What does LTFT mean?

[LavaRand]

I know LTFT means long term fuel trim...but what does that actually mean and what does it mean it it's positive?

I guess it means the car is dumping in an amount of fuel, in order to maintain a good air/fuel mixture (per O2 sensor feedback), which is more than expected based on the map. Right? But if it's still a good/stoichiometric mix, then what's the problem?

My car throws 2187 and 2189 codes and has high LTFT. But it runs absolutely fine, so I'm trying to figure out what the actual problem is.

 

[JimPghPA]

Sounds like an intake manifold leak or a vacuum leak someplace that is allowing excess air to get into the intake after the throttle body.

 

[Lubener]

You basically answered your own question. You didn't mention what your actual LTFT reading was. Anything within +/- 5 either way of zero is nothing to worry about. You should list all information from sensors and fuel trims to really diagnose anything.
Even something as simple as an exhaust leak at the right spot can set off a lean mix code.

 

[adams355]

Fuel and/or injectors, run some quality cleaner through it. Injectors spray pattern diminish causing more fuel into chamber etc. Carbon build up it can still run 'fine'.

 

[Jetronic]

I know LTFT means long term fuel trim...but what does that actually mean and what does it mean it it's positive?

I guess it means the car is dumping in an amount of fuel, in order to maintain a good air/fuel mixture (per O2 sensor feedback), which is more than expected based on the map. Right? But if it's still a good/stoichiometric mix, then what's the problem?

My car throws 2187 and 2189 codes and has high LTFT. But it runs absolutely fine, so I'm trying to figure out what the actual problem is.

The problem is the calculated fuel was off by the fuel trim % and it shouldn't be off.

 

[Astro14]

Fuel trim works like this:

Computer knows how much fuel to add based on air volume (measure by MAF, or other sensors).

As the car runs, computer looks at O2 sensor values, and adjusts the amount of fuel delivered to optimize air fuel ratio.

That adjustment is the long term fuel trim. Fuel delivery is “trimmed” up, or down, from the original value to keep the engine running properly.

When the trim needed exceeds threshold, the computer throws a code, because something is wrong.

Usually, when the LTFT is high, it’s because air that isn’t measured is entering the engine, so, the computer has to add a lot more fuel than it should to keep the engine running at proper air fuel ratio (as measured by O2 sensor).

You need to figure out why the LTFT is out of range. You have a problem. Often a vacuum leak.

 

[mightymousetech]

Think of it like tire pressure. It’s like one of your front tires has a puncture and getting low on pressure, so the steering wheel is off center. The LTFT acts like adjusting the alignment to keep it straight. Tire keeps getting lower, so you keep adjusting the tie rods, further and further. What you should be doing is fixing the puncture and fix the tire pressure to make them even.

Plus, that air leak may only be affecting one cylinder. The LTFT will be adjusting the average for that bank, which means you now have one lean cylinder, and the rest on that bank are running rich. That’s a good way to burn an exhaust valve or melt a piston.

 

[brages]

Vacuum leak usually gives high ltft at idle with the ltft dropping down at higher loads and rpms. I would expect a fuel delivery problem to be the opposite.

I think misfires can throw off the fuel trim as the sensor gets oxygen from the unburned cylinder.

 

[brages]

There are some good videos of this stuff on YouTube. (Probably true for 99% of the topics discussed here)

 

[Trav]

What kind of car is this? Whatever it is it is affecting both banks, an air leak in the air intake from the air box, loose throttle body, evap purge valve, etc.

 

[spasm3]

IF it has a MAF check for a leak or loose connection PAST the MAF sensor.

 

[Slow Car Sport Mode]

I know LTFT means long term fuel trim...but what does that actually mean and what does it mean it it's positive?

I guess it means the car is dumping in an amount of fuel, in order to maintain a good air/fuel mixture (per O2 sensor feedback), which is more than expected based on the map. Right? But if it's still a good/stoichiometric mix, then what's the problem?

My car throws 2187 and 2189 codes and has high LTFT. But it runs absolutely fine, so I'm trying to figure out what the actual problem is.

LTFT means Long Term Fuel Trim.

There is also STFT, or Short Term Fuel Trim.

The closer to zero these values are, the better..

 

[ARCOgraphite]

But if it's still a good/stoichiometric mix, then what's the problem?

Most engines don't have lambda on each cylinder ( but SAAB trionic) , though it can look at the crank trigger and guess at cyl balance issues. You could have one cylinder running dead lean.
When you make a post like this it would be good to know what your LTFT is and what engine this is and any recent maintenance or mods.

 

[LavaRand]

It's a 2006 Mazda MPV with Ford 3l V6 engine.

LTFT is about 15 and stays pegged at idle but moves down to 5 or less when driving.

Unless I'm getting something wrong it means the engine can still maintain fuel mix while driving, which matches that the car drives fine. So I am safe to wait till it's warmer to fix it.

 

[Slow Car Sport Mode]

It's a 2006 Mazda MPV with Ford 3l V6 engine.

LTFT is about 15 and stays pegged at idle but moves down to 5 or less when driving.

Unless I'm getting something wrong it means the engine can still maintain fuel mix while driving, which matches that the car drives fine. So I am safe to wait till it's warmer to fix it.


View attachment 87861

Very nice Torque Pro pic.

Here is some info that may help.

 

[spasm3]

Vacuum is higher at idle, so look for a leak. Both banks are the same. Perhaps spray a bit of carb spray and listen for an rpm change when it gets sucked into the leak.

 

[mightymousetech]

If both banks are the same, most likely a leak between the MAF and the throttle body.

 

[ripcord]

Everything everybody else has mentioned, plus how old is the fuel filter? Have you tested fuel pressure?

 

[Slow Car Sport Mode]

Everything everybody else has mentioned, plus how old is the fuel filter? Have you tested fuel pressure?

Video I linked says if 1 Bank LTFT and Bank 2 LTFT are different, can rule out fuel pump since they should be the same.

 

[ripcord]

If you look at the pic the OP posted, both banks are almost identical.