LTFR why so important, am I wrong?

[dsmlights]

Why do we care for LTFT if they are not used when the car is WOT from what I read on a post. Is this correct or am I just messing up..

From what I have aquired the LTFT are for Partial throttle right? So how do they adjust to WOT … can someone please explain .

Thanks,

Ed

[TAQuickness]

Good question Ed.

During CL, the PCM has several cells for various conditions with LTFT values stored in each cell. In short, this let's the PCM adjust the fueling for various driving condions....

Now, when you transition from CL cruising to OL WOT, a few things happen:

1) Being OL WOT, the PCM is no longer adjusting fueling based on NB feedback. It just commands an AFR and assumes the airflow and fuel flow tables are correct to achieve the commanded AFR (CAFR).

2) The WOT CAFR is determined by OLFA and PE tables - commanded will = the richer of the two.

3) When you transition to WOT, if the LTFT was positive, the PCM assumes the tune is leand and will add additional fuel to the WOT CAFR

3a) When you transition to WOT, if the LTFT was negative, the PCM will derive WOT CAFR based on #2 above. No additional fueling for this condition.

Does that help?

[TAQuickness]

Also - don't hesitate to search the board a bit. I'm not trying to discourage you from asking questions. There is a lot of really good info on PCM functionality floating around here.

[dsmlights]

believe me I been searching but I read all those already ...

Ok so if my car has -7LTFT then i am fine as long as it is not positive?

what are the advantage of having 0 LTFT over -7LTFT

[joecar]

what are the advantage of having 0 LTFT over -7LTFT

LTFT -7% means that one or more of the IFR, VE, MAF tables is in error by some amount(s) (adding up to -7%).

LTFT 0% means all the tables are correct.

All this is with respect to the NBO2 sensors functioning correctly.

During thottle transitions, the PCM ignores the MAF and uses the VE table...
if the VE table is correct (0%), then engine's throttle response is very quick (assuming you have a suitable commanded AFR)...
if the VE table is not correct (-7%), then transient throttle response is poor (too rich or too lean during the transition), engine responds [comparatively] more slowly.

Cheers
Joe

[dsmlights]

LTFT -7% means that one or more of the IFR, VE, MAF tables is in error by some amount(s) (adding up to -7%).

LTFT 0% means all the tables are correct.

All this is with respect to the NBO2 sensors functioning correctly.

During thottle transitions, the PCM ignores the MAF and uses the VE table...
if the VE table is correct (0%), then engine's throttle response is very quick (assuming you have a suitable commanded AFR)...
if the VE table is not correct (-7%), then transient throttle response is poor (too rich or too lean during the transition), engine responds [comparatively] more slowly.

Cheers
Joe

k thianks for this info. so Now everyone tried to get to 0 so they can get the fastest response avail. IE no bogging or sputtering ???

thannks for the help.

Ed

[SSpdDmon]

I think of it this way...

1) We know positive fuel trims carry over to WOT.

2) Our cars run richer in colder weather (at least this is what I have noticed).

3) A -7% LTFT means the PCM will have to see a +7% change in part throttle fueling before it'll start adding fuel to WOT.

With those three facts/theories, I would say tuning a car to 12.7:1 at WOT when there are -7% fuel trims is rather risky. If fueling does change back to 0% LTFTs (or higher), it's very possible you'll be running 7% leaner at WOT too....which puts you at 13.6~13.7:1. Definitely not good. You follow?

[dsmlights]

but that is initially when i go full Throtle or during the hole power band.

[TAQuickness]

if you transition from a +LTFT to WOT, extra fuel will be added thru the duration of WOT.

[dsmlights]

I think of it this way...

1) We know positive fuel trims carry over to WOT.

2) Our cars run richer in colder weather (at least this is what I have noticed).

3) A -7% LTFT means the PCM will have to see a +7% change in part throttle fueling before it'll start adding fuel to WOT.

With those three facts/theories, I would say tuning a car to 12.7:1 at WOT when there are -7% fuel trims is rather risky. If fueling does change back to 0% LTFTs (or higher), it's very possible you'll be running 7% leaner at WOT too....which puts you at 13.6~13.7:1. Definitely not good. You follow?

but I though -LTFT do not carry over to WOT?