
So does fifth get you into the power band enough to provide the needed maneuver? If so, can you pull back on the throttle after the initial kickdown (say 75% instead of 100%) and allow it to accelerate in 5th?
 

WhereRU_A-A-Ron

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“Full throttle? Are you sure? Surely you can’t be serious. Alright fine. (Checks throttle position again to be sure). Okay still full throttle huh? Just letting you know, this is gonna use a lot of fuel soooo… (checks throttle position again). FINE!! — accelerates —
 
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So does fifth get you into the power band enough to provide the needed maneuver? If so, can you pull back on the throttle after the initial kickdown (say 75% instead of 100%) and allow it to accelerate in 5th?
I'll admit, full throttle and some steering come more naturally to me when trying to avoid someone pulling into my side in traffic, but I'm committed to testing with 75%. If just to see how the transmission's reaction differs.

In the big picture, my strong preference is for the vehicle to respond properly to an ordinary human input and not for the human to work around a vehicle's odd deficiency. More so when it involves a safety issue. (And more so that I suspect that many others have unknowingly shared the same problem.)

Still, as far as workarounds go, you know what? I think you've probably nailed it! I'll aim to confirm this later today.
 
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jmccorm

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So does fifth get you into the power band enough to provide the needed maneuver? If so, can you pull back on the throttle after the initial kickdown (say 75% instead of 100%) and allow it to accelerate in 5th?
I wasn't able to do extensive testing, but it looks like a sudden jump to 75% or even 50% throttle resulted in the same behavior. The transmission played a lot nicer when the pedal was engaged more slowly. The best was a downshift from 7th to 6th which was hard to even notice, then an immediate jump to 4th (which took a fraction of the time) but avoiding 3rd.

The transmission seems to make poor judgements in the presence of abrupt acceleration. Going full throttle more slowly can result in multiple single-gear shifts which feel more continuous (no big delays while the engine is disconnected form the road).

Downshifting 1 gear = near invisible
Downshifting 2 or 3 gears = typical automatic delay
Downshifting 4 gears = WTF! turbo lag?? throttle response?? 😉
 

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I wasn't able to do extensive testing, but it looks like a sudden jump to 75% or even 50% throttle resulted in the same behavior. The transmission played a lot nicer when the pedal was engaged more slowly. The best was a downshift from 7th to 6th which was hard to even notice, then an immediate jump to 4th (which took a fraction of the time) but avoiding 3rd.

The transmission seems to make poor judgements in the presence of abrupt acceleration. Going full throttle more slowly can result in multiple single-gear shifts which feel more continuous (no big delays while the engine is disconnected form the road).

Downshifting 1 gear = near invisible
Downshifting 2 or 3 gears = typical automatic delay
Downshifting 4 gears = WTF! turbo lag?? throttle response?? 😉
Well, I wonder if that's not something that could be built in one of the throttle controllers, but is pretty much the opposite of their intended use, lol. May actually be their eco mode.
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