Hello all I have a 97 f-150 4.6L 5 speed with the PO 174 system too lean bank #2 code, the engine has about 136,000 on it , this is the only code in memory. I have Recently cleaned the m.a.s. (with crc electronic cleaner), changed fuel filter and cleand k&n air filter. This was also the only code on before i did these things and erased after i completed them. If I erase the code the check engine light stays off for 3 days of driving( about 3/4 a tank of gas). It starts and runs/drives and idles fine, seems to have more power and throttle respone is better since the all maintenance, though gas milage still is about 14 mpg, when i got it (59,000) it averaged 21mpg highway and had been getting 18ish lately. Could it be a o2 sensor and if so is their a way to test them with a multimeter. Maybe a cracked hose ?
Any suggestions would help, Thanks

 

Check the PCV hose elbows, especially the one that connects to the rear of the intake manifold. They are known to crack and cause a vacuum leak. Might want to run some Techron injector cleaner thru a tank of gas just to be safe.

 

thanks ill give that a shot

 

I got that code on my 97 and it turned out to be the O2 sensor on the passenger side. You can test an O2 sensor with a good multimeter such as a Fluke 87 by checking the voltage output from the sensor.
If the O2 sensors have never been changed on your engine it probably wouldnt hurt to change them. And BTW the sensor on the passenger side is a pain in the a$$.

 

A little update, first thanks for the info everyone, I took my truck in to the local Ford dealer and had them check the codes, while they did some recalls. They found no codes but, the mechanic found a hole rusted thrue the exhaust manifold right next to the 02 sensor. I was told that it is more common on 5.4's than 4.6's, due to the salt the state uses and type of metal. He also said that their is a new updated manifold but it doesnt seem any better. I have purachsed a set of pacesetter ceramic coated headers and new cats, sensors, pipe and muffler. as it was in need of replacement any way .