High fuel trims and intermittent P0171

[Subietech]

Hey guys, I’m absolutely at my wits end chasing this so I think it’s time to reach out. Car is a 2015 non PP. Has 160 t-stat, 542 plugs, 3 bar map, EPP dual intake and hot pipes, LMS catted downpipes, corsa cat back, LMS HPFP, GH Intercooler, AD trans mounts, and running a GH tune.

I’m having trouble chasing down my high fuel trims. At idle, long term fuel trims sit at around +20. Under load, they drop to around 8. If I run E30 or it gets cold outside, the fuel trim goes high enough to finally pop a P0171 or P0174, but even when the codes aren’t present the fuel trims remain very high. If I reset my KAM, as soon as the car goes in closed loop, the short term trims jump up until the long term starts to take over.

I have swapped between GH, my LMS, and my stock tunes with no changes so I know the issue is not tune related. That also eliminates my MAP sensor and my HPFP since both of those have been swapped to stock to flash the stock tune.
I have inspected and cleaned my MAF, no changes. I’ve replaced the rear bypass valve due to a torn diaphragm, no change. I’ve replaced both upstream AF sensors, no change. I’ve disconnected the catch can and returned the PCV system to stock, no change. I’ve smoke tested the exhaust system and confirmed no leaks are present.

I’ve spoke with Matt about it and he suggested trying a fuel rail pressure sensor which I have not yet had the opportunity to try. My local ford dealer basically told me to kick rocks.

Any Ideas?

 

[SM105K]

How does your total trim look? Have you actually changed out your MAP?

 

[Subietech]

How does your total trim look? Have you actually changed out your MAP?

LTFT sits at roughly 20 on both banks at idle and STFT is at 0. I have swapped the map between my 3-bar and the stock sensor when changing between tunes and no change.

 

[SM105K]

So your total trim is roughly +10? Correct?

Have you tried different fuel stations? I see that you replaced the upstream O2 sensors. Did you replace them with direct OEM Ford replacements?

 

[Subietech]

So your total trim is roughly +10? Correct?

Have you tried different fuel stations? I see that you replaced the upstream O2 sensors. Did you replace them with direct OEM Ford replacements?

It was my understanding that STFT and LTFT added for the total trim, putting it at 20 but maybe I’m misunderstanding that. I’ve tried fuel from multiple stations, this has been occurring for close to a year. They were genuine OEM replacements from the local dealer

 

[SM105K]

It was my understanding that STFT and LTFT added for the total trim, putting it at 20 but maybe I’m misunderstanding that. I’ve tried fuel from multiple stations, this has been occurring for close to a year. They were genuine OEM replacements from the local dealer

I am sorry, I misunderstood. Yes is it STFT + LTFT = Full Fuel Trims. So yours would be +20.

Maybe Matt is heading in the right direction with the fuel pressure sensor, since you are have switched both MAP sensors and HPFP back to stock. I dont know what to say.

Are you seeing much knock?

 

[Subietech]

I am sorry, I misunderstood. Yes is it STFT + LTFT = Full Fuel Trims. So yours would be +20.

Maybe Matt is heading in the right direction with the fuel pressure sensor, since you are have switched both MAP sensors and HPFP back to stock. I dont know what to say.

Are you seeing much knock?

No abnormal knock or any driveability issues. I’ll see if I can get ahold of the specs for the sensor and see if I can pull it out and check the resistance on it to see if it’s obviously *****. I don’t think they’re super expensive.

 

[Jordan_R]

No abnormal knock or any driveability issues. I’ll see if I can get ahold of the specs for the sensor and see if I can pull it out and check the resistance on it to see if it’s obviously *****. I don’t think they’re super expensive.

Fuel pressure sensor is an absolute dick of a sensor to get to. Have to pull the intake manifold to get to it. Might have to see if you can check it on the car if you can get to the plug.

 

[b4black]

I have inspected and cleaned my MAF, no changes.

If you have a MAF, (early model year?) then check for vacuum leaks. Leaks effect idle LTFT at a much greater percentage then at higher rpms.

(small leak/small airflow >> small leak/large airflow)

 

[FiveLeeter918]

Sounds like you've done your due diligence. Boost leaks are such a pain on these cars and it sucks trying to chase them down.

If it's mainly present at idle and not so much under boost, focus on the intake manifold and evap system.

Do you ever see the fill neck code?

