P0171, P0174, P0113 on '01 Ranger Edge 4x4 3.0... Stumped!

Long time lurker and I've found advice here that has helped me in the past, but I'm completely out of ideas and need some help. Forewarning, this will be a little long as I want to say exactly what I've done so far and the results. I've posted a few other places but so far I've just been pushed back to re-checking what I've already checked. Please, please help if you can as I need a vehicle running so I can go for job interviews after being laid off due to outsourcing!

OK, I have a 2001 Ford Ranger Edge 4x4 with a 3.0L NA engine that has thrown the infamous P0171 and P0174 combination codes, but also recently showed a confirmed the P0113 code (Intake Air Temperature Circuit High Input).

This all started a few months back when the truck would lurch at highway speeds between gears and I'll also note that I have an exhaust leak in the muffler I think as I've been seeing exhaust come up between the bed and cab since winter (whether this is irrelevant or not, I'm not sure). Eventually the truck started coughing and sputtering when pulling out of idle... this building to a crescendo one evening when the wife was out and it died on her completely when pulling out from a stop light in the middle of town. Then it started happening at highway speeds, actually dying out on me on the interstate. I was able to idle/gently tap the gas with my flashers on until I hit an offramp, coasted to a gas station, and got her towed home.

It idles rough at initial start up from cold, and I can get her a few miles up the road before she sputters and dies out on me again. It seems that once the truck is up to operating temperature and the pedal is pushed down after pulling out (or if trying to go slightly uphill), the truck begins sputtering and coughing with absolutely no power and the RPMs won't go over 1,500 or 2,000-ish most times. If you let off the gas to idle again, the truck will seem to regain consciousness for a moment then once you push at the gas again it does the same thing. It usually does this a few times, RPM max getting less and less, before absolutely dying where she stands.

I've run a diagnostic tool on it and will post the results below. Not sure beyond the trim levels as to what would be considered relevant information, so I'll just put everything I wrote down. I took notes of the finding at both idle and at 2,500 RPMs. I'll post those findings below.

CODES: P0171, P0174, P0113

Short Term Fuel Trim (Bank 1): (Idle) -3.9 to 0.0 ........ (2500 RPM)-9.6 to -2.3
Short Term Fuel Trim (Bank 2): (About Same for Both as Above)
Long Term Fuel Trim (Bank 1): (Idle) 7.8 to 8.6 ........ (2500 RPM)5.5
Long Term Fuel Trim (Bank 2): (Idle) 9.4 .......... (2500 RPM)7.0 to 10.2
Fuel Trim Bank Sensor: (Idle) -2.3 to 0.8 ......... (2500 RPM) -5.5 to -3.1
MAF (LB/M): (Idle) 0.64 .......... (2500 RPM) 1.80
ABSLT (TPS): (Idle) 16.1 .......... (2500 RPM) 21.6
Fuel System 1 Closed Loop Status: Closed
Fuel System 2 Closed Loop Status: N/A
02 Voltage Bank Sensor: 0.200
Fuel Pressure (Key ON): 43
Fuel Pressure (Idle): 67


So far, I have:
* Cleaned the throttle body out
* Cleaned the MAF/IAT combo twice
* Checked for the obvious vacuum leaks (hoses to sensors and main hose from MAF to TB, brake booster hose, PCV hose, etc., all seem good)
* Cleaned Idle Air Control Valve
* New fuel filter
* New fuel filler hose (old one was rusted out bad and leaking)
* New PCV valve and elbow
* New EGR Valve
* New Throttle Position Sensor
* Multimeter check on MAF/IAT combo, all looks smooth and good there
* Fuel Pressure tested on rail

Given the codes and the resulting findings from running the fuel trims, what (in your opinions) are the most likely culprit?

Failing fuel pump? Sticky injectors? A vacuum leak I'm not seeing yet? I'm at a loss, the only garage in range I can get it to without it dying on me again is a joke of pure highway robbery, and I just got laid off after being outsourced. I need to fix my truck to get another reliable job and currently at a loss for funds to just throw parts at it.

What would you all check first and how? Any tips on how to narrow down the culprit so I can get Ol' Red back at it and me working again?

I've completely run out of options to check and just hoping there's something I'm missing. Thanks in advance, y'all. I would greatly appreciate any feedback on what you think the problem is!

Check resistance on all injectors, should be about 16ohms. Run E-85 through it if it's flex fuel, ethanol is a great fuel system cleaner.

Have you checked for a plugged catalytic converter? Take a hand vacuum pump and test the brake booster, I've seen those fail before and cause a massive vacuum leak.

STFT numbers are odd with p171 and 174, I would expect "+" fuel trim numbers

And O2 sensor at .2v as well, .45 volts is where computer likes to keep O2 voltage, it does this by changing the Pulse width on the fuel injectors, shorter pulse width is less open time so less fuel is added, longer pulse width is more fuel added.
And the STFT number is the pulse width, so "-" is less fuel added and "+" is more fuel added.

