2008 JK Wrangler - First tune with description

[Mr.T]

Being somewhat new to this, I thought some notes might help others, and more experienced tuners may have some thoughts to add as well. The stock and modified files are below, and supersede what I added to the repository back when it was active.

The tune has evolved over time, including adjustments at different altitudes and ambient temperatures. Here's the notes, last modified in July 2023:

3.8L 2008JKR Wrangler Manual Trans
General Purpose Off-Road Crawl Tune

• Low RPM: Better low RPM idle-crawling from a combination of various Airflow, Idle Torque Spark & Throttle PID as well as Spark table changes bring out the low end torque smoother. It's also better when letting out the clutch with little to no throttle pedal.
  
• Spark: The Spark tables have changes to minimize spark knock and KR (Knock Retard) in less than perfect conditions like normal carbon buildup, hot weather, and heat soak at high load/slow speeds (sand dunes for example). Regular 87 (85 at higher altitude) octane is typically underwhelming, and the stock spark tables are optimistic -- at least on this engine. For example, at 1696 RPM the stock PT (Part Throttle) spark table is actually 3 degrees higher at 100 kpa than the WOT (PE Spark) table! Less spark advance when enriched (open loop) at the same MAP/RPM is obviously backwards. It probably made sense under test conditions, but makes the engine prone to spark knock in real life conditions.
  
• Cooling Fans: The temperatures and hysteresis (deadband) are reduced. This is probably better for everything, except fan lifespan and the tiny power it takes to spin. The new "on" setting is about where the thermostat is full-open.
  
• Fuel Temperature Compensation: In stock form the fuel trims go progressively positive as underhood temperatures increase, which is particularly noticeable off-road in slow speed heat-soak conditions. Changes to the Fuel Temperature-Fuel Mass Multiplier table fixes this problem. Note that the ECT (Engine Coolant Temperature) multiplier tested good during a cold start and warm up with the hood open -- very little trim change. But closing the hood and letting underhood temperatures rise created a positive trim change. After experimenting, the final values in the Fuel Temperature-Fuel Mass multiplier table ended up being about the equivalent of the coefficient of expansion for E10 gasoline, roughly 0.001/Deg C -- Which makes sense if it's designed like I think. Experimenting showed that if the slope is increased too much, the trims will instead start going negative as the underhood temperature increases.
  
• Volumetric Efficiency: VE tables changed to minimize the fuel trim change from zero. Only a small number of changes were beyond 1.5% and the graphed tables look smoother.
  
• Stoich and PE (Power Enrich): Delay bypassed under certain conditions and PE is slightly richer. Stoichiometric is increased slightly richer for today's E10 pump gasoline with about 10% alcohol. Note that the extra cooling from additional PE enrichment appears to delay entering the cat over-temperature enrichment which takes lambda into the crazy rich .7 zone.
  
• Speed limiter is raised from 99 to 128 MPH. You never know when that might be necessary...
  

In the attachments, the OEM file is the stock tune.

[Mr.T]

I uploaded a minor change to the tune file in the above post, and below is a Scanner log file of about 16 minutes of testing with the that tune, and some .xml files that may be useful.

For easier adjustment of VE (volumetric Efficiency) the Graph uses the Pressure Ratio (MAP/Barometric Pressure) for logging LTFT and STFT exactly like the calibration in the editor for the 3.8L JK. Less barometric pressure equates to less exhaust back pressure, and thus better VE. However, there isn't a separate barometric pressure sensor -- It's learned by default from the MAP sensor at startup, and also when there's high throttle opening at relatively low RPM. In the log file below the barometric pressure varies from 100 kpa where I started the engine and begin the test drive to 97 kpa at the end.

[Mr.T]

Went back to no PE Delay at all. The logs show over temperature enrichment kicking in, around lambda .7x occasionally. Entering PE earlier reduces the chances of entering over temp enrich, which happens a lot more on a heavy somewhat under-powered Jeep.

Disabled Bobble Torque. Got the idea from a newer 3.8L JK stock tune in the repository. On comparison, it feels like the bobble torque algorithm occasionally was sensing that the slack and torsion in the drivetrain could be smoothed out, then would over compensate due to the variable and unanticipated effect of the terrain -- The end result being a small buck-boost that might oscillate a couple times.

