AVLS problem in 3.0R 6MT

[jbrizz]

Hi guys

For a long time now I've had a surging problem in my Spec B. Had the car to a load of different mechanics and no one has been able to offer any guidance. It has spent literally months away having every possible sensor and electrical part swapped out with no change.

Tonight, I think I've finally figured it out. The variable lift solenoid isn't being told to actuate when it should. Physically the AVLS seems to be working correctly because it always kicks in over 4000 RPM, but between 2000 and 4000 it should kick in based on a bunch of parameters which loosely seems to translate to how much you want to hoon.

Attached is a screenshot of some logging. The first column is of a shift from 2nd to 3rd, the red part is just when I shifted into third gear and went WOT, but AVLS mode is 1 (low lift/duration) for a period of time while at WOT then switches to 3 (high lift/duration) and I get the surge. The second column is of me stomping on the throttle in third, not such problem there, the AVLS goes straight to 3 even at only 2200 rpm. There is no annoying surge in this circumstance because AVLS engages and I'm still putting my foot down. The higher the load (going up a hill, in 5th, changing gear etc) the more likely I'm going to get the lag and surge.

I've had an XRT tune, well currently in progress in fact, and Ed isn't aware of the problem so I don't think it's typical of these cars. It's actually bloody annoying to drive like this because you never know when AVLS is going to kick in because it's always at a different time. And the power comes on strong and suddenly, the car squats and I probably look like a moron.

One thing Ed brought to my attention in the logging is that in pulls the RPM generally counts up but every few log points it there will be a value lower than the last. My first guess of what would cause this is a failing DMF, and I do have a wee bit of clutch shudder and harshness if I'm sloppy with changes. The car is also very jerky and shunty at low RPM and driving in car parks is difficult. If the engine RPM is fluctuating even very slightly because the DMF is stuffed then one would think that perhaps the load isn't being calculated correctly and that is possibly much of the reason why the lag is so bad after a shift.

My car is actually JDM but Ed convinced me to flash an ADM ROM but the problem was still there.

Anyone seen this before? Can anyone give any ideas as to what might cause the AVLS to misbehave like this?

This has been ongoing for over 6 months and I would really love to get this problem resolved! Thanks!

[Robbks]

OK. First. AVCS and AVLS operation are different.
Second ALL 6 speeds have a normal flywheel.
Third. AVLS/ AVCS mode will change when throttle changes and also with rpm as per your logs.
Look at the tables in a ROM and you will see it.

You should be logging ACVS angles too.

[jbrizz]

Yes, I know all of that, thanks. I am logging everything but I only showed those three columns to keep things simple.

I didn't mention AVCS in my post as it's operation is unrelated to my problem, it is working as it should be.

I'm not sure about the JDM pre facelifts having a normal flywheel. I know of a place who says they have converted a bunch of DMF ones to SMF. My understanding was all post facelifts are SMF, pres were DMF. Perhaps JDM is different. It doesn't feel like a SMF that's for sure. This one I'm not sure of anyway, lots of conflicting info so I won't know for sure until I see it with the gearbox off.

AVLS operation is based on load if between 2000 and 4000, but is always on after 4000.

AVLS never comes on consistently between 2000 and 4000, if you drove my car it would drive you crazy because AVLS mode seems more like fixed delay + random seconds than load based.
I just need to figure out why the ECU isn't always telling it to engage when presented with the same conditions.

[alessandro132]

I'm not sure about the JDM pre facelifts having a normal flywheel. I know of a place who says they have converted a bunch of DMF ones to SMF. My understanding was all post facelifts are SMF, pres were DMF. Perhaps JDM is different. It doesn't feel like a SMF that's for sure. This one I'm not sure of anyway, lots of conflicting info so I won't know for sure until I see it with the gearbox off.

All 3.0R Spec Bs are SMF - the only preface Spec B that was DMF was the GT Spec B as it has the 5sp.

