Trying to understand LTFT issues

[mattspeed3]

(scratch)
Okay, so I'm in the market for a CAI or SRI. After hearing about the long term fuel trim variances people were getting with this intake or that intake, I was flip flopping between choices until I sort of realized that seemingly all aftermarket intakes affect LTFTs - correct?

I guess the bigger question I have is, if you're getting a higher than acceptable LTFT variance (say +/-10 or so), does that mean your ECU is actually pumping more or less fuel into your engine than it should be (and is that what the +/- number represents)? Or is it simply that the ECU is correcting to the increased air flow and adjusting by said variance? Or am I getting this all wrong?

It seems intakes with straighteners tend to avoid throwing CELs, so their resulting variance is "acceptable" as deemed by the ECU. What is actually happening when an intake causes a CEL due to unacceptable LTFTs?

 

[mazdaspeedster3]

You are typically going to run lean.

 

[AutoEuphoria]

Which PID monitors the LTFT again? What section in the DH is it under?

 

[Silver Ecstasy]

From what I understand:

+#'s mean the ECU is adding fuel since it recognizes a lean conditon.

-#'s mean the ECU is pulling fuel since it recognizes a rich condition.

The car runs rich as it is, and installing my MSCAI with air straighteners resulted in a +3.7 LTFT at WOT and a +10 LTFT at idle.

I haven't seen too many people with CAI's that are over +10 period. Most of the SRI guys are over +10.

 

[mazdaspeedster3]

Which PID monitors the LTFT again? What section in the DH is it under?

Fuel

 

[CWPspeed3]

maybe most SRI guys are over +10 but I'm usually +4.7 to +7.8 and occasionally see something over 10. I think people worry too much about LTFT's, just adding an intake isnt going to kill your car. Just drive and watch boost.

 

[Sport6]

From what I understand:

+#'s mean the ECU is adding fuel since it recognizes a lean conditon.

-#'s mean the ECU is pulling fuel since it recognizes a rich condition.

The car runs rich as it is, and installing my MSCAI with air straighteners resulted in a +3.7 LTFT at WOT and a +10 LTFT at idle.

I haven't seen too many people with CAI's that are over +10 period. Most of the SRI guys are over +10.

I have the MSCAI in SRI and have not ever seen anything close to +10.

Usually its -6 at idle, -2.3 at light throttle, 3.0 at WOT

 

[Silver Ecstasy]

Possibly just need to pull my battery and reset it. I was not driving it easy when I first got it installed in the bitter cold.

 

[Bravnik]

LTFT need to be as close to zero as possible but single digit if possible. If you run too lean/rich on your LTFT's you will get a CEL.

 

[Silver Ecstasy]

Damn, mine went up today. 10.9% idle, 8.7% WOT. Hmm.

 

[matsuda]

(scratch)
Or is it simply that the ECU is correcting to the increased air flow and adjusting by said variance? Or am I getting this all wrong?

The ECU is not adjusting to differences in airflow. It is adjusting to differences in the way that the incoming air is metered.

For example: The engine is idling and the MAF sensor is reporting X amount of air through the intake. The ECU is programmed so that it knows (ideally) how much fuel it would take to achieve a correct (stoichiometric in this case) A/F ratio for any given amount of air. Using the wideband O2 sensor for feedback, it will adjust the amount of fuel to get the correct A/F. The difference between the ideal (programmed) and the actual amount of fuel needed is the STFT. The LTFT is then derived from the STFT.

Large LTFT corrections (> 10%) may indicate a problem such as an air leak, or a poorly designed intake (incorrect MAF housing size or excessive turbulence).

 

[Wurf]

I read on mazda speeders forum that the ECU in these cars will "learn" your mod so that eventually you won't see the gains from it that you did when you first installed it.

I'm not sure how the ECU can kill gains in HP made by increasing the efficiency of the intake system and I'm not sure I believe this information.

What's the general opinion here?

 

[Silver Ecstasy]

General opinion of mine is everyone thinks they're an engineer. No one has actually dyno-proven any type of progress or longevity of the car and it's mods. Not a single person has done the exact process of:

Stock Dyno
Modded Dyno
Re-checked Modded Dyno

We all just "guess" by the seat of our pants, sometimes with theories built on observations, others on guesses and doubts. And guess who benefits regardless? All those vendors lol.

 

[matsuda]

I read on mazda speeders forum that the ECU in these cars will "learn" your mod so that eventually you won't see the gains from it that you did when you first installed it.

I'm not sure how the ECU can kill gains in HP made by increasing the efficiency of the intake system and I'm not sure I believe this information.

What's the general opinion here?

If you changed the intake and that caused the A/F to become leaner, the ECU will correct for that. In that respect, you cannot "fool" the ECU.

However, almost any mod that enables the engine to breathe easier will improve performance.

 

[mattspeed3]

The ECU is not adjusting to differences in airflow. It is adjusting to differences in the way that the incoming air is metered.

For example: The engine is idling and the MAF sensor is reporting X amount of air through the intake. The ECU is programmed so that it knows (ideally) how much fuel it would take to achieve a correct (stoichiometric in this case) A/F ratio for any given amount of air. Using the wideband O2 sensor for feedback, it will adjust the amount of fuel to get the correct A/F. The difference between the ideal (programmed) and the actual amount of fuel needed is the STFT. The LTFT is then derived from the STFT.

Large LTFT corrections (> 10%) may indicate a problem such as an air leak, or a poorly designed intake (incorrect MAF housing size or excessive turbulence).

Great reply - that makes sense.

 

[dread]

I read on mazda speeders forum that the ECU in these cars will "learn" your mod so that eventually you won't see the gains from it that you did when you first installed it.

I'm not sure how the ECU can kill gains in HP made by increasing the efficiency of the intake system and I'm not sure I believe this information.

What's the general opinion here?

This is true, the ecu tries to meet set load targets. When you add a mod a/f or boost are temporarily higher but the ecu will lower them to meat the load targets. If want power that lasts more than a week you need to increase the load targets in the ecu.

 

[Wurf]

So with a stock map ECU, adding an intake system simply adds noise after about a week, and that's about it? That's pretty lame.

 

[matsuda]

So with a stock map ECU, adding an intake system simply adds noise after about a week, and that's about it? That's pretty lame.

No. Read my previous post.

 

[Wurf]

Ok did that.
Now it makes more sense to me. If your new intake isn't metering the way the ECU is expecting IE stock, it will use fuel trims to correct based upon the other parameters it measures. So long as your new intake isn't completely whack and metering so far out of range that the ECU can't compensate giving you a CEL.

Otherwise if your new intake reduces restriction in the intake system you should still see an increase in performance in addition to intake noise because of it.

So what the other posters were trying to say is the ECU won't learn around your modification as it relates to increased efficiency or reduced restriction, only in inaccurate metering that might lean the motor thereby adding power. It will eventually fatten it up again if need be.

Cool.