Help! P0171, making me pull my hair out!

[augy88066]

Hello! I took ownership of my father’s expedition last year and did a bunch of work to it getting back up to speed. It’s a 98 Expedition XLT 5.4L.

Short story, when I inherited the vehicle it had code P0171 on it and nothing else. A year later, it’s still the same after all of the repairs below. Note, P0174 has never popped up. The code is intermittent and once cleared, pops up again in a day or a month. It only happens while driving. Vehicle drives fine but you smell gas (sometimes when vehicle is turned off, only right after running). The only other I can think of is maybe the fuel injectors but I don’t know how to rule them out. My thought is maybe one or more are having problems with open/close. Connections are tight as well to all injectors (injectors are original). Any insight or help would be appreciated!

My dad also historically put good fuel injector cleaner in every 3,000 miles and is the original owner.

I have already replaced (mostly using OEM parts):
- Head Gasket
- Timing Chain
- Spark Plugs
- MAF (good brand) and Air Filter (less than 6 months ago)
- All Vacuum Lines (incl. PCV and throttle body rear line)
- Idle Control Valve
- Cleaned Throttle Body
- Replaced Throttle Controller
- Front (before CAT) 02 Sensor
- Evap Hose to canister
- Fuel pump replaced
- Fuel filter replaced
- Fuel neck hose

Only thing to note is exhaust is about six years old. Little bit of rust, no visible rot.

Any help would be appreciated!

 

[JamaicaJoe]

I wonder if the CAT on the affected side Bank 1 is clogged and impeding flow of air into the combustion chambers?

 

[jr1under]

What value are you getting for Long Term Fuel Trim on Bank 1?

 

[Hamfisted]

Smoke test the intake system. That's the best way to find vacuum leaks. With all that you've done, about the only thing left is a crack in the intake manifold on the passenger side. But a smoke test would reveal that.

Mechanics Smoke Test Machine on Amazon




.

 

[jr1under]

Smoke test the intake system. That's the best way to find vacuum leaks. With all that you've done, about the only thing left is a crack in the intake manifold on the passenger side. But a smoke test would reveal that.

Mechanics Smoke Test Machine on Amazon

I've seen this response so many times that I'm buying one. The hoses, tubes, etc. in my 1999 Exp and 2005 F150 range in age from six months to factory-original. There's no specific problems right now but at that age there's bound to be some cracks and it'd be nice to find them before they get bigger.

 

[augy88066]

Hello all! Just an update, I am going to do another smoke test shortly. Also, I did replace the fuel pressure regulator as it was badly corroded. The issue still persist however, I suspect the regulator needed to be replaced anyway due to rust / buildup at the ports (e.g., completely green).

The only thing I could think is that maybe it is the EGR valve as that is still factory or possibly the oil cap. More to come!

 

[augy88066]

What value are you getting for Long Term Fuel Trim on Bank 1?

I will be checking that next, post the smoke test.

 

[JerryT]

Hello! I took ownership of my father’s expedition last year and did a bunch of work to it getting back up to speed. It’s a 98 Expedition XLT 5.4L.

Short story, when I inherited the vehicle it had code P0171 on it and nothing else. A year later, it’s still the same after all of the repairs below. Note, P0174 has never popped up. The code is intermittent and once cleared, pops up again in a day or a month. It only happens while driving. Vehicle drives fine but you smell gas (sometimes when vehicle is turned off, only right after running). The only other I can think of is maybe the fuel injectors but I don’t know how to rule them out. My thought is maybe one or more are having problems with open/close. Connections are tight as well to all injectors (injectors are original). Any insight or help would be appreciated!

My dad also historically put good fuel injector cleaner in every 3,000 miles and is the original owner.

I have already replaced (mostly using OEM parts):
- Head Gasket
- Timing Chain
- Spark Plugs
- MAF (good brand) and Air Filter (less than 6 months ago)
- All Vacuum Lines (incl. PCV and throttle body rear line)
- Idle Control Valve
- Cleaned Throttle Body
- Replaced Throttle Controller
- Front (before CAT) 02 Sensor
- Evap Hose to canister
- Fuel pump replaced
- Fuel filter replaced
- Fuel neck hose

Only thing to note is exhaust is about six years old. Little bit of rust, no visible rot.

