Do you have a low RPM stutter/misfire/hesitation? I HAVE THE FIX

[bmpcamry09]

Hey Gladitor peeps,

I was sent over here from the JL Wrangler forum. Be warned, this will be a LONG and detailed post.

If you want, check out my thread on the JL Wrangler forum for all the progression of this project.

https://www.jlwranglerforums.com/fo...g-what-jeep-won’t.163856/page-10#post-3380173


I am the proud owner of a new 2025 JL after previously owning a 2020 and a 2018. The Wranglers suffer from a nasty hesitation/stutter/misfire at low load/low RPM situations. Brand new off the showroom floor I noticed the issue. Most noticeably felt between 3rd and 4th gear at RPMS below 2000, but can also be felt at highway cruising speeds in the same area.

Well, little about me, one of my side hobbies/gigs for the last few years has been tuning/calibrating via HP Tuners. I've tuned a few hundred vehicles locally and remotely, mostly on the Ford Ecoboost platform and some occasional GM stuff. Look up my user name on the HP Tuners forums and you'll see I'm a total nerd when it comes to this stuff. I am OCD about the way my own vehicles drive. After buying the first F150 with a 10 speed trans years ago and experiencing what a nightmare the factory programing was on that, I dove head first into tuning and making factory vehicles run right.

A few Jeep mastertechs on the JL forum have dealt with this issue and determined it was a tuning related problem, but no one had a fix, not even Jeep. Jeep Cares and their tech support area has known about this since as early as 2023 and they have not been able to fix it. SO, I unlocked my PCM and busted out the laptop and my MPVI4 and got to work. Within a few days of testing and development, I found the problem. Here is a brief summary:

JL Wranglers and Gladiators with the PUG (2nd gen) Pentastar 3.6 have new features, namely VVL (variable valve lift, an add on to the existing VVT), and EGR. For years, people have thought the VVL system was like Honda VTEC, activating at high load/high RPM to increase power. I discovered in my weeks of testing and datalogging that is NOT the case with this VVL system. At no point in a wide open throttle run are our vehicles using the "high lift" feature of the VVL system. They are on the low side the whole pull. The ONLY time VVL high lift is active is low load/low RPM situations. It works hand in hand with the EGR system. The high lift is activated by cutting the 12 volt power supply to the VVL solenoids (see attached TSB). Normally they are always powered up to keep it in low lift mode. This is backwards compared to similar systems from Honda. When deactived, the high lift mode engages, locking out the center rocker of our complex rocker arms. At the same time, the VVL system adjusts cam timing, making it nearly fully advanced on the intake side (lower numbers=advancing). Below is a screenshot of this activation event from a datalog, which as you can see, occurs at low load/low RPM, gears 3-4. This VVL activation to supplement the EGR system with extra air is what is causing this stumble.

I discuss this datalog and discovery in this Youtube video:



I have corrected this issue with tuning via HP Tuners. There is a considerable amount of up front cost to get into this (PCM unlocking, MPVI3 or MPVI4 device, access cable, credits, then paying a tuner like me), but its the only forseeable fix since Jeep hasn't issued anything. They probably won't because it could possibly alter EPA ratings.

I have fixed this issue by changing the VVL and VVT functions within the tune. The cam can be advanced at low load and RPM naturally (the way the gen 1 pentastar worked), and EGR can still be integrated safely to keep emissions concerns at bay. This requires refinement of multiple cam tables, spark tables, spark adder tables, and a few other things that I take care of.

After I fixed the stumble, I developed full tuning on the whole platform for all 3.6 owners (except ETorque). My 2025 JL on 93 octane is showing gains of 20-25 horsepower and a shift in the torque curve to the left, making it more usable. These figures are based on datalogging FYI, but I am putting it on the dyno for those who don't believe datalogs in the coming weeks.

I'll go into detail on the process in the next post, this one is long enough.

