Hi, im having an issue with my truck throwing the headache 171/174. Ive taken it to one place, they told me i needed intake gaskets, so i changed the uppers and the fuel manifold gasket. codes came back. next i took it to a ford dealership. the only thing they found was a disintegrating vacuum line coming off the bottom of the throttle body connecting to a tee, which im assuming goes to the evap canister. now i replaced this hose, and the truck runs better, but im still getting the same codes. Now ive read in these forums that the code is for a perceived vacuum leak and has nothing to do with the o2 sensors, is that they are not the cause, but my question is whether or not its possible. using a scan tool ive checked the fuel trims and o2 sensor readings. bank 1 sensor 2 fluctuates very little, but for the most part is stuck at 0 volts. thats not normal, and ive also noticed that when the sensor is stuck at 0 volts, the fuel trims stay at around +25. so is it the o2 sensor thats causing this? i dont have any codes for an o2 sensor because although the sensor may stay at 0 volts for sometimes up to 5 minutes, i do think it works just enough to not throw a code. please help point me in the right direction with this.

 

as i suspected the 02 sensor has thrown a p0136. hopefully im one step closer to figuring this out

 

The O2 sensor is cheap and easy to replace. If the current one has more than 50,000 miles on it, you might just do so. It is used by a lot of the engine tests, so you need one that's functioning properly.

 

in case anyone wants to know whats going on...I replaced the o2 sensor, and the iac. the reasoning behind replacing the iac was because A: it was starting to howl more frequently. B: i had read that it could have been a possible cause for the high fuel trims. (admittedly grasping for straws, but at least i had another reason to replace it)C: at the same time i got the codes for the vacuum leak my truck would try to stall during sudden stops, and i put 2+2 together.

Long story short, my LTfuel trims are right where theyre supposed to be, and so is that 02 voltage signal.

i guess well see what happens once i drive it.

 

alright. new update. I drove the truck today, and LT fuel trims are still too high. so far hasnt triggered the CEL but im sure it will soon. i didnt take into account my LT fuel trims would be reset to 0 by disconnecting the battery and resetting the kam. it does seem like the fuel trims are lower now though, as in the havent really went over 20, and at idle they hover around 14-15+. im working on getting access to a smoke machine...

 

ok so new update for anyone following. I have NO clue as to whats wrong with this truck.

i smoke tested the truck and found no leaks. same with propane and carb cleaner.

fuel pressure is at 60psi running. no dropouts. maf sensor tests good.

short term fuel trims are high negatives compensating the long terms bringing the total between the 2 close to 0. ex: -18 short term and 20 long term= 2 total, but that spread is huge. and for whatever reason while i was testing it, the truck started running alittle rough and i saw bank 2 short term fuel trim shoot up to -23.4 and stay stuck there until i shut the truck off. Someone PLEASE help me figure this out.