Any help would be appreciated!

I do not believe it’s a fuel injector, if so you would throw a cylinder misfire code.
I had the exact same intermittent P0171 code on my 1998 Expy. It took me about 6months to fix. I did a smoke test and found a small leak at the hose connector to the charcoal canister located under the fuel

Hello! I took ownership of my father’s expedition last year and did a bunch of work to it getting back up to speed. It’s a 98 Expedition XLT 5.4L.

Short story, when I inherited the vehicle it had code P0171 on it and nothing else. A year later, it’s still the same after all of the repairs below. Note, P0174 has never popped up. The code is intermittent and once cleared, pops up again in a day or a month. It only happens while driving. Vehicle drives fine but you smell gas (sometimes when vehicle is turned off, only right after running). The only other I can think of is maybe the fuel injectors but I don’t know how to rule them out. My thought is maybe one or more are having problems with open/close. Connections are tight as well to all injectors (injectors are original). Any insight or help would be appreciated!

My dad also historically put good fuel injector cleaner in every 3,000 miles and is the original owner.

I have already replaced (mostly using OEM parts):
- Head Gasket
- Timing Chain
- Spark Plugs
- MAF (good brand) and Air Filter (less than 6 months ago)
- All Vacuum Lines (incl. PCV and throttle body rear line)
- Idle Control Valve
- Cleaned Throttle Body
- Replaced Throttle Controller
- Front (before CAT) 02 Sensor
- Evap Hose to canister
- Fuel pump replaced
- Fuel filter replaced
- Fuel neck hose

Only thing to note is exhaust is about six years old. Little bit of rust, no visible rot.

Any help would be appreciated!

I do not believe it’s a fuel injector as that would through a cylinder misfire code. I had the exact same problem with my 1998 Expedition (P0171) and I took me about 6 months to diagnose and 15 minutes to fix. During a smoke test I found a small leak at the connector hose input to the EVAP canister located behind the fuel tank, along the driver side frame rail behind the rear wheel. I pulled the connector from the canister, replaced and greased the o-ring on the connector and securely snapped it back into place. No more code. Worth giving it a try. Btw, there are additional Evap hoses and connectors worth looking at, located on and around your gas tank. Good luck, I know how frustrating this can be.

 

[augy88066]

Thanks for the insight!

Smoke test confirmed that I have a super tiny leak on the egr valve. So going to replace the valve and the metal line. Both motorcraft as the replacement parts.

Also, major leak at the ICV. Hose looks fine so something else may be going on.

Also considering replacing the evaporator canister as I shouldn’t smell that much gas. Thoughts?

 

[augy88066]

Another update. ICV was not the issue. EVAP charcoal cannister (incl. rotten line to it), EGR valve and tubing replaced with motorcraft original parts. Code is still persisting but actually is also on Bank 1 and Bank 2.

Confirmed that there were no other vacuum leaks with a smoke test being completed.

The current fuel pressure is around ~25 for each injector. When removing the emissions line from the fuel pressure regulator (regulator is new), pressure goes up to 35 which is still low. When pinching the return line, the pressure goes up to 150. I am suspecting it is something with the fuel system and / or fuel pump. Fuel filter was replaced 9 months ago.

Any thoughts? The fuel pump was replaced last November with a Delphi pump but I guess it could be possible that it is failing? Any help would be appreciated.

 

[augy88066]

I do not believe it’s a fuel injector, if so you would throw a cylinder misfire code.
I had the exact same intermittent P0171 code on my 1998 Expy. It took me about 6months to fix. I did a smoke test and found a small leak at the hose connector to the charcoal canister located under the fuel

I do not believe it’s a fuel injector as that would through a cylinder misfire code. I had the exact same problem with my 1998 Expedition (P0171) and I took me about 6 months to diagnose and 15 minutes to fix. During a smoke test I found a small leak at the connector hose input to the EVAP canister located behind the fuel tank, along the driver side frame rail behind the rear wheel. I pulled the connector from the canister, replaced and greased the o-ring on the connector and securely snapped it back into place. No more code. Worth giving it a try. Btw, there are additional Evap hoses and connectors worth looking at, located on and around your gas tank. Good luck, I know how frustrating this can be.

I am suspecting it may be something similar.