My very own lean condition

I've read around the site for the past couple of years, but this is my first post. Thanks to those of you who contribute. I have considered your advice when maintaining and repairing my truck! I've read around the forums to get leads on (the MANY) possible causes of a lean engine condition, and I'm not managing to solve it, so I thought I'd post this.

I have a CEL P0171, lean engine condition in a 2000 Ranger, 2WD, 2.5L, manual, with 80K miles. The check engine light corresponds with the following freeze frame data:

Topic First CEL
Fuel system 1 Closed loop
Fuel system 2 Not supported
Throttle position (didn't note)
Load value 54.9%
Coolant temperature 177F
Short term fuel trim 0%
Long term fuel trim 0.7%
Engine RPM 1007
Vehicle speed 4 mph
Intake air flow rate (didn't note)

Topic Second CEL
Throttle position 16%
Load value 48.2%
Coolant temperature 185F
Short term fuel trim 0.7%
Long term fuel trim 5.4%
Engine RPM 1050 rpm
Vehicle speed 2 mph
Intake air flow rate 0.06 lb/min

I've noticed a low rough idle, especially just after I take it out of gear into neutral (as I come to stop, for example). Doesn't stall, and the idle recovers pretty quickly.

Here's what I've done since seeing the CEL.

REPLACED: spark plugs and wires, PCV valve, upstream O2 sensor, MAF sensor ($$dealer$$), fuel filter, air filter, and gas cap. I ran several Techron bottles through the engine, SeaFoam'd it (top end, intake clean), and have been running 87 octane (which is "Plus" in the Rockies) through the engine for awhile. I was running 85 through the engine for awhile (which is "regular" in the Rockies). I tried to test the EGR by covering the EVR solenoid hole during idle (to establish vacuum). The engine nearly stalled, which suggests a functioning EGR, according to YouTube. I'm ScannerDanner videos on YT, by the way. Pretty cool dude.

SPEAKING TO VACUUM LEAKS: I ran some propane along the vacuum lines during idle and didn't hear any change in idle. A homemade smoke machine produced a little bit of smoke from the IAC valve, but that may be normal (don't know yet).

SPEAKING TO FUEL PRESSURE: I measured fuel pressure on the rail. Key on, engine off pressure measured within spec. Interestingly, fuel pressure increased ~5 psi (to 68 psi) when I turned on the engine. I say interestingly because Chilton predicted a drop in pressure when starting the engine. I don't know the significance of that yet. Chilton suggests using a handheld vacuum pump to further investigate, but I haven't reached that yet. I would be interested to hear if someone thought the above suggests that I might have a fuel pressure problem that could be causing my CEL.

SPEAKING TO READINESS TESTING: I used a scanner to run readiness tests, and I saw a failure, namely: "delta pressure for downstream DPFE hose test." This might be causing my CEL, but I'd like some advice on how to go about identifying the specific problem. I'll probably pull the hoses and look for obstructions, and I could test voltage to the DPFE (?). Is there a quick test I can use to test the function of the DPFE itself?

SPEAKING TO REAL TIME MONITORING: I could post this if some thought that it would be useful. I'm having a hard time interpreting the data. ScannerDanner (YT) says that relatively high short term fuel trim (I'm seeing 25-30% at idle, warm engine) that decreases with increased RPM (which is what I see, 0% at 3000 RPM) points to a vacuum leak. The smoke test only produced a bit coming from the IAC valve (but that might be normal). I could have a different internal (i.e. non-visible) leak . . . hoping that's not the case.

There's one other concern. I had the dealer do some suspension work on the truck shortly before the CEL came on. The suspension repairs worked out pretty well, but my truck had engine trouble on the drive home. Grinding noise when I gave it gas, and big drop power. It went right back in, and they replaced the MAF sensor. A short time after that, I saw my CEL. I didn't go back to them. If any of you more experienced members have an idea about what sort of "mistake" they could have made that would lead to this CEL, I'm all ears. I don't know that it's the case. I'm just putting that out there in case it drives one of you to a bingo moment.

Taking the above into account (it's a long post, but I'm trying to give you as much info as I can), I'd like to hear any ideas you all might have about this CEL.

Thanks!

Check the part number on the MAF....make sure it is correct...

Short of that...

Get fuel trims at idle and at 20000 RPM.

20000 rpms? It's a Ford, captain, it canna give anymore rpms ore she'll blow (in Scotty voice)

Sent from my Samsung Galaxy Note 4 while sitting in my underwear

I figure if he blows it up he can get a real engine.

That's supposed to be 2000, or where ever the rev limiter kicks in, which ever happens first.

On your scanner switch MAF to grams per second, gr/s, at warm idle that should be about the same as displacement, i.e. 3.0l would be 3gr/s, 5.0l 5gr/s, 2.5l 2.5gr/s
That should tell you if MAF is under reporting air flow at idle but working OK at higher RPM

Lean or Rich codes come from STFT, Short Term Fuel Trim.
You can see your LTFT creeped up in the second list, + number means computer is adding more fuel.

So you need to watch those while driving if possible.

