Project Ragnar/Lean Codes

[Ragnar]

My 98 Ranger XLT 3.0 4X4 automatic was purchased used a few months ago with existing P0171 and P0174 codes. It has 188000 kms on it. I thought this shouldn't be too hard a repair, so I bought it. So far I've replaced the MAF sensor, Differential pressure sensor,,TPS, PCV, Idle Air Control Valve, EGR valve and all 3 o2 sensors. I've pressure checked the fuel system (58psi), and run a torch all around the intake manifold and throttle body looking for vacuum leaks. At cold start up, the engine sometimes will start and idle up and down over and over until I shut it off and recycle the ignition and start it again. I recently discovered that after market IAC valves don't always work well, causing high or inconsistent idle, so I replaced it again with the old Motorcraft part and it seemed to help. It will idle normally around 850/900 rpm when warm. About 1000RPM until warm. No pinging or knocking! At that point you try and accelerate, it will bog out like it's getting too much/not enough fuel. Once it warms up I can drive it normally for awhile and then it may stall when you decelerate coming to a stop or turn. I have to pull over, recycle the ignition and I can go again for awhile. It doesn't do this all the time, but usually when you least expect it. I can't make it happen! At this point I've put spent a bundle on parts and labor and I'm running out of ideas and cash.

 

[Dirtman]

Did you put a new fuel filter on it...

 

[Ragnar]

Yes. I have replaced it. Forgot to mention it.

 

[RonD]

Welcome to TRS

Yes, many have found 3rd party IAC Valves do not work well on their Rangers

Simple test for a vacuum leak is to warm up engine fully, and let it idle
Unplug the 2 wire connector on IAC Valve
It will close and RPMs should drop to 500 or so, engine may even stall either is GOOD, it means no vacuum leaks
If RPMs do not drop then there is a leak

(there is an anti-diesel screw on the throttle linkage, often confused with an idle screw, because it does control throttle plate's closed position, this should not be adjusted unless engine is fully warmed up and IAC Valve unplugged.
At that time you can adjust it to set minimum voltage for TPS, under 1 volt, then you would start the warm engine and let it idle, if idle is below 600 then all is well, if higher then unscrew it until engine is barely running, its set)

Codes P0171 and P0174 means the computer's on the fly calculations are off by more than 20%, the computer is having to opening the fuel injectors more than 20% longer than it calculated according to O2 sensor feedback
And on both banks of a V engine, so not a lower intake leak or exhaust manifold leak, or an upstream O2 sensor issue
It needs to be something common to both banks of the engine

The Computer "knows", in this case, its running a 3 LITER engine, so it "knows" exactly how much air will be pulled in at any RPM, its just math and that's what these computer are made to do, fast math for on the fly air/fuel mix calculations
It also knows the size of the fuel injectors, and the fuel pressure specified, but has no way to confirm pressure.
What the computer doesn't know are the variables in all vehicle engines
Engine temp, ECT sensor
Air Temp, IAT sensor
Air weight, MAF sensor
Throttle position, engine load, TPS sensor
Actual Fuel pressure, NO sensor

O2 sensors see Air/oxygen in the exhaust, too much is Lean too little Rich, this is feedback
And the computer itself, while uncommon these do fail

Since you have already replaced alot of parts, I would spend another $25 on a Bluetooth OBD2 reader so you can watch Live Data and see what all the sensor are reporting to the computer, this is what the fuel mix is based on after warm up
The computer calculates Short Term fuel trims(STFT) on the fly, based on RPMs and above sensors
STFT 0 is computer's calculation
After it is burned O2 sensor gives computer lean/rich voltage
If lean computer opens injectors on that bank 2% longer, STFT 2, then STFT 4, and STFT 6, ect..... until O2 sensor shows good voltage
If rich then STFT -2, then -4, ect......less open time for injectors
These are percentages of calculated open time

The computer has a Long term fuel trim(LTFT) for each bank, this allows the system to "age gracefully", smaller air leaks, changes in compression, valve guide seal leaks(burning oil) and fuel pressure changes, will cause LTFT to change over time
LTFT is the average of STFT over time, so if engine was running best at STFT 5 then LTFT would be set as +5
LTFT is saved each time computer is shut off and then reload on restart, it can't be cleared with a reader or by unhooking battery, wouldn't be much good if it could be, I think a Ford Reader can clear it but not sure
LTFT is used on cold start when sensors are not warned up, computer has preset air/fuel mix tables it used and offsets those with LTFT
After warm up computer calculates STFT the adds/subtracts LTFT to that for STFT 0
So if LTFT was 5 then STFT 0 is actually +5
If average STFT during this drive time was -1 then LTFT would change to +4, if average was +1 then LTFT changes to +6

