I had P0172 and P0175 for awhile among a few other codes.. Here is what I've done so far.. New plugs, new coils, new egr, new pcv and vacuum that goes to it. Fixed a few vacuum leaks that I can find. And just replaced MAF on after market intake . Codes went away for 50 miles ,then the P0175 kicked on.. What do I do next ??
This is on a 2003 F150 4x4 5.4
thnx

 

It is important to complete the entire diagnostic process when diagnosing P0175. Many people will replace the air-fuel sensor or O2 sensor as soon as they get a bad reading, but the root cause is often a dirty or faulty Mass Air Flow (MAF) Sensor or vacuum leak, thus causing the O2 or A/F sensor to read differently to compensate. Reading and analyzing fuel trims and the freeze frame data is the key to properly diagnosing P0175.

That is Bank2 if you don't know. (Drivers side of engine)
Check the boot on the valve cover and that tube out of it to the intake and see if either of them are bad.
Check and make sure that the MAF sensor is plugged all the way in at both connections.
You need to see what your fuel trims are as a leaking injector can give you a P0175 as the O2 thinks something is wrong.
Other things are fuel sensor regulator vac line to it maybe off and leaking. (Since you were working all over that little red vac line.)

 

it has been several years, but when i had that code on my 2001 5.4 ......... it was the two 1/4 inch vacuum hoses about 8 inches long , on top of the drivers valve cover, that go to the EGR ( if i remember right)... hard / brittle / small cracks from heat.

 

I have seen that code(burned into my retinas) on older trucks on several occasions and my first thought was vacuum leak. Like the other posts suggest, carefully inspect hoses and connections.
Disconnect the negative battery cable while working on the truck too.

 

Back than I had rust at bottoms of coil packs. It did throw code and I did make tread about it but can not find it. Brushed and silicon greased bottom of both coil packs and never problem with that after. Was 8 years go or so.

 

I did a vacuum leak test with the propane method.. I hit every vacuum line and connection I could find. Idle never fluctuated.

 

CODES 172/175 is excessive fuel.
Has very little to do with a vacuum leak.
Excessive fuel can only come from leaking fuel injectors or a leaking fuel regulator through its vacuum control diaphragm into the intake or excessive fuel pressure.
Excessive fuel pressure can be from a restricted return line or a faulty regulator.
.
The code/s are set when the Long Term Fuel table/s are shifted Lean at about 25%. This come about because the computer ids trying tp 'counter' the excess fuel so it leans out the fuel tables. This sets the codes, otherwise you would have even less of a clue to your trouble..
The code tells you what is going on but not why.
Let other things alone.
Good luck.

 

I pulled the vacuum line from the fuel regulator and shook it and there was no gas in the vacuum line.
How do you check for leaky injector ?
Thnx

 

Measure fuel pressure at the test port with a gauge.
If the pressure does not stay over a 5 + minute period, injector leakage may be the issue or even the fuel pump check valve may not hold.
Note: if the pump check valve is not holding, this won't cause excess fuel but possibly affect crank time to starting from delayed fuel pressure.
.
Another possibility could be a faulty thermostat stuck open cooling the engine to low in temperature. The cylinder head temperature sensor will detect this and richen up the fuel.
All these except the pump check valve not holding point to excess fuel causes in different ways.
A way to get more of a feel to the cause is to clear the code, then watch how long it takes for the long term fuel table to shift causing a code to set.
For this you need to use a Scanner to observe the rate of change over time and number of driving cycles.
Sometimes one needs to get in deeper diagnostic and thinking to clear some problems.
You own a complex relationship of computer controlled functions that need to be understood.
Good luck.

 

I don't have all the testing equipment needed . Instead of throwing money at it, probably best to take it somewhere and get it tested right..
Thnx

 

To your question yes. Take it to see what is wrong.