 

[FiveLeeter918]

I am curious though, why the suggestion for the FRPS to be replaced? Are you having fuel pressure issues?

Fuel trims are due to an afr imbalance from commanded fueling, so unless your measured afr is out of whack it's a vacuum leak 99% of the time. The other 1% of the time it's due to an ethanol variance.

 

[Subietech]

I am curious though, why the suggestion for the FRPS to be replaced? Are you having fuel pressure issues?

Fuel trims are due to an afr imbalance from commanded fueling, so unless your measured afr is out of whack it's a vacuum leak 99% of the time. The other 1% of the time it's due to an ethanol variance.

The FRPS was just a suggestion from Matt. The only thing I haven’t done yet as far as vacuum leak checking is disconnecting absolutely every vacuum / boost reference source on the charge piping and the manifold and plugging them all off all at once. At that point, The only possible leak would be a cracked manifold or gasket.
Do you know if either the coolant temp sensor, intake air temp sensor, or ambient temp sensors could affect the fueling without popping a code for their circuits? None of those sensors have been replaced yet....

 

[Subietech]

Also, is it possible that the PCV system could have an internal leak inside the valve covers? I thought our PCV systems are baffled.

 

[FiveLeeter918]

The FRPS was just a suggestion from Matt. The only thing I haven’t done yet as far as vacuum leak checking is disconnecting absolutely every vacuum / boost reference source on the charge piping and the manifold and plugging them all off all at once. At that point, The only possible leak would be a cracked manifold or gasket.
Do you know if either the coolant temp sensor, intake air temp sensor, or ambient temp sensors could affect the fueling without popping a code for their circuits? None of those sensors have been replaced yet....

Pre turbo the system doesnt care. Trimming only occurs between the turbos and the front O2 sensors.

 

[b4black]

Pre turbo the system doesnt care. Trimming only occurs between the turbos and the front O2 sensors.

If it has a MAF, then couldn't it be a leak anywhere downstream of the MAF? Unmetered air.

 

[FiveLeeter918]

If it has a MAF, then couldn't it be a leak anywhere downstream of the MAF? Unmetered air.

Yes, but the ecoboost engine doesnt have a MAF its speed density.

 

[b4black]

OK, I didn't think so, but the OP said he inspected and cleaned the MAF. I thought maybe the early models might have had one like the F-150 supposedly had. (Look like now the first posts says its a 2015)

 

[Johnbigdog]

If there is a boost leak, the car wont run lean becuase the MAP will read it and the P.C.M. will fuel accomidfielder. You can block off the p.c.v. and purge valve if you want.

There is no SHO of our body style with M.A.F. it may look like a M.A.F. but it's just a temp sensor.

There isn't a good way to test the fuel rail pressure sensor. The closest test you can do is conect a fuel gauge to the low pressure system and purge the air out of the system. You can then compare the FLP pid to the gauge. They should be 15 psi of each other.

Disconect the conector to the high pressure fuel pump. This will cause the h.p. pump to creat no h.p. fuel. The FRP (fuel rail pressure) sensor should be 30-45 psi of your gauge. Gauge pressure will increase when you disconect the volume control valve to the h.p. pump. But there isn't a good way to test the sensor at high pressure.

Make sure your M.A.P. sensor matched barometric key one engine off. If your baro is biased, the engine will misfuel.

I have seen cases where the injectors are not injecting the proper amount of fuel causing a lean condition. There are people that clean injectors if you are able to have some down time and dont want to buy new ones and get that far.

 

[FiveLeeter918]

If there is a boost leak, the car wont run lean becuase the MAP will read it and the P.C.M. will fuel accomidfielder. You can block off the p.c.v. and purge valve if you want.

You'd think so, but this is not true unfortunately. Leaks before the wastegate solenoid have a big effect on fueling and can completely through off the tune.

Fuel trims at idle are based on the manifold, fuel trims under load will be isolated between the turbos and throttle body.

 

[Johnbigdog]

You'd think so, but this is not true unfortunately. Leaks before the wastegate solenoid have a big effect on fueling and can completely through off the tune.

Fuel trims at idle are based on the manifold, fuel trims under load will be isolated between the turbos and throttle body.

I've been thinking on this one and dont quite understand, unless this is "tune" specific. My understanding of the map before the t.b. was to monitor available boost and operate the recirculation valves to prevent stall. The throttle body controls the air in the intake, rpm controlled with spark.

I guess this kinda details the o.p. thread. Maybe an i.m?