Hopefully this isn't too dumb of a question....
Under normal circumstances, when you go to WOT and enter power enrichment mode (WOT), do LTFTs get used for fueling adjustment?
Thanks in advance.
-AT
Hopefully this isn't too dumb of a question....
Under normal circumstances, when you go to WOT and enter power enrichment mode (WOT), do LTFTs get used for fueling adjustment?
Thanks in advance.
-AT
No, you are in open loop when in PE mode. When they go "0" is when you have entered PE mode.
2001 Z06 - 417 LS3 - LPE CNC LS3 heads - LPE GT-11 cam - ARH 1 7/8" - LPE C6 intake - RPM 3.73 diff - tuned with HP Tuners
2008 Silverado 5.3 - Dynatech LT headers - Volant Cool Air intake - 280whp/303wtq - tuned with HP Tuners
www.davenportmotorsports.com
Short answer, positive LTFTs are used to calculate fueling adjustments in WOT conditions, depending if you have LTFTs activated in the tune.
Last edited by CarsonTech; 01-15-2011 at 02:09 AM.
So I got one vote for Fuel Trims can add/subtract fuel under Power Enrichment Mode, and one vote for they dont.
Anybody want to be a tie breaker?
True, but you have missed the question being answered. You are correct, No trimming is being done when in PE. But...Originally Posted by Sherminator
LTFTS are used for PE calculations IF!! the ECM is in a Closed Loop Design when entering PE
When you enter PE, the PCM takes the last known Long Term Fuel Trims(%) and uses them for the base fueling, then looks in the Power Enrichment table for a value to add or subtract fuel from that baseline.
All the reason to have your FUEL TRIMS close to zero (or minutely rich) when running closed loop. A solid MAF curve and/or VE table and injector tables.
Last edited by smithers; 01-15-2011 at 12:25 PM.
As far as I know it depends on the OS. Most OSes ADD fuel if the LTFTs are positive but don't SUBTRACT if they are negative. Other OSes ADD and SUBTRACT (ex. V6 ECMs).
'97 Jeep Grand Cherokee ZJ, 5.2L (Canada Import), 2" Lift
(CAI, Modded Kegger, Ported TB, 3" Cat-Back, SCT Custom Tune)
'98 Jeep Grand Cherokee Limited ZG, 5.9 V8, Stock
'03 Skoda Fabia, 1.4L 16v
'98 Chevrolet Camaro V6, 3.8L, Targa, ZZP GT1 Cam, Dynomax Cat-Back [sold]
Let's suppose that LTFT adjustments are used in PE mode, but LTFT is not updated while in PE.
It seems like for stockish Gen III PCMs, if the LTFT boundaries are set to under 77 kPa or no updates higher than 4000 rpm, that the "real" fuel adjustment will not really exist because there were never non-PE throttle conditions that would enable the computer to learn LTFTs at full throttle manifold pressures/RPMs....
anybody follow my logic?
-AT
under help >> Tuning How to >> Advanced... there is a chart that shows i think what you are getting at....
The LTFT uses cells to “cover” the VE table. The current cell in use is called the Fuel Trim Cell (FTC). There are 16 cells (0 – 15). Cells 20,21,22 are used by the VCM when it does not want to make a permanent correction to the VE table values (examples would be Decel Fuel Cutoff, Power Enrich Fuel, Charcoal Canister Purge off).
Its the last known LTFT value in that cell block regardless of RPM... so if your rich the second before you punch it, regardless if you eventually enter an area never "recorded"... it takes that last LTF trim value...
perhaps someone can explain better than I
Its all the more reason to TUNE your entire VE table or MAF curve... and then you dont have to think about this in too much depth or run Open loop?
Last edited by smithers; 01-16-2011 at 06:04 PM.
what if your ltft's are out of sync ? one@ 25% and one at 15% at idle ? once i start to drive they return to zero
the PCM cannot run closed loop to adjust fuel trims in PE mode because you are commanding a richer AFR than 14.7:1 and O2 sensors only work at 14.7
Generally for all GM PCM's positive LTFT's are used at WOT to prevent a lean WOT condition, negative LTFT's not used (0 instead). On some of the later ECM's the LTFT's & STFT's will still show their value in the scanner, but they are not being used (if negative).
I count sheep in hex...
idle fueling
2015 Yukon SLT 5.3
Why is there a variation up to 10% like that tho? Essentially, I would think, both sides of the motor *should* be using the same amount of fuel...
I have seen mine go as much as -3% on bank 1 while +20% on bank 2, that's almost a 25% difference in the 2 banks. I originally thought it was an intake gasket leak on the bank 2 side, but intake gasket has been replaced and all ports except the brake booster plugged. I have also replace the narrowband O2 sensors....
exhaust leak
I count sheep in hex...
While I could see this, the headers have new seal4good gaskets and go in to an x-pipe that is pushed on the collector about 3 inches. File trims would show the same with 18" straight pipes attached as well
Its either a exhaust leak, mani leak or injector(s), did you have them flow matched?
2015 Yukon SLT 5.3
NThe injectors were flow matched before being installed 5 years ago, its possible the need cleaned and checked
mine were about 2% bank 1 and 25% bank 2 and my widebands were about 1.5 points out of sync then i bought flow matched injectors and have narrowed the gap down to about 10% but i have checked the headers for leaks and dont see or hear any thing and my widebands are synced pretty well now they are only about .5 off at times.. and my fuel pressure is consistantly 58 psi with very little flux
can you tune the banks sepratly?
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