HELP! I've been chasing the dreaded P1071 - P1074 lean conditions for months on my '04 Expedition 5.4. I've replaced the entire PCV tubing + Valve system with the factory replacement, used a smoke test, replaced purge lines, and pulled out a lot of my hair. The only thing that I think I haven't replaced is the Intake gaskets. I can't see any smoke coming from them, but that's about the only thing left that I can think of. Could I please ask a BIG favor? Could someone use their crystal ball and interpret the freeze frame data I recorded the last time the p0171 code threw and let me know what they think? Is it possible there's a bad O2 or MAF sensor? Replacing the intake gaskets looks like a long job in 17 degree weather and I really don't want to do it if the code is just going to come right back. Here's what I've got:

Fuel System - Closed
Calc Load - 20%
ECT - 176°
STFT B1 - 11.7%
LTFT B1 - 25.8%
STFT B2 - 10.9%
LTFT B2 - 18.8%
Engine RPM - 614
Speed - 0
Spark Adv - 12°
IAT - 39.2°F
MAF - 0.7 lb/min
TPS - 18.8%
O2S B1 S1 - 0.310v
STF1 S1 - 11.7%
O2S B1 S2 - 0.195v
STFT B1 S2 - 99.2%
O2S B2 S1 - 0.070v
STFT B2 S1 - 10.9%
O2S B2 S2 - 0.320v
STFT B2 S2 - 99.2%

Does this all still scream "vacuum leak"?

 

Have you verified adequate fuel pressure? "Lean" codes, although most frequently caused by un-metered air in the intake that hasn't been measured by the MAF, can also be caused by a weak fuel supply.

The only thing that looks out of the ordinary (beside the trims) is the ECT at 176°. Does it get fully up to temperature of 190-210° during normal operation?

 

I’m gonna guess that you really mean P0171 - P0174.

I agree that unmetered air is typically the cause of these lean codes, and the fact that the freeze frame data snapped when the code last tripped shows that the engine was at 614 RPM, and the calculated load on the engine was 20%. This indicates that the engine was more than likely at high vacuum when a vacuum leak would have a significant effect, and the engine was under very light load which would require minimal fuel flow. So I still think unmetered air is the bigger possibility.

When you smoked it did you use a high intensity light to look for the smoke? And did you look very closely at the point where the oil dipstick tube enters the engine block?

And did you carefully check the PCV fresh air side for leaks?

Since you are getting codes for both banks, probably both head gaskets didn’t let go at once so I would put them down lower on the list of possibilities. You could disconnect and cap the EVAP purge line and see if it still throws the lean code. If it does, the EVAP system is not the cause. Has the MAF ever been cleaned?

 

Thank you for the quick replies. Here are some answers:
1. Yes, I meant P0171-P0174. Sorry.

2. No, I haven't checked fuel pressure. I think I could with a loaner tool from an auto parts store right? What's the correct pressure range?

3. I have a home-made smoker that uses low PSI. When I did smoke it, it was at night, I used a super bright flashlight. I connected the smoker to the brake boost line. Most of the smoke was coming out through the air filter joint where the two halves of the Filter housing separate. I could not see any smoke coming from anywhere else. I did not check the oil dipstick entry point.

4. I will try capping the evap purge line. Last night I took it off, and put my finger in one end while blowing through the other, couldn't feel any leak.

5. I'm not really sure what you mean by the fresh air side of the PCV. The whole line from the PCV, to the back of the throttle body adapter was replaced with a new part from Ford this past week. ($85! Ouch!)

6. Is there any possibility of the EGR valve playing into this? Probably not right, it would throw a code if it weren't working right, or the DPF sensor? I did just replace one of the two rubber lines going from the EGR tube to the DPF sensor because it was starting to crack.

Has anyone tried the trick of testing Intake Gaskets where spray around the intake base with a bottle of water with the engine running to see if it stumbles? Any harm in trying this?

