1998 5.4L 105k e250 - P0171 P0174 codes

[TimRiker]

1998 e250 Sportsmobile, penthouse, uJoint 4x4 conversion, etc. 105k miles.

Spent last week seeing sites around Utah. We had a blast. About 100 miles off-road on various trails, and 1000 miles or so total.

Picture of the trip on https://4x4tent.com/ including our first river (creek?) crossing.

On the trip home, then engine threw these codes:

• P0171 System too Lean (Bank 1)
• P0174 System too Lean (Bank 2)

Still drives fine, with plenty of power, etc.

I suspected the air cleaner as a lot of the off-road trails were dry and dusty. I removed, cleaned and replaced the air cleaner, and it was not nearly as dirty as I expected. It looked good.

Other posts like this one:

https://www.sportsmobileforum.com/forums/f33/issues-with-a-po171-code-5-4l-27394.html

mention replacing the forward sensors. Where are these? On the downpipes I presume? I don't know if they have been replaced, but we did just recently cross 100k miles. Also, where is the mass air sensor? Is that worth cleaning and/or replacing?

 

[posplayr]

vacuum leak. Forget what I did but forgot to reconnect a vacuum line and got similar codes, 2002 5.4L e-250

 

[TimRiker]

With the engine running, I'm listening under the hood and not hearing any tell tale hissing. I've not tried opening the doghouse and listening there yet.

 

[N147JK]

vacuum leak. Forget what I did but forgot to reconnect a vacuum line and got similar codes, 2002 5.4L e-250

Yup, exact same thing happened to me. I poked around and found a huge crack hiding down in the folds of the intake ducting. Fixed and codes never came back.

 

[posplayr]

With the engine running, I'm listening under the hood and not hearing any tell tale hissing. I've not tried opening the doghouse and listening there yet.

The standard test is to spray carb cleaner and listen for a rise in RPM.

 

[kbeefy]

Don't start throwing parts at it....


Just water in a spray bottle can be used for finding a vacuum leak as well, or an un-lit propane torch. The folds of the intake as @N147JK mentions are popular, as is all the plastic/rubber vacuum lines around the manifold.

 

[Mikerson]

Double check around the pcv valve they tend to pop out randomly. I had the same set of codes and that was the issue.