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[bmpcamry09]

SO HERE WE GO, ANOTHER LONG POST

If you don't have anything purchased yet, here is what you need to get FROM HP TUNERS, NOT ME, as explained in that JL Wrangler forum thread:

-MPVI4 ($400)
-Dodge 2018+ Smart Access Cable ($80)
-PCM Unlock Service ($250, not needed if you want transmission only tune)
-HP Tuners Credits
GPEC2A - 2 Credits needed for PCM, 4 additional needed for TCM
GPEC5 - 4 credits needed for PCM, 4 additional needed for TCM
-If you are a new customer and buy a new MPVI4 plus 6 credits at the
time of purchase, your unlock service will be FREE!!!! Not sure if website
automatically applies this discount, so you may have to call or email
HP Tuners to confirm.

Just FYI, by purchasing an MPVI, you will have access to other things like check engine light diagnosis, transmission adaptive reset, rear diff gearing changes, tire size changes, power steering disable, and more as HP Tuners adds more features. Those are the ones currently available in addition to the tuning.

Since I'm new to this forum, I won't post pricing, but pricing is listed on the JL forum. DM me on here for questions. I am very responsive.

Trans Only Tune

-Cleaner crisper shifting, reduced shift times, less shift slop
-Less clutch slip = longer lasting trans and better temp management
-Better shift schedule, much easier downshifts, no more engine bogging
-Can customize shift schedules and shift firmness to your liking.
-Datalogging not required unless needed to fix an issue
-PCM unlock technically not needed, but recommended as there could be
datalog issues.

- Stutter Fix Tune

- Fixes the annoying low load low RPM stutter felt between 1500-2000 RPM.
- This stutter was caused by the way VVL and VVT are activated and used from the factory.
- Better throttle response from revised cam settings.
- No datalogging needed unless there is an issue.
-Any octane fuel can be run.
- No need to datalog
- Everything else is bone stock

-Complete Daily Driver Tune

- Includes the stutter fix
- Will tune for whatever octane you want to run. 87 octane will have stock spark timing minus a few minor changes due to EGR tuning. Higher octanes will have more spark and cam advance for more midrange and top end perforamce. Initial datalogging shows 20 HP gain on 91-93 octane and a shift in torque curve more towards the low RPM range. Dyno graphs to come in the next few months.
- FREE 87 tune included if your primary tune is for higher octane that way you have something to fall back on if needed.
- Complete engine and transmission tune with datalogging before and after to
make sure your Jeep is running good.
- Cam timing and VVT operation revised.
- Dramatically enhanced throttle response, no more spongy throttle
- Torque management changes to put power to the ground better
- Deeper customization upon request for throttle response, fan settings, stop
start permanent disable, etc.

The full tune is a dramatic night and day difference in your ride. It is what I recommend the most.

Remember, I only provide the tune file and I do it all remotely through email, it is on you to buy the MPVI4, Access Cable, and PCM unlocking.

I will likely have same day or next day turn around once you supply me with your read and a stock datalog. I am abnormally responsive to emails and DMs because I HATE unread notifications on my phone. I'm a bit OCD about that. LOL

Be warned, I WILL make you sign a liability release form before supplying your tune. My files are tested and safe and used in my daily driver. I have tuned hundreds of vehicles and never had a single issue. But at the end of the day, I am just a nerdy car guy who knows a lot about tuning who does this on the side, so it's to protect me. If you don't like that, sorry bout cha! If you are worried about having a "random" guy calibrate your vehicle, look me up on HP Tuners forum and look at all the nerdy crap I've developed with some of the pros over the years. Or DM me and quiz me. I'm ready

Additionally, I will be locking the files I send to you. You will not be able to edit them or see the changes. This is to protect my work. Tune theft is a thing in the HP Tuners world unfortunately. However, if you want to know the tables I tune on, I am more than happy to send you screenshots of the comparison log. I'm not afraid to show what I change like some guys.

