Just got a po 174 code while out of town. Any idea where to start looking? I heard it was fuel injector or O2 sensor related.

 

PO 174 is your front left bank (driver side) O2 sensor. Its the easy one to replace.
PO 171 is the front right bank (passenger) and is a bitch, so if you ever do this one, do it cold.
Don't be surprised if any of the others throw a code after replacing this one...tempermental *******s they can be.

You may want to check your IAC valve and make sure the plastic elbow going to it isn't cracked or worn through. Just follow your PCV valve line to it.

 

Yeah, the Autozone guy printed me off the code "diagnosis" and it mentioned O2 sensor but he also told me to run injector cleaner so I wasn't sure if he knew what he was talking about.
So, I'm a complete newbie to the Ford gas engines. How many O2 sensor are there on this engine? Are they all the same sensor part number (left bank/right bank)? I'm going to check everything out in the morning when I have some light. My mileage has been low, although I've never run a 5.4. Getting about 14.5-15 on the freeway at 75-80 with a few hills here and there. Is that low and could the sensors be the (possible) culprit?

Thanks

Sorry just realized I gave no truck info.
2003 EB 5.4 78,000 miles. Bought it about 2 months ago, don't know the service history at all.

 

I get 17-19 hwy, so the O2 may be that issue. There are 4 O2's, 2before the cats just below the manifolds and 2 post cats (these I have only done once when I replaced my exhaust). The Autozone Dude will get you the proper sensor because they are specific. You may as well grab a Haynes manual ($15) and keep it in the vehicle along with an ODB II scanner ($50-80) in case you run into trouble away from Autozone.

 

The P0174 indicates that the PCM's adaptive fuel control has exceeded ~30% on the DS bank, trying to adjust full rich to compensate for a lean condiction.

If you have both the P0174 AND P0171, then you are looking for something that affects both banks, like the problematic PCV vacuum leak, dirty MAF, or fuel delivery problems..

Since you only have the P0174 your looking for something that only affects the left (DS) bank.

My guess is that its probably not the O2 sensor as the PCM runs tests on the upstream O2 senors to check for their ability to switch in under 100msec and to see that they can put out the min and max voltage. If the O2 sesnor fails that O2 monitor the PCM should set a code for a failed O2 sensor.

Do you have any exhaust leaks ahead of the upstream DS O2 sensor? (That can make the O2 sensor read a lean condiction and the PCM would drive the DS bank injectors rich to cover up for it.)

Unmetered air getting past an injector o-ring could also cause a lean condiction. Also a leaking intake manifold gasket.

If you can read the freeze frame data and the code is set at idle/light load, your probably looking for a vacuum leak that effects the DS - if the code set under load, your probably looking at fuel delivery issues on the DS bank.

Also, look at the LTFT (Long Term Fuel Trim) on bank one - it may be a wisker away from setting the P0171 code so you could be looking at something effecting both banks.

Good luck - and keep us posted on your progress..........

 

Ok. Checked codes again and actually have both 171 and 174. Excuse my ignorance but could you guys explain what the pcv valve looks like. I'm looking at a hose that goes from the top of the intake area and loops around the back of the engine, has a plastic cylinder, then goes into what I believe is the IAC. Can't tell if I hear a hiss of leaking air or not. Am I looking in the right area for the pcv "elbow"?

 

The PCV is located on the passenger side valve cover in the center. It has a silver aluminum base with a black plastic 90 degree fitting pointing toward the back of the manifold with a semi-rigid plastic pipe going behind the throttle body to the IAC valve. Barring it had not been replaced. I used fuel line to replace mine. It beat the heck outta paying $115 for the OEM piece.
To check the PCV for function, simply shake it when you pull it and it should rattle. If it doesn't or sounds more like a thud than a tinny noise, replace it.

Along with what PDQ said, you may want to clean your throttle body inlets.

 

OK. I checked all the fittings from the PCV back to the IAC, PCV to the side of the throttle body, etc. Pulled each 90 degree fitting and looked them over really well. Couldn't see anything that looked abnormal. Pulled the PCV, rattled like it should. Cleaned throttle body inlet. Didn't know how to check or clean the MAF, but I peered through the air intake tube and inspected it and it looked brand new.(Don't know how scientific that test was). Air filter looks good.

I don't know if I'm just trying to hear an air leak or what, but it seems like there is a slight "static" hiss below the clicky sound of the injectors and the roar of the fan.

Is there any way for me to test the IAC? Are o2 sensors my next step? I really don't want to take it to a mechanic to figure this out.

 

I'd say that's your call, but I wouldn't expect BOTH sensors to go bad at nealy the same time.

You could probably take the belt off and let it idle a minute or two so you could hear better. If you suspect a vacuum leak in some specific area, you could spray the area with carb cleaner. If the idle abruptly changes your "diggin near the 'taters".