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[Guide] Fixing rev hang

54K views 91 replies 18 participants last post by  Octal450 
#1 · (Edited)
After owning my 2018 hatch for more than half a year, I decided that enough was enough and decided to figure out how to get rid of the rev hang. As we all know, the rev hang for the 5 speed manual transmission is extremely annoying, especially at higher RPMs. Thankfully, it can be fixed by flashing the ECU. Unfortunately, it does require spending some $$$ for some hardware and software.

Before we continue, please do note that flashing your ECU is a potentially dangerous activity. If you change parameters without knowing what they do, you could render your car immobile. I am only an enthusiast and do not tune any cars professionally, so these findings are from the best of my knowledge, and may not be completely accurate. If you are not willing to take the risk, it is best to consult a professional tuner instead.

Please proceed at your own risk!

The following tools/software are required:
- tactrix 2.0
- subaruEdit Personal

I will not be guiding you on setting that up as there is already plenty of information online about it.

Once you received the stock ROM dump from epifan, we can begin modding.

1) Open up your ROM in subaruEdit
2) Find the tables for (Fueling \ Overrun)

Blue Green Aqua Yellow Sky


3) Open up the table for "Desired Overrun Mass Air Flow A"

You should see something like this:

Text Line Colorfulness Slope Plot


As we can see, the overrun table adds a lot of air (and correspondingly, lots of fuel) at high RPMs. This contributes to the rev hang we experience when we clutch in, or decelerate.

The values of interest are located between the coolant temps 80 - 110C. We only need to modify these values because they are in the range of normal driving coolant temperatures.

For my current setup, I made the following adjustments. Feel free to adjust more or less to your liking.

Decreasing these values more will cause the RPMs to drop faster, and may also make stop and go driving more difficult.

For RPM >= 4400 and coolant temp >= 80, use 50% of value (reduce 50%)

Text Line Font Screenshot Parallel


For 2800 >= RPM = 80, use 70% of value (reduce 30%)

Text Line Font Colorfulness Screenshot


For 1600 >= RPM = 80, use 80% of value (reduce 20%)

Text Line Font Screenshot Parallel


In the end, we should get a table that looks something like this:

Colorfulness Text Line Font Parallel


You may have to manually adjust some values so that the map is smooth, and such that the values increase monotonically as the RPMs increase.

4) Perform the same steps on tables "Desired Overrun Mass Air Flow B" and "Desired Overrun Mass Air Flow C"

5) Upload ROM to ECU with flash utility

With the rev hang delete, I noticed the following changes:
- The car is less jerky between shifts. I no longer burn the clutch shifting between 1->2 trying to get a smooth transition.
- Rev hang completely eliminated at high RPM (> 4000).
- Throttle seems more responsive

Credits:
RalliSport Automotive for dropping hints on what to modify for rev hang. The original thread discussing FB20D tuning is here: subaruxvforum [dot] com/forum/performance-modifications/171066-2018-fb20d-tuning.html

I hope you will find this guide useful.
 
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#3 ·
I have the tactrix 2.0 adapter and the subaruEdit Personal. So far, I've just had Rallisport delete the rev hang (which IS awesome with it gone) from my tune and adjust a couple of other settings. But that was with the original tune. I have the new ECU tune from the recall saved as a loadable ROM, but haven't been able to get in contact with Rallisport for a while to get the rev hang from the new tune deleted. This seems like it might be worth experimenting with. Thanks for posting.
 
#4 ·
~$300 to get rid of rev hang seems worth it but I'm a little nervous about messing around with things like this.

NoSlushbox4Me, did your tune from Rallisport look similar to what grfaust has concerning the 'Desired Overrun Mass Air Flow' charts? I'm just looking for some sort of verification that the info is legit. A google search on the topic yielded nothing else.
 
#5 ·
It looks like I have the lite version of subaruEdit, not the personal version. I can't see or modify the maps, yet. Looking into upgrading to the personal version.
 
