Finally fixed 3 year old rando CEL (vacuum leak) P0171 P0174

[Blk2kXLT]

Jeez finally. So every time the weather gets cold I would get this vacuum leak CEL. I could not figure it out forever. I thought it was the EVAP feed line to the engine (crumbled in my hands if touched), replaced. Nope. Thought it was the EVAP solenoid, replaced. Nope. Paid to get the truck smoke tested, passed fine =( this is like a long time years over years trying to fix with a lot of RTV and parts swapped OMG about to just sell the truck since it would not go away.

Finally I got a "gentle" fail by the CA Star smog guy (technically just told me to go home) since I had left the evap service port disconnected as I cannibalized that hose for something else.

Anyways, I go and rip out my PCV plastic 3/8" F shaped piece in the back since I had plugged the old PCV connection with a bolt way back when. I had re-routed the PCV connection to the MAC intake a long time ago and I guess I must or just barely cracked the plastic or it happened to go bad on its own after 20 years.

Here is my crazy adaption since the rubber piece feeding the vacuum booster and EVAP solenoid was totally shot too. So perhaps it was removing all of that old stuff together that got rid of the combined tiny leaks.

Oh and the star SMOG guy kind of shamed me since he said the vac routing was confusing, I added labels for a re-visit =)

Capped the original 3/8" metal feeder off the back of the engine and then pulled the old hose to the front. Thankfully didn't snap whatever that hose was connected to and then adapted down to the small F connector.

 

[Blk2kXLT]

Anyways, hope this comes up in a google search and helps someone else with the bank1 bank2 lean P0171 P0174 Ford Explorer codes. I know I had clicked on every link trying to fix it.

 

[Blk2kXLT]

Ok spoke too soon. P171 came back but not the P174. Perhaps I need to add a similar F style plastic setup for the EGR and FPR since I think that larger rubber connector to the 3/8" barb (back left of engine) could be worn.

Or it is time to replace the intake manifold gaskets.

 

[410Fortune]

or your fuel pressure is low

 

[Blk2kXLT]

I will check my fuel pressure. I need to wait until Saturday for the schrader valve to 1/4" flare adapter for fuel pressure gauge.

Good news is that on hot days the air density is low and does not trip the CEL. I was able to pass CA smog yesterday fine. My light throttle cruise or coast is right at the limit (LTFT 29-30%) but under acceleration drops to 7% and idle is never high more around 12-14%. It can idle forever and not set any CEL.

Maybe it is a fuel pressure thing or exhaust leak? I did replace the fuel filter and fuel pump fairly recently.

 

[Blk2kXLT]

At idle the fuel pressure is fine. Not sure how to check it during the mid throttle cruise where the A/F thinks lean and needs more fuel.

I am guessing an exhaust leak or intake manifold gasket leak. I do have new injectors that I plan to install when doing the intake manifold gaskets.

2022 Update:
My codes went away when I swapped back to the stock intake. The MAC aftermarket intake adapter has the laminar flow screen of the MAF removed. I am guessing that air is bypassing the sensor. Had that P171 and P174 forever and a day and glad they are gone now.