STFT 0 = MAF sensor data and computer's calculation of the 14:1 air:fuel ratio for gasoline
Once that amount of fuel is added to the air, and it is burned in the cylinders, the computer checks the O2 sensor to see if O2 voltage is at .45v, or lower(rich), or higher(lean)
If voltage was .3v(rich) then computer would set shorter pulse width, so -5 STFT
If voltage was .6v(lean) then computer would set longer pulse width, so +5 STFT

Lean codes p171 and p174 are set when STFT gets up around +15 to +20.

Yours are -9 so Lean codes don't make sense.
They do match, -9 and O2 at .2v, which both show rich operation

At no time should the engine actually be running lean or rich, the codes are a "heads up" from the computer telling you the calculations it is making for the 14:1 ratio is not correct, it is having to correct that calculation by alot to keep O2 sensor at .45v


However a free test for vacuum leak is to warm up the engine to normal temp, then unplug the IAC Valve, it will close and engine idle should drop down to 500rpm or engine may even stall, either is good it means no vacuum leak.
If idle stay above 700 then you have a leak.

Thanks for the advice, guys!

First off, how do I test the catalytic converters? I haven't checked those yet. It's not the flex fuel model, but that's a good bit to know about the ethanol for anybody else out there.

I unplugged the IAC and the idle went way down... didn't stall, but went way down and stayed there until I plugged it back up again.

Does that rule out a vacuum leak for the most part? I didn't find any signs of a leak in the places I could reach/see without taking off the upper intake, so was wondering there.

What's the best way to test the fuel injectors? Don't I have to get the intake plenum off to reach the 3 on the driver's side of the car on the 3.0? If I do have to take off the intake, can I test those fuel injectors with it off (truck not running) or do I need to have the truck on, and if so will that hurt having the intake open and gaping?

Thanks in advance, y'all! I really appreciate this feedback!!!

Correction on the IAC unplugging!

So, I let the truck get warmed up just then. Took readings on the scan tool of the RPMs with IAC plugged up then unplugged at idle.

IAC plugged: 879 - 915 RPM
IAC unplugged: 790 - 818 RPM

Then when I plugged it back up again it surged up to about 1200 RPM for a moment and then went back to the 879-915 RPM again.

Does this seem right after the truck had warmed up or is it a possible vacuum leak after all?

Idle w/ IAC seems high even for what I assume is an automatic trans truck with 3.0l.
Was the A/C off?

To meet emissions standards idle "target" in computer will change year to year, so 900 could be normal for '01 3.0l w/automatic.
And it does read like computer is setting the idle at 900rpms warm, and the fact it drops when IAC is unplugged means there is probably not a vacuum leak, at least not a leak that would cause problems you are having.
Yes, plugging IAC Valve back in will cause a surge in idle when computer retests it, it opens all the way and then closes to set "target" idle.
Same happens on startup, computer opens IAC valve all the way then close it to set "target" idle based on coolant/engine temp.

Yep, A/C was off when running that IAC test.

Just got the upper intake pulled off. Upper gasket looks in pretty good condition; nothing to indicate a vacuum leak there.

And tested the fuel injectors with multimeter while down there.

All showing 12.0 Ohms resistence (give or take about .2 to the good or bad between the 6 of them).

Anything else y'all can think of to check while I'm in the middle of it all down there?

Are you getting your Fts freeze frame or live data?

The LTFT indicates possible vac leak but bank2 should get you a lower number at 2500 RPM as intake vac leaks are not as drastic at higher loads.

To me the LTFTs don't point to the reason the truck is stalling out.

A smoke test would have saved you removing the intake and guessing as to what looks like a leak and what does not. Did you try the propane method first?

Tried just a generic smoke test with a cigar through the main intake hose, but saw nothing. Not sure if the cigar was enough smoke to generate anything to see or not, but still. I blew it into the little hose that connects between the main intake air pipe and passenger-side valve cover.

Wanted to get the upper intake off so I could check resistance on the 3 fuel injectors hidden below it.

Could the injectors be leaking or "bad" still even though the ohms all look stable across the board for their resistance?

And it's the Live Data after it load up the PID numbers.

Keene1981 said:

Could the injectors be leaking or "bad" still even though the ohms all look stable across the board for their resistance?

Click to expand...

The injectors are normally closed. The "leaking" would be crud on the injector tips that prevent fully closing, or maybe a sticking injector. Bad resistance would probably mean not opening or not staying open.

Since your got the intake off you can send the injectors to witchhunter.com and they'll test, clean and re-test with a before and after report. About $22 per plus 15 shipping total.