Longterm Fuel trim High at idle

[Rsalazar35SHO]

Good morning everyone,

I"m new to these forums and owning a SHO so I'm looking for some expertise and some help along the way.

i have a 2015 SHO non-PP its got 107,000ish on it, Its got a fresh set of Cam phasers, timing chains guides tensioners and fresh water pump. as well as a brand new PTU, spark plugs and coil boots.

I"m trying to run an Ortiz Performance tune on the car, went with the cold plugs, 175 thermostat and 2.5 Bar MAP sensor, with the SCT BDX for cloud tuning. so long story short, i get all the parts in no problem piece of cake, however when i get to the actual data recording part, i seem to have a fueling issue.

Ortiz and his team have been awesome at helping me with limits capacity not being near the car.
the issue is my longterm fuel trim. its reads around 1.17 on bank 1 at idle and around 1.15 on bank 2 idle.


Ortiz and his team have consistently told me i have a Lean issue but i cannot conclude where or what is causing it. i have tried doing a 'boost leak test' as i was told by them this was a good way to find air sneaking into the engine and making it run "lean" since its adding average 16% fuel at idle. when under loan it drops to around 1.07 or lower on both banks. so i think its a leaky CAC tube. i've replaced majority of the screw clamps on the boost side of the intake system with T-bolt clamps and seem to have found a few leaks that i've addressed but i cannot figure out why my fuel trim is still so high at idle.

i don't thinks it's the high pressure pump, as it would have a permanent lean issue under load and idle.
i don't think it's O2 sensors since i have no codes for either up stream or down stream O2 sensors.
i'm at a loss for fixes and i need help.

could it possibly be leaky injectors ? like i mentioned it has 107K on it but idk if that could be a cause.
any help would be greatly appreciated and i'll try to jump in and out of this forum pretty often to see about getting some tips and tricks fro correcting this issue.

 

[802SHO]

try this simple test. Remove the 2.5 bar map and tune it back to stock. Then start it, datalog what it’s doing at idle. That way you can determine if this is an issue with your car or an issue with the tune.

It’s possible it’s not a mechanical issue at all but a tune problem.

 

[Rsalazar35SHO]

try this simple test. Remove the 2.5 bar map and tune it back to stock. Then start it, datalog what it’s doing at idle. That way you can determine if this is an issue with your car or an issue with the tune.

It’s possible it’s not a mechanical issue at all but a tune problem.

thanks so much for getting back to me.


unfortunately i already tried this fix thinking it was the tune adding fuel or making it run lean.

i have it stock now as Ortiz Performance has advised driving it on that level of increased fuel could cause problems until the high trim at idle is corrected.

it makes sense for there to be a vacuum leak at idle thats why un metered air is entering the engine throwing off fuel levels but i cannot determine where it"s coming from.


wouldn't a boost leak test, show or "indicate" where air could be slipping by ?

sorry for rambling, i'm losing my mind trying to get this solved so i can tune the car!

 

[802SHO]

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 wont 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

 

[Ta2dResqr]

Outside of an exhaust leak, you can look at fueling problems. Try a can of SeaFoam through the tank to clean up injectors, check fuel pressures, etc. 107k things can be getting weak or dirty.

 

[802SHO]

Might be a good idea to consider replacing the primary o2 sensors if they’re very old even if no code for them. I’ve had to replace mine at around 71k as the culprit of a fueling issue found in a log recommended by my tuner and it fixed the issue. If you buy new primary o2 sensors stick with Motorcraft.

 

[HellCow]

I have the same issue on both banks (LTFT almost same as yours during idle) for over a year now. A vacuum lines replaced, cold side redone, new downpipe gaskets, and new turbos (exhaust leak @ wastegate arm). Lee took a look at my logs and noticed my fuel pressure was dropping hard too.

2 things that a few FB users had success with.
1. Replace Fuel Control Module/Unit: GA8Z-9D370-A
Done. Same issue.

2. Replace Fuel Pressure Sensor: AA5Z-9F972-A
Just received it. To be installed.

3. Bad Injector O-Ring
Unlikely as this is affecting both banks

 

[Rsalazar35SHO]

so I've been doing ALOT of reading on this problem trying to better understand LTFT.
since only at idle I'm experiencing a high LTFT, I believe it has to be a vacuum leak. unmetered air in entering somewhere and making it into the combustion chamber causing the PCM to adjust fuel to equal it. since I put it under load it drops drastically, like 1.05 or better.

from the reading I've been doing, it has to be a vacuum leak past the throttle plate, entering where the MAP wouldn't pick it up. however I just had the Phasers and timing and water pump done less then 1000 miles ago and they replaced these gaskets. I made sure to get the old ones back as proof they were replaced. I did the throttle body gasket myself super easy a few 8MM. idk where else to look for a vacuum leak past the MAP unless its a cracked intake ?

it was doing this before I had the timing done, so I don't think the shop did anything. has to be an vacuum leak at idle and a boost leak under load. anyone got ideas on where to look?

p.s. i also had the canister purge valve replaced as well.