#6 ·
Ok, I have the necessary version of subaruEdit now. The maps in the previously tuned ROMs I have are hidden (which I understand) so I can't see what was done to them. I did these overrun fueling changes to the new recall tune and it does reduce the rev hang, but it's not as good as the rev hang delete in the tunes done by Rallisport. That eliminated the rev hang. To be closer, I think the changes should be applied across the entire RPM range and be more significant reductions. But, I really really really hate rev hang.
 
#7 · (Edited)
If a little rev hang deletion is good, a lot of rev hang deletion must be better. For all 3 maps (A, B, and C) I went ahead and set 0% overrun fuelling for 1000 RPM and higher for the 80 deg F and warmer tables. For the same RPM range in the 70 deg F table, I set the overrun fuelling to 50%. After a quick test drive, it's very good now. The revs drop how they should, considering there's no lightweight flywheel or anything like that. From a quick internet search, I didn't see any reason to keep any of the overrun fuelling. Eventually I may zero it all out if I find a rev hang quirk that bothers me. If the temperature of the air coming in is the 70 deg F, 80 deg F, etc., then I might at least zero out the overrun fuelling at lower temperatures than 80 deg F. However on a 43 deg F day here (today) it seemed really good with these current settings.

22804


This modification is being done to my own personal car and I accept responsability (and enjoyment) only for how my personal car changes because of this. If you are uncomfortable making this sort of modification to your personal car, then consider that before proceeding.
 
#10 ·
I'm going to do exactly as you've done. Before I proceed I would like a little clarification. Did you actually go by degrees Fahrenheit or degrees Celsius? I see you've written the temps in °F but I see the screenshot is °C. I don't want to mess anything up if I don't have to.
 
#9 ·
The only affect I've noticed is that without the forced overrev, in low gears if you dump the clutch too fast you get the slight jerkiness of a manual transmission car that has had the clutch dumped too fast at too low of a throttle setting. It's more an effect of poor shifting habits than it is engine tuning. Any manual trans car without rev hang would do the same thing if the clutch is engaged too quickly without enough throttle. I'm ok with the car giving me direct feedback on how well I'm shifting.
 
#11 ·
:D
I made the incorrect assumption that the temperatures were degrees F because this adjustment had to do with air flow and those temps made some sense for air temp in degrees F too. But the label on the left does indeed say coolant temp in degrees C. That's what I used.
 
#13 ·
No problem. Good catch. I don't mind having details I missed pointed out. I'm learning stuff here too.
 
#14 ·
I went ahead and zeroed out everything on all 3 maps a couple of days ago. This is what I should have done to begin with. There's no reason to suffer with rev hang when the engine is still cold.
 
#15 ·
I got a tune from Rallisport made from the new Subaru recall tune. I asked for the rev hang elimination and some throttle smoothing. He delivered, and then some. The rev hang deletion seems similar to what I already had (I can't see his protected maps) but the smoothing has resulted in more natural and predictable throttle response, and also awesomely smoother clutch engagement and disengagement. My clutch wasn't grabby before, but it is noticeably less grabby now. A very pleasant surprise, and very happy with the new tune.

I was satisfied with my own rev hang elimination tune, but the refinement in my new Rallisport tune is a clear improvement.
 
#16 ·
I'm currently working with Mike at Rallisport, and we're getting close to being done, I have another tune (I think this is the fifth revision he's sent me) currently sitting in my inbox, and I'll be flashing that this afternoon and doing some data logs to send his way. My only mod is a Nameless Performance axle back (8" muffler), and the car is so much better than before, can't recommend Mike at Rallisport enough.
 
#18 ·
I use a real Tactrix. It's a nice unit. I'm very impressed with the quality of it.
 
#20 ·
Just picked up a used legit one on eBay. I'm going to do the rev hang delete myself until I can stash the funds for a pro tune; probably sometime end of June or early July. What's the process like having a Rallisport tune? Also, what are you guys doing for a tune? I'd like to get a more torque-y low end if possible. I guess what I'm asking is, what's the possibilities for a tune on a car with no performance mods other than an intake? Sorry about all the questions!
 