LTFT is so Computer doesn't have to start from scratch every time you drive the vehicle
There is more to LTFT, rear O2 is also used for this

But if LTFT gets to +20 because of long term air leak or ??? then you will get Lean codes
And even after you fix the problem, fix the leak, it will take awhile for LTFT to start getting lower, weeks driving every day

The Live data would show you STFT and LTFT, +15 to +20 is when Lean codes start showing up
If you fix a "lean" problem then STFT will go -2, -4, ect.......which, over time, will bring down the +20 LTFT


A partially block exhaust system can also set lean codes, but run vehicle at highway speeds, you will notice a lack of power as exhaust back pressure builds up
You can also use a vacuum gauge to detect this and many engine running issues, still a great tool to use/have

 

[RonD]

Since this is a new to you vehicle, could a previous owner have changed the injectors or computer?

The 3.0l Ranger came in Gas Only and Flex Fuel models
Main difference is the computer and fuel injector sizes
Larger injectors are needed for Ethanol so Flex computer "knows that"

If gas only injectors were used with Flex computer, computer's on the fly calculations would be off, because less fuel is flowing thru the smaller injectors
So similar outcome if fuel pressure is lower than expected by computer, lean codes on both banks

 

[Ragnar]

Since this is a new to you vehicle, could a previous owner have changed the injectors or computer?

The 3.0l Ranger came in Gas Only and Flex Fuel models
Main difference is the computer and fuel injector sizes
Larger injectors are needed for Ethanol so Flex computer "knows that"

If gas only injectors were used with Flex computer, computer's on the fly calculations would be off, because less fuel is flowing thru the smaller injectors
So similar outcome if fuel pressure is lower than expected by computer, lean codes on both banks

I bought this truck with all repair receipts he had from 2007 till 2019. He was the second owner. However that doesn't mean he gave me everything.They are mostly regular service records. The receipts I do have don't show any work done with the injectors or computer. The interesting part is they do show he had concerns with lack of power going uphill and passing and had asked to check if converter was plugged (2016). They replied they could not duplicate the problem. No service was done. That being said it does sound possible that a partially plugged converter may be causing the stalling and lean code issues. It doesn't usually stall until I have been driving it for awhile after warm up, and when it does stall, after restarting I often get a strong converter smell.

 

[RonD]

Well break out the vacuum gauge, best way to tell running engine condition

 

[Bgunner]

I read that you checked for air leaks at the throttle body and engine manifolds. If your 3.0 has the air meter at the air cleaner box you will also need to check for leaks from the meter to the intake. My intake hose had large cracks when purchased causing a major unmetered air leak and a running issues. RonD has give you plenty of info to help track this bugger down but I wanted to add that this part was not listed in the you have already checked section and if not checked it is an important spot to go over.

 

[RonD]

+1 ^^^

The air tube from MAF sensor(air cleaner) to upper intake is Ported Vacuum, so as Bgunner said, air leaks in this tube is "unreported air" coming into the engine, same as a vacuum leak is "unreported air", so computers "air" data would be incorrect

 

[Ragnar]

Is there a way I can print out this thread so I can give all this to my mechanic? Can't seem to find a thread tools section on this forum as in others.

 

[Dirtman]

Sure, mechanics absolutely love getting told what to do by the internet.

 

[Ragnar]

LOL How long have you been waiting for an opportunity to post this one?

 

[Uncle Gump]

copy and paste...

I sure do like the term... "unreported air"... I've always considered it an air leak.

 

[RonD]

Find an old mechanic
They look at an engine as a self powered air pump, which is what it is, and all it is

Ask mechanic if he has a vacuum gauge, walk away if he says no


Naw, an air leak leads to a flat tire, unreported air leads to a lean code


Yes, just copy and paste then DUCK when you hand it to the mechanic

 

[Ragnar]

Problem solved and I'm embarassed !!!


I took one more kick at the can today before I sold the truck. When I told you all before hand that I had checked the fuel pressure, I had hooked up the gauge and started the truck, reved it up several times and the reading came up as steady 58 psi.I should have taken the truck for a drive and watched the gauge for any variation in the reading as I drove. I didn't until the other day. Turns out as I accelerated or decelerated at any point, fuel pressure dropped as low as 25 psi and the truck would stumble and or stall. I'm embarrassed. I knew I should have taken it for the drive the first time, but for some reason I thought reving it up would tell me the same thing, and that the fuel pressure was ok. I have Installed a new fuel pump and fuel filter and cleared the codes. By the way I used a genuine Ford fuel filter also, as I have learned once again after market parts are not always the way to go because the are cheaper. I can't believe the difference in power and the CEL light hasn't come back on. Once again, thanks RonD and others for your help and wisdom.