The process with me after you have everything purchased and ready is as follows:

-DM me on here for my email address.
-Tell me what tune file you want and give me your $$$$$.
-Do a "Read" on your PCM and TCM, Save your file, back it up, and email it to me.
-Email me your MPVI serial number and VIN number
-Sign a waiver
-Get the tune back from me.
-Flash the tune to your Jeep.
-Enjoy your refreshed ride.

I've already tuned three of these in the past two days, plus my own. I'm sure some good reviews are forthcoming.

Thanks!

-Brad

 

[bmpcamry09]

Yall may notice on the HP Tuners website in some places of the site it may say something along the lines of “Only works with MPVI3”

This is a dated part of the website. Yes, you used to HAVE to use a 3 because the older 2 and 2+ models did not work with GPEC2 and GPEC5. But now, the 3 is obsolete and they only sell the 4. The MPVI4 is what you want. I actually traded my 3 in for a 4 when I had my PCM unlocked.

you can probably find the 3 on marketplace for a good price, but just understand that it’s Datalogging and flashing is significantly slower than the 4 and it’s not future proof like the 4. The performance difference between the units is insane especially in Datalogging.

 

[bmpcamry09]

Here ya go guys. Check out these datalogs. Real dyno numbers in a month or so will show similar results, but drivetrain losses will take effect obviously on a dyno.

Running 93 octane since day 1 of ownership on the stock tune, the BEST numbers were 251 HP/249 TQ, peak TQ of 249 was at 2600 RPM, with sustained torque the the middle of the torque band of 223. These numbers will be a tad lower on 87 octane due to the timing strategy as the stock tune pulls timing on 87 at WOT. Those numbers were actually usually about 10/10 lower, yes, you make a tad more power stock with premium in the tank!. This was the best run. See below pictures of the stock pulls.

After my tuning, I am seeing 279 HP/272 TQ, peak TQ of 272 at 2500 RPM, with sustained TQ through the middle of the torque band at 246. See pictures.

The data doesn't lie. Check out the air charge difference! Almost 100 MG more aircharge with the right cam changes. This number could be even higher with intake and exhaust. This is on my bone stock 2025.

I'll get dyno logs eventually, but you guys can enjoy these for now.

 

[ChecksOut]

This is looking pretty good. Is it compatible for use with the manual 6 speed?

 

[bmpcamry09]

This is looking pretty good. Is it compatible for use with the manual 6 speed?

Yep I tune the 6 speeds as well

 

[ChecksOut]

Yep I tune the 6 speeds as well

It's a lot of reading on the JL forums side so I haven't gotten through it all, but just two more questions for now.

The manual trans Rev the engine supposedly for emissions sake when driving and clutching in between gear changes. Can this be removed so there's no automatic blip, and would you recommend leaving it or removing?

Second. Since you're already going into various systems, are you able to lock the module that controls key fob programming to prevent new keys being made (theft deterrent)?

 

[Thunderspud]

The manual trans Rev the engine supposedly for emissions sake when driving and clutching in between gear changes.

I definitely do not have this "automatic blip" you speak of.

 

[ChecksOut]

I definitely do not have this "automatic blip" you speak of.

I suppose rev hang is the more appropriate wording.

https://www.jeepgladiatorforum.com/forum/threads/any-fix-for-the-awful-rev-hang.51877/

 

[bmpcamry09]

Rev hang is a whole other issue unrelated to what I'm talking about, but for whatever reason GPEC5 units 2022 and up have this programming error causing the stutter. Don't plan on Jeep releasing a fix for it especially with rumors of phasing the 3.6 out in favor for the next gen 2.0 turbo thats already out in the new GC.

 

[bmpcamry09]

It's a lot of reading on the JL forums side so I haven't gotten through it all, but just two more questions for now.

The manual trans Rev the engine supposedly for emissions sake when driving and clutching in between gear changes. Can this be removed so there's no automatic blip, and would you recommend leaving it or removing?

Second. Since you're already going into various systems, are you able to lock the module that controls key fob programming to prevent new keys being made (theft deterrent)?