Edit: Re-enabled Bobble Torque, and replaced clutch. The problem was that the clutch center was worn out and had 5-10 degrees of slop plus loose springs. All that extra drivetrain slop was more than "Bobble Torque" was calibrated for, and it probably over-compensated making the problem worse.

[Mr.T]

HPcompare 57F 100kpa.jpg
It's 2nd gear acceleration from 2000 to 5400 RPM. Entering PE mode immediately and being a bit richer helps. Barometric pressure and intake air temperature are the same. This was the best run for the stock tune, right after warm-up and only .5 KR, and PE doesn't ramp in until 5360 rpm.

10HP is probably a rounding error with a Hellcat! But with a 5000+ pound Jeep and a tiny V6 every little bit helps. Will be in some sand dunes in a couple weeks, need every pony I can get!

[TJamesWilson]

Good info Mr. T Thanks! Just getting started on a built 3.8.

[Mr.T]

Good info Mr. T Thanks! Just getting started on a built 3.8.

Thanks! Your post was a reminder to update the tune file above with the latest version. It sure runs better after a proper tuning, it still logs some KR (as it should) but without hearing it -- plus the fuel trims are always close to zero regardless of altitude/temperature. Tell me about your built 3.8L ...

[LS4PWR]

Is there a way to get better power enrichment out of the 3.8 right from the get at a lower RPM? I'm used to tuning LS engines which are very different when tuning with HP Tuners. ?Ive read over this whole thread and there is awesome information here. I have a customer who would like a tune on his 2008 Jeep Wrangler 3.8 Manual. We are in Lansing,MI and not many sand dunes around unless you go to northern Michigan and this customer is also a kid. I'm sure he'd like the Jeep to have a little more giddy up right from a lower RPM. On my 07 Impala SS we set PE for 20% throttle opening at 1350 RPM and ramping up more from there. Any way to get something similar to that from a Jeep? Ive noticed after looking at some of your tune files from the repository the menu setup for tuning a Jeep is very different. Also compared the stock tune file against the modified tune file to get a feel for the Jeep stuff. Any help is greatly appreciated!
Sincerely
LS4PWR

[Mr.T]

Is there a way to get better power enrichment out of the 3.8 right from the get at a lower RPM? I'm used to tuning LS engines which are very different when tuning with HP Tuners. ?Ive read over this whole thread and there is awesome information here. I have a customer who would like a tune on his 2008 Jeep Wrangler 3.8 Manual. We are in Lansing,MI and not many sand dunes around unless you go to northern Michigan and this customer is also a kid. I'm sure he'd like the Jeep to have a little more giddy up right from a lower RPM. On my 07 Impala SS we set PE for 20% throttle opening at 1350 RPM and ramping up more from there. Any way to get something similar to that from a Jeep? Ive noticed after looking at some of your tune files from the repository the menu setup for tuning a Jeep is very different. Also compared the stock tune file against the modified tune file to get a feel for the Jeep stuff. Any help is greatly appreciated!
Sincerely
LS4PWR

Yep, it goes into PE (power enrich) mode immediately after the acc pedal voltage is above a threshold. The time delay is inactive because of setting the VSS Min (permissive for the delay) to 127 MPH. See the Fuel>Power Enrich Tab. There's a separate spark table for PE mode, so between enrichment and spark advance it feels a bit more lively when the pedal hits the floor.

Download the tune in the first post above, that's my latest revision (the repository upload isn't functional currently) -- I think you'll like it. Since mine has a manual trans, one thing I wondered about at first was which tables apply -- The P/N are the only tables used for a manual trans.

One of these days I'll probably tune an LS, and I'll think everything is backwards!

[Mr.T]

Changed plugs out to NGK Iridium IX 2314 (from Denso TT). The Iridium IX plugs (copper core w/ iridium tip) have less tendency for KR at higher IAT/ECT temperatures. This allowed advancing the spark closer to stock, mainly with IAT/MAT and ECT base corrections, but also a bit on the WOT and the WOT Thermal base table. Compared to stock; the WOT spark at 100 KPA is running about 1.5 to 2.0 degrees less than stock. The KR occasionally bounces 2-3 degrees on a 90F day and is barely noticeable.

