I have an ADM 09 STI (AZ1G202G) with the following mods:
- K&N Filter
- X-Force TBE 3" / High Flow Cat
- Custom Tune
- 98 RON (Shell V-Power)ISSUE
The car runs great, it makes 205KW at the wheels, good on fuel and learning view FLKC is all zero's
However, there is a funny surge / flat spot at light throttle and light load that I need to solve.
When you reproduce it kind of surges slightly then backs off a bit and surges slightly again. (The is no observable speed increase as it is very slight)
I have researched extensively the so called "GR Stumble" that is here and on other sites and tested many of the solutions. None of which have worked which is why I am posting.
My tuner and I road tested and even put the car back onto the dyno where we could reproduce the problem but still couldn't diagnose it.
We have been able to "tune" around it with reasonable success but I would like to solve it as it makes the car less enjoyable to drive.SYMPTOMS
The problem seems to happen right on the CL to OL transition, Once in OL it is fine and further down the rev range in CL it is fine.
It is like the ECU can't make up its mind if it should go to OL or stay in CL.
It feels very similar to an old school 4 barrel carburettor that opens the secondaries without adding fuel from the accelerator pump.
It also seems to make a slightly different noise from the intake(?) when it happpens
NOTE: I never noticed anything like this in the stock tune.STEPS TO REPRODUCE
The problem is reproduced under the following conditions:
- Around 20% Accelerator (Held constant under light load)
- Between 1.10-1.60 g/rev load
- Between 2500 - 2900 RPM
- 3 or 4 gear is bestWHAT HAS BEEN CHANGED IN THE TUNE
The base tune is actually very simple with only the following changes (AZ1G202G), No scaling has been changed and any table not shown below is the same as stock.
Modified tables: 17
(P0420) CAT EFFICIENCY BELOW THRESHOLD changed
Max Wastegate Duty changed
Initial Wastegate Duty changed
Target Boost changed
Rev Limit (Fuel Cut) changed
Primary Open Loop Fueling changed
Primary Open Loop Fueling (Failsafe) changed
Boost Limit (Fuel Cut) changed
Advance Multiplier (Initial) changed
Base Timing Primary Cruise changed
Base Timing Primary Non-Cruise changed
Base Timing Reference Cruise (AVCS related) changed
Base Timing Reference Non-Cruise (AVCS related) changed
Knock Correction Advance Max Non-Cruise changed
Intake Cam Advance Angle Cruise (AVCS) changed
Intake Cam Advance Angle Non-Cruise (AVCS) changed
Checksum Fix changedWHAT HAS BEEN TRIED
I have tried many different changes on many tables to try and determine where the issue is. All of these changes were made individually and settings moved both ways to determine if there is any impact. I have been able to alter the characteristics of the flat spot but not change the rev range it occurs or get rid of it.
- Changing Intake AVCS both ways
- Changing Primary Open Loop Fueling
- Changing CL to OL Transition with Delay (Throttle)
- CL to OL Transition with Delay Throttle Hysteresis
- Changing Requested Torque (Accelerator Pedal) SI-DRIVE Sport Sharp
- Changing Requested Torque Base (RPM)
There have been two changes that have worked best:
- Changes the tuner made to the CL to OL Transition with Delay (Throttle) and CL to OL Transition with Delay Throttle Hysteresis.
- Changes I made to the DBW tables
The changes to the OL to CL tables worked OK but used a lot more fuel. (Basically kicking it into open loop sooner)
The changes I made to the DBW tables worked well but the throttle response was similar to Sport up to about 60% Accelerator.
The DBW changes were tried as after reading throttlehappy's post http://www.romraider.com/forum/viewtopic.php?f=15&t=4911&hilit=gr+stumble&start=225LOGS
I have attached a log of a few pulls, The data that was outside the criteria was stripped and the runs that are left are all basically when it was happening.
Log.csv [60.25 KiB]
Downloaded 30 times
I would really appreciate any suggestions that have worked on similar issues on the 08+ STI, Or any comments on the logs. It is a minor but annoying issue!