[jbrizz]

All 3.0R Spec Bs are SMF - the only preface Spec B that was DMF was the GT Spec B as it has the 5sp.

Ok thanks for that, that pretty much rules that theory out. The H6 really is that smooth then, no a single bit of vibration even at very low RPM

[cliffo3rb]

Get a Kido tune.

[Robbks]

I'm not sure about the JDM pre facelifts having a normal flywheel. I know of a place who says they have converted a bunch of DMF ones to SMF. My understanding was all post facelifts are SMF, pres were DMF. Perhaps JDM is different. It doesn't feel like a SMF that's for sure. This one I'm not sure of anyway, lots of conflicting info so I won't know for sure until I see it with the gearbox off.

If you read my post it says this.

ALL 6 speeds have a normal flywheel.

From what I've seen, VVL mode changes dependent on load/ RPM/ Throttle/ road speed/ coolant temp and AVCS angle.
From what i can tall it's all related to engine VE and is used a various setpoints
including low load/ rpm at times

read in here
http://www.romraider.com/forum/viewtopi ... +Lift+Mode

I suspect your surge is related to the VVL mode, but is a tuning issue.
throttle maps have to be very carefully designed around the AVCS angles and VVL mode as they drastically alter the airflow into teh engine,
E.g. if you have the throttle open too much and you suddenly get extra lift, you end up with slow intake velocity and that can cause surging issues.

vvl.jpg (93.2 KiB) Viewed 4824 times

Have a look here it shows you the Minimum throttle angle required for the VVL mode to change
Also there's two of them depending on which other Mode the ECU is in already (high load or low load)

Also to complicate things Throttle Pedal angle and throttle Plate angle are two very loosely related items with the Subaru throttle mapping.
I'm unsure if this relies on Accelerator pedal angle or Throttle Plate Opening.

So Again I'm going with the Engine is doing what it's told properly by the tune that is in it.

[Robbks]

Matt has posted this before, But i'll stick it in here anyway for reference

OK, so this is the 2.5i VVL system explained for PZEV - Excuse the Copy/Pasta from where I wrote it originally

So I had a few questions lately about how the VVL system(aka AVLS) in the 2.5i works and have devised a brief summary based on the email replies that should cover the blanket response

The EJ25 AVLS is not for 'performance' the VVL system is there for fuel economy, with the concept actually stolen from Honda with their VTEC-E Engines... that is VTEC - E with the E for Economy and is one reason why the USA has the 2.5i listed as a PZEV. Here is an article on the VTEC-E engine
http://www.b18c5eg.com/VTEC/sohcvtece.html
which further explains how fuel economy is achieved by only having one inlet valve open below 3000rpm and the factory tune running fully in closed loop with 14.7:1 AFR's for fuel economy and lower emissions. Above 3000rpm, the factory tune actually richens up by 7% to account for the sudden rush of airflow generated by the second cam lobe activating


As you can see, only 1 inlet valve opens with the second yellow pin activating the second inlet valve when required

Once exhaust mods or intake mods are done, the added engine flow dictates that the AVLS RPM point should be lowered to eliminate the single inlet valve as being a restriction but if you want to keep fuel economy, it can still be achieved with stock AVLS rpm by tweaking the AVLS airflow value so once airflow goes past a predetermined value that is considered a restriction, the AVLS activates, even if engine rpm is not high enough, just need to set the fuel table to add fuel above this value

[jbrizz]

Thanks for the info Robbks. Apologies for being skeptical of your advice around DMF, it was not that I was ignoring your advice, just that I'm skeptical of any info until it's backed up by evidence or someone else.

I'm not sure if it is tuning related as the surging affected my stock JDM tune and the ADM tune I flashed onto the ECU. Ed at XRT has not altered any of the AVLS parameters as of yet.

