question about stfts

[mtnman]

I was under the impression that short term fuel trims can be tweaked and run in the -4 to +4 range. Is this true? I've done searches on the forum for STFT, short term , short term fuel change and cannot find any information about adjusting these values. My short term fuel trims are averaginig -20.8 and if they run the same as LTFT as far as the best being zero, this seems way too rich. Any ideas or links I havent found? My tune is the result of running Auto VE tuning then following the steps for the custom 3 tune for a '03.

[Tordne]

There are no values to adjust. You adjust your VE so that the Fuel Trims are between +- 4% for both short and long term.

[mtnman]

{B0101} modifications adjusts the Short term fuel trims? I thought {B0101} was only for Long term fuel trims.

[Tordne]

B0101 adjust the fuelling requirements for the specific RPM vs. MAP points. If done well your trims naturally fall in line. Basically IMO you don't tune trims, you tune and trims follow nicely.

[mtnman]

so if my B0101 table is returning very accurate LTFTs (-4 to 0), then my STFTs should be closer to the -4 to 0 range, right? Am I missing something here?

[Tordne]

LTFT and STFT are basically the same thing with the obvious difference being Long Term or Short Term.

If your Short Term trims are returning -4 to 0 then your VE (B0101) must be pretty good. If your Short Term trims look good the your Long Term will look good also. The Long Term trims are learnt over a much longer period tan the Short Term.

But, if your trims are 0 to -4 then why bother enabling Closed Loop (trimming) and just stay Open Loop? I have been running Open Loop speed Density for a year and a half now :)

[mtnman]

No, my STFTs are averaging -20.8.

[Tordne]

Then you are totally over fuelling! I think I mentioned this in our last series of emails a few weeks ago ;) Your VE table was WAY TOO HIGH!!!!

I think you need to:
1) Go back into Closed Loop
2) Set the AFR in your B3605 or B3647 table to 14.7:1 (NOT 14.63) as in the V3 custom Os this will run Semi-Open Loop
3) Redo the AutoVE

[Tordne]

I just checked a tune of yours against a stock truck.. And your VE in the high areas is 27% higher than stock. I'm sure it's not just me but that just does not sound right :eek: :eek: :eek:

[SinisterSS]

That would explain the -20 trims.

[Tordne]

Yup, my thoughts exactly

[mtnman]

I just checked a tune of yours against a stock truck.. And your VE in the high areas is 27% higher than stock. I'm sure it's not just me but that just does not sound right :eek: :eek: :eek:

Andrew,
This doesnt make sense unless you're referring to cells in the VE table which I'm not hitting. Cells above 2800 rpms arent being hit during the logging (not fond staying that high in RPMs a long time with a 2500 4WD Crewcab, although towing something heavy could enable hitting these cells). Are you referring to these cells, although, they should be close to stock, since they never get changed. Cells in the 2000 rpm, 25-80 MAP area should be "spot on". I'm recording only 0.99, 1.00, and 1.01 in these cells. I'll send you a tune and the log from that tune.

[mtnman]

Then you are totally over fuelling! I think I mentioned this in our last series of emails a few weeks ago ;) Your VE table was WAY TOO HIGH!!!!

I think you need to:
1) Go back into Closed Loop
2) Set the AFR in your B3605 or B3647 table to 14.7:1 (NOT 14.63) as in the V3 custom Os this will run Semi-Open Loop
3) Redo the AutoVE
No B3605 in Custom OS 3, B3647 table is set per the Custom OS tutorial, 1.00, 1.06, 1.13, and 1.17 . Dont quite understand what you mean by step #2. I dont see 14.7 in the table.

Ok, found the change in the "properties" dialog. Disregard my question here.

[SSpdDmon]

Hmmm...wideband says you're close...nbo2's say your not. When's the last time you recalibrated the wideband? Did you ever check for voltage variance (i.e. does the voltage commanded = the voltage read by flashscan)?

[mtnman]

Hmmm...wideband says you're close...nbo2's say your not. When's the last time you recalibrated the wideband? Did you ever check for voltage variance (i.e. does the voltage commanded = the voltage read by flashscan)?

It's a PLX, can those be calibrated? I think it automatically recalibrates on startup. Part of the problem may have been that my AFR was set to 14.63 instead of 14.7 Dont know why it was set to this number.

[Tordne]

PLX auto calibrates (somehow) so I don't suspect the WB - anymore. I also have a PLX and it is rock solid!!!

But if you are running Custom OS V3 and commanded 14.63:1 (1.0 EQ) then while you were tuning you would have been in Semi-Open Loop. Therefore trimming would have been happening. This means that you could increase the VE by 10% and the trims would take care of it by removing 10%. Therefore hitting your Commanded AFR and making you BENS look good.

Is this starting t making sense yet?

[mtnman]

Yes, that makes sense. Question about the "stoich" afr setting in properties. How do I keep the value of 14.7? Everytime i close the tune app, the freakin thing goes back to 14.63 as stoich. Isnt there a file i can change the value in (that the properties gui is reading from).