The heat range is the stock #5, but I'm tempted to try out the same plugs in heat range #6 (NGK 2315, one step colder).

[huskynox]

Great post Mr T, thank you. Can you share how you came up with your PID numbers for spark and throttle? I've been messing with my 2007 JK 3.8/manual for months trying to get the idle to stop surging. I installed a Magnuson supercharger which works pretty well. With the extra manifold pressure it's been tough to get it to idle steady.

Also, have you found a way to stop the idle RPM increase in 4-low? That's irritating to me! I don't see an adjustment for it in the map..?

[Mr.T]

Thanks for the nice words! 30+ years tuning control loops in industrial systems was a big help. It really is a very complex control loop with a lot of interactions, and we don't have the luxury of documentation about exactly how it's designed and programmed.

Easy question first, the RPM increase to 900 in 4Lo has no parameters to adjust in HPT at the moment.

Did Magnuson have a tune to start with? I'd contact them in any case, it may save time -- this is a time consuming process. Also, was there a cam change too?

I'd start by turning both the spark and throttle derivative numbers way down (toward zero) first and see what happens. Then reduce the proportional throttle way down and check it. The throttle integral probably isn't an issue, but it can't hurt to reduce it and see if the surging stops. Presuming the surging stops, it's a matter of adding back in where it's possible for best performance, keeping nice curves in the graphical view. There's a near infinite number of possible spark and throttle PID combinations, so it's an iterative process of adjusting and testing. It's about 50% art, 50% science...

There is also a setting for the intake manifold volume (6.07 L) in Airflow>Speed Density. This may need changing depending on how the supercharger affects it. This is a factor because of the lag time to change pressure, which depends on volume.

I'm in the Northwest, if you're nearby I might be able to give you a hand with it.

[rdmelton]

Good info in this thread. (Yes, I know it is 2.5 years old but not many that I've found that are relevant).

I have a 2008 Wrangler Rubicon auto trans. Are any auto trans settings like shift points able to be changed? Are the overall gains worth the cost? I have an old MPVI, so it would cost $200 for the upgrade to MPVI2 and then $100 for the credits.

[Mr.T]

I'm still using the MPVI as well. Eventually I'll upgrade, but it works quite well with the latest version. Suggest looking in the repository for an '07-'10 JK tune with an auto trans, then load it to see what's available to adjust on the transmission.

Edit: Upgraded to MPVI2. The smaller size is a lot better, and the logging seems better/faster.

[rockroaster]

Mr.T, will your tune work with an 08 with an auto transmission?

[Mr.T]

Mr.T, will your tune work with an 08 with an auto transmission?

Much of it can. Using the compare feature against your stock file will show the differences, then decide what changes to copy over.

[rockroaster]

ok thanks!

[rockroaster]

So I downloaded this tune to put on mine. I had 4 credits at the start of this. I had to use 2 to register this file with my MPVI2, at which point I tried to write to my vehicle, and it then said "Unlicensed vehicle". SO I had to use 2 more credits to license my vehicle, and now when i try to write it, it says "write calibration selected (NGC4) but operating system IDs are different". How do I write this file to my vehicle then?

[Mr.T]

Just updated the first post with the latest evolution of this tune.

Still using version 4.10.7, so that's probably the minimum to read the file. One can open it as a compare file, look at the differences, and edit your own tune file as desired.

[Mr.T]

Latest evolution attached in the first post. The percent power pedal request changed so the torque is very gradual and linear right off idle. The stock pedal request has an initial bump off idle that gets annoying when trying to be precise with the throttle and clutch in some off-road situations.

Also added more spark advance back as carbon cleaning continues, stoichiometry increased to 0.070 (14.28), plus a few more minor changes.

[rays04gtx]

Thanks for keeping the community updated, I tell anyone who listens tunes need to constantly evolve as time goes by. there are things I do to my personal rides that I don't think I would of tried when I 1st tuned them.