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That's definitely _"ONE"_ cause, but THAT opinion fails to consider relevant factors and can send someone off chasing their tail.
Lean code come SOLELY from a very ridged bit of binary logic in the PCM. (LTFT > 25% -AND- STFT >5%). Logical meaning - Positive Fuel trim is being added (lengthening injector pulse width) exceeding factory fixed limit. (O2 sensor "VOLTAGE" readings have been trending to low). Another way of saying it, the PCM has reached its factory LIMIT of adjustment (trying to keep fuel/air ratio proper for it to run RIGHT). Up to this point, power should NOT have been effected, so that would be an improper, snap decision conclusion.
o- If injectors are dirty and delivering less fuel per given pulse width - this same thing will happen.
o- If fuel rail pressure is low (because of faulty FRP sensor, faulty FPDM or Fuel Pump) - this same thing will happen. Injectors are calibrated to deliver exact amount of fuel / at a certain pressure across them / during a specified period.
o- Random Misfires (from ALL their various causes) - will cause this to happen. Dumping unburned oxygen into the exhaust.
o- Low 'bias' voltage on O2 sensors will cause this. Altering the proper calibration of the O2 sensor output voltage.
o- Cross currents around MAF sensor as @BareBonesXL points out will cause this. (Common from moving MAF on aftermarket CAI additions)
o- Valve Cover gasket or Oil Pan gasket leak (which is technically a vacuum leak) will cause this.
My point - is; this, like so many diagnosis require a look at other things to get the problem in prospective before diving in with a snap diagnosis.
Thats very good info you've provided, but I have a question. What is "bias" voltage on the o2 sensors is that voltage coming into the sensor or voltage in the sensor itself (bad sensor)? Out of all the things you labeled as possible causes I can say that I've bench tested all injectors, fuel pressure test i'm unsure of because i tested 3 times and had bleed off after shut down on the 2nd test but the numbers seem fine other than that.Test results for fuel and vacuum are on post #9 sorry i havent figued out how to do the quote thing to bring it here, I have no misfires, MAF was cleaned and new air filter installed plus its all stock, and I do have a slight bit of oil pan gasket leak, as for the o2 "bias" voltage im unsure as well.
Thanks for all the help (everyone)
Goinwheelin
"Laminar" in my example just means that the MAFS elements see the same air velocity as the total cross section of the intake tube.
That's not what "laminar flow" means. The MAF element is never in a dead zone or eddy; it's in the middle of a tiny tube which creates a slight restriction in the airflow, so some air is forced to pass through the small tube & over the element. There's a LOT of turbulence there, which is the opposite of laminar flow. But there is no dead zone or substantial eddy anywhere in the intake, cylinders, or exhaust (the engine's airstream).
Our O2 sensors don't technically 'output' a voltage in the sense many descriptions lead us to believe. They are like 'semiconductors'. The sensor 'element' inside changes in resistance (becomes conductive) when Oxygen is in its presence. But it's conductivity is NOT exactly 'all or none' between presence of oxygen and NO oxygen. And the change takes a 'fraction' of a second. So in a circuit, one side of the element is connected to ground and the other side of the element has a 'bias' (with very accurately controlled voltage and current) applied to it. This bias makes the voltage on the output wire side (ungrounded side) of the element read ~ .9 volt when NO oxygen is present, and .1 volt when oxygen IS present. The PCM increases and decreases STFT (around 6 times a second) making O2 sensor voltage swing above and below the mid-point (.45 v) trying to maintain that perfect balance (or average voltage) JUST WHERE THERE IS NO OXYGEN left in the exhaust stream.
As one can see, if this 'bias' supplied to an O2 sensor has poor connection, partial short to ground or positive ------ all bets are off on what the O2 sensors reading might be - and it is the ONLY thing that drives STFT.
OBDII scanner tools that read Mode $06 data gives the 'instantaneous' reading and the RMS (or average voltage) the PCM is seeing from the O2 sensor.
Regrettably, I'm not real familiar with configuration of your truck model (with respect to injectors / fuel pressure sensor / regulator) - but Fuel Pressure can be 'tricky'. It has to be considered relative to where the injector 'nozzle' is located. ie: Fuel flow through an injector is 'rated' at a given pressure =across the injector-, like 40 lbs. ///THAT is across the injector from input to nozzle ///. If nozzle is in the intake port subjected to Intake manifold vacuum - then a fuel pressure reading 'relative' to atmospheric pressure has to be offset by vacuum reading (converted from InHg into PSI) and added to it. (My '04 has a fuel pressure sensor that reads 'relative to Intake vacuum' and runs around 39 pounds.).
In your case, I am concerned about LTFT trending higher at higher RPM and load. Fuel Pressure 'regulator' maybe???. The sag in pressure on shutdown doesn't bother me so much. Could be check valve in fuel pump, but shouldn't 'F-U' LTFT.
The MAF element is never in a dead zone or eddy; it's in the middle of a tiny tube which creates a slight restriction in the airflow, so some air is forced to pass through the small tube & over the element. There's a LOT of turbulence there, .
Not sure why this is an argument. Maybe I post too much.
Your sentence is correct for the factory design. The whole point of the comments was about somebody having their filter element in backward which COULD cause a dead zone or eddy, or turbulence before the elements.
The MAF element should never be in a dead zone or eddy, or receive turbulent air from the intake tube.
