Hey y'all, been a long time lurker here and thanks to many of you my truck is still on the road. I have a 1996 Ranger 3.0l 2wd, Recently i had a p1443 error code which i was able to fix by replacing the sensor and solenoid near the charcoal canister. I then went to have my truck smogged and they told me i failed because of the p1000 code and a damaged connector for the fuel pressure regulator, i drove the truck around for a couple days and the code eventually cleared and ran all the tests its supposed to. I also replaced the 90 degree rubber elbow that connects the vacuum line to the fuel pressure regulator as it had a huge hole in it (this was after the p1443 and p1000 error codes cleared themselves).

NOW, here's where the F#$*ery begins, the day i was going to get retested for emission, my truck threw a check engine light and it was code p0174 lean on bank 2. The first thing i checked was vacuum lines as i had a few crappy looking ones. I sprayed them with brake cleaner to see if thats where the leak was and i didn't notice any changes in how the truck ran.

The truck runs fine currently, i haven't noticed any issues regarding acceleration or anything (although occasionally if I'm really trying to accelerate hard it will hesitate slightly but its done that for along time). I seen alot of posts where people are seeing this code and p0171 but i only have p0174.

So after finding nothing in regards to damaged vacuum lines on bank 2 side, i watched the live data and freeze frame for my trucks code. The freeze frame triggered while in stop and go traffic.

Freeze frame data:
Calculated Engine load: 56.1%
Engine coolant temp: 87° C
STFT Bank 1: 6.2%
LTFT Bank 1: 19.5%
STFT Bank 2: 6.2%
LTFT Bank 2: 24.2%
Engine RPM: 1344rpm
Speed: ~5mph (again stop and go traffic)

As for the live data, i only charted the fuel trims and it seems that my long term fuel trim will remain around 25% no matter what load or speed i am at. Its always somewhere in that range. The STFT will be around 10-15% at idle, then begin to drop depending on how fast or how much load is on the engine.

At this point i have replaced the air filter, and cleaned the MAF sensor. I did notice that the crankcase vent tube is slightly popping off due to the rubber vacuum line that connect the snorkel to the crankcase vent tube is degrading so im going to try replacing that tonight. But that has been that way for as long a i have had the truck and its never been an issue. Not to say it isnt the problem, but i feel like its probably going to be something else.

Please help! Thanks in advance.

 

Welcome to the forum

Yes, P1000 code means battery was disconnected and computers emissions memory was cleared, so you need to drive it a few days so it can re-learn and test emissions systems

P0174 is being set because LTFT Bank 2 is above 20%, LTFT = long term fuel trim
+ or - 20% is usually the threshold for these codes, + is Lean, - is Rich
The STFT(short term fuel trim) of -5 to +5% is expected at steady speed, but 6% is not that unusual

These fuel trim numbers are base on O2 sensor feed back, and O2 sensors wear out, they are THE ONLY sensors that wear out, 12 years or 100k miles and they start to go Lean, lower voltage
Since these are the only sensors the computer has to base STFT on as they age they will cause lower MPG and then lean codes
O2's generate their own voltage, not a "powered sensor", they generate 0.1v to 0.9v, under 1volt, after being fully heated up above 600degF
0.1v = lean
0.9v = rich
As they get older the voltage goes down.................so lean

LTFT is used so the computer doesn't have to re-learn the vehicles engine system on every startup, its an average of STFT on that bank
LTFT is stored in memory and can not be cleared by OBD2 readers, or unhooking battery

Computer does its fuel calculations(open time for injectors) and that is STFT 0%
It then ADDS LTFT to that calculation, so on your Bank 2 STFT 0% is actually STFT 24%, but you don't see that
After warm up Bank 2 STFT is 6% which is actually STFT 30%

Disregard STFT and LTFT until engine is warmed up fully, i.e. 5 to 8 min, and not at idle, O2s are ignored at idle and at Wide Open Throttle(WOT)

If you do not know the age of your 3 O2 sensors then change them, otherwise you can chase your tail because fuel trims are based on FALSE feedback
After the next warm up you should see -5% or so STFT. this will bring down LTFT on that bank, as the - STFT reduces the average of + LTFT

Failing Cat converter can also cause higher LTFT, the Cats get HOT by burning left over gasoline in exhaust, the O2 sensor after the Cats should have a steady voltage of 0.75v to 0.85v
If computer sees lower voltage, like 0.70v then it adds more gasoline to engine, so Cats have more left over gas in the exhaust to get hotter, this cause LTFT to go up on its own, above the average of STFT
On your OBD2 reader you should be able to see O2 sensor voltages
B1S1 is passenger side upstream(closest to engine)
B2S1 is Drivers side upstream, upstream O2 voltage will bounce around alot
B1S2 is downstream O2 after Cat converters, should be steadier voltage than upstream and 0.75v or higher

B1 = bank 1
B2 = bank 2
S1 = upstream O2
S2 = downstream O2

 

Thank you very much for your response Ron, I've actually read all of your other responses in other posts and was hoping you'd chime in here so thank you lol.