Fuel trims are done like this:
Computer gets MAF air flow data, it calculates 14.7:1 air:fuel ratio for gasoline engine
That calculation is 0 STFT
Computer adds that calculated amount of fuel

After fuel is burned O2 sensor will show if there is too much oxygen(lean) or too little oxygen(Rich), in the exhaust gases
Computer adjusts fuel injector "open time" if oxygen level is high or low
+1 fuel trim means computer is adding more fuel than calculated so injector is opening longer because O2 showed too much oxygen.
-1 fuel trim would mean computer is adding less fuel than calculated.
(Forget the % on fuel trim, it isn't a percentage of anything, lol)

Computer will have a range for fuel trim that will cause it to set a code, at no time is the engine running lean or rich, computer is adjusting the fuel.
On some if fuel trim gets up to +15 for any length of time, computer will set Lean code, -15 Rich code, on some it needs to be +20 or +25

So the lean code is because computers calculation is off and it is letting the driver know.

Why is computers calculation off?
MAF sensor could be under reporting air coming in
Could be an air leak, between MAF and intake/throttle, or Vacuum leak, so all the air is not going thru the MAF sensor.
Could be low fuel pressure, computer expects a certain fuel pressure, if it is low then "open time" for each injector lets in less fuel, computer calculation would then be off. Above 60psi is fine on yours

O2 sensor could be failing, but look at the spark plugs, if they are dark brown or blackish then may be bad O2, if they look good, light brown, then O2 is good.
If O2 is bad it gives a False Lean or a False Rich, so spark plug would show that engine is running rich(false lean), or if lean then you would get pinging/knocking when accelerating(false rich)


And no, there should have been no smoke coming out of the IAC valve, it is closed when power is off.

Thanks for your replies. I'll spend a few minutes thinking about RonD's comments, but here is a quick run down of fuel trims as I measured them using scanner and real time monitoring:

Cold engine idling: 8-22 (oscillating) STFT and 2-12 (oscillating) LTFT
Warm engine idling: 25-30 (oscillating) STFT and 9-10 (oscillating) LTFT
Warm engine (3000 RPM): 0 STFT and 25 LTFT

I measured these a while ago, so I didn't know to target 2000 RPM. I just wanted to take the engine up in RPM at the time, so I hope these figures are helpful. I don't have a tach (stripper truck), so I was relying on the scanner, which reported 3000 RPM while monitoring.

Thanks again!

I just converted Intake Air Flow Rate data from lb/min to gr/s for the same conditions that I reported STFT and LTFT (above):

Cold idling engine: 2.66-2.95
Warm idling engine: 2.27-2.34
Warm engine at 3000 RPM: 6.80

It would appear that the MAF is underreporting at warm idle, which suggests that there is a an air leak. I didn't see any smoke emitted when I pumped smoke into the brake booster hose, except for a little coming out of the IAC valve. The smoke was leaking out (just a little) from the black round cap that faces the rear of the engine compartment. Could this be pointing to a leak, and the cause of the lean condition? If no, perhaps there's a leak somewhere that I can't see (internal?).

I previously replaced my spark plugs and O2 sensor. The plugs were a light brown, so that looked okay.

Here's a picture of that IAC. You might not be able to see the smoke, but it was coming out of the black round cap that faces the rear of the engine compartment.

The black cap snaps off.
It is the vent for the valve so it can open and close, it equalizes pressure on the back side of the IAC Valve.

With IAC valve closed you might get smoke from there, would depend on the design.
It looks like this one: http://www.explorerforum.com/forums/showthread.php?t=84220

When unpowered/unplugged the valve is closed, in the pictures you can see the back side looks to be open all the way to that vent area, so would be a "planned" vacuum leak.
I would pop off the cap and see if filter is in place.

MAF sensor numbers are based on RPM and engine displacement, cold idle is usually 1,200rpm or higher, warm idle 600-750rpm, so gr/s looks about right, but may be a bit low, never tested a 2.3l or 2.5l

Idle will always be richer STFT than driving, this prevents cylinders from overheating with too lean a mix, +5 to +10 would be expected, yours is way to high.
Then drop to -5 to +5 when throttle is open.
Yes the STFT(and O2 sensor) numbers jump around very fast, it is "on the fly" tuning, this is what give the better MPG fuel injection provides................when everything is working right, lol.

Vacuum is highest at idle so any vacuum leak will pull in a higher percentage of extra air at idle, so would make for higher STFT at lower RPMs, when RPMs are higher vacuum is lower and percentage is lower because of the volume of air coming in thru MAF.

One trick I try is to warm up the engine then unplug the IAC Valve, it will close and idle should drop down to 500rpm, or engine may even stall, either is OK it usually means no vacuum leak.
If idle stays up above 650rpm then there is a leak, and it seems to be easier to find with IAC unplugged, pop off one hose at a time and plug port with finger, if no change move on.
Don't forget power brake booster, that should be a sealed unit.
And on some models there are "ported" vacuum ports on the throttle body, these can be leaks as well, so check under side of throttle body.
If all ports check out with no leaks then you can start on gaskets, throttle body especially.