p0171, p0174 - but it is NOT what you think.

[Madman54]

I have posted about this ranger before, and it has a kind of long back story to it, so bear with me.....

It my buddies 04 ranger xlt 4.0 SOHC. he started having issues not long after he swapped a motor and exhaust from a 2001 ranger. Its been a while so i could be wrong but here goes...
It started with a P2195 and P2197 and a MAF sensor code. he was out of town late at night so he bought a MAF sensor and threw it in, Which did not solve his problem because it was the wrong one and the part store was now closed. he called me and I told him that I thought it was probably an o2 sensor problem. then i told him to unplug his MAF and drive the last 30 miles to home. which he did. the next day he exchanged the MAF sensor for the correct one and installed it which took away the code for the MAF sensor, but the engine running lean codes remained.

He continued to drive it like this for about 6 months and said that the truck was running great despite the 2 lean codes. as it got closer and closer to emmissions testing time he started trying to fix everything without any knowledge. which is where it all went really really bad. he rewired EVERY connector on the truck...by the end of this time truck truck was not driveable and smoked more than a freight train pulling up a steep hill.

he got a scanner that supported live data from a friend and called me. I walked him through some things and determined that it was defiantly an o2 sensor issue. and he said to me, "yeah, the scanner shows that there should be 4 o2 sensors, but there is only 3 holes in the exhaust". At the time, I didnt know that he had swapped exhausts from the 2001 into the 2004, so i told him "if there are only 3 holes in the exhaust, it only needs 3 sensors."

another 3 months go by and he calls me and ask me if there is anyway i would tow it to my house (100miles away) and just go through it for him. So I did. first thing i did was go through and replace all the scotch lock wire connectors with properly soldered connections and correct all the custom wiring he did, and watched about 20 codes disappear. so first things first I started working on the oxygen sensor problem. by now he has put several different o2 sensors that he snagged from the junkyard in, trying to fix his problem.... so I put 3 new o2 sensors in, that were OEM. (2 of the 3 he had in there were bad 1 was not the correct type) but the problem persisted.... so i posted about it in these forums and did some more research on all data. I found that his 2004 ranger did indeed need 4 o2 sensors. thats when he told me he had swapped exhausts with the engine. okay no big deal, got an o2 bung, drilled hole welded bung installed a 4th new sensor.

truck was now drivable, but a few problems persisted....the K&N filter he installed was WAY over oiled so i washed it out and lightly oiled it, clean the MAF sensor with MAF cleaner a few times. truck was really starting to run good, but still not right. So I smoked it with a cheap smoke machine i made and found a few leaks. sealed them up and the truck was running great... decided that with as many vac leaks as i found, i better do a better test. Took it to the shop at the college i attended (they let me use their resources quit often as I established a pretty good relationship while i was there). put their good smoke machine on it gradually bumping up the psi all the way to 75psi. Not one bit of smoke coming from anywhere. truck now running amazing! I drive it around the small town i live in for 3-4 days mostly lower speeds but i did make sure to get some highway driving in too.... no problems. Friend gets a ride down here and picks up the truck. leaves here and drives 60 miles over the mountains and BAM! p0171, p0174. he drives the last 40 minutes home and calls me the next day and here we still are a month later. almost a year and a half after original problem, truck still cant pass emissions.

So here is what i know has been replaced by him and what has been done and what i personally know about it either from testing or being told.
Pcv valve - new
pcv elbow tubing connections - good - not leaking
Intake Manifold gaskets - Just replaced - new
MAF -New (since i had cleaned the other one)
Fuel filter - new - old one was terrible
fuel leak in line right above exhaust manifold - repaired
Fuel Pressure - KOER 62psi - KOEO drops to 40psi and holds
fuel pressure damper - new because he thought it was a regulator
Fuel pump - he says its new, i have my doubts.
exhaust manifold gaskets - New
ECT - new (both sensor and sender)
4 new O2 sensors hooked up correctly and reading correctly in scan tool data
Cat's - Would say that the scan tool data shows them doing their job.
EGR valve - new
DPFE - tested good. I broke one of the plastic deals where the line hooks up, but was able to JBweld it back on. DPFE still tested good.
TPS tested with spec range
IAC - cleaned and tested by unplugging it with engine running, engine dropped to a steady 500 rpm.

at this point i am at a loss.... not sure what i have missed here. I asked him to go buy a vacuum gauge and the video call me while we test it, but who knows when he will.
He says it take a while before the codes come back after clearing them and that when they set he is usually traveling down the road at higher, steady speeds.
but this is a problem he really needs help with, before he starts re wiring again. lol. its also driving me insane, because i live far enough away that i cant go be there in person, and his truck is no longer licensed so he cant drive the 100 miles to me. All of the basic stuff is done. it is not the pcv or anything related. but im stuck.....
what do you guys think?

