P0175 - system too rich

[Bain64]

2003 5.4 2v
207k miles
P0175 code started yesterday.
Driveability unaffected, no stumbling or hesitation noticed. Coolant temp gauge appears to operate as expected, starting cool and warming up.

PCV Valve (motorcraft) replaced 2 months ago.
Long term fuel trim bank 1 -22.66%
Long term fuel trim bank 2 -25.78%

I cleaned the MAF sensor and looked for vacuum leaks, then reset the error code, but what's the next logical step if/when this returns?

From the shop manual:

P0172 - System Too Rich (Bank 1)
Description: The adaptive fuel strategy continuously monitors the fuel delivery hardware. The test fails when the adaptive fuel tables reach a rich calibrated limit. Refer to Section 1, Powertrain Control Software Fuel Trim for more information.
Possible Causes: Fuel System:

• Fuel pressure regulator (vacuum hose off, diaphragm leak).
• Leaking fuel injectors.
• Fuel return line restricted.
• Fuel rail pressure sensor (incorrect reading).
• EVAP canister purge valve leak (when canister is full).

Base engine.

• Engine oil contamination.

Air Measurement System:

• Mass air flow (MAF) sensor (contaminated, damaged, or corroded connector).

Diagnostic Aids: View freeze frame data to determine the operating conditions when the DTC was set. Observe the LONGFT1 and LONGFT2 PID(s). Refer to Section 2, Adaptive Fuel DTC Diagnostic Techniques for more information.


P0175 - System Too Rich (Bank 2)
Description: See the description for DTC P0172.
Possible Causes: See the possible causes for DTC P0172.
Diagnostic Aids: See the diagnostic aids for DTC P0172.



Data:

 

[Hamfisted]

Both side long term fuel trims are being cut way back by the computer. Meaning you have raw unmetered fuel going to both banks. (Or a very dirty MAF ...) Look on the driver's side fuel rail and you'll see a fuel dampener with a vacuum tube attached to it. Pull that vacuum tube off and see if you have raw fuel present, or even shooting out with the key ON. Meaning the diaphragm is ruptured and the dampener needs to be replaced. You can order one from Rock Auto. It's held in with a snap ring. So you'll need a good pair of snap ring pliers to remove it. That's my best guess anyway.... Other than that I would just say smoke check all vacuum tubes. But a vacuum leak would cause the computer to go the other way ...


https://www.rockauto.com/en/catalog...uel+&+air,fuel+injection+pressure+damper,6120

 

[Bain64]

Thanks Hamfisted, the code hasn't returned since cleaning the MAF sensor. I have not yet checked the diaphragm but will in the next few days. LTFT on both banks are in the -10% and -15% ranges now on 2 different days of testing, is this more reasonable LTFT numbers for long term use?

 

[Hamfisted]

Ok, sounds good ! One thing I didn't notice in your earlier post was the engine load. Did you take a snap shot while you were driving down the road ? Disconnect your negative battery terminal for about 10 minutes to reset the PCM. ( Good time to clean the battery terminals too....) Then warm up the motor and look at your LTFT readings again and tell us what they are at idle / parked .Should reset to " 0 " and start from scratch. Drive it around a bit to let the PCM relearn, and look at the LTFT's again. Should be in the 10 to 15 % range which is normal. You can still check that dampener diaphragm if you want to, but it may very well be fine and no leaks.


-Mike

 

[Bain64]

Not sure why the engine load shows 30% in the photo, it was at idle. I did reset the PCM (battery unplug) when cleaning the MAF, and the new fuel trim of -10% to -15% is the new learned LTFT after driving for a couple days (short trips). So 10-15% negative is still normal?

Planning to chase a sunroof leak tonight... Drains are clear but the sunroof seal is 15 years old and it shows..

 

[Hamfisted]

Are you sure it's a negative 10 - 15 % on the LTFT ? A positive in that range would be normal, but not really a negative 10 -15 % . But if you're not getting any more codes and your performance and gas mileage seem normal, I wouldn't worry about it on a motor with over 200k on it.

 

[Bain64]

Are you sure it's a negative 10 - 15 % on the LTFT ?

Unfortunately yes I'm sure of the negative, at least as sure as seeing that the tool is reporting a negative. In the screenshot below of LTFT1, the first half is at idle and the second half at around 1500 rpm, it reports -10% and -13% respectively. Bank 2 is similar within 2%.

 

[Hamfisted]

Have you noticed a decrease in gas mileage in the last few months? Or since you started getting the DTC's ? Do you have a fuel pressure gauge you can read fuel pressure at the rail with ? Has the fuel pump assembly ever been replaced ? Pressure should read 40-50 lbs, and hold pressure with the key off. If you see the pressure drop to zero slowly with the key off it may be a leaky injector(s).
I guess we'll just look at it again if the codes come back.

 

[Bain64]

I just bought the Expy in January this year, and idle it sometimes to keep the 3 young kids comfortable, so fuel mileage is hard to accurately track for me at this time. I'm getting 13.x mpg currently but that's 100% in town and occasional idle so it's not too far from what I'd expect. The prior owner averaged around 17 mpg, but drove 95% highway.

I don't own a fuel pressure gauge, but realized I'd like one while researching the code. Thanks for the note on normal fuel pressure, I plan to buy or borrow and test.

Fuel pump assembly history is unknown. Fuel filter history unknown too, but I'd expect a lean code if it was clogged.

 

[BRIANGEE]

Your engine load is probably because you have the AC on. Mine is similar to yours but if you turn off the accessories it will drop considerably.