#21 · (Edited)
When you have the Tactrix openport 2, you buy the subaruEdit software, use it to get an ECU ROM dump and send that to the software creator (epifan) for him to make an editable ROM for you. You will need the personal edition software, not the lite version. He will need your VIN etc for software registration.

Getting rid of rev hang is great. Getting a personalized tune is even better.

Yes there are gains to be had even with an unmodified car. That doesn't necessarily mean peak output at peak rpm. Useable power band improvement is also important.
 
#23 ·
When you have the Tactrix openport 2, you buy the subaruEdit software, use it to get an ECU ROM dump and send that to the software creator (epiphan) for him to make an editable ROM for you. You will need the personal edition software, not the lite version. He will need your VIN etc for software registration.

Getting rid of rev hang is great. Getting a personalized tune is even better.

Yes there are gains to be had even with an unmodified car. That doesn't necessarily mean peak output at peak rpm. Useable power band improvement is also important.
Thank you! Not at all how I thought the subaruEdit software works. It's good to know. I'm excited for the Tactrix to arrive. Hopefully next weekend I can be rev hang free. (y)
 
#22 ·
I looked at some of the eBay listings for the Tactrix openport 2. Some said they came with adapters for Subaru and Mitsubishi. No adapters are needed for us. The openport 2 connects directly to the standard OBDII port near the hood release latch, and then a USB cable (mini, not micro) is used to connect it to a laptop. For mine, I bought an OBDII extension cable so it could sit by my laptop on the passenger seat for data logging while driving. Not necessary, just seemed like a good idea to me so I didn't kick it.
 

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#24 ·
sedrubaru, I just went through that exact process, it's not bad, a little back in forth with the registration for the software, but Mike is awesome, very clear, concise, step by step instruction. I'm still working with him after eight revisions, and what a day/night difference, power band starts much lower in the rpms, and is smooth all the way up, considerably quicker than without the tune, and he also lowered my cold start idle down to 1100, so much nicer. Don't expect turbo power from this, it's definitely not that, but it is much better, and feels like it should, it's fun to drive now.
 
#27 ·
Being in Canada won't stop Mike from working with you.

My dealership knows I have a tune. I had to put my original, unlocked tune back on my car so they could put the 'ignition recall' tune on my car. I then gave that recall tune to Mike so he had a new base tune to work with for my car. Having a tune doesn't automatically void the warranty, but it could be a consideration if they have to do warranty work specially on the engine, depending on what is wrong with the engine To me, I'm willing to accept that trade-off because getting rid of the rev hang allows me to save wear on my clutch. I'm now in control of the engine speed and can do normal engagement without excessive rub.
 
#28 ·
I was planning on messing around with this back in the spring, but then all the COVID crazyness happened. My job had us working from home so the car didn't get driven and the need was overshadowed with other concerns. I'm trying to drive the car more just to get it out and everytime I do, I am constantly reminded that I need to take care of this. I just ordered an Openport 2.0 from Tactrix and I since I like to dabble in tuning stuff I am going to do it myself. I downloaded the latest version of EcuFlash from Tactrix's website in lieu of buying the SubaruEdit software. I've used it in the past on our previous 02 WRX wagon, plus it's free. From reading Slushbox's comparison from a DIY vs Mike tune, it won't be as good, but I'll be OK with it if my investment is a 3rd of what it would cost otherwise.
 
#32 ·
The ROM handling template that I currently use in the subaruEdit software is:

FB16/FB20/FB25 2018+ Impreza/Legacy/FXT/XV
 
#33 ·
The ROM handling template that I currently use in the subaruEdit software is: FB16/FB20/FB25 2018+ Impreza/Legacy/FXT/XV
Looking into it some more, it seems like I would need some kind of template, or "definitions" as they call it, in order to make changes to the map. I assumed you read in your map from your stock ECU and do a "Save As" but the more I am researching, it seems like you need a blank template that information that is read from the ECU gets filled out into.

I have had no luck finding such a template for ECUflash. Unless someone is willing to email me a template, I'll keep searching.
 
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