 

[Rsalazar35SHO]

Might be a good idea to consider replacing the primary o2 sensors if they’re very old even if no code for them. I’ve had to replace mine at around 71k as the culprit of a fueling issue found in a log recommended by my tuner and it fixed the issue. If you buy new primary o2 sensors stick with Motorcraft.

when you say primary o2 sensor. are you referring o the upstream or down stream O2? the ones the monitor LTFT right (down Stream) ?

or do you think the up stream ones, that help control overall AFR would be the culprits ?

 

[Rsalazar35SHO]

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 wont 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

for the exhaust leak? wouldn't i hear a typical "ticking noise" from the pipes if it was cracked like a manifold or something ?

 

[802SHO]

when you say primary o2 sensor. are you referring o the upstream or down stream O2? the ones the monitor LTFT right (down Stream) ?

or do you think the up stream ones, that help control overall AFR would be the culprits ?

Front or upstream (primary).

 

[802SHO]

for the exhaust leak? wouldn't i hear a typical "ticking noise" from the pipes if it was cracked like a manifold or something ?

Not sure but spray some soapy water on the end of the downpipes however I feel like it’s either o2 sensors or that fuel pressure sensor.

 

[Rsalazar35SHO]

Not sure but spray some soapy water on the end of the downpipes however I feel like it’s either o2 sensors or that fuel pressure sensor.

okay ill try some soapy water, maybe its a cracked manifold or something. but also I think replacing the O2 might be beneficial however, also might no considering its both banks.

still gives me the impression its the intake manifold or some CAC tube maybe since its affecting both banks. but at the same time the O2 sensors could also be toast after 107K idk if they are the factory ones or not. such a confusing issue lol and frustration considering I just want to start tuning this thing.

 

[802SHO]

I’m not a mechanic but if it was my car, if the fuel relay thing in the backseat didn’t fix it, I’d do the o2 sensors. The primary o2’s are so important, I’d replace them and go from there. It could solve the problem but it’s also a good idea to do anyway, like replacing spark plugs.

If that doesn’t help I’d be curious if your in-tank fuel pump should be replaced. I don’t want to send you down a rabbit hole. So again I’m not a mechanic but to solve this I’d be attacking it straight on. O2 sensors, lpfp, injectors and HPFP.

I think the exhaust thing is highly unlikely unless it’s a rust bucket. And air escaping after the downpipes wouldn’t cause it to suck in air…I’ve ran open downpipes with no issues.

To further make things confusing I read that Ford allows upwards of 20+% before it activates a check engine light. So technically it’s well within that limit.

 

[Ta2dResqr]

I agree with @802SHO. If you are seeing it on both banks, I would be looking at something that impacts the entire system. LPFP weak, fuel regulator, air leaks at the intake manifold, throttle body, etc. (Even though they were just done, they could have been damaged or improperly installed. Easiest to detect with some type of accelerant sprayed near the suspected area.), PCV system leaks, failing MAP, etc. Once you eliminate things like that, start looking at items that impact individual banks but wear at the same rate. Dirty injectors, weak/dirty O2 sensors, leaking exhaust, etc.

 

[76FoMoCo]

Don't forget to check the line going to the brake booster for cracks. It is past the throttle body and will have a whole system impact. You can cap off the part of the line going back into the intake with no problems. I'm with 802 change your primary O2's at that mileage.

 

[Rsalazar35SHO]

I did a smoke test on it and a boost leak test and found a few boost leaks under about 8PSI. all have been corrected now.

the smoke test came back inconclusive, no smoke leaks found, I started it at the intake manifold and smoke made it all the way to the filter housing.

I'm going to check that brake booster line, and see. this isn't the first time I've been told to look there and I haven't done a very through inspection.

also ill see about getting a set of up stream O2 sensors for it. it is quite possible if they are reading incorrectly, they could be adding fuel and air mixture incorrectly. you recommended Motorcraft ones ill see where I can pick a set up cheapest. I found quite the mark up at some ford dealers here in Denver.


would you guys recommend unplugging the battery for like an hour or two and let the car relearn everything. i have reset KAM before with no actual impact. i feel this might help with some parts corrections.

 

[Ta2dResqr]

Rockauto has Motorcraft for $72 for upstream.

 

[Rsalazar35SHO]

Rockauto has Motorcraft for $72 for upstream.

dude your the best, ill see if I can get them close to that in town if not, ill get them from rockauto and get them in this old girl.

 

[Bluezone]

I did a smoke test on it and a boost leak test and found a few boost leaks under about 8PSI. all have been corrected now.

the smoke test came back inconclusive, no smoke leaks found, I started it at the intake manifold and smoke made it all the way to the filter housing.

I'm going to check that brake booster line, and see. this isn't the first time I've been told to look there and I haven't done a very through inspection.

also ill see about getting a set of up stream O2 sensors for it. it is quite possible if they are reading incorrectly, they could be adding fuel and air mixture incorrectly. you recommended Motorcraft ones ill see where I can pick a set up cheapest. I found quite the mark up at some ford dealers here in Denver.


would you guys recommend unplugging the battery for like an hour or two and let the car relearn everything. i have reset KAM before with no actual impact. i feel this might help with some parts corrections.

Is the PCV vent connector to the intake manifold sealing correctly? You would have found this with a smoke test already, but I was having an issue and located my problem there.