hey guys i have a 2004 f150 heritage 4.2l v6 stx regular cab with 815xx miles, my service light came on about 3 months ago. scanner showed error codes p0174 and p0171. i almost have to floor it to go up steep hills or to pass people running 75mph. gas mileage is between 12-13 on medium grade. also idles high while cold (no tach so idk how high exactly). what can be causing all this? how do i fix it? how much would it cost?
thanks

 

Welcome!

 

Hi Tx - I moved your thread into the V6 engine forum. You should get more ideas regarding your problems here than in the Introduction forum.

Just a question, have you ever had the plugs changed?

The P0174 code is for a lean condition. I'm not sure about the P0176 code, but it may relate to using fuel with too much ethanol. Your engine should not be burning fuel with more than 10% ethanol.

- Jack

 

Both are lean codes, which means the computer is making it run rich which can kill the cats. Most likely you have a major vac leak. Start with the PCV system and look for soft/rotten hoses. Also check that the tube from the air cleaner is tight and not broken or split. Make sure that the rubber plug in the bottom of the air cleaner box is in place (that is where the MAF plugs in). I'm not sure if your year has the new and improved isolator bolts, if not then it might be time to change them out. An exhaust leak can trip those codes too, but that isn't likely in your case because you have the lean code for both banks. Last but not least would be a cracked plenum (the big black box on top of the motor.)

I don't mean to sound like a butt, just don't know what your abilities are. So I threw a quick list of maybes. Let us know what you find and we can walk you through it.

If you put p0171/174 in the search box for the v-6 forum you will have plenty of reading.

Good luck

 

Plenum gaskets and isolator bolts is a common issue with the 4.2.

 

Ive been using the medium grade gas from Pilot cuz it seems like i get better mileage with that

 

Everything on the air cleaner and tube look good except for the dirt. I havent had much time off of work to look for vacuum leaks or a cracked plenum. Exhaust manifolds and headers and the cats still look fairly good for a 04 that sits outside in the weather. Ill look around more tomorrow on my day off to see if i find anything

 

Thanks! Had no idea where to post this. And i havent changed the plugs and i doubt the old man who bought the pickup new did either.

 

If you need to do the plenum gaskets and isolator bolts, here's how:

https://sites.google.com/site/fordf1...P0171P0174-Fix

 

If you want to check for vacuum leaks, use a propane torch (unlit of course) to test for broken hoses and other areas.

Don't use carb cleaner or the like. They eat the rubbers.