Tech Bulletin - AVCS Activation Improvement

Owned by Mike McGinnis
Last updated: Oct 13, 2021
5 min read

 


Tech Bulletin - AVCS Activation Improvement

Date: 9/16/21
By: Mike McGinnis

Vehicles affected:

  • All CCF ECU Types for EJ 2.5 liter engines with AVCS

Software affected:

  • 3.4.0+18499.22716 and newer

Firmware affected:

  • 1.7.4.2-18500 and newer



Purpose

After an ECU reset, the AVCS system goes through a system of checks and adaptation prior to the ECU entering standard operating conditions. In addition, whether the ECU has been reset or not, a reduced set of checks needs to occur after each engine start.

The ECU is reset when new, after a reflash, when the ECU loses all power, or when it is specifically reset via the AP or a scan tool. 

For the vast majority of vehicles, this poses no concern, but we wanted to provide an improvement for the following use cases:

  • Situations where it's advantageous to get the AVCS system active VERY quickly i.e. at the drag strip, on a drag car which gets pushed to the line, then started and driven aggressively within seconds.
  • Vehicles which exceed 1100 RPM at warm idle may not complete the AVCS activation process easily.



Solution

The applicable ECUs were further reverse engineered to find tables related to the AVCS thresholds and how the tests work. We narrowed down which tables offer an easy method of improving the AVCS activation process on certain vehicles and have made them accessible in our tuning software.




New Tables

AVCS Control Activation (Min. Engine Run Time)

  • This is the minimum engine run time before active AVCS control can take place. Note: the post-reflash/reset idle activation test must complete before AVCS control can be active. The "AVCS Intake Activation Post Reset Flag" and "AVCS Exhaust Activation Post Reset Flag" monitors will show 1 when this occurs.

Tuning Suggestion

You can set the warm temperature cells to 0 if you feel 2 seconds is too much.



AVCS Post-Reflash/Reset Idle Activation (Max. RPM) A, AVCS Post-Reflash/Reset Idle Activation (Max. RPM) B

  • After an ECU reset (including a map reflash), the ECU disables AVCS control and requires certain conditions to be hit at idle before AVCS becomes activated. This table governs one of those conditions. When RPM at idle is less than the first threshold (over a short period), AVCS will potentially be moved to an active state. When RPM at idle is higher than the second threshold, AVCS will not be moved to an active state. Other conditions that must be met include coolant temp generally greater than 122F (50C), vehicle stationary, engine run time exceeding the "AVCS Post-Reflash/Reset Idle Activation (Min. Engine Run Time)" table, AVCS position near a learned "neutral" state, and others.

  • Stock values may vary between vehicles, but ones tested were set to enable under 1100 RPM, do not enable over 1200 RPM.
  • The wording "Do Not Enable AVCS Above" is only related to the post reset, post engine start checks. It has no bearing on AVCS operation otherwise, so that does NOT need set beyond max engine speed.

the "AVCS Intake Activation Post Reset Flag" and "AVCS Exhaust Activation Post Reset Flag" monitors will show 1 when the post-reflash/reset idle activation test is complete.

Tuning Note

If necessary due to high idle speed, increase both values in both tables, by the same amount. Choose an amount sufficient that engine RPM will not exceed them during the AVCS checks, but isn't unreasonable. Values successfully used in testing were: Enable AVCS Below 2000 RPM, Do Not Enable AVCS Above 2100 RPM.



AVCS Post-Reflash/Reset Idle Activation (Min. Engine Run Time)

  • After an ECU reset (including a map reflash), the ECU disables AVCS control and requires certain conditions to be hit at idle before AVCS becomes activated. This table governs one of those conditions. When the engine run time is greater than this table's threshold, AVCS will potentially be moved to an active state. Other conditions that must be met include coolant temp generally greater than 122F (50C), vehicle stationary, RPM less than the "AVCS Post-Reflash/Reset Idle Activation (Max. RPM)..." tables, AVCS position near a learned "neutral" state, and others.

  • Keep in mind built engines often won't zero out the cams that quickly anyway, and this process should not complete until the cams are stable and zero out. While this may seem a nuisance, this active zeroing is a powerful feature which can make stock ECU cam control more accurate than other ECU options.
     

the  AVCS Intake Activation Post Reset Flag and AVCS Exhaust Activation Post Reset Flag monitors will show 1 when the post-reflash/reset idle activation test is complete.

Tuning Suggestion

If necessary for faster switching to normal operation, reduce to 5 seconds. If necessary for extreme conditions, I did also test at 0, successfully.




Associated Calibration Suggestion

Set your calibration to target AVCS positions of 5 degrees or more in the 0-2000 RPM range. That's likely already the case, but this will help satisfy one of the ECU test procedures.



New Monitors

PC SoftwareAccessportDescription
AVCS Intake Control FlagAVCS In Control FlagIs AVCS Intake Control Active? 1 = yes, 0 = no
AVCS Intake Activation Post Reset FlagAVCS In Activate Post Reset FlagHave the phase 1 post ECU reset AVCS Intake checks passed yet? 1 = yes, 0 = no
AVCS Exhaust Control Flag

AVCS Exh Control Flag

Is AVCS Exhaust Control Active? 1 = yes, 0 = no
AVCS Exhaust Activation Post Reset FlagAVCS Exh Activate Post Reset FlagHave the phase 1 post ECU reset AVCS Exhaust checks passed yet? 1 = yes, 0 = no





Suggested Vehicle Operation and Monitoring

  1. Start engine, let idle until the following conditions are all met:
    1. AVCS Intake Post-Reset Idle Activation Flag and AVCS Exhaust Post-Reset Idle Activation Flag monitors read 1
      1. These will be 1 already unless the ECU was reset and AVCS has not gone through its post reset checks successfully yet.
      2. Reminder: Flashing the ECU involves an ECU reset. If a vehicle is custom wired in a manner that powering it off removes power from the ECU (i.e. battery cutoff for racing), it will reset.
    2. Coolant temperature is over 122 F (50 C)
  2. Gently press the accelerator pedal to bring engine speed up to 1500-1700ish RPM and hold there until Post Start AVCS Disabled Map Ratio is 0. This will only take about 2 seconds, but don't rush it. If your vehicle operator cannot hold RPM well, you may need to increase AVCS Post-Reflash/Reset Idle Activation (Max. RPM) A and B values more than suggested to help them out.
  3. Release accel pedal, confirm Post Start AVCS Disabled Map Ratio remains at 0. If not, repeat hold at 1500-1700ish RPM then check at idle again.
  4. If Post Start AVCS Disabled Map Ratio remains at 0, you're good to go.





That sounds complicated. How long does it take to start the engine and be ready to launch?

With practice I'm sure you can beat these times, but my first time performing the tests it took me:

Ecu Immediately After Reset (Approximately 5 seconds)

  • Start Engine
  • Wait for Post-Reset flags to go to 1
  • Bring RPM to 15-1700RPM for 2 seconds
  • Done

ECU without recent reset  (Approximately 2.4 Seconds)

  • Start engine
  • bring RPM to 1500-1700 for 1-2 seconds
  • Done

The AVCS system can phase the cams while Post Start AVCS Disabled Map Ratio is 1, as long as the activation flag monitors we've added are at 1 and the vehicle is off idle. However, you'll be operating in alternate ignition tables which are generally not desirable and this is not suggested. This is why I'm suggesting having the vehicle operator simply use Post Start AVCS Disabled Map Ratio of 0 on the AP gauge, as the chief indicator that the AVCS system is ready to drive aggressively.


Copyright 2024 © COBB Tuning Products LLC. All Rights Reserved. | www.cobbtuning.com