I'm at 51,000 miles in a 2003 4.2L F150 and my first check engine light came on. Ran by Autozone and got them to scan for codes. I have the P0171 and P0174, lean on both banks. The thing that gets me is the engine runs fine. No rough idle, cranks fine, holds mph and still has plenty of acceleration. I checked the pcv valve hose and elbow for leaks but dont seem to have any. I havent ever changed the pcv but that might be a good idea. If anyone has advice o where to start I'm all ears.

 

You have to check freeze frame data with a more advanced diagnostic tool than what they have at auto zone to see what temperature the code was set at. Most of the time the freeze frame data will have the ect below normal operating temperature below 190 or so. If this is so then you will have to replace intake o rings and isolator bolts on your upper and middle intake manifolds, the plastic manifolds. They are sealed with rubber o rings that get saturated with oil and start to leak when they are cold, when the engine warms up it does not run lean anymore because the heat expands the rubber seals making them seal again, it's something that is hard to catch, but happens very often in the 3.8l and 4.2l engines.I've done so many of them that we call it the "cold weather package " now.If the ect is normal, 190 or above, then suspect a vacuum leak.

 

thanks for the info. you wouldnt happen to know how much that will cost me at the dealership if thats the case?

 

All the parts are around $60 and they should have them instock.

 

I also heard that a dirty MAF sensor could cause the computer to throw these codes. I thought i would check that before pulling off the intake manifold. would i use electrical contact cleaner for that and a small shot of compressed air to dry it? I had a fram air filter that the cap on the end of the filter fell off and i dont know how long i drove it like that. I'll never use fram again.

 

Oh yeah, if your air filter fell apart then clean it first. I've always used carb cleaner, the good kind that has amonia (spell?) in it then clean it off with some brake clean, that stuff dries fast so you won't have to blow it off. Try that first, also do you notice that it runs rough when you crank up cold in the morning, that is usually a sign of the intake manifold o rings.


-ryan

 

It doesnt run rough just idles high for 2 or 3 seconds. I cleaned the MAF and reset the computer and the light hasnt come back on yet. Waitin for it to get cold here and see if it throughs the code again.