98 F150 Fault Code ( System Too Lean )

Just recently I got a check engine light on a 1998 F150 truck. It has the 4.6 liter engine.

Checked it with a code scanner and got a PO171 code, which according to the chilton book, is system too lean (bank 1).

Any advice on how to pursue this. Could it be an injector problem? Ignition timing?

Not too sure on were to start on troubleshooting this.

The truck has been maintained well and hasn’t had any real issues till now. Also which bank is bank one. Is it the one with #1 cylinder?

Thanks in advance.

Bank 1 refers to the O2 sensor before the CAT. It is seeing too much air for some reason. There may be an air leak in the manifold after the airflow sensor or an exhaust leak before the sensor taking in air. Check the air filter and make sure it is good also.

The odds are your PCV valve hose is leaking as this is common. Check all your vacuum hoses for leaks. Spray carb cleaner around the engine and hoses and if you have an air leak the rpm’s will rise slightly. You can then locate the leak and fix it.

Bank 1 is the side with plug number one. Look for a vacuum leak on that side or something making the other side rich like a leaking injector or leaking fuel pressure regulator if vacuum line to it is piped to that side.

Thanks for the information. I checked most the vacuum hoses and the only real obvious leak was the grommet gasket around the PCV valve that seals it with the valve cover. Will replace it as soon as the Ford dealer gets one and will also replace the PCV hose just to be sure it isn’t leaking also. The PCV hose has a thick cover around it making it hard to determine any leaks or not.
Thanks all