Introducing “Long Term Trim”

The ME range of ECUs allows Long-Term Trim (or LTT for short) to take place. It’s used extensively in most modern OEM ECUs as a way to ensure proper engine functioning when using the same map over tens of thousands of units, with the inherent manufacturing differences between them and to cater for the wide range of conditions in which they are required to function. You can use this functionality built into the ME range of ECUs to cater for the differences between the base maps we provide and the particulars of your own setup. Please do bear in mind that its purpose is to correct fueling during normal operation, so it won’t be able to help with idle issues, warm-up, or ensure that the ignition advance is perfectly optimized for your engine and use. For that, you’ll need the help of a tuner.

When correctly set up, Long Term can be used to accurately adjust your VE table over time – even without the laptop connected!

You should be sure to check out the relevant sections of our online manual for more details on how to install and configure a wideband lambda sensor with your ME221/ME442 to really get the best from LTT.

Initial Checks

Please make sure to check each individual item below. Failure to do so will make the LTT system to not operate properly, potentially damaging your engine!

  1. “Lambda Curr AFR” reading is valid and very similar to what your wideband controller’s gauge shows. For units with built-in wideband (ME442), please make sure that the “Int WB Status” is not showing any faults.
  2. Both the “Lambda LTT Trim” and “Lambda LTT Conf.” tables have the same input axes as the main fueling table – “Inj. Base VE(1)”. Double-check that the “Primary Load” axis goes at least as high as your intended boost level (if using MAP as Primary Load). Please see the picture below for what axes we are referring to. There is another table that needs to be checked (not pictured here), “Lambda LTT Conf” (Highlighted with red and green boxes.)
  3. Your “Inj. Target AFR” table (under ‘Injection’ in the tree view) contains the correct AFR targets for your engine.
  4. Verify that your other fueling-related parameters are set correctly:
    1. Engine Driver:
      1. Displacement
      2. Number of cylinders
    2. Injection Driver
      1. Pri. Inj Size
      2. Fuel Pressure / Inj Ref Pressure (set them to the same value if unsure)
    3. Injector Dead Time Table (this will seriously affect the idle areas during autotune)

Setting it Up

    1. A complete guide on the settings in the Lambda driver can be found in the manual. But here are the most important ones for the operation of the LTT system. If you’re unsure on how to set a value, please get in touch or leave it default:
      1. Type: Wideband Prop (recommended)
      2. Bank 1 Src. – selected to the correct source for your setup
      3. Startup Delay(s): set it high enough such that your wideband controller has enough time to heat the sensor and that your after-start enrichment delay elapses
      4. CLT Min: set a few degrees C above the final warm-up temperature. 
      5. RPM Min: determines the RPM above which wideband control starts operating. Normally set just below idle.
      6. MAP Min/Max: Range of MAP values in which the wideband algorithms operate
      7. TPS Max: maximum throttle position reading 
      8. Max TPS/MAP Delta: the process to set these up is to monitor them with a histogram while steady-state driving and then set them a few units higher than that. Authority: how much change you want to allow. Normally 20-25% should be more than enough to cater for differences between basemaps and car setups. 
      9. WB Algo P: what fraction of the observed fueling error to be added to the lambda trim. Recommended 0.2-0.5. Lower if you’re seeing fueling oscillations between rich/lean.
      10. WB LTT Mode: Active
      11. LTT Req. Conf: how many passes through one cell until it’s considered tuned. Anywhere between 500-1000 should be enough.
  1. As mentioned above, please make sure that the three tables involved in the process have the same axes – Inj. Base VE (1), Lambda LTT Trim, and Lambda LTT Conf.
  2. Make sure that all the cells in the “Lambda LTT Trim” table are set to ‘1’ to begin with and the ones in “Lambda LTT Conf” are set to 0. You can do this by selecting all the cells in the table, pressing backspace and entering the desired value there.

Running the Autotune

  1. At this point, if you followed all the steps above correctly, you should be ready to start the process. Make sure your car is at operating temperature, all your sensors are reading correctly and you’re ready to begin!
  2. Drive your car on the road or on the dyno, focusing on keeping transient conditions (accelerating/braking) to a minimum and spending several seconds at constant throttle before moving on. Not doing so will make the process much slower to reach the desired results. 
  3. As you drive along, the two LTT tables won’t be updated in MEITE, but you should feel and see (if you have an AFR gauge) improvements in how the car behaves as you go. If you want to see the actual changes, simply restart MEITE and the changes that happened up to that point will be in the “Lambda LTT Trim” table. 
  4. Please do consider that the ECU only saves the data every 5 minutes and only while above idle. If you drive it for 20-30 minutes, there should be enough data accumulated in there anyway, but if you want to be sure that everything is saved please look at the “Lambda LTT Store Tmr” variable and wait for it to cycle around (drop to 0 and then go back to 300s). 

Congratulations! If all the steps above have been performed as described, your car’s fueling should now be significantly better than how it started. It’s unlikely that only one driving session will be enough to cover the entire fueling table, so have a look at the “Lambda LTT Conf” table to get a better idea of what areas of the map you should focus your future driving on.  Areas with a lower number are areas that require move “drive time” spent on them.