So I recently bought a '97 3.0L ranger and the check engine light turned on with in a few days. it's got the p0172 and p0175 running too rich codes. it also smells like it, the smell is pretty bad. It struggles a little starting up and idle a little rough, it drives fine, but I don't really knot how much power it could have. I cleaned the MAF with MAF cleaner, ran some seafoam spray through the engine, checked for vacuum leaks, all to no avail. I am thinking the MAF may be bad from what I heard. My OBDII scanner gives me some numbers, it's saying 6 g/s at idle, 11.4ish at 2000 rpm, and 20ish at 3000 rpm. Both O2 sensors are jumping between 0 and 0.8 volts. Is this normal? Most of what I know about cars if what I researched in the past few days, so anything would help.

 

Check your vacuum ports going into the intake manifold. My fuel tank evap vacuum was completely plugged with carbon at the manifold. I pulled off the hose and cleaned it up with a wire and carb cleaner. Runs great now.

 

MAF sensors Grams per second should be approximately engine displacement at idle, so for 3.0l engine should be about 3g/s at 700-800rpms, just a rule of thumb, 4.0l engine 4g/s, 5.0l 5g/s


1997 and older Rangers had a Fuel Pressure regulator(FPR) on the engine's fuel rail.
It has the Fuel Return hose attached to it AND a Vacuum hose
If FPR leaks that vacuum hose will suck gasoline into the intake causing Rich running and poor idles
Find the FPR and check that vacuum line for gasoline, if there is gas in it replace FPR

 

Here is what my reader came up with. Does anything stand out?
Engine RPM 923/min
Ignition Timing Advance 16.5
Intake Temperature 58 C
Fuel System 1 Status CL
Fuel System 2 Status ---
Engine Coolant Temperature 96 C
Calculated LOAD Value 40.0%
Air Flow Rate From Mass Air 6.20 g/s
Flow Sensor
Absolute Throttle Position 16.9%
Oxygen Sensor Output Voltage 0.170V (B1-S1)
Short Term Fuel Trim (B1-S1) 10.9%
Short Term Fuel Trim – Bank 1 9.4%
Long Term Fuel Trim – Bank 1 25.0%
Short Term Fuel Trim – Bank 2 9.4%
Long Term Fuel Trim – Bank 2 25.0%
Oxygen Sensor Output Voltage 0.405V (B1-S2)
Short Term Fuel Trim (B1-S2) 99.2%
Oxygen Sensor Output Voltage 0.095V (B2-S1)
Short Term Fuel Trim (B2-S1) 11.7%

 

Where is the fuel tank evap vacuum line located?

 

At idle, about 750RPMs MAF should read about 3.0-3.5 g/s, it matches engine displacement fairly close, so 3.0l engine would show 3-3.5 g/s
You are showing 6.2 g/s and 900rpm which "looks" high, but that would cause RICH code not lean

 

93 Ranger 3.0L starts up and then sputters and dies, won't idle, replace fuel filter, cap, rotor and coil no help. Checked fuel pressure it was 38 psi, which seems right in the sweet spot. Pulling my hair out what next

 

So I cleaned that out and now I have another code... p1443. the evap system isn't working. not sure if it's just that it can detect it now that the hose is clear or what, but i guess i will fix that now and see what happens.

 

OK guys I was looking to see if my year had a Flex Fuel Sensor and found something shown in the pic below. The question is what is it?

 

Don't see a picture

Try unplugging the MAF sensor and starting it. (when its unplugged the computer commands from a fixed chart instead of a reading. If all else is ok... it will start and run somewhat smoothly)

Those STFT look overly rich to me.

So I think that either its being commanded to add fuel or the fuel is mechanically leaking in. Since the fuel trims are that high (assuming those numbers are from a hot engine) I think its commanding richness. Which tells me some signal to the ECU is wrong. Is the temp sensor bad? Check the voltage on that. Other things to check: MAF, MAP (or what ever checks manifold pressure), atmosphere pressure, TPS, how quickly do the 02's swing up/down?

Also, what about RonD suggestion?