So this vehicle has 3 o2 sensors right? Ill try swapping all of them this weekend to see if that's the problem. Im looking at a spreadsheet of all of the live data i captured this morning and i can see my B1S1 sensor voltage range from 0.02 - 0.80v. Should the voltage fluctuate that much?

Could a mass airflow sensor be an issue here? I would assume that would affect both banks. Would you agree?

Outside of the o2 sensors, what else could cause this?

 

Yes, 2 upstream O2s and 1 downstream O2 after Cat converters, they are all the same "model" just longer or shorter attached wire leads

Yes, upstream O2s change very fast that's the computer varying the open time for each injector to try and get a 0.45v average for best MPG

Check B1S2 O2 voltage, that will tell you if Cats are OK, should be steadier than upstream and 0.75 or higher, but change the O2 in any case because it could be a FALSE lower voltage and Cats may be fine

Yes, clean the MAF sensor, once a year if you can, lol, easy to do

 

Ok, ill be swapping those o2 sensors out this weekend. I cleaned the mass air flow sensor last night, that puppy is shining like a diamond lol.

If the o2 sensors dont fix it, where should i look next?

 

You will have to tell me

Here is a quick "the way it works"
Computer KNOWS it is operating a 3 Litre engine, so it KNOWS exactly how many litres of air is coming in at ANY RPM, its just math
Gasoline air/fuel ratio is 14.7 to 1 and this is a WEIGHT RATIO, so litres don't help
A litre of air at sea level weighs more than a litre of air at 5,000ft(Denver)
A litre of Cold air weighs more that a litre of Hot air, i.e. "hot air rises" because its lighter, that is how "hot air balloons" fly, they float above the cooler air
MAF sensor WEIGHS the air
Computer already knows how many litres of air is coming it but it doesn't know the WEIGHT of each litre, so needs the MASS Air Flow sensor

If all the air coming into the engine doesn't pass by/thru the MAF sensor then computer calculates the wrong air weight so the wrong fuel mix, this is why "vacuum"/air leaks cause lean and rich codes, computer has the wrong data
There is also an Incoming Air Temp(IAT)sensor, to help calculate air weight, aka ACT sensor
Air weight is a BIG DEAL for the computer to get right

1996 Computer EXPECTS 35psi of fuel pressure at each injector, there is no fuel pressure sensor, but 25 to 45psi is fine
Gasoline weight doesn't change much, cold or warm
But when the computer Opens an injector less fuel will flow out at 20psi than at 30psi, so fuel pressure matters as well
14.7 to 1
14.7 POUNDS of Air to 1 POUND of gasoline
14.7 grams of air to 1 gram of gasoline
Weight, Weight, Weight

Its why fuel injectors are rated in pounds per hour of flow, your 3.0l probably uses 14lb/hr injectors, 14 pounds per hour of flow

So computer now has Air Volume and Air weight and expected fuel flow from injectors
It calculates STFT for say 2,500rpm, and STFT 0 is 100ms(milliseconds) open time for each injector
Fuel is injected
Computer then looks at O2 sensor(either upstream O2) and it sees O2 voltage of 0.2v high oxygen/lean
Computer instantly changes open times to 102ms, STFT is now +2%
If O2 now show 0.3v then computer changes to STFT +4%, then STFT +6%, ...........ect until it see O2 average voltage of 0.45v

So all the calculations come down to O2 sensor feed back, there is no other check, no other sensor the computer can use to double check if O2s are "OK"

So when there are fuel trim codes, lean or rich, Lean codes especially, knowing that your O2 sensors are not older than 12 years so are still dependable is good you can then investigate other possibilities for Lean codes
If you have no idea of how old the O2 sensors are then that should be the first thing you change, as they do for sure wear out.after 12 years


So now you know, or have surmised, that Lean codes do not mean engine is actually running Lean, these codes are strictly Fuel Trims being out of range(+/- 20%) so computer is letting you know that the data its using for its calculations is not correct

Could be MAF sensor issue
Vacuum/air leak
Low fuel pressure

But ALL based on what O2 sensor's "tell" the computer about it's calculation


Computer's can also go "insane" but very very very rare

 

Quick little update for anyone that may find this in the future. I had found a small vacuum line for my heater was broken, so i fixed that. I also replaced my fuel filter and cleared the code but the code came back on the first test drive. Then I replaced all 3 of my o2 sensors on RonD's recommendation. While doing so i realized that all 3 of them were the originals, so they were well past due for replacement.
I disconnected the battery while doing the o2 sensors and since reconnecting it i have not gotten anymore CELs. Its currently been 3 days and i have gone through about 5 drive cycles. The p1000 code is still present, so once that self clears i will update the forum with whether or not the issues if 100% fixed.

 

Another update for y'all, It is fixed. I just got my truck smogged and she has been running great as of late. In the end i had repaired all vacuum lines(in my case it was 2 lines and neither of them were on bank 2 side but still), confirmed Fuel pressure was good, did the sound check and OHM check on the injectors, replaced fuel filter, and lastly replaced all 3 of my o2 sensors.

I believe the root cause was the o2 sensors

RonD i cannot verbally express how grateful i am for your advice not only here, but also from what I've seen you post in other forums. You're a Gem and i appreciate you greatly! THANK YOU!