Lean long term fuel trims

[pmezo33]

I'm kind of stumped here.  Maybe you guys had some ideas because I'm out of them.

Long term fuel trims at idle at about 17% for B1 and 14% for B2.  ST fuel trims are find at about 0%.  When i put the car under load, the trims will dip down to about 10-12%, but as soon as i let off the gas, they go back up.  No CEL because Ford doesn't set codes to about 25% to my understanding, but still don't like those LT fuel trims over 10%. 

So far I've smoked the intake through the brake booster vacuum line and it's definitely not leaking at all, so the intake manifold is definitely sealed.  Everything is connected and in good working condition and no other issues, but I really don't like those fuel trim numbers where they are.  I've also cleaned the MAP sensors.

I can't imagine these leaner conditions being normal LT fuel trims for these engines, CEL on or not.  Any ideas?

[SHOdded]

I have had this constant battle with winter gas.  I find adding 1 oz of full synthetic tcw3 oil per gallon pumped alleviated to a great extent.  So does 104+ but cannot recommend it for obvious reasons.  I am thinking fuel injectors might be at the root, but will know when I finally pull them.

[SHOdded]

Does this happen with fuel at any fill level?

[pmezo33]

I'm running some techron through the system right now.  I'm not expecting results, but i had some laying around, so figured i'd throw it in.

Mileage is still fine at about 21 mpg combined.  No codes and it's running fine.  Just bothers me that it's running so lean and there doesn't seem to be any vacuum leaks.  Something can't be right.

[pmezo33]

Does this happen with fuel at any fill level?

You mean octane or how much gas is in the tank? 

[derfdog15]

Does this happen with fuel at any fill level?

You mean octane or how much gas is in the tank?

I think the question is if this behavior happens regardless of how full or empty the tank is, or if it only happens at certain fuel levels. If you are constantly changing octane, then you should stop doing that (atleast for now) to let the system stabilize.

[pmezo33]

Does this happen with fuel at any fill level?

You mean octane or how much gas is in the tank?

I think the question is if this behavior happens regardless of how full or empty the tank is, or if it only happens at certain fuel levels. If you are constantly changing octane, then you should stop doing that (atleast for now) to let the system stabilize.

LT fuel trims are high at any tank capacity.  I always use the regular 87.  It's a stock tune and i do a lot of highway miles.

[AJP turbo]

If there is an exhaust leak from the exhaust ports to the last downpipe connection the pulses can cause air to be sucked in and that can show things as being lean then your ltft's will add fuel.

The reason your stft is ok I'd because your ltft's have compensated.

I would look to an exhaust leak somewhere pre primary 02 or maybe the last downpipe connection

One of the benefits of speed density is even if your intake was leaking you won't see it in your fuel trims because the fueling is happening based on the pressure it sees...so even if you had a leak there that wouldn't cause your fuel trims to be off

[pmezo33]

If there is an exhaust leak from the exhaust ports to the last downpipe connection the pulses can cause air to be sucked in and that can show things as being lean then your ltft's will add fuel.

The reason your stft is ok I'd because your ltft's have compensated.

I would look to an exhaust leak somewhere pre primary 02 or maybe the last downpipe connection

One of the benefits of speed density is even if your intake was leaking you won't see it in your fuel trims because the fueling is happening based on the pressure it sees...so even if you had a leak there that wouldn't cause your fuel trims to be off

I was hoping you'd weigh in.  Appreciate it.

I figured that was the case why ST's are normal.  I'm not hearing any exhaust leaks, but I'll get under there with the car running and check closer and feel around for puffs of air.  I'm just a little hesitant about an exhaust leak because both banks seem to be high.

Out of curiosity, what would be normal LT fuel trims for a bone stock 2010?  Probably around that 10% range or less, right? 

[FoMoCoSHO]

All three of mine ran about +7% on the oem tune.

[AJP turbo]

Yeah it does seem odd that both banks are high...Hard to believe that both banks of exhaust have bad leaks especially if this just happened.....Since it's a 2010 I suppose injectors could be bad or coils...But that would probably make ltft's less than 1.0 since a misfire or overfueling would show rich which would require trims to pull fuel.

At idle and cruise you should see LTFT's way less than 1.10 but probably less than 1.05

At WOT I have seen the 2010-2012 SHO/MKS have better fuel trims because the fuel tuning from the factory seems better than the 2013+ cars

At WOT I see a lot of 2013+ cars have 1.13 ltft but the older ones seem better...But to answer your question I would say you should see about 1.05-1.10 for LTFT

[pmezo33]

Yeah it does seem odd that both banks are high...Hard to believe that both banks of exhaust have bad leaks especially if this just happened.....Since it's a 2010 I suppose injectors could be bad or coils...But that would probably make ltft's less than 1.0 since a misfire or overfueling would show rich which would require trims to pull fuel.

At idle and cruise you should see LTFT's way less than 1.10 but probably less than 1.05

At WOT I have seen the 2010-2012 SHO/MKS have better fuel trims because the fuel tuning from the factory seems better than the 2013+ cars

At WOT I see a lot of 2013+ cars have 1.13 ltft but the older ones seem better...But to answer your question I would say you should see about 1.05-1.10 for LTFT

I'm not getting any misfiring at all.  They are the original coils.  Plugs (motorcraft sp534's) have about 15k miles on them, so fairly new.  Car has just over 160k miles.  Agreed that it would be in the negatives and would be cutting fuel if i were misfiring.  Already dealt with a leaky injector a few months back and i was maxed out at -25 FT's.  Positive trims typically are vacuum leaks or bad sensors giving bad info.
 
Haven't been under the car yet to check, but I'm definitely not hearing any exhaust leaks.  Agreed with you how it would be hard to believe both of them to have leaks causing the lean condition.  Plus i'm sure i'd be able to hear it too.

At WOT, LT dips down to about 11%.  I let off the throttle and it stays around 16% to 14% range when moving on the highway.  If i'm parked idling, it's at about 17% B1 and 14% B2.

[AJP turbo]

If those 02's are original I would change them with ford sensors then look to exhaust leaks

[pmezo33]

If those 02's are original I would change them with ford sensors then look to exhaust leaks

Changed the o2 sensors at about 80k miles when I was getting code for them.

I was thinking about swapping the sensors to see if it changes the numbers at all.  See if the higher FT numbers change from B1 to B2 with the swap.   

[FoMoCoSHO]

How are temps where you are?

Very cold temps causes your stoich target to drop...not as bad as E85 but it still drops.

If you can't find a leak you might consider waiting to hang parts till the temps warm up.