 

I have replaced almost every sensor except the oxygen sensors. I have had it with three different mechanics including the dealership. What ever the problem is it happens or seems to happen after the truck is driven some distance and the engine is warm. It seems like the computer is flooding out the truck and thinks it is not gwgetge enough gas.

 

P0172 and P0175(Rich on BOTH banks) at the same time means a system issue that effect BOTH sides of the engine, so BOTH upstream O2 sensors would have to fail at the same time, very long odds on that ever happening.

O2 voltage graph here: https://www.aa1car.com/library/o2volts.gif
.1v is Lean, high oxygen in exhaust
.9v is Rich, low oxygen in exhaust

Your O2s read:
0.170V (B1-S1) passenger side lean
0.095V (B2-S1) drivers side lean
( 0.405V (B1-S2) this is the O2 after the cat, should stay steady at about .7-.8v)

Your Fuel trims are +10 which means LEAN O2 sensor voltage and that is what we see, under .2v at upstream O2 sensors, and lower voltage at downstream as well

But you are getting RICH codes, which are ONLY SET by -20 fuel trims

Short term Fuel trims are the % difference in the open time for fuel injectors as computer calculated them
+10 STFT means computer is opening injector 10% LONGER than it calculated to get O2 sensor to .4v average
-10 STFT would mean injector is open 10% LESS TIME than computer calculated to get O2 sensor to .4v average

i.e. say computer calculates 100millisecond(ms) open time for injectors, it then looks at O2 voltage, if its lower than .4v computer changes to 102ms open time(adds more fuel), if its higher than .4v then it changes to 98ms open time(adds less fuel), then computer checks O2 voltage again............and that adjustment continues until O2s are averaging .4v
In this example +10 STFT would mean open time of 110ms, -10 STFT would mean 90ms open time

Computer sets lean or rich codes at 20% differences, + or -

Long term fuel trims are +25% which should set LEAN CODES not Rich codes, P0171 and P0174

So did you leave out the "-" on those numbers?

If not I would suspect computer issue

 

Is there any way I can check the computer without having to replace it?

 

No, not really

Are you sure the codes were 172 and 175?
And are you sure the LTFT was +25%

These would make sense if it was -25%, check your OBD2 readers manual to make sure it has a designation for negative fuel trims

The +10% STFT are not a concern if LTFT is low

You can unplug sensors like MAF and TPS(one at a time) to see if computer sets correct codes for that, like a sanity check

The air:fuel mix ratio is the sole purpose of these computers, on the fly calculations happening in milliseconds, hard to do a sanity check on that, you just have to look at the results which are opposite in this case, i.e. Rich Codes but Lean fuel trim corrections from computer

Reset and test again, but you can't reset LTFT(+25%?) that must correct itself after any problems have been repaired, you just have to drive vehicle and they will come down as you do, if problem was fixed that is, lol.

 

I have tried to upload a picture but it doesn't seem to be working. It shows a positive fuel trim.

 

I just replaced all the oxygen sensors and it runs and the transmission shifts better, but when I drive it around town doing errands it still stumbles (runs rough) at startup after about the second or third place I go. I have not thrown any codes yet but I think it is only a matter of time. I feel the engine warming up before the issue starts is a symptom. I have replaced all the sensors in the equation and now may just break down and replace both intake gaskets. I was hoping not to not do this as I see no smoke in the leak test. Beside replacing the computer, I am all out of options. This issue has been a nightmare as I have been trying to fix this for a year.

 

OK I had the oxygen sensors replaced a few weeks back and the codes have not come back and my truck seems to shift better, but I still have the stumble after the engine gets warm and then sits for about 20 minutes and I try to start it again. When I put it in gear and try to drive it the engine smooths out in about 10-15 seconds. Today it continued and left me hanging trying to get out in traffic. The check engine light flashed for a period of time and then cleared on its own. When I checked the codes I had:
1. P11511 Lack of H02S21 Switches - Sensor Indicates Lean
2. Cylinder 4 misfire detected
3. Cylinder 5 misfire detected

This is different from the bank 1 and bank 2 lean codes. I am thinking about replacing the fuel injectors.

