Intermittent OBD 2 code P0171

[ehnco]

96 Explorer w/ 4.0 Pushrod. I am getting an intermittent P0171 code for system lean. CEL light comes on every 3 months or so. So far I have replaced: Both upstream O2 sensors, IAC, Cleaned MAF, Fuel filter, Plugs/Wires, Ran propane enrichment test for vacuum leaks and found none, used Seafoam in vacuum line and gas tank. It runs excellent with no driveabilty problems. Occasionally I also get code P0174, but 9 times out of 10 it is just code P0171. Went on many long trips without the CEL light coming on, towing the boat, etc. It seems to be a random thing ?? Anyone have any ideas ?? Last year I had both codes every three drive cycles, After all th eparts have been replaced above, it only happens like I said every three months or so....

 

[Runnin'OnEmpty]

Ehnco, those codes are for system lean on bank 1 and bank 2. Since they alternate, my best guess is that you have an intake vacuum leak. (Even though the propane test didn't pick it up.) I would try re-torqueing the lower intake bolts as a first step. Since the light goes on and off, the leak probably isn't major.

Concentrate on the passenger side, (bank 1); that's the side the P0171 indicates.

 

[ehnco]

Will try re-torqueing them early next week.

Thanks !

 

[ehnco]

Fixed

Figured it out that I was getting a check engine light and codes P0171, P0174 right after I change my oil (everytime). One of the reasons for lean codes according to Ford is "base engine oil overfill". I usually put in 5 quarts of oil and it is right at the full mark. First drive after the oil change after 3 drive cycles I got the CEL light. Went home, scanned it (just P0171 this time but sometimes P0174 as well). Drained 1/2 quart so it's a hair below the full mark on the dipstick and it's been a week and no CEL. I was a hard drive up to the Pocono Mountains in Pa (from Chesapeake City, Md-3 hour drive). Mostly 85 - 90 MPH up, lots of stop and go on the way home with traffic. I guess the 4.0 is sensitive to oil fill level ??

 

[Runnin'OnEmpty]

Ehnco, thanks for posting back your results. There is a list of causes a yard long for the code P0171, and you are indeed correct that oil overfill is one of them. A loose dipstick is another.

Congratulations in finding this out. It's not one of the "normal" causes for this code, and I don't know exactly why an oil overfill will set it, but apparently it does. Thanks again for letting us know, it may help someone else.