Without knowing the exact algorithm used to make the AVLS low/high mode switch it will be difficult to know if it's a fault or just the way the tuning is, but given that no one else complains about a surge except for me I suspect it's a fault. I would expect it to enter high lift mode after a gear shift and go WOT instantly, exactly as it did when I stomped the throttle without shifting. Something about the conditions that changing gear creates seems to be making it worse. There will be a sudden change in vacuum pressure when shifting.

[Robbks]

Something about the conditions that changing gear creates seems to be making it worse. There will be a sudden change in vacuum pressure when shifting.

Bingo,
It's all in the DBW mapping.

The majority of changes I've seen in Matt's tune on my car were
1. reduce ign timing to stop it pinging, but totally rework the IGN maps to make the base maps correct and have very simple Knock Correction Advance maps unlike Subaru who just plugged in random numbers to the base maps and rely totally on the knock correction/ advance to add/ subtract timing.

2. DBW Maps
Smoothing, smoothing, smoothing
Ensuring that Accelerator angle vs Requested torque is smooth and relevant to the engine loads that will actually be used.
And on the Requested Torque vs Throttle opening, again smoothing and making sure that the thottle plate is only opened far enough to get the air into the motor while maintaining intake velocity when needed.

[jbrizz]

Ok, thanks. I will see if Ed can work on this. I still don't know why it would do this on the factory tune, but it might be related to the crappy fuel here and subsequent retarded timing that it learns.

[Robbks]

the factory tune pings it's ass off, even on 98RON so timing is all over the shop,
it holds onto closed loop far too long,
DBW maps were written by a 3 year old with no concept of how a throttle has worked since the invention of the internal combustion engine.

mine used to surge for the entire rev range at any throttle opening before I had it tuned.

I was blaming dirty MAF, dodgy o2 sensors, dirty filters, dodgy FPR.
dropped in Matt's "Base" Revision1 and it all went away

[jbrizz]

I'm about to about 11th or 12th rev from Ed at Xtreme Racing Tuning. The car is flawless apart from the surge in power at low RPM, doesn't matter if running 95 or 98 octane fuel. It's not a surge as you are describing, it's just a single point where I get all the power. The problem is it's just not consistent when this actually happens.

[west_minist]

I will post here briefly, since it seems some cannot look at past events and make decent suggestions but contests between tuners.

The information posted and the reference links are very rewarding and highlights the complexity of how variables are adjust. Example ECT, Throttle, Load, etc.

As a JDM model and the rom revision, an updated rom could not be found and a similar rom was use to see if it was a JDM issue. So stock JDM and Stock ADM shows the same behaviour. That is, "surging", which implies not really a tuning issue, but one of those issues that plaque some models.

In finalising the tuning for roms for difference ron of gas used, the customer highlighted the issue again, which was the only one left on the table, since it presents itself strongly on low octane gas.

Reviewing the new log with the vvl variable, shows its effect so low into the table, but again curious to see even in stock its presence, since the DBW operation is not aggressive at all.

To fix this issue on this car would be to make the necessary conditions for vvl activation for an appropriate RPM, engine load and throttle.

I personally never had to deal with the vvl issue with customers and never make an adjustment to it. Hence why my tune on this model with a predominate issue with VVL as identify with the customer present never fix it.

As a person who seek precise information, I pray the thread would remain so, where future internet users can use the info here to help them analysed their cars effectively.

[Robbks]

Top Post Ed.

And yeah, tuner bashing aside it's an interesting issue.

I know mine used to behave similar on 1-2 changes.
take off, change gears, release the clutch, press accelerator, ....waaaiiiit...... POHWAZ...

Now that lag isn't there
I put it down to a CL-OL transition issue. Or simply being too lean to produce the torque requested

I'm not sure on Ed's tune on how long the ECU holds Closed Loop for of the AFR targets, but i know Matt has mentioned it here before that he brings it out of CL sooner than factory and likes to add fuel to get them making torque.

SO it may be a funny combo of timing/ EGT's/ OL/ CL/ Road Speed/ VVL Mode/ AVCS angles.