 

[600$04Ranger]

I think you're one heck of a good friend to have! Really enjoyed reading your post since I have basically the same truck and although I currently have no codes or any issues I know it's only a matter of time. The 3 O2 sensors was kind of funny. Which of the 4 O2 sensors was missing? An upstream or downstream? Could the lean codes be occuring because of a failing fuel pump combined with not refilling the tank until the fuel light comes on? Would the amount of fuel in the tank affect the fuel pump in any way? It's a wild and uneducated guess but all I got

 

[racsan]

Fuel rail gasket? I know you said intake gaskets and this should be included but sometimes that damn thing can get forgotten. Had that issue with a 93 4.0 (yes different 4.0 but Id guess there is still a fuel rail gasket to go bad), mine was “drawn inward” at front & rear.

 

[Madman54]

im not sure what you mean when you say fuel rail gaskets?
Ar you maybe talking about fuel injector gaskets?

 

[Orca]

[...]He says it take a while before the codes come back after clearing them and that when they set he is usually traveling down the road at higher, steady speeds.[...]

No need to guess about the vehicle's conditions when the DTC (Diagnostic Trouble Code) sets. Use the scantool to pull the "freeze frame" data. It may or may not help the diagnosis, but it beats "He said..." or "He thinks...".

 

[Madman54]

No need to guess about the vehicle's conditions when the DTC (Diagnostic Trouble Code) sets. Use the scantool to pull the "freeze frame" data. It may or may not help the diagnosis, but it beats "He said..." or "He thinks...".

yeah. I have looked at the freeze frame data, just this morning actually. it doesnt offer any insight. except that the "he said" in this scenario is incorrect.

 

[RonD]

Lean codes on BOTH banks means its something general that can effect BOTH banks, so lower intake leak or small vacuum leak is off the table
Lean codes mean Computers calculation's were off by more than 20% on BOTH banks, but engine was never actually running Lean
So not O2s since they are bank specific, and not bad injector(s) since they are also bank specific

(O2s use a chemical coating to detect Oxygen in the exhaust, that coating is gone after 12 years or 100k miles, O2s are the ONLY sensors that "wear out", just FYI, so not a part to get at a junkyard , lol)

In this case the computer is able to compensate for the miscalculation because you/he doesn't have the "stuck on lean" code from BOTH O2s
And engine seems to run OK, no pinging/knocking that would come if engine was truely running Lean under load, even with Knock sensor

The Computer does need to ASSUME some things it has no sensors for
Its a 4 liter engine
Fuel pressure is 60psi at any RPM and load
Fuel injectors are, say 19lb/hr, haven't looked it up, lol, but stock size

With the absents of other sensor codes, I would say your fuel pump/filter guess is a good one
If he can hook up a Live Scanner and then watch STFT when driving at speed, uphill, so high engine load but at a steady speed, he might see STFT going to higher and higher, showing + fuel trims, indicating lower and lower fuel pressure with higher demand

Might be able to see that with fuel pressure gauge and hold engine RPMs at 2,500 in a static test, slowly dropping pressure would indicate the problem

 

[Madman54]

Lean codes on BOTH banks means its something general that can effect BOTH banks, so lower intake leak or small vacuum leak is off the table
Lean codes mean Computers calculation's were off by more than 20% on BOTH banks, but engine was never actually running Lean
So not O2s since they are bank specific, and not bad injector(s) since they are also bank specific

(O2s use a chemical coating to detect Oxygen in the exhaust, that coating is gone after 12 years or 100k miles, O2s are the ONLY sensors that "wear out", just FYI, so not a part to get at a junkyard , lol)

In this case the computer is able to compensate for the miscalculation because you/he doesn't have the "stuck on lean" code from BOTH O2s
And engine seems to run OK, no pinging/knocking that would come if engine was truely running Lean under load, even with Knock sensor

The Computer does need to ASSUME some things it has no sensors for
Its a 4 liter engine
Fuel pressure is 60psi at any RPM and load
Fuel injectors are, say 19lb/hr, haven't looked it up, lol, but stock size

With the absents of other sensor codes, I would say your fuel pump/filter guess is a good one
If he can hook up a Live Scanner and then watch STFT when driving at speed, uphill, so high engine load but at a steady speed, he might see STFT going to higher and higher, showing + fuel trims, indicating lower and lower fuel pressure with higher demand