 

The misfires on 4 and 5 would cause the O2 sensor S2/1(drivers side upstream) to show Lean because no Oxygen was being burned in 2 of the 3 cylinders on that side of the engine
So the O2 code is not a cause but a result.

Flashing CEL means engine damage may occur so "back off the throttle", misfires can cause engine damage

Steady CEL means check the codes when you have a chance, no hurry
Flashing CEL means "heads up" right now

I would pull out Cylinder 1 spark plug, and then cylinder 4 and 5 spark plugs and compare the tips
Cylinder 1 being the known working one to compare the others to

 

I am drawing at straws right now as it has had a tune-up including a new coil pack and plug wires. It has had the MAF sensor replaced twice, ERG replaced twice, IAC replaced twice, all three oxygen sensors, the Fuel pump assembly 4 times, and the Throttle body. Other items have been replaced but I don't remember their names at the moment.

The symptoms have changed over the course of the last year when things were replaced with one exception. After you drive the truck for about 30 minutes or more and then stop and turn off the engine, then try to start it about 20-30 minutes later, the engine stumbles like it is missing real bad. If you put it into gear and drive it, it seems to go away and run fine after 10-15 seconds in most cases. Myself and three different shops have worked on it including the dealership. Things have been fixed but the original issue has not.

Up to now I have been concentrating on sensors. I think all of them with the exception of the CAM position sensor have been replaced. Whatever the issue is, engine temperature seems to be a factor. Also If I drive it and let it sit for two or three hours then crank it there are no issues. Yesterday I drove it up two interstate exits to a store and when I cranked it up it was real bad. When i pulled out I could only manage about 15 miles per hour and when it finally started going faster the check engine light started flashing.

 

I would pull over, turn off the key and then restart, reboot computer, see what computer "thinks" engine temp is at that time, and intake air temp

If possible do the same before starting engine after the 20-30min shut down, then start engine while watch the live data

Computer is either getting the wrong info or is processing the info incorrectly

 

Purge valve stuck open?

 

Ok i look at my temperature when warm and running. It was 96C. I shut the engine off and monitored it for 20 minutes. It peaked at 99C and was coming down. Maybe it is just me but I thought it would rise more when I shut off the engine.

 

OK Now I am reading only 32 PSI on my fuel rail. That actually sounds low. It does not drop off after I shut off the truck. The Fuel pump assembly has been replaced 4 times by the dealership. is there something I need to look at that could cause low fuel pressure?

 

OK went to a fourth mechanic who had the truck for two weeks and gave up. The Temperature sensor for the computer and he says the fuel regulator have been replaced, but I think he replaced the one that keeps the fuel from pulsing on the fuel rail, with no change in the symptom. He was trying to tell me that a fuel pressure of 35 PSI for a 2001 ford ranger 3.0 flex fuel was normal. I thought it was supposed to be 55 + or - 8 PSI. The fuel pump has been replaced by the dealer 4 times. I have replaced the fuel filter twice. I have also replaced the fuel pump relay. If you read my list of items there are no more sensors to replace and the EGR valve has also been replaced twice. What else can cause low fuel pressure? I am at a loss with this truck!!

 

2001 Ranger should run 55psi, it would run fine with 35psi but may set Lean code now and then, engine is never running Lean, Lean and rich codes are computer calculation error codes

Have to get down under 25psi to cause running issues but only at high demand, going up hills are higher speeds, engine would stumble

There are only 2 exits for fuel pressure, when engine/fuel pump is running
The injectors, of course, lol.
Then the Fuel Pressure regulator on top of the gas tank, it is connected to the 3rd fuel hose on the fuel filter

If fuel pressure drops to 0psi with engine off then check valve inside fuel pump could be the problem, it should only allow fuel to flow OUT of the pump, so one-way valve, its inside the pump not a separate piece.
Without an obvious leak of fuel there could be a crack in the hose from pump to top of gas tank, so fuel is spraying out inside the gas tank, which would lower pressure but no loss of fuel

The Pressure Damper on the fuel rail can't effect pressure unless it is leaking, and its vacuum hose would suck that leaking fuel into the engine causing RICH codes and poor running
Its there to stop pressure waves from building up as injectors open and close, just a rubber diaphragm inside