Reversing the filter will not affect the flow pattern across the MAF, or cause eddies. There will never be laminar flow inside or anywhere near an automobile.
Reversing the air filter on the truck being discussed will make it fall flat on it's face as nearly all intake air is blocked, ask me how I know. It'll idle but step into the gas and you ain't going no where fast.
.
NASA's not what it used to be but the people there probably still know some stuff. Maybe I should use the term "not turbulent" in place of laminar? Works for me.
"Most of the mass flow sensors used today are the hot wire variety. Hot wires can be fragile and cannot accurately measure a turbulent or reversing flow, which is often encountered in an intake manifold."
Our O2 sensors don't technically 'output' a voltage in the sense many descriptions lead us to believe. They are like 'semiconductors'. The sensor 'element' inside changes in resistance (becomes conductive) when Oxygen is in its presence. But it's conductivity is NOT exactly 'all or none' between presence of oxygen and NO oxygen. And the change takes a 'fraction' of a second. So in a circuit, one side of the element is connected to ground and the other side of the element has a 'bias' (with very accurately controlled voltage and current) applied to it. This bias makes the voltage on the output wire side (ungrounded side) of the element read ~ .9 volt when NO oxygen is present, and .1 volt when oxygen IS present. The PCM increases and decreases STFT (around 6 times a second) making O2 sensor voltage swing above and below the mid-point (.45 v) trying to maintain that perfect balance (or average voltage) JUST WHERE THERE IS NO OXYGEN left in the exhaust stream.
As one can see, if this 'bias' supplied to an O2 sensor has poor connection, partial short to ground or positive ------ all bets are off on what the O2 sensors reading might be - and it is the ONLY thing that drives STFT.
OBDII scanner tools that read Mode $06 data gives the 'instantaneous' reading and the RMS (or average voltage) the PCM is seeing from the O2 sensor.
Regrettably, I'm not real familiar with configuration of your truck model (with respect to injectors / fuel pressure sensor / regulator) - but Fuel Pressure can be 'tricky'. It has to be considered relative to where the injector 'nozzle' is located. ie: Fuel flow through an injector is 'rated' at a given pressure =across the injector-, like 40 lbs. ///THAT is across the injector from input to nozzle ///. If nozzle is in the intake port subjected to Intake manifold vacuum - then a fuel pressure reading 'relative' to atmospheric pressure has to be offset by vacuum reading (converted from InHg into PSI) and added to it. (My '04 has a fuel pressure sensor that reads 'relative to Intake vacuum' and runs around 39 pounds.).
In your case, I am concerned about LTFT trending higher at higher RPM and load. Fuel Pressure 'regulator' maybe???. The sag in pressure on shutdown doesn't bother me so much. Could be check valve in fuel pump, but shouldn't 'F-U' LTFT.
G.L. Hope this helps some.
Thats great info again. Thanks so much.
I too agree that the LTFT at higher rpm and under load is concerning. I have already replaced the fuel pressure regulator in the recent past (maybe a year ago). Would that not show up when i did the fuel pressure test? Also what about failing cats could that be a possibility? My exhaust is still factory with the exception of the manifolds which i just replaced cause one was leaking, what a job that was. I do know that theres no exhaust leaks pre cat but a I do have a small one in my muffler.
Thanks again F150Torqued.
PS im going to figure out how to post pics of my live data yet lol
....
Also what about failing cats could that be a possibility? My exhaust is still factory with the exception of the manifolds which i just replaced cause one was leaking, ...
???? Don't think so. I believe partially plugged CATs will cause the opposite effect. Inert gasses accumulate in the exhaust and the O2 senses less and less or NO oxygen causing fuel trims to trend into negative territory. Id does seem that RPM or load would make that effect worse.
However, I really have difficulty rationalizing increased LTFTs with increased RPM and Load - if the fuel pressure is maintained like your test results indicate. FOR SURE, if fuel pressure doesn't increase as vacuum decreases - that would result in injectors delivering less fuel during a given pulse width - and thus the PCM would INCREASE fuel trims. (Short Term first - which 'migrates' into LTFT trying to zero out STFT adjustments over time.)
///Referring back to a prior post in which you expressed concern about short term being '+' when LTFT was negative. This certainly CAN be. Short Term is present 'RIGHT NOW' condition. A weighted algorithm migrates present STFT into LTFT. So the condition you described indicates that present conditions were 'correcting' LTFT in the correct direction.
Have you ever replaced O2 sensors? What live data scanner facility are you using?
I wrote the stuff below then went back to see what has been talked about and see that Steve 83 and F150Torqued have already mentioned it. That's three votes for clogged or contaminated injectors. If you didn't flow test them then you don't really know that they're "clean".
I haven't put the level of thought in to this particular situation as you guys have. But, wouldn't clogged fuel injectors cause high trims at high RPM and load. That would be when the injectors are open the longest and flow through the injector body might have the most impact. At low injector open durations the effect of poor flow would be less.
I've tested injectors on older cars by running them wide open and collecting the fuel. An injector can get pretty well clogged up if the fuel is wet/dirty/rusty. I've seen 20-30% variation between injectors.
You said that you "cleaned" the injectors, but didn't say that you had them flow tested. And one of Steve83's diagnostics is "contaminated injectors" in Post #6. F150Torqued says the same thing in Post #20.
06-11-2018, 02:40 AM