Might be able to see that with fuel pressure gauge and hold engine RPMs at 2,500 in a static test, slowly dropping pressure would indicate the problem

ah. ive been waiting for you to chime in. lol. you post information that is the most useful and easily understandable in my opinion.

so he decided, the day before yesterday to drive it down to me... I again went through so many things until i felt all bases had been covered... found a few more issues. found 3 spark plugs with badly carbon tracked procelean. replaced them and the wires with know good ones(off my sons explorer) to test but no change. clogged cats.... Broke out the honey comb to test, since theyre going to have to be rep[laced anyhow. truck did run better and less lean but LTFT remained at 25%. one of the o2 sensors (post cat) that i installed, rattled loose. since it was a post cat i didnt bother to recheck data as i know it has no effect on AFR.

fuel trims... I understand them, but i have to renew my understanding everytime i have to deal with them in any length. So we did take a drive and i did see results just like what you mentioned.... kind of....
while doing any sort of hard acceleration (but not WOT) the STFT on both bank did rise... I never thought to use that as a tool for finding fuel restrictions/weak pumps etc..... so thanks for that!
so there was a couple really odd issues... while driving down the road, monitoring O2 sensors, under hard accel (bot WOT and not WOT) bank1's sensor would go high voltage, and bank 2's sensor would go low..... talking of sensor 2's of course.... any insight on that?

 

[Madman54]

also had another weird anomily....

decide4d to start my diag over again from the begining just to make sure i started with the basics... so i was testing the mMAF sensor circuit. power and ground were present. while testing the pcm ground to the MAF sensor (ltblu/tan wire in position 4) the procedure said to go from position 4 on the connector, connector unplugged to battery positive, and was looking for a result of 12v. the first time i tested it i only showed 6.xxx VDC. i then realized i had not told my helper to turn the ignition off and got the correct result of 12V.

so... with the connector unplugged and the ignition on, should i be seeing any voltage on that wire when going to battery positive?

my mind says there should be no current flowing on that line with the connector disconected.... so I left it disconnected and checked the ohms on the wire from the connector to the PCM connector and got 0.001 Ohm. I also put 12v to the pcm side wire then connected an incandecent light between the connector and batt positive. the light lit brightly.

so really i dont see anything wrong with that part of the circuit, but i see no reason for there to be 6.xxx v on that line when the connector is off...

 

[RonD]

6 Wire MAF will have 5volt Air Temp sensor, 5v MAF sensor and 12volt MAF heater, none of the wires should have voltage key off

You can see voltage on computer wires key off, but usually under 1 volt

LTFT does effect air/fuel ratio as LTFT is added or subtracted from computer's STFT calculation, the point of LTFT is so the fuel system can "age gracefully", lol

When you cold start an engine O2 sensors can't work(they need to be heated above 650degF), so LTFT is used to compensate for any "aging" in the system, i.e. lower fuel pressure, smaller vacuum leaks, dirty MAF sensor, ect......
And its also used after O2 sensors are working, so computer doesn't have to "re-learn" the system at every key on and startup, warm or cold

Computer calculates STFT then adds, or subtracts LTFT from that and that's what 0 STFT represents

So if LTFT is +20 and you are seeing +10 STFT then actual fuel trim is +30

When you fix a problem and LTFT is +20 then you might see STFT as -10 for awhile which brings down LTFT on each averaging update of LTFT
So you end up with +5 LTFT over time and STFT at -5 to +5

Rear O2s should be steady at 0.7v to 0.8v, which is "called rich" in other circumstances, but in this case its an absence of Oxygen in the exhaust after the Cat, which is Good, as the Cats are suppose to used up/burn up the oxygen when it burns up pollutants
If computer "sees" lower voltage it "thinks" the Cats are not Hot enough so it adds more gasoline, +STFT to feed the Cats, and that can help a bit but you do end up with higher LTFT numbers as failing Cats "need" the higher fuel trims to stay Hot

 

[Madman54]

So after talking to my friend this morning, he finally gave me the bit of information i was looking for.... the gas that was in the truck when he swapped the engine was 13 years old.....
he replaced the pump and filter but didnt bother to clean out the tank. he also said that when he last change the filter (this week) he was still getting nasty black stuff thats beiing picked up in the tank....

100% certain he has a fuel delivery issue now. lmao
told him he needs to clean the tank out and at the very least put a new sock on the pumps pickup. he has injectors that he has been wanting to install. im sure after doing those couple things his troubles are over.

thanks guys for helping me sort out all the problems i have posted about this truck.

 

[RonD]

Yes, that would certainly cause lean codes