 

Usually doesn't work, the computer is way too fast. What you can do is set up your scan tool to monitor the STFTs in real time and watch those while spraying with a combustible (I use brake cleaner). When it gets sucked in, the trim(s) will spike.

 

That hose carries crankcase fumes from the PCV valve back to the intake manifold to be burned.

Typically there will be another hose that brings fresh FILTERED air (downstream from the air filter and the MAF) and directs it to the valve cover opposite of the side where the PCV valve lives. This is what I call the fresh air side of the PCV system. It supplies fresh filtered air (metered by the MAF) to replace the crankcase air pulled out via the PCV valve.

If this fresh air hose has a leak (or is missing), unmetered air will get sucked in this hose, go through the crankcase, through the PCV valve and into the intake manifold and cause lean codes. (Ditto if your dipstick tube has a rusted out hole in it or a poor fitting dip stick seal.

When you do your smoke test, pull the air filter off, or disconnect the inlet tube from the air box and fit a plastic clove over the end to seal it so smoke doesn’t spill out of it. That will allow a couple of pounds of smoke pressure to make leaks more evident.

 

Cool, thanks Jim. I'll try the glove trick. I was getting a lot of smoke coming out of the air box, and maybe that "clouded' (hahaha) my sight line of other smoke escaping.

 

It snowed here overnight, so I wasn't able to get down to the parts store to get a pressure gauge for the fuel rail. But I did make progress. I tried spraying all the usual vacuum lines with carb and brake cleaner, with no change to engine RPM. Then gave the water bottle a try and hosed down all the connections. Still fine. Moved on to intake manifold gasket, and bam! The front driver's side started sucking in the water with a distinct hiss and ran rough. When I moved to the back I didn't hear a hiss, but it also ran rough. I did try torquing the intake bolt just a tiny smidge, and re-sprayed. Now it doesn't seem to hiss, but I am still going to replace the intake gaskets. I'll still check the fuel pressure when I get a chance, but since the code only seems to throw at idle, not higher RPM, I'm thinking I'm on the right track with the intake gasket. If this doesn't fix it, I'll check be in in case anyone finds this thread in the future.

 

Just wanted to follow up on this thread in case anyone in the future stumbles accross it. (I hate when I find an old thread that just dried up with no resolution.)

So my quick-fix of tightening the intake some more did not work. I ended up replacing the Intake Gaskets. When I ordered the parts I got the upper Intake seal, lower gaskets, crossover pipe gaskets, thermostat and thermostat O-Ring. I certainly could have done the job without taking the coolant crossover pipe off, but I figured, since I'm there...

The job took a long time, and I ran into three problems:
1. This engine has 249,xxx miles on it, so all the plastic is old and brittle. One of the retaining clips on the rear coil on the passenger side broke. I had to do a hack job with some zip-ties to fix it. I will likely have to find a replacement harness at some point to fix that for real.
2. The coolant crossover pipe is held on with six or so bolts. One of them was stuck, and snapped off. Luckily it snapped off above the threading, so I could get some vise-grips on it and turn it off with some lubricant. And Luckily I had a metric bolt on hand to use in its place.
3. While taking off the vacuum line "tree" or harness that goes from the vacuum reservoir around the top of the engine to the fuel regulator, purge valve, EGR valve, ect... The manual says to disconnect the line at a coupler located right in front of the PCM on the passenger firewall. This coupler was buried under enough cables and lines that it took me several attempts to locate it and isolate the correct line by tracing back from the engine. When I did my guts sank because the stupid coupler was rotted and had a huge crack in it. I replaced it with some new hose I had on hand.

In retrospect I'm thinking this is likely what was causing my codes. But the intake was sucking in air as well, I had the parts, so I went ahead and replace the intake gaskets anyway for peace of mind.

I got a new OBDII bluetooth interface today, hooked it up, and my fuel trims are back to normal at idle now. So that fixed that problem. Now I just need to pretend I don't hear that clicking coming from the engine....