Yes this should be able to be tuned out, I have a couple of MT Wranglers on the schedule coming up and I'll be able to give a more detailed answer.

And HP Tuners doesn't cover all modules in the vehicle like that, their main thing is PCM/TCM. I think the fob stuff is through the Win module if I remember correctly from my tech days.

 

[Badunit]

What you found about the VVL is surprising. Are you able to verify it by watching the 12V control signal for the VVL solenoids? I don't know if I ever saw an official Mopar source that said it goes into high-lift at 2800 RPM but this is what we were all told:

I am starting the process to start tuning. I decided to tune using a fresh ECM and keep my original as a backup. It is on order.

Is it true that tuning will set a "you've voided your warranty" code that is stored somewhere other than the ECM and cannot be erased?

You said you will be locking your tunes. Does that mean if I later want to make/test other changes, I will have to start from the original tune, not your tune?

The only real issue I have with transmission shifting is its tendency to downshift hard. An example on the road is when slowing down for a speed bump. If my foot is on the brake when I hit the bump, it downshifts hard and throws me through the windshield due to the extra engine braking. If I let off the brake immediately before the bump, it does not downshift at all and I can continue on my merry way. Does your transmission tune fix any of that?

 

[bmpcamry09]

What you found about the VVL is surprising. Are you able to verify it by watching the 12V control signal for the VVL solenoids? I don't know if I ever saw an official Mopar source that said it goes into high-lift at 2800 RPM but this is what we were all told:

I am starting the process to start tuning. I decided to tune using a fresh ECM and keep my original as a backup. It is on order.

Is it true that tuning will set a "you've voided your warranty" code that is stored somewhere other than the ECM and cannot be erased?

You said you will be locking your tunes. Does that mean if I later want to make/test other changes, I will have to start from the original tune, not your tune?

The only real issue I have with transmission shifting is its tendency to downshift hard. An example on the road is when slowing down for a speed bump. If my foot is on the brake when I hit the bump, it downshifts hard and throws me through the windshield due to the extra engine braking. If I let off the brake immediately before the bump, it does not downshift at all and I can continue on my merry way. Does your transmission tune fix any of that?

You’d be the first person to report hard down shifting on the factory tune. Before messing with downshift timers and pressures, I would probably verify that you have one of the newer transmission calibrations. I have most of the available transmission calibrations to compare with, so I can verify that. It’s custom tuning so we can literally set up just about anything exactly how you want it with revisions. That’s the beauty of going with me versus an off the shelf solution like livernois or super chips.

I lock my tunes so that people won’t try to sell it as their own work and profit off of the now hundreds of hours I’ve put into it. It is a big problem in the tuning world. There’s nothing stopping you from doing your own stuff with a base as read file. If customers ask, I can provide them with a change log that shows every single part within the tune that was modified, it just won’t show exactly what I did.

I haven’t seen a single official source say that VVL kicks on at 2800 RPM. And you will see when you do your factory read that there is not a single table within the tune that references 2800 RPM or anything around it. I have discovered there are about seven missing tables regarding VVL operation that I have asked HP Tuners to dig for to shed more light on this.

Something else that I have discovered now that I’ve tuned a few of these is GPEC2 models don’t have the same VVL hesitation issues that GPEC5 models do, but there are no differences in the tune files that would indicate as to why, which is why I believe there are some hidden tables that have not been discovered by the engineers at HP tuners.

Even the in-depth diagnosis sections within the Mopar repair manuals don’t say anything about it. I have verified VVL operation. On WOT runs the VVL solenoids have a constant 12 volts. Only time voltage is cut is pressure loss low load scenarios.

 

[bmpcamry09]

Also sorry forgot to answer one question, no one yet has had that P1400 warranty void code come on, I’ve only seen it on SRT models like a couple Scat Packs I did recently. I disable it as a safeguard anyways to be sure.

 

[Badunit]

Thanks

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