Tuning with fuel trims

[68problemchild]

Just wondering, since short and long term fuel trims are pretty accurate, can you use the % change in fuel trims as a sensor to adjust overall fueling?

I have never gotten my 02 sensor to work but need to roughly dial something in as I am having lean codes on both banks.

Most of the time the fuel trims are not pinned so I have a real % reading to work with.

Sorry this is a newbie question.

Also my STFT are normally below 10% while long terms can get as high as 24%. Do I ignore LTFT''s and just tune with STFT's?

[mr.prick]

Use LTFTs if you're going to tune this way and
be aware that improper fuel injector settings will screw up fuel trims.

[WeathermanShawn]

If your Narrowbands (NB) are in good shape they can definitely be used in the closed-loop portion of a Tune. I personally use LTFT's as in essence they are STFT's integrated over time. But, you can use either.

[Taz]

Gentlemen, as always your advice is sound - for Gen III tuning. Patrick’s Camaro is using an E38 (6.2L L92 - aftermarket cam, LS3 intake and injectors) and T42 (4L70) setup. I have never undertaken the VVE tuning tutorial as outlined by Swingtan … but I believe that’s probably the only accurate tuning option for this particular setup ?

Gen IVs are not my area of expertise … merely thinking out loud …


Cheers,
Taz

[WeathermanShawn]

OP, check out the Swingtan's Tutorial thats applicable to your OP..

Thanks Taz..

[68problemchild]

I can't catch a break.

Anyone have any ideas on this unit? Searching for a V2 compatible O2 sensor.

http://forum.efilive.com/showthread....t-work-with-V2


Thanks for the input guys. Been trying to get the O2 meter to work for about 6 months now. Its been back to Innovate 3 times. No joy.

[swingtan]

Depending on the Gen IV controller being used....

The E38 and maybe others suffer from "LTFT Persistent Memory" the LTFT cells ( and others ) are not cleared on calibration updates and possibly even full flashes. This can lead to errors being introduced if they are either not eliminated all together, or are not taken into account if you are performing CL NB corrections. My advice would be....

• Disable LTFT correction in the tune. Please note that this will affect the PE mode fueling as LTFT's are used in PE mode. So limit the use of WOT from this point on.
  For the E38,
  • B1508 = 120'C
  • B1509 = -140'C
  • B1510 = 120kPa (for NA) or 256 (for FI)
• Clear the LTFT data be either using the DVT controls in ScanTool, or performing an ECM reset.
• Drive the car logging...
  • STFT's
  • Commanded AFR
  • MAP
  • RPM
  • MAF Frequency
• When driving, use gentle throttle applications, and try and keep steady loads on the engine. Also vary the engine RPM and load but not in quick succession. YYou want long periods of stable loads. This is best done on a dyno, but can be done by going for a long drive. At least 30 minutes after the car is fully warmed up.
• Take the log data and set up a map to suit what you are trying to correct ( VVE or MAF ). The STFT's are in a "%" reading, so you will need to create a custom PID to convert the +/- percentage into a BEN. Model your new map on the existing VVE or MAF BAN maps, but using the STFT-BEN as the data.
• Perform the std Auto VVE / MAF process to apply the correction factors to the VVE or MAF.
• Rinse and repeat till happy.

Be warned... This process will optimise your closed loop cells, but do nothing for the cells controlling fueling in the PE range. This means that even if you turn on the LTFT's again, their effect will be reduced in the PE range. While most factory tunes run quite rich in these cells, you may find that by reducing the LTFT effects, you end up leaning out in the PE cells.

This is why all "decent" tuners will recommend the use of a Wide Band controller to ensure the heavy load ranges do not run excessively lean.

Simon.

[nevinsb]

Great post! I used a similar approach when I tuned my truck with the LTFTs, and the part that gave me the most grief was creating the map with BEN values. I'll have to try the tutorial out when I get back this summer.

[68problemchild]

Thanks all! New AEM is scheduled to arrive tomorrow.

Simon, after I get the MAF dialed in, what table do I use to start tuning on for fuel? (Assuming we are back to Wo2 again and I get the new one working)
Also, on my table in scan, I have the options of showing max value, min values, or average. Do I use average?

Great stuff guys.

If this thing does not work, at least I have a plan!

[joecar]

Does anyone know the details on